Building a Vector Map from Scratch

I’ve always been fascinated with maps, and they’re one of my favorite type of UX on the web. So when I wanted to learn a bit more about 3D programming and WebGL, it made sense to try and implement something I was already familiar with; a vector map.

This article covers my process of building a vector-tile map from the ground up. I've broken it up into three main parts:

TL;DR - You can also head straight to the source or check out the final product.

Part 1: WebGL Rendering and Interaction

If you've ever wondered exactly how vector maps like Mapbox or Google Maps are rendered, this aticle should break down a few of the lower-level concepts for what goes on under the hood when using a vector based map. The implementation details in these examples won’t match exactly what other maps do, but the concepts should still be more-or-less the same.

I'm also still fairly new 3D programming, so feel free to shoot me a note if there are any suggestions or improvements to the code. 😅

Web Mercator Projection

To start, we should probably talk a bit about map projections, in particular the Mercator projection. It’s the standard projection you’ll see in almost all web-based maps. One thing to note, is the distance between latitudes becomes greater near the poles, so there’s a decent amount of distortion the further north and south points are.

circles indicate level of distortion near the poles.

circles indicate level of distortion near the poles.

The Web Mercator projection is a slight variation on Mercator, but the formulas still mostly apply. For web maps, the origin (0, 0) is considered to be at the top-left, with x+ increasing to the right, and y+ increasing downwards.

mercator coordinate system

So we can use the projection formulas convert our latitude & longitude values to an XY value on the map. For these examples, I’m going to use code from the MercatorCoordinate class that is a part of the Mapbox GL JS library.

class MercatorCoordinate { static mercatorXfromLng(lng) { return (180 + lng) / 360; } static mercatorYfromLat(lat) { return (180 - (180 / Math.PI * Math.log(Math.tan(Math.PI / 4 + lat * Math.PI / 360)))) / 360; } static fromLngLat(lngLat) { const x = MercatorCoordinate.mercatorXfromLng(lngLat[0]); const y = MercatorCoordinate.mercatorYfromLat(lngLat[1]); return [x, y]; } }

So if we take an example point [-73.9911, 40.7343] (NYC), we can convert it to a point in the XY space. We'll call this coordinate system the "world space". We can think of this as a single map tile at zoom level 0.

const [x, y] = MercatorCoordinate.fromLngLat([-73.9911, 40.7343]); x // 0.294469 y // 0.375901
lat/lng coordinates converted to XY world space.

lat/lng coordinates converted to XY world space.

WebGL Clip Space

Now that we have our “world space” coordinates, we can convert them to the “clip space” coordinates that WebGL uses to render a scene. The clip space is slightly different than our world space, in that the origin is at the center, and going from [-1, 1] on the axes.

webgl clip space

webgl clip space

So we can convert our world space -> clip space with some pretty basic math. This can also be done via a matrix transformation (which we’ll cover later), but for simplicity we can just do this conversion in our MercatorCoordinate utility.

static fromLngLat(lngLat) { let x = MercatorCoordinate.mercatorXfromLng(lngLat[0]); let y = MercatorCoordinate.mercatorYfromLat(lngLat[1]); // adjust so relative to origin at center of viewport, instead of top-left x = -1 + (x * 2); y = 1 - (y * 2); return [x, y]; }
lat/lng coordinates converted to webgl clip space.

lat/lng coordinates converted to webgl clip space.

Rendering a bounding box

Now that we have a way to convert latitude & longitude to our WebGL coordinate space, lets go ahead and draw something! We’ll start simple and draw a basic bounding box.

Since our initial view is zoomed all the way out (zoom level 0), we’ll use a box large enough to see, so we’ll bound the continental US.

const USA_BBOX = [ [-126.03515625, 23.079731762449878], [-60.1171875, 23.079731762449878], [-60.1171875, 50.233151832472245], [-126.03515625, 50.233151832472245] ];

In order to render a box in WebGL, we need to convert it into a set of triangles, which is the smallest primitive type for rendering a surface. A rectangle is a pretty simple shape, which can be drawn with two triangles. Since the box has 4 coordinates, we can arrange them like so to form a rectangle from two triangles.

Note: Since WebGL only supports a few primitives, this is generally where something like three.js would come in handy, as it has better abstractions for drawing shapes.
a webgl box can be formed with two triangles.

a webgl box can be formed with two triangles.

To render the triangles, we’ll convert each lat/lng from our box into clip-space, and construct an array with each of the vertices for the triangles (so 6 points in total).

const [nw_x, nw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[0]); const [ne_x, ne_y] = MercatorCoordinate.fromLngLat(USA_BBOX[1]); const [se_x, se_y] = MercatorCoordinate.fromLngLat(USA_BBOX[2]); const [sw_x, sw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[3]); const positions = [ // triangle 1 nw_x, nw_y, ne_x, ne_y, se_x, se_y, // triangle 2 se_x, se_y, sw_x, sw_y, nw_x, nw_y, ];

Now that we have our vertices, we need to render it to a <canvas>.

Unfortunately, there is a lot of boilerplate needed to setup a WebGL scene, so I’ll document most of this in the code snippet below. But the gist is:

  • Get a WebGL context from our canvas element
  • Compile the shaders, and setup our program
  • Convert our lat/lng’s to clip-space vertices
  • Tell WebGL to render the triangles

After doing all that, you can see the rectangle in the upper-left quadrant of the grid. This is where we'd expect it to be based on the image we've been using as a reference so far. You can also toggle the map on to check that it's rendered correctly.

map reference image
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 import MercatorCoordinate from './mercator-coordinate'; import { createShader, createProgram } from './webgl-utils'; ////////////////////// // constants ////////////////////// const USA_BBOX = [ [-126.03515625, 23.079731762449878], [-60.1171875, 23.079731762449878], [-60.1171875, 50.233151832472245], [-126.03515625, 50.233151832472245] ]; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; void main() { gl_Position = vec4(a_position, 0, 1); } `; // color is constant for all vertices const fragmentShaderSource =` precision mediump float; void main() { gl_FragColor = vec4(1, 0, 0.5, 0.5); } `; ////////////////////// // main program ////////////////////// const run = (canvasId) => { // get GL context from canvas const canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer for vertices const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); // add vertices to buffer const [nw_x, nw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[0]); const [ne_x, ne_y] = MercatorCoordinate.fromLngLat(USA_BBOX[1]); const [se_x, se_y] = MercatorCoordinate.fromLngLat(USA_BBOX[2]); const [sw_x, sw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[3]); const positions = [ // triangle 1 nw_x, nw_y, ne_x, ne_y, se_x, se_y, // triangle 2 se_x, se_y, sw_x, sw_y, nw_x, nw_y, ]; gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW); // enable on the position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); const draw = () => { // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = 6; gl.drawArrays(primitiveType, offset, count); } draw(); }; export default run;

Adding Interactivity

To have a useful map, we’ll also want the ability to move around. We can add some basic map behaviors such as pan & zoom.

To do this, we’ll need to introduce the idea of a “camera” for moving the viewport around the scene. This differs from a traditional camera, in that instead of moving the camera around, we’ll actually move the world around the camera. For instance, if we want to pan to the left, we’ll actually move all the vertices in our scene to the right by that same amount (we’re basically inverting the behavior we’d expect).

For our purposes, the camera will keep track of the XY position, and the current zoom level. These will then be represented as vectors, that when applied to a matrix (ie. the projection matrix) will make up the final state of the scene.

We can think of each vertex on our map as vector with three points: [x, y, z]. The idea behind using a matrix is that we can multiply the vector by the matrix to get the new vector position. For instance, if we take our vertices from above and multiply them by the identity matrix, we can see we get the same result (ie. no transformation).

identity matrix
Note: since WebGL is a 3D interface, it expects vertices to have x, y, and z values. Since we’re only dealing with xy values, z can mostly be ignored.

If we wanted to pan the map to the right, we need to translate all of the vertices by the same amount the mouse has moved (in this case, in the x+ direction). So if the map was panned 20 pixels to the right, we’d convert that 20px to clip-space (0.92), and can represent the translation with the following matrix.

translate matrix

Similarly, if we wanted to apply a zoom, we can add a scale factor that gets multiplied to the vertices. For zooming, that factor is 2zoom. So if we at a zoom level of 1, our scale factor is 2.

scale matrix

One other caveat with zoom, if we want to zoom in on the mouse position, we'll need to grab the pre & post transformation positions of where the mouse is, and translate accordingly. There's a great article at webglfundamentals.org that covers this in depth, so I won't go into too much detail there.

The matrix containing the scale and translation values is what we’ll then pass into our vertex shader, so these vertex computations can be done on the GPU.

attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); }

Once we setup the event handlers and update our matrix, we should be able to pan & zoom the bounding box. I'm using the glMatrix library to handle the matrix math.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 import { mat3, vec3 } from 'gl-matrix'; import MercatorCoordinate from './mercator-coordinate'; import { createShader, createProgram } from './webgl-utils'; ////////////////////// // constants ////////////////////// const MIN_ZOOM = 0; const MAX_ZOOM = 16; const USA_BBOX = [ [-126.03515625, 23.079731762449878], [-60.1171875, 23.079731762449878], [-60.1171875, 50.233151832472245], [-126.03515625, 50.233151832472245] ]; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // color is constant for all vertices const fragmentShaderSource =` precision mediump float; void main() { gl_FragColor = vec4(1, 0, 0.5, 0.5); } `; ////////////////////// // map state ////////////////////// const camera = { x: 0, y: 0, zoom: 0, }; let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); mat3.scale(cameraMat, cameraMat, [zoomScale, zoomScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } updateMatrix(); ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e, canvas) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } ////////////////////// // main program ////////////////////// const run = (canvasId) => { // get GL context from canvas const canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer for vertices const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); // add vertices to buffer const [nw_x, nw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[0]); const [ne_x, ne_y] = MercatorCoordinate.fromLngLat(USA_BBOX[1]); const [se_x, se_y] = MercatorCoordinate.fromLngLat(USA_BBOX[2]); const [sw_x, sw_y] = MercatorCoordinate.fromLngLat(USA_BBOX[3]); const positions = [ // triangle 1 nw_x, nw_y, ne_x, ne_y, se_x, se_y, // triangle 2 se_x, se_y, sw_x, sw_y, nw_x, nw_y, ]; gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW); // enable on the position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); const draw = () => { // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = 6; gl.drawArrays(primitiveType, offset, count); } draw(); // initial draw //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent, canvas); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // save current pos for next movement startX = x; startY = y; // update matrix with new camera and redraw scene updateMatrix(); draw(); }; const handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent, canvas); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events const handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent, canvas); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const zoomDelta = -wheelEvent.deltaY * (1 / 300); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); draw(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); }; export default run;

Rendering GeoJSON

Let’s now take a stab at rendering something a little more complex than a rectangle. For instance, this polygon of Washington state (my home state!)

geojson polygon for washington state

geojson polygon for washington state

Like the rectangle, we’ll also need to divide the shape up into triangles, though it’s a little less obvious how to do that for a shape of this complexity. Fortunately, there are a number of libraries that do just that. We’ll use Mapbox’s earcut, since it has support for GeoJSON geometries out-of-the-box.

To use earcut, we’ll first need to flatten the polygon into a single array of coordinates, and then pass that into the earcut for triangulation. The result is an array of indices for how to draw the triangles. One thing to note, each point in triangles array is for both the latitude & longitude, so you’ll need to get the vertices from vertices[i] and vertices[i + 1].

// convert a GeoJSON geometry to webgl vertices const geometryToVertices = (geometry) => { const data = earcut.flatten(geometry.coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; }

Now that we have our vertices, let’s swap that out for our bounding box from earlier. We'll also need to set the initial camera position to be closer to the actual geometry. We can see the triangles by changing the primitive type to gl.LINES.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import MercatorCoordinate from './mercator-coordinate'; import { createShader, createProgram } from './webgl-utils'; ////////////////////// // constants ////////////////////// import WASHINGTON from '../data/washington.json'; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // color is constant for all vertices const fragmentShaderSource =` precision mediump float; void main() { gl_FragColor = vec4(1, 0, 0.5, 0.9); } `; ////////////////////// // map state ////////////////////// const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation camera.x = -0.6718187712249346; camera.y = 0.29662864586475735; camera.zoom = 5; let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); mat3.scale(cameraMat, cameraMat, [zoomScale, zoomScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } updateMatrix(); ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e, canvas) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const data = earcut.flatten(geometry.coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } ////////////////////// // main program ////////////////////// const run = (canvasId) => { // get GL context from canvas const canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer for vertices const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); // add vertices to buffer const vertices = geometryToVertices(WASHINGTON); gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); // enable on the position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); const draw = () => { // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); } draw(); // initial draw //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent, canvas); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // save current pos for next movement startX = x; startY = y; // update matrix with new camera and redraw scene updateMatrix(); draw(); } const handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent, canvas); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events const handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent, canvas); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const zoomDelta = -wheelEvent.deltaY * (1 / 300); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); draw(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); }; export default run;

And if we want to do render a MultiPolygon, we can just combine the vertices from each polygon into a single array.

const geometryToVertices = (geometry) => { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } // concat all vertices from each polygon if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import MercatorCoordinate from './mercator-coordinate'; import { createShader, createProgram } from './webgl-utils'; ////////////////////// // constants ////////////////////// import USA from '../data/usa_polygon.json'; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // color is constant for all vertices const fragmentShaderSource =` precision mediump float; void main() { gl_FragColor = vec4(1, 0, 0.5, 0.5); } `; ////////////////////// // map state ////////////////////// const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation camera.x = -0.6585079014803341; camera.y = 0.3261614716054737; camera.zoom = 1.64; let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); mat3.scale(cameraMat, cameraMat, [zoomScale, zoomScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } updateMatrix(); ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e, canvas) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { const vertices = verticesFromPolygon([polygon[0]], i); // doing an array.push with too many values can cause // stack size errors, so we manually iterate and append vertices.forEach((vertex) => { positions[positions.length] = vertex; }); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } ////////////////////// // main program ////////////////////// const run = (canvasId) => { // get GL context from canvas const canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer for vertices const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); // add vertices to buffer const vertices = geometryToVertices(USA.geometry); gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); // enable on the position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); const draw = () => { // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); } draw(); // initial draw //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent, canvas); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // save current pos for next movement startX = x; startY = y; // update matrix with new camera and redraw scene updateMatrix(); draw(); } const handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent, canvas); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events const handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent, canvas); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const zoomDelta = -wheelEvent.deltaY * (1 / 300); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); draw(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); }; export default run;

At this point, we have a pretty solid foundation for our map. We can pan, zoom, and render complex geometries. In Part 2, will cover adding vector tile support.

Part 2: Vector Tiles

In Part 1 we created a map that can render GeoJSON polygons. While this is fine if you’re rendering a handful of geometries, it doesn’t scale well if you want to render many more layers, and across the whole planet. For instance, if we wanted to display every building in the US, we'd need to load and render millions (or hundreds of millions) of vertices for the scene.

This is where tiling comes in. I cover this a bit in previous articles, but the idea is the world is broken down into a grid at each zoom level, so we only need to load the data visible in our viewport.

For these examples, we'll be using a tile size of 512px (meaning each tile is 512 X 512 pixels).

Web tile pyramid

Determine Visible Tiles

The first thing to do, is figure out which tiles are in view given our viewport. To do this, we can figure out the lat/lng position of each corner of our viewport (we’ll need to do some conversion math to go from the screen pixel to lat/lng). Once we have a lat/lng and zoom level, we can use that to determine which tile it’s in.

Mapbox has a nice utility library tilebelt for doing these lookups. We can use pointToTile to lookup the min & max tiles once we know the bounding box of our viewport.

// get bbox from viewport const bbox = getBounds(); // find min and max tiles const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); // top-left const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // bottom-right // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } }

One thing to keep in mind, is our viewport might be larger than 2 tiles (> 1024px) so we’ll probably want to consider all tiles between the min and max as “in view”. For example, we could have something like the image below, where the viewport bounding box spans 12 tiles.

web tiles visible in viewport

As we move the map around, the tiles in view should update. Panning left & right should change the tiles in view once we cross a border.

Zooming in & out though is where the real “magic” of a vector map comes into play. Instead of jumping between discrete levels (1, 2, 3 etc…) we can just scale the geometries according to the zoom values in between integers (ie. 1.25 … 1.98). Once we cross into a new zoom integer, we’ll need load a new set of tiles based on that level.

The best way to see how this works in action is to render the tile boundaries as we move around the map. We can use the code above for finding the tiles in view, and run them through tilebel.tileToGeoJSON to render them on the map.

Note: the demo here is using a 256px tile size for demonstration purposes.

Load Vector Tiles

Now that we have a way to determine which tiles are in view, we can go ahead and fetch the vector data from a tileserver.

I covered setting up a vector tile server in a previous article, so I’m going to reuse the existing tile server from there. We just need to replace the x, y, and z values in the URL to fetch the correct tiles.

`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf`

You’ll notice the URL ends with .pbf, so we’ll be getting the data back in Protobuf format. This is a binary format, that we’ll need to deserialize into an object that we can use. Fortunately mapbox has a library that does this for us. @mapbox/vector-tile can deserialize PBF data into a VectorTile object according to the vector tile spec.

const [x, y, z] = tile; const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf`, { responseType: 'arraybuffer', }); const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf);

If we inspect a tile, we can see a .layers field, which contains all the different layers we can potentially render for that tile.

Object.keys(vectorTile.layers); // ['water', 'waterway', 'landcover', 'landuse', 'park', 'boundary', 'transportation', 'building', 'water_name', 'transportation_name', 'place', 'poi', 'aerodrome_label']

You’ll notice VectorTile also has a toGeoJSON function that we can call on each feature in the layer. As we demonstrated in Part 1, we have the ability to render a GeoJSON polygon using earcut. Given that, we should be able to render tiles using the following process:

  • Detect changes to tilesInView
  • Fetch each tile in view from the server
  • Convert the features to GeoJSON
  • Render the feature
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 import axios from 'axios'; import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], }; let tileKey; let tilesInView = []; let tileData = {}; // tile -> layers async function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load tile features from server const key = tilesInView.map(t => t.join('/')).join(';'); if (tileKey !== key) { // tile changed tileData = {}; // process each tile const tileReqs = tilesInView.map(async (tile) => { const [x, y, z] = tile; const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = {}; // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const features = []; for (let i = 0; i < numFeatures; i++) { // get geojson representation of tile const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); // vertices for feature const vertices = geometryToVertices(geojson.geometry); // add to features features.push(vertices); } // store features in layer layers[layer] = features; } }); // store layers for tile tileData[tile.join('/')] = layers; }); await Promise.all(tileReqs); // run concurrently tileKey = key; } } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { const vertices = verticesFromPolygon([polygon[0]], i); // doing an array.push with too many values can cause // stack size errors, so we manually iterate and append vertices.forEach((vertex) => { positions[positions.length] = vertex; }); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// const run = (canvasId) => { // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); const draw = async () => { await updateTiles(); // load tiles // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles Object.keys(tileData).forEach((tile) => { Object.keys(LAYERS).forEach((layer) => { const features = tileData[tile][layer]; const color = LAYERS[layer].map((n) => n / 255); // RGBA to WebGL color // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // render each feature (features || []).forEach((feature) => { // create buffer for vertices const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, feature, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = feature.length / 2; gl.drawArrays(primitiveType, offset, count); }); }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const positionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); } draw(); // initial draw //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); draw(); } const handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events const handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); draw(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); }; export default run;

If you’re familiar with New York City, you should be able to make out the outline of the waterways and the parks. You’ll also notice some flashing, and lag when maneuvering around some of the more complex shapes. This is still a pretty rough implementation, and we’ll cover some performance enhancements and optimizations in Part 3.

Part 3: Optimization and Cleanup

Part 2 of this series left off with a working map that can render geometries from a vector tile server. However, the experience is still rather laggy and has some unpleasant flashes of content. Up to this point, we’ve also just been writing the map code as one-off scripts, with most the values hard-coded.

In this part, we’ll address these performance issues, as well as refactor our code into a more generic, reusable library.

Adding a render loop

Up to now, we’ve just been re-rendering the map whenever there is an interaction, such as a pan or zoom. While this does save us some CPU cycles to not have the canvas constantly re-drawing, it does have some UX implications, especially when it comes to loading the tiles asynchronously.

Rather than calling draw() whenever a state change happens, we’ll just use window.requestAnimationFrame to let the browser render the frame when ready. So when panning & zooming, we’ll just make updates to the camera & matrix values, and those changes will get picked up in the next loop.

A similar approach can also be used for loading the tiles. Instead of awaiting for all the responses to complete and blocking the loop, we can just update the tile data for each request as it completes. So tile requests that are quicker, will get rendered earlier.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 import axios from 'axios'; import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], }; let tileKey; let tilesInView = []; let tileData = {}; // tile -> layers function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load tile features from server const key = tilesInView.map(t => t.join('/')).join(';'); if (tileKey !== key) { // tile changed tileData = {}; // process each tile concurrently, and update data on complete tilesInView.forEach(async (tile) => { const [x, y, z] = tile; const reqStart = Date.now(); const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = {}; // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const features = []; for (let i = 0; i < numFeatures; i++) { // get geojson representation of tile const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); // vertices for feature const vertices = geometryToVertices(geojson.geometry); // add to features features.push(vertices); } // store features in layer layers[layer] = features; } }); // store layers for tile tileData[tile.join('/')] = layers; }); tileKey = key; } } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let timestamp; let slowCount; let frameStats; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0, features: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles Object.keys(tileData).forEach((tile) => { Object.keys(LAYERS).forEach((layer) => { const features = tileData[tile][layer]; const color = LAYERS[layer].map((n) => n / 255); // RGBA to WebGL color // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // render each feature (features || []).forEach((feature) => { frameStats.features++; // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, feature, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = feature.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= feature.length; }); }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop on mobile if (mobile) { stop(); if (abort) { abort(); } return; } // kill loop if gets too slow // 5 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 5) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_TILE_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getFrameStats = () => { return frameStats; } export default run;

Now that we’re loading the tiles concurrently, you'll notice the flashing happening on a per-tile basis, rather than all-at-once. However, you might have got into a state where the map was killed (trying not to crash your browser!).

Since we’re now calling draw many times per second (ideally 60), we are making a ton of calls to shuffle data into GPU. For instance, here are the stats for the most recent frame that was rendered:

// last render stats
no. of gl draw calls: undefined
no. of vertices: undefined

That means for each frame, it needs to buffer data into WebGL times. Which is (probably) a lot, considering we're trying to aim for 60 frames per second.

To fix this, we can cut down the number of times we're buffering data into the GPU.

Reducing WebGL buffer calls

In the current approach, we’re storing the vertices for each individual feature, for each layer, for each tile. In other words our tileData, which is storing the data per-tile, looks something like:

tileData: {
  '1/1/1': {
    layer_1: [
      feature_1 vertices,
      feature_2 vertices,
      …
      feature_n vertices,
    ],
    … // more layers
  },
  '1/1/2': {
    …
  }
  … // more tiles
}

Since all the features for a given layer are rendered the same (ie. same color), we can just combine all of the feature vertices into a single array for the layer. This will cut down the number of times we need to reset the buffers and call gl.drawArrays to once per layer, per tile. So our new tileData structure will look something like:

tileData: {
  '1/1/1': [
    { layer: ‘layer_1’, vertices: […] },
    { layer: ‘layer_2’, vertices: […] },
    …
  ]
  …
}

And the updated code that processes the tile:

const layers = []; Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; // concat vertices for all features of layer so they can all be rendered at once const vertices = []; for (let i = 0; i < numFeatures; i++) { const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); vertices.push(...geometryToVertices(geojson.geometry)); // concat all vertices } layers.push({ layer, vertices: Float32Array.from(vertices) }); } });
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 import axios from 'axios'; import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], }; let tileKey; let tilesInView = []; let tileData = {}; // tile -> layers function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load tile features from server const key = tilesInView.map(t => t.join('/')).join(';'); if (tileKey !== key) { // tile changed tileData = {}; // process each tile concurrently, and update data on complete tilesInView.forEach(async (tile) => { const [x, y, z] = tile; const reqStart = Date.now(); const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = [] // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const vertices = []; for (let i = 0; i < numFeatures; i++) { const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); vertices.push(...geometryToVertices(geojson.geometry)); } layers.push({ layer, vertices: Float32Array.from(vertices) }); } }); // store layers for tile tileData[tile.join('/')] = layers; }); tileKey = key; } } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let timestamp; let slowCount; let frameStats; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.clearColor(0, 0, 0, 0); gl.useProgram(program); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles Object.keys(tileData).forEach((tile) => { tileData[tile].forEach((tileLayer) => { const { layer, vertices } = tileLayer; if (LAYERS[layer]) { const color = LAYERS[layer].map(n => n / 255); // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= vertices.length; } }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop if gets too slow // 10 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 10) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getFrameStats = () => { return frameStats; } export default run;

You’ll notice the frame rate is consistently much higher, and navigating is much smoother. In fact, the jump in performance was high enough that we easily added an additional buildings layer (the brown-ish rectangles rendered at high zoom levels).

// last render stats
no. of gl draw calls: undefined
no. of vertices: undefined

Even though the frame rate is higher, we’re still getting some flashing when loading the tiles, so let’s address that next.

Tile caching

The tile flashing is a relatively simple fix. In our updateTiles code, we just need to check if we’ve already loaded that tile at some point, and just re-use the data if it already exists (instead of fetching it from the server).

// process each tile concurrently, and update data on complete tilesInView.forEach(async (tile) => { if (tileData[tile.join('/')]) { return; // already loaded, no need to fetch } const [x, y, z] = tile; const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf`, { responseType: 'arraybuffer', }); ...
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import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], }; let tilesInView = []; let tileData = {}; // tile -> layers let cacheStats = { tilesLoaded: 0, cacheHits: 0 }; function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // process each tile concurrently, and update data on complete tilesInView.forEach(async (tile) => { if (tileData[tile.join('/')]) { cacheStats.cacheHits++; return; // already loaded, no need to fetch } const [x, y, z] = tile; const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); cacheStats.tilesLoaded++; const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = [] // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const vertices = []; for (let i = 0; i < numFeatures; i++) { const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); vertices.push(...geometryToVertices(geojson.geometry)); } layers.push({ layer, vertices: Float32Array.from(vertices) }); } }); // store layers for tile tileData[tile.join('/')] = layers; }); } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let timestamp; let slowCount; let frameStats; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.useProgram(program); gl.clearColor(0, 0, 0, 0); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles tilesInView.forEach((tile) => { const data = tileData[tile.join('/')]; (data || []).forEach((tileLayer) => { const { layer, vertices } = tileLayer; if (LAYERS[layer]) { const color = LAYERS[layer].map(n => n / 255); // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= vertices.length; } }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop if gets too slow // 10 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 10) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getCacheStats = () => { return cacheStats; } export default run;

As we move around, we can see how many requests we're saving by not refetching tiles already loaded. There's still some flashing the first time a tile is loaded, but cached tiles should render seamlessly when moving between them.

tiles loaded: undefined
cache hits: undefined

Buffering tiles

Now that we’ve solved the issue of repeatedly flashing tiles, let's clean up the flash on the initial load, that can sometimes be seen when moving the map quickly.

We know that cached tiles will render seamlessly when moved back into view, so we can actually pre-load tiles that are near the viewport (ie. tiles we will likely navigate into).

We just need to configure how much we want to buffer. For now, let's just load an additional tile in each direction (min - 1, max + 1) to make sure the nearest tiles are covered for panning, as well as the parent (tiles above). We'll talk about the child tiles in the next section.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 import axios from 'axios'; import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], }; const TILE_BUFFER = 1; // 1 tile in each direction let tilesInView = []; let tileData = {}; // tile -> layers let cacheStats = { tilesLoaded: 0, cacheHits: 0 }; function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load additional tiles outside of viewport const bufferedTiles = []; for (let bufX = minX - TILE_BUFFER; bufX <= maxX + TILE_BUFFER; bufX++) { for (let bufY = minY - TILE_BUFFER; bufY <= maxY + TILE_BUFFER; bufY++) { bufferedTiles.push([bufX, bufY, z]); // buffer in xy direction // load parent tiles 2 levels up bufferedTiles.push(tilebelt.getParent([bufX, bufY, z])); bufferedTiles.push(tilebelt.getParent(tilebelt.getParent([bufX, bufY, z]))); } } // remove dupes (and convert to strings) let tilesToLoad = [ ...new Set([ ...tilesInView.map(t => t.join('/')), ...bufferedTiles.map(t => t.join('/')) ]) ]; // make sure tiles are in range tilesToLoad = tilesToLoad.filter((tile) => { const [x, y, z] = tile.split('/').map(Number); const N = Math.pow(2, z); const validX = x >= 0 && x < N; const validY = y >= 0 && y < N; const validZ = z >= 0 && z <= MAX_TILE_ZOOM; return validX && validY && validZ; }); // process each tile concurrently, and update data on complete tilesToLoad.forEach(async (tile) => { if (tileData[tile]) { cacheStats.cacheHits++; return; // already loaded, no need to fetch } else { tileData[tile] = []; // temp hold for request } try { const [x, y, z] = tile.split('/').map(Number); const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); cacheStats.tilesLoaded++; const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = [] // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const vertices = []; for (let i = 0; i < numFeatures; i++) { const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); vertices.push(...geometryToVertices(geojson.geometry)); } layers.push({ layer, vertices: Float32Array.from(vertices) }); } }); // store layers for tile tileData[tile] = layers; } catch (e) { console.warn(`Tile ${tile} request failed.`, e); tileData[tile] = undefined; // release hold } }); } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let frameStats; let slowCount; let timestamp; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.useProgram(program); gl.clearColor(0, 0, 0, 0); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles tilesInView.forEach((tile) => { const data = tileData[tile.join('/')]; (data || []).forEach((tileLayer) => { const { layer, vertices } = tileLayer; if (LAYERS[layer]) { const color = LAYERS[layer].map(n => n / 255); // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= vertices.length; } }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop if gets too slow // 10 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 10) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getCacheStats = () => { return cacheStats; } export default run;

With the exception of zooming in/out really quickly, the flashing should be greatly reduced when moving around. But we can take it a step further by scaling the data we already have to fill in missing tiles.

Scaling Tiles as a Placeholder

The last thing we’ll do to prevent the flashing you see when zooming, is to just keep scaling the data that we already have in place of tiles that are still downloading.

Take zooming in for example. If we’re on zoom level 8, we will keep scaling the tiles up until we hit zoom level 9, at which point we render the level 9 tiles in view. But if those aren’t done being downloaded and parsed yet, we’ll see a white square in its place. So what we can do, is continue to scale the level 8 tile up in its place, until we have the data for the correct tile (ie. we’ll still be rendering the level 8 tile at 9+).

Similarly with zooming out, we can render all of the children for a tile if the one at the lower level isn’t available. This one is a bit more noticeable, since as we zoom out, we might only have partial children available for a parent tile. Take the screenshot below for instance, notice that not all of the child tiles are available. So while still not perfect, it’s slight improvement on the whole tile being blank.

rendering a tile with partially loaded child tiles

rendering a tile with partially loaded child tiles

To accomplish this, we just need to introduce some fallback behavior for when tile data from tileInView is not available. We’ll favor the case where the parent tile is available, since that will always cover more area, but we can still fallback to the child tiles in cases where we’re zooming out.

We can leverage the tilebelt library again for determining the parent tilebel.getParent and children tilebelt.getChildren tiles.

function getPlaceholderTile(tile) { // use parent if available const parent = tilebelt.getParent(tile)?.join('/'); const parentFeatureSet = tileData[parent]; if (parentFeatureSet?.length > 0) { return parentFeatureSet; } // use whatever children are available const childFeatureSets = []; const children = (tilebelt.getChildren(tile) || []).map(t => t.join('/')); children.forEach((child) => { const featureSet = tileData[child]; if (featureSet?.length > 0) { childFeatureSets.push(...featureSet); } }); return childFeatureSets; } ... // in draw: tilesInView.forEach((tile) => { let data = tileData[tile.join('/')]; // use placehodler if tile in view is not available if (data?.length === 0) { data = getPlaceholderTile(tile); } (data || []).forEach((tileLayer) => { // ... render code }

And adding this fallback behavior to our code, should provide a smoother experience (ie. fewer flashes) as we move around the map.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 import axios from 'axios'; import Protobuf from 'pbf'; import { mat3, vec3 } from 'gl-matrix'; import earcut from 'earcut'; import tilebelt from '@mapbox/tilebelt'; import { VectorTile } from '@mapbox/vector-tile'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], }; const TILE_BUFFER = 1; // 1 tile in each direction let tilesInView = []; let tileData = {}; // tile -> layers let cacheStats = { tilesLoaded: 0, cacheHits: 0 }; function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load additional tiles outside of viewport const bufferedTiles = []; for (let bufX = minX - TILE_BUFFER; bufX <= maxX + TILE_BUFFER; bufX++) { for (let bufY = minY - TILE_BUFFER; bufY <= maxY + TILE_BUFFER; bufY++) { bufferedTiles.push([bufX, bufY, z]); // buffer in xy direction // load parent tiles 2 levels up bufferedTiles.push(tilebelt.getParent([bufX, bufY, z])); bufferedTiles.push(tilebelt.getParent(tilebelt.getParent([bufX, bufY, z]))); } } // remove dupes (and convert to strings) let tilesToLoad = [ ...new Set([ ...tilesInView.map(t => t.join('/')), ...bufferedTiles.map(t => t.join('/')) ]) ]; // make sure tiles are in range tilesToLoad = tilesToLoad.filter((tile) => { const [x, y, z] = tile.split('/').map(Number); const N = Math.pow(2, z); const validX = x >= 0 && x < N; const validY = y >= 0 && y < N; const validZ = z >= 0 && z <= MAX_TILE_ZOOM; return validX && validY && validZ; }); // process each tile concurrently, and update data on complete tilesToLoad.forEach(async (tile) => { if (tileData[tile]) { cacheStats.cacheHits++; return; // already loaded, no need to fetch } else { tileData[tile] = []; // temp hold for request } try { const [x, y, z] = tile.split('/').map(Number); const res = await axios.get(`https://maps.ckochis.com/data/v3/${z}/${x}/${y}.pbf?apiKey=${config('mapsApiKey')}`, { responseType: 'arraybuffer', }); cacheStats.tilesLoaded++; const pbf = new Protobuf(res.data); const vectorTile = new VectorTile(pbf); // process only the layers we are using const layers = [] // layers -> features Object.keys(LAYERS).forEach((layer) => { if (vectorTile?.layers?.[layer]) { const numFeatures = vectorTile.layers[layer]?._features?.length || 0; const vertices = []; for (let i = 0; i < numFeatures; i++) { const geojson = vectorTile.layers[layer].feature(i).toGeoJSON(x, y, z); vertices.push(...geometryToVertices(geojson.geometry)); } layers.push({ layer, vertices: Float32Array.from(vertices) }); } }); // store layers for tile tileData[tile] = layers; } catch (e) { console.warn(`Tile ${tile} request failed.`, e); tileData[tile] = undefined; // release hold } }); } function getPlaceholderTile(tile) { // use parent if available const parent = tilebelt.getParent(tile)?.join('/'); const parentFeatureSet = tileData[parent]; if (parentFeatureSet?.length > 0) { return parentFeatureSet; } // use whatever children are available const childFeatureSets = []; const children = (tilebelt.getChildren(tile) || []).map(t => t.join('/')); children.forEach((child) => { const featureSet = tileData[child]; if (featureSet?.length > 0) { childFeatureSets.push(...featureSet); } }); return childFeatureSets; } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // convert a GeoJSON geometry to webgl vertices function geometryToVertices(geometry) { const verticesFromPolygon = (coordinates, n) => { const data = earcut.flatten(coordinates); const triangles = earcut(data.vertices, data.holes, 2); const vertices = new Float32Array(triangles.length * 2); for (let i = 0; i < triangles.length; i++) { const point = triangles[i]; const lng = data.vertices[point * 2]; const lat = data.vertices[point * 2 + 1]; const [x, y] = MercatorCoordinate.fromLngLat([lng, lat]); vertices[i * 2] = x; vertices[i * 2 + 1] = y; } return vertices; } if (geometry.type === 'Polygon') { return verticesFromPolygon(geometry.coordinates); } if (geometry.type === 'MultiPolygon') { const positions = []; geometry.coordinates.forEach((polygon, i) => { positions.push(...verticesFromPolygon([polygon[0]], i)); }); return Float32Array.from(positions); } // only support Polygon & Multipolygon for now return new Float32Array(); } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let timestamp; let slowCount; let frameStats; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.useProgram(program); gl.clearColor(0, 0, 0, 0); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles tilesInView.forEach((tile) => { let data = tileData[tile.join('/')]; if (data?.length === 0) { data = getPlaceholderTile(tile); } (data || []).forEach((tileLayer) => { const { layer, vertices } = tileLayer; if (LAYERS[layer]) { const color = LAYERS[layer].map(n => n / 255); // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= vertices.length; } }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop if gets too slow // 10 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 10) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getCacheStats = () => { return cacheStats; } export default run;

One issue with the current approach, is the CPU overhead of running lots of requests concurrently, and parsing the geometries (which is a CPU blocking operation). For instance, the initial load of the map fires off ~30 requests to load all the buffered tiles.

tiles loaded: undefined
cache hits: undefined

Since a lot of this is work that can happen in the background, we can offload it to a Web Worker to free up resources on the main thread.

Using a Web Worker

The most resource heavy part of our code right now is probably the HTTP request to fetch a tile, followed by converting the geometries to vertices & triangles. Luckily, both these tasks are part of the same operation (fetch then parse), so we can pretty easily move this code to a WebWorker, which leaves the main thread free to handle the render loop, and other map interactions.

If we abstract a way the fetching / parsing code into a fetchTile helper, our worker is pretty simple:

import { fetchTile } from './map-utils'; addEventListener('message', async (event) => { const { tile, layers, url } = event.data; try { const tileData = await fetchTile({ tile, layers, url }); postMessage({ tile, tileData }); } catch (e) { console.warn('Worker error.', e); postMessage({ tile }); // undefined tileData will unset cache hold } });

And then when looping through our updated tiles, we can hand them off to the worker for processing

tileWorker = new Worker(new URL('./tile-worker.js', import.meta.url)); tileWorker.onmessage = (event) => { const { tile, tileData } = event.data; tiles[tile] = tileData; }; ... tilesToLoad.forEach(async (tile) => { if (tiles[tile]) { return; // already loaded, no need to fetch } tiles[tile] = []; // temp hold for request // load buffered tiles in web worker tileWorker.postMessage({ tile, layers: LAYERS, url: TILE_SERVER_URL }); });
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 import { mat3, vec3 } from 'gl-matrix'; import tilebelt from '@mapbox/tilebelt'; import MercatorCoordinate from './mercator-coordinate'; import Stats from 'stats.js'; import { createShader, createProgram } from './webgl-utils'; import { geometryToVertices, fetchTile } from './map-utils'; import config from '../config'; ////////////////////// // constants ////////////////////// const TILE_SERVER_URL = `https://maps.ckochis.com/data/v3/{z}/{x}/{y}.pbf?apiKey=${config('mapsApiKey')}`; const TILE_SIZE = 512; const MAX_TILE_ZOOM = 14; const MIN_ZOOM = 0; const MAX_ZOOM = 16; ////////////////////// // shaders ////////////////////// // vertex shader just passes through the position, // no modification to the vertices const vertexShaderSource = ` attribute vec2 a_position; uniform mat3 u_matrix; // 3 X 3 matrix void main() { vec2 position = (u_matrix * vec3(a_position, 1)).xy; gl_Position = vec4(position, 0, 1); } `; // set color via uniform const fragmentShaderSource =` precision mediump float; uniform vec4 u_color; void main() { gl_FragColor = u_color; } `; ////////////////////// // map state ////////////////////// let loopRunning = true; const camera = { x: 0, y: 0, zoom: 0, }; // initial transformation (Brooklyn) camera.x = -0.41101919888888894; camera.y = 0.2478952993354263; camera.zoom = 13; // DOM elements let canvas; let overlay; let statsWidget; const LAYERS = { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], }; const TILE_BUFFER = 1; // 1 tile in each direction let tiles = {}; // tile -> layers let tilesInView = []; let tileWorker; function updateTiles() { const bbox = getBounds(); const z = Math.min(Math.trunc(camera.zoom), MAX_TILE_ZOOM); const minTile = tilebelt.pointToTile(bbox[0], bbox[3], z); const maxTile = tilebelt.pointToTile(bbox[2], bbox[1], z); // tiles visible in viewport tilesInView = []; const [minX, maxX] = [Math.max(minTile[0], 0), maxTile[0]]; const [minY, maxY] = [Math.max(minTile[1], 0), maxTile[1]]; for (let x = minX; x <= maxX; x++) { for (let y = minY; y <= maxY; y++) { tilesInView.push([x, y, z]); } } // load additional tiles outside of viewport let bufferedTiles = []; for (let bufX = minX - TILE_BUFFER; bufX <= maxX + TILE_BUFFER; bufX++) { for (let bufY = minY - TILE_BUFFER; bufY <= maxY + TILE_BUFFER; bufY++) { bufferedTiles.push([bufX, bufY, z]); // buffer in xy direction // load parent tiles 2 levels up bufferedTiles.push(tilebelt.getParent([bufX, bufY, z])); bufferedTiles.push(tilebelt.getParent(tilebelt.getParent([bufX, bufY, z]))); } } // remove dupes from in view let tilesToLoad = [ ...new Set([ ...tilesInView.map(t => t.join('/')), ...bufferedTiles.map(t => t.join('/')) ]) ]; // make sure tiles are in range tilesToLoad = tilesToLoad.filter((tile) => { const [x, y, z] = tile.split('/').map(Number); const N = Math.pow(2, z); const validX = x >= 0 && x < N; const validY = y >= 0 && y < N; const validZ = z >= 0 && z <= MAX_TILE_ZOOM; return validX && validY && validZ; }); // process each tile concurrently, and update data on complete const inView = tilesInView.map(t => t.join('/')); tilesToLoad.forEach(async (tile) => { if (tiles[tile]) { return; // already loaded, no need to fetch } tiles[tile] = []; // temp hold for request try { if (inView.includes(tile)) { // prioritize tiles in-view on main thread (I dont know if this actually helps...) const tileData = await fetchTile({ tile, layers: LAYERS, url: TILE_SERVER_URL }); tiles[tile] = tileData; } else { // load buffered tiles in worker tileWorker.postMessage({ tile, layers: LAYERS, url: TILE_SERVER_URL }); // handle with web worker } } catch (e) { console.warn(`Error loading tile ${tile}`. e); tiles[tile] = undefined; // release hold } }); } let matrix; function updateMatrix() { const cameraMat = mat3.create(); // translate mat3.translate(cameraMat, cameraMat, [camera.x, camera.y]); // scale const zoomScale = 1 / Math.pow(2, camera.zoom); const widthScale = TILE_SIZE / canvas.width; const heightScale = TILE_SIZE / canvas.height; mat3.scale(cameraMat, cameraMat, [zoomScale / widthScale, zoomScale / heightScale]); // update matrix matrix = mat3.multiply( [], mat3.create(), // identity matrix mat3.invert([], cameraMat) // invert camera position ); } ////////////////////// // helpers ////////////////////// function getClipSpacePosition(e) { // handle mouse and touch events const [x, y] = [ e.center?.x || e.clientX, e.center?.y || e.clientY ]; // get canvas relative css position const rect = canvas.getBoundingClientRect(); const cssX = x - rect.left; const cssY = y - rect.top; // get normalized 0 to 1 position across and down canvas const normalizedX = cssX / canvas.clientWidth; const normalizedY = cssY / canvas.clientHeight; // convert to clip space const clipX = normalizedX * 2 - 1; const clipY = normalizedY * -2 + 1; return [clipX, clipY]; } // get bbox coordinates for viewport function getBounds() { const zoomScale = Math.pow(2, camera.zoom); // undo clip-space const px = (1 + camera.x) / 2; const py = (1 - camera.y) / 2; // get world coord in px const wx = px * TILE_SIZE; const wy = py * TILE_SIZE; // get zoom px const zx = wx * zoomScale; const zy = wy * zoomScale; // get bottom-left and top-right pixels let x1 = zx - (canvas.width / 2); let y1 = zy + (canvas.height / 2); let x2 = zx + (canvas.width / 2); let y2 = zy - (canvas.height / 2); // convert to world coords x1 = x1 / zoomScale / TILE_SIZE; y1 = y1 / zoomScale / TILE_SIZE; x2 = x2 / zoomScale / TILE_SIZE; y2 = y2 / zoomScale / TILE_SIZE; // get LngLat bounding box const bbox = [ Math.max(MercatorCoordinate.lngFromMercatorX(x1), -180), Math.max(MercatorCoordinate.latFromMercatorY(y1), -85.05), Math.min(MercatorCoordinate.lngFromMercatorX(x2), 180), Math.min(MercatorCoordinate.latFromMercatorY(y2), 85.05), ]; return bbox; } function atLimits() { const bbox = getBounds(); return bbox[0] === -180 || bbox[1] === -85.05 || bbox[2] === 180 || bbox[3] === 85.05; } ////////////////////// // main program ////////////////////// let handlePan; let handleZoom; let timestamp; let slowCount; let frameStats; const run = (canvasId, mobile, abort) => { // setup loop state loopRunning = true; timestamp = 0; slowCount = 0; // create stats object for widget const stats = new Stats(); // get GL context from canvas canvas = document.getElementById(canvasId); const gl = canvas.getContext("webgl"); // get overlay overlay = document.getElementById(`${canvasId}-overlay`); // setup tile worker tileWorker = new Worker(new URL('./tile-worker.js', import.meta.url)); tileWorker.onmessage = (event) => { const { tile, tileData } = event.data; tiles[tile] = tileData; }; tileWorker.onerror = (error) => { console.error('Uncaught worker error.', error); }; // setup initial state updateMatrix(); updateTiles(); // setup viewport gl.viewport(0, 0, gl.canvas.width, gl.canvas.height); // compile shaders const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource); const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource); // init gl program const program = createProgram(gl, vertexShader, fragmentShader); gl.useProgram(program); gl.clearColor(0, 0, 0, 0); // create buffer const positionBuffer = gl.createBuffer(); const draw = () => { frameStats = { drawCalls: 0, vertices: 0 }; stats.begin(); // set matrix as uniform const matrixLocation = gl.getUniformLocation(program, "u_matrix"); gl.uniformMatrix3fv(matrixLocation, false, matrix); // render tiles tilesInView.forEach((tile) => { const tileData = tiles[tile.join('/')]; (tileData || []).forEach((tileLayer) => { const { layer, vertices } = tileLayer; if (LAYERS[layer]) { const color = LAYERS[layer].map(n => n / 255); // set color uniform for layer const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, color); // create buffer for vertices gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.TRIANGLES; offset = 0; const count = vertices.length / 2; gl.drawArrays(primitiveType, offset, count); frameStats.drawCalls++; frameStats.vertices+= vertices.length; } }); }); overlay.replaceChildren(); // clear labels to redraw // render boundaries and label for tiles in view tilesInView.forEach((tile) => { const colorLocation = gl.getUniformLocation(program, "u_color"); gl.uniform4fv(colorLocation, [1, 0, 0, 1]); const tileVertices = geometryToVertices(tilebelt.tileToGeoJSON(tile)); gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer); gl.bufferData(gl.ARRAY_BUFFER, tileVertices, gl.STATIC_DRAW); // setup position attribute const positionAttributeLocation = gl.getAttribLocation(program, "a_position"); gl.enableVertexAttribArray(positionAttributeLocation); // tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) const size = 2; const type = gl.FLOAT; const normalize = false; const stride = 0; let offset = 0; gl.vertexAttribPointer(positionAttributeLocation, size, type, normalize, stride, offset); // draw const primitiveType = gl.LINES; offset = 0; const count = tileVertices.length / 2; gl.drawArrays(primitiveType, offset, count); // draw tile labels const tileCoordinates = tilebelt.tileToGeoJSON(tile).coordinates; const topLeft = tileCoordinates[0][0]; const [x, y] = MercatorCoordinate.fromLngLat(topLeft); const [clipX, clipY] = vec3.transformMat3( [], [x, y, 1], matrix, ); const wx = ((1 + clipX) / 2) * canvas.width; const wy = ((1 - clipY) / 2) * canvas.height; const div = document.createElement("div"); div.className = "tile-label"; div.style.left = (wx + 8) + "px"; div.style.top = (wy + 8) + "px"; div.style.position = 'absolute'; div.style.zIndex = 1000; div.appendChild(document.createTextNode(tile.join('/'))); overlay.appendChild(div); }); // kill loop if gets too slow // 10 frames under 10 FPS const now = performance.now(); const fps = 1 / ((now - timestamp) / 1000); if (fps < 10) { slowCount++; if (slowCount > 10) { console.warn(`Too slow. Killing loop for ${canvasId}.`); stop(); if (abort) { abort(); } } } timestamp = now; // end of loop stats.end(); if (loopRunning) { window.requestAnimationFrame(draw); } } window.requestAnimationFrame(draw); // start loop //////////////////////// // interaction handlers //////////////////////// // handle touch events const Hammer = require('hammerjs'); const hammer = new Hammer(canvas); hammer.get('pan').set({ direction: Hammer.DIRECTION_ALL }); hammer.get('pinch').set({ enable: true }); // handle pan events let startX; let startY; // handle drag changes while mouse is still down const handleMove = (moveEvent) => { const [x, y] = getClipSpacePosition(moveEvent); // compute the previous position in world space const [preX, preY] = vec3.transformMat3( [], [startX, startY, 0], mat3.invert([], matrix) ); // compute the new position in world space const [postX, postY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // move that amount, because how much the position changes depends on the zoom level const deltaX = preX - postX; const deltaY = preY - postY; if (isNaN(deltaX) || isNaN(deltaY)) { return; // abort } // only update within world limits camera.x += deltaX; camera.y += deltaY; // update matrix with new camera updateMatrix(); // prevent further pan if at limits if (atLimits()) { camera.x -= deltaX; camera.y -= deltaY; updateMatrix(); return; // abort } // save current pos for next movement startX = x; startY = y; updateMatrix(); updateTiles(); } handlePan = (startEvent) => { // get position of initial drag [startX, startY] = getClipSpacePosition(startEvent); canvas.style.cursor = 'grabbing'; window.addEventListener('mousemove', handleMove); hammer.on('pan', handleMove); // clear on release const clear = (event) => { canvas.style.cursor = 'grab'; window.removeEventListener('mousemove', handleMove); window.removeEventListener('mouseup', clear); hammer.off('pan', handleMove); hammer.off('panend', clear); }; window.addEventListener('mouseup', clear); hammer.on('panend', clear); } canvas.addEventListener('mousedown', handlePan); hammer.on('panstart', handlePan); // handle zoom events handleZoom = (wheelEvent) => { wheelEvent.preventDefault(); const [x, y] = getClipSpacePosition(wheelEvent); // get position before zooming const [preZoomX, preZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // update current zoom state const prevZoom = camera.zoom; const zoomDelta = -wheelEvent.deltaY * (1 / 500); camera.zoom += zoomDelta; camera.zoom = Math.max(MIN_ZOOM, Math.min(camera.zoom, MAX_ZOOM)); updateMatrix(); // prevent further zoom if at limits if (atLimits()) { camera.zoom = prevZoom updateMatrix(); return; } // get new position after zooming const [postZoomX, postZoomY] = vec3.transformMat3( [], [x, y, 0], mat3.invert([], matrix) ); // camera needs to be translated the difference of before and after camera.x += preZoomX - postZoomX; camera.y += preZoomY - postZoomY; updateMatrix(); updateTiles(); } canvas.addEventListener('wheel', handleZoom); hammer.on('pinch', handleZoom); // setup stats widget stats.showPanel(0); // frame rate statsWidget = stats.dom; statsWidget.style.position = 'absolute'; statsWidget.style.left = mobile ? 0 : '-100px'; statsWidget.style.zIndex = '0'; canvas.parentElement.appendChild(statsWidget); }; export const stop = () => { loopRunning = false; // clear event handlers if (canvas) { canvas.removeEventListener('wheel', handleZoom); canvas.removeEventListener('mousedown', handlePan); overlay.replaceChildren(); statsWidget.remove(); } }; // get the latest frame stats export const getCacheStats = () => { return cacheStats; } export default run;

The results aren’t that indistinguishable from the previous buffered example, probably due to the bottleneck being the latency on the http request, which is the same regardless. We could probably measure the difference in CPU, but it’s likely negligible given we’re only rendering a few layers.

Wrapping it all up

Up until this point, I’ve been using a one-off JS script for every map. While this is fine for quick prototyping, it’s not very reusable, and makes it difficult to configure settings on-the-fly since most values are hard-coded.

The last piece, is wrapping this all up into a reusable library with a standard map-like interface than we can instantiate with our configuration, and easily update.

const map = new WebGLMap({ id: 'myCanvasId', tileServerURL: 'https://maps.ckochis.com/data/v3/{z}/{x}/{y}.pbf', width: 800, height: 600, center: [-73.9834558, 40.6932723], minZoom: 4, maxZoom: 18, zoom: 13, debug: true, layers: { water: [180, 240, 250, 255], landcover: [202, 246, 193, 255], park: [202, 255, 193, 255], building: [185, 175, 139, 191], } }); ... map.setOptions({ zoom: 10, debug: false });

You can find the code for it at webgl-map on Github as well as the demo-page built with the library.

If you’ve followed along, I hope you’ve enjoyed, or at least found it helpful. If you have any questions or comments, feel free to get in touch.

Mapping data is provided by OpenStreetMap contributors.