How can I show the distance a polyline has covered while animating it in Mapbox GL JS? - html5-canvas

Question

I am using Mapbox GL JS to capture frame by frame video of the animation of a geoJson (similar to what is described here: https://docs.mapbox.com/mapbox-gl-js/example/animate-a-line/).
The strategy for encoding mapbox animations into mp4 here are described here:
https://github.com/mapbox/mapbox-gl-js/issues/5297 and https://github.com/mapbox/mapbox-gl-js/pull/10172 .
I would like to show the distance the polyline has covered as I draw each frame. I need the distance to be in the GL itself (as opposed to, for example, an HTML element on top of the canvas), since that's where I'm capturing the video from.
Can someone help describe a performant strategy for doing this to me?

Answer 1

Aside from tearing apart the Mapbox GL JS, why not simply try drawing directly onto the mapbox canvas?
In this example, there are two canvases, created identically.
With the second, there is another requestAnimationFrame loop that adds an overlay.
I've also shown how it can be recorded with MediaRecorder.
const canvas1 = document.getElementById('canvas1')
const canvas2 = document.getElementById('canvas2')
const video = document.getElementById('output')
const status = document.getElementById('status')
let x = 0 // Value to be displayed
const setupCanvas = (canvas) => {
canvas.height = 300
canvas.width = 300
const canvas1Ctx = canvas.getContext('2d')
canvas1Ctx.fillStyle = 'black'
canvas1Ctx.fillRect(300, 100, 100, 100)
const animateCanvas = () => {
x += 2;
if (x > 300) x = 10
canvas1Ctx.fillStyle = 'rgba(20,20,20,1)'
canvas1Ctx.fillRect(0, 0, canvas.width, canvas.height)
canvas1Ctx.beginPath()
canvas1Ctx.arc(x, 100, 20, 0, 2 * Math.PI)
canvas1Ctx.fillStyle = 'rgba(250,0,0,1)'
canvas1Ctx.fill()
requestAnimationFrame(animateCanvas)
}
animateCanvas()
}
const addOverlay = (canvas) => {
const canvasCtx = canvas2.getContext('2d')
function animateOverlay() {
canvasCtx.font = '48px serif'
canvasCtx.fillStyle = 'white'
canvasCtx.fillText(`X: ${x}`, 10, 50)
requestAnimationFrame(animateOverlay)
}
animateOverlay()
}
const initVideoCapture = () => {
var videoStream = canvas2.captureStream(30)
var mediaRecorder = new MediaRecorder(videoStream)
var chunks = []
mediaRecorder.ondataavailable = function(e) {
chunks.push(e.data)
}
mediaRecorder.onstop = function(e) {
var blob = new Blob(chunks, {
'type': 'video/mp4'
})
chunks = []
var videoURL = URL.createObjectURL(blob)
video.src = videoURL
}
mediaRecorder.ondataavailable = function(e) {
chunks.push(e.data)
}
mediaRecorder.start()
status.textContent = 'Recording...'
setTimeout(function() {
mediaRecorder.stop()
status.textContent = 'Complete'
}, 5000)
}
setupCanvas(canvas1)
setupCanvas(canvas2)
addOverlay(canvas2)
initVideoCapture()
<canvas id="canvas1"></canvas>
<canvas id="canvas2"></canvas>
<video id="output" autoplay controls></video>
<p>Status: <span id="status">Loading</span></p>

Answer 2

Try this :
// show the distance a polyline has covered while animating it in mapbox gl js
var map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/streets-v9',
center: [-74.5, 40],
zoom: 9,
})
var geojson = {
type: 'Feature',
properties: {},
geometry: {
type: 'LineString',
coordinates: [
[-74.5, 40],
[-74.45, 40.7],
[-74.36, 40.8],
[-74.36, 41.2],
],
},
}
map.on('load', function () {
map.addLayer({
id: 'route',
type: 'line',
source: {
type: 'geojson',
data: geojson,
},
layout: {
'line-join': 'round',
'line-cap': 'round',
},
paint: {
'line-color': '#888',
'line-width': 8,
},
})
var lineDistance = turf.lineDistance(geojson, 'kilometers')
var arc = []
var maxTravelTime = 0
for (var i = 0; i < lineDistance; i += lineDistance / 200) {
var segment = turf.along(geojson, i, 'kilometers')
arc.push(segment.geometry.coordinates)
}
map.addLayer({
id: 'point',
type: 'symbol',
source: {
type: 'geojson',
data: {
type: 'FeatureCollection',
features: [
{
type: 'Feature',
properties: {},
geometry: {
type: 'Point',
coordinates: arc[0],
},
},
],
},
},
layout: {
'icon-image': 'car',
'icon-rotate': ['get', 'bearing'],
'icon-rotation-alignment': 'map',
'icon-allow-overlap': true,
'icon-ignore-placement': true,
},
})
function animate() {
map.getSource('point').setData(geojson)
if (maxTravelTime < lineDistance) {
maxTravelTime += lineDistance / 200
} else {
maxTravelTime = 0
}
requestAnimationFrame(animate)
}
animate()
})