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How to animate several dots moving here and there in html canvas

I have a requirement to move many dots here and there inside a canvas.
Hence I created several arcs with different radius and placed them at random places.
var context = document.getElementById('stage').getContext('2d');
var radian = Math.PI / 180;
var x = 40;
var y = 40;
var r = 20;
var colorPoints = [];
var frames = 50;
var currentFrame = 0;
var toggle = false;
var iconsLoaded = false;
context.beginPath();
context.arc(x,y, r, 0 * radian, 360 * radian, false)
context.fill();
var drawMultipleCurves = function(ctx){
if(!iconsLoaded){
for (let i = 0; i < 600; i++) {
ctx.beginPath();
ctx.filter = 'blur(5px)';
ctx.fillStyle = '#B835FF';
colorPoints.push({x: Math.floor((Math.random() * 700) + 0), xMove: Math.floor((Math.random() * 2) + 0) , yMove: Math.floor((Math.random() * 2) + 0) , y: Math.floor((Math.random() * 700) + 0), radius: Math.floor((Math.random() * 20) + 5)});
ctx.arc(colorPoints[colorPoints.length - 1].x, colorPoints[colorPoints.length - 1].y, colorPoints[colorPoints.length - 1].radius, 0 * radian, 360 * radian, false);
ctx.fill();
ctx.closePath();
iconsLoaded = true;
}
}
else{
for(let i =0;i< colorPoints.length; i++){
if(frames === currentFrame ){
toggle = !toggle;
currentFrame = 0;
}
if(!toggle){
colorPoints[i].xMove === 1 ? colorPoints[i].x = colorPoints[i].x + 5 : colorPoints[i].x = colorPoints[i].x - 5;
colorPoints[i].yMove === 1 ? colorPoints[i].y = colorPoints[i].y + 5 : colorPoints[i].y = colorPoints[i].y - 5;
}
else{
colorPoints[i].xMove === 1 ? colorPoints[i].x = colorPoints[i].x - 5 : colorPoints[i].x = colorPoints[i].x + 5;
colorPoints[i].yMove === 1 ? colorPoints[i].y = colorPoints[i].y - 5 : colorPoints[i].y = colorPoints[i].y + 5;
}
ctx.beginPath();
ctx.arc(colorPoints[i].x, colorPoints[i].y, colorPoints[i].radius, 0 * radian, 360 * radian, false);
context.closePath( );
ctx.fill();
currentFrame = currentFrame + 1;
}
}
}
var animate = function(){
setTimeout(()=>{
context.clearRect(0,0,400,400);
context.beginPath();
drawMultipleCurves(context);
context.fill();
requestAnimationFrame(animate)
}, 1000/30)
}
requestAnimationFrame(animate)
<canvas id="stage" width="400" height="400">
<p>Your browser doesn't support canvas.</p>
</canvas>
Above is the code that I have tried.
I have first created and placed several dots at random places with random radius.
When I created them I saved all these random places in an array 'colorPoints'
Now I'm looping into this array and moving all the dots everytime 'requestAnimation' is called.
I'm able to achieve my animation of moving the dots randomly but as I have used 800 dots and then saving them into an array and then again looping them to move their position, the animation is not looking smooth.
It looks like it is moving and strucking. How can I achieve this animation smoothly?
Thanks in advance :)

Render "fill" once per style
Your code is slowing down due to where you placed fill (same if you use stroke)
When you have many objects with the same style call fill only once per frame for each object.
You had something like
for (const c of circles) {
ctx.beginPath();
ctx.arc(c.x, c.y, c.r, 0, TAU)
ctx.fill();
}
With a filter active the fill command forces the filter to be reset, which for blur is complex.
Rather add all the arcs then fill.
ctx.beginPath();
for (const c of circles) {
ctx.moveTo(c.x + c.r, c.y);
ctx.arc(c.x, c.y, c.r, 0, TAU)
}
ctx.fill();
The move ctx.moveTo(c.x + c.r, c.y); is used to close the previous arc.
You can also close the arc with ctx.closePath but this can be a lot slower when you have many arcs in the path buffer.
// slower than using moveTo
ctx.beginPath();
for (const c of circles) {
ctx.arc(c.x, c.y, c.r, 0, TAU)
ctx.closePath();
}
ctx.fill();
Example
Example draws 600 arcs using the blur filter as it only calls fill once per frame. This should run smooth on all but the most low end devices.
See function drawCircles
requestAnimationFrame(animate);
const ctx = canvas.getContext('2d');
const W = canvas.width;
const BLUR = 5;
const CIRCLE_COUNT = 600;
const MIN_RADIUS = BLUR;
const MAX_RADIUS = 30;
const MAX_DELTA = 1;
const MAX_CIR_R = MAX_RADIUS + BLUR;
const MOVE_SIZE = MAX_CIR_R * 2 + W;
const TAU = 2 * Math.PI;
const setOf = (c, cb, i = 0, a = []) => { while(i < c) { a.push(cb(i++)) } return a };
const rnd = (m, M) => Math.random() * (M - m) + m;
const style = {
filter: "blur(" + BLUR + "px)",
fillStyle: '#B835FF',
};
var currentStyle;
function setStyle(ctx, style) {
if (currentStyle !== style) {
Object.assign(ctx, style);
currentStyle = style;
}
}
const circle = {
get x() { return rnd(-MAX_CIR_R, W + MAX_CIR_R) },
get y() { return rnd(-MAX_CIR_R, W + MAX_CIR_R) },
get dx() { return rnd(-MAX_DELTA, MAX_DELTA) },
get dy() { return rnd(-MAX_DELTA, MAX_DELTA) },
get r() { return rnd(MIN_RADIUS, MAX_RADIUS) },
move() {
var x = this.x + this.dx + MOVE_SIZE + MAX_CIR_R;
var y = this.y + this.dy + MOVE_SIZE + MAX_CIR_R;
this.x = x % MOVE_SIZE - MAX_CIR_R;
this.y = y % MOVE_SIZE - MAX_CIR_R;
}
};
const circles = setOf(CIRCLE_COUNT, () => Object.assign({}, circle));
function drawCircles(circles, ctx, style) {
setStyle(ctx, style);
ctx.beginPath();
for (const c of circles) {
ctx.moveTo(c.x + c.r, c.y);
ctx.arc(c.x, c.y, c.r, 0, TAU);
}
ctx.fill();
}
function updateCircles(circles) {
for (const c of circles) { c.move(); }
}
function animate() {
ctx.clearRect(0,0,W, W);
updateCircles(circles);
drawCircles(circles, ctx, style);
requestAnimationFrame(animate);
}
<canvas id="canvas" width="600" height="600"> </canvas>
If you have several colors, group all the same colors so you can keep the number of fill calls as low as possible.
There are many ways to get the same effect with many colors (each circle a different color) but will need more setup code.

The CanvasRenderingContext2D blur filter is quite heavy - especially if you use it on a canvas consisting of 600 circles. That means on every screen update it has to re-draw 600 circles and apply a blur filter afterwards.
The usual approach is a little different. Initially you create a master texture with a blurred circle. This texture can then be re-used and drawn onto the canvas using the drawImage() method. To vary the size of the circles there is no radius anymore though. We can get the same effect by using a scale instead.
Here's an example:
var context = document.getElementById('stage').getContext('2d');
var radian = Math.PI / 180;
var x = 40;
var y = 40;
var r = 20;
var colorPoints = [];
var frames = 50;
var currentFrame = 0;
var toggle = false;
var iconsLoaded = false;
var texture = document.createElement("canvas");
var textureContext = texture.getContext("2d");
texture.width = 80;
texture.height = 80;
textureContext.filter = 'blur(5px)';
textureContext.fillStyle = '#B835FF';
textureContext.arc(texture.width / 2, texture.height / 2, 25, 0 * radian, 360 * radian, false);
textureContext.fill();
textureContext.closePath();
var drawMultipleCurves = function(ctx) {
if (!iconsLoaded) {
for (let i = 0; i < 600; i++) {
colorPoints.push({
x: Math.floor((Math.random() * 700) + 0),
xMove: Math.floor((Math.random() * 2) + 0),
yMove: Math.floor((Math.random() * 2) + 0),
y: Math.floor((Math.random() * 700) + 0),
scale: 0.2 + Math.random() * 0.8
});
iconsLoaded = true;
}
} else {
for (let i = 0; i < colorPoints.length; i++) {
if (frames === currentFrame) {
toggle = !toggle;
currentFrame = 0;
}
if (!toggle) {
colorPoints[i].xMove === 1 ? colorPoints[i].x = colorPoints[i].x + 5 : colorPoints[i].x = colorPoints[i].x - 5;
colorPoints[i].yMove === 1 ? colorPoints[i].y = colorPoints[i].y + 5 : colorPoints[i].y = colorPoints[i].y - 5;
} else {
colorPoints[i].xMove === 1 ? colorPoints[i].x = colorPoints[i].x - 5 : colorPoints[i].x = colorPoints[i].x + 5;
colorPoints[i].yMove === 1 ? colorPoints[i].y = colorPoints[i].y - 5 : colorPoints[i].y = colorPoints[i].y + 5;
}
ctx.drawImage(texture, colorPoints[i].x, colorPoints[i].y, texture.width * colorPoints[i].scale, texture.height * colorPoints[i].scale);
currentFrame = currentFrame + 1;
}
}
}
var animate = function() {
setTimeout(() => {
context.clearRect(0, 0, 400, 400);
context.beginPath();
drawMultipleCurves(context);
context.fill();
requestAnimationFrame(animate)
})
}
requestAnimationFrame(animate)
<canvas id="stage" width="400" height="400">
<p>Your browser doesn't support canvas.</p>
</canvas>

Making HSL pallet with selectable gradient problem

I am trying to make a color pallet in which the user can click on the gradient and it will show you the RGB and HSL values so far I have printed out all the Hue values and now what I want to do is make the appropriate display of Saturation and Luminesance/lightness values as can be seen here https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Colors/Color_picker_tool
I have tried to use a double nested loop as a generator such as:
function * hslGen(hue){
for(let s = 0; s < 100; s++){
for(let l = 100; l > 0; l--){
yield `hsl(${hue}, ${s}%, ${l}%)`;}
}
}
But the result looks the following https://codepen.io/superpauly/pen/XWMQboe?editors=1010 which confivuration should I have the loops to display a collor pallet like shown in the example above?
So I have got the generator and the rest of the code is as follow:
const canvasContext = canvRef.current.getContext("2d");
for (let hue = 0; hue < 360; hue++) {
// Generates Hue Spectrum
canvasContext.fillStyle = "hsl(" + hue + ", 100%, 50%)";
canvasContext.fillRect(5 * hue, 0, 5, 75);
}
canvRef.current.addEventListener("click", (e) => {
data = canvasContext.getImageData(e.layerX, e.layerY, 1, 1).data;
color.rgb = `rgb( ${data[0]}, ${data[1]}, ${data[2]})`;
color.h = rgbToHue(data);
color.hsl = `hsl( ${color.h}, 100%, 50%)`;
let pixel = 0;
for (let m of hslGen(color.h)){
canvasContext.fillStyle = m; //HSL Generator string
canvasContext.fillRect(pixel+=1, 75, 1440, 500); // Here is where I try to make the gradient bu it fails.
}
Thank you.

You need track x and y coordinates for each pixel:
import React, {
useEffect,
useRef,
useState
} from "https://cdn.skypack.dev/react#17.0.1";
import ReactDOM from "https://cdn.skypack.dev/react-dom#17.0.1";
console.clear();
function * hslGen(hue){
for(let l = 100; l >= 0; l--)
{
for(let s = 0; s <= 100; s++)
{
yield `hsl(${hue}, ${s}%, ${l}%)`;
}
}
}
const RGBToHex = (r, g, b) => {
r = r.toString(16);
g = g.toString(16);
b = b.toString(16);
if (r.length == 1) r = "0" + r;
if (g.length == 1) g = "0" + g;
if (b.length == 1) b = "0" + b;
return `#${r+g+b}`;
};
function rgbToHue(getImageData) {
let rgbHue = {
red: getImageData[0] / 255,
green: getImageData[1] / 255,
blue: getImageData[2] / 255
};
let maxValueKey = Object.keys(rgbHue).reduce((a, b) =>
rgbHue[a] > rgbHue[b] ? a : b
);
let maxValue = Math.max(rgbHue["red"], rgbHue["green"], rgbHue["blue"]);
let minValue = Math.min(rgbHue["red"], rgbHue["green"], rgbHue["blue"]);
let hue = 0.0;
switch (maxValueKey) {
case "red":
hue = (rgbHue["green"] - rgbHue["blue"]) / (maxValue - minValue);
break;
case "green":
hue = 2.0 + (rgbHue["blue"] - rgbHue["red"]) / (maxValue - minValue);
break;
case "blue":
hue = 4.0 + (rgbHue["red"] - rgbHue["green"]) / (maxValue - minValue);
break;
}
hue = hue * 60.0;
if (hue < 0.0) {
hue = hue + 360.0;
}
console.log("Hue in Deg: " + hue);
return hue;
}
const ColorPicker = () => {
const canvRef = useRef();
const color = { rgb: "", hsl: "",
h:0};
let [col, setCol] = useState({});
let data = 0;
useEffect(() => {
const canvasContext = canvRef.current.getContext("2d");
for (let hue = 0; hue < 360; hue++) {
canvasContext.fillStyle = "hsl(" + hue + ", 100%, 50%)";
canvasContext.fillRect(5 * hue, 0, 5, 75);
}
canvRef.current.addEventListener("click", (e) => {
data = canvasContext.getImageData(e.layerX, e.layerY, 1, 1).data;
color.rgb = `rgb( ${data[0]}, ${data[1]}, ${data[2]})`;
color.h = rgbToHue(data);
color.hsl = `hsl( ${color.h}, 100%, 50%)`;
setCol({
rgb: color.rgb,
hsl: color.hsl
});
debugger;
let x = 0,
y = 0,
pix = 3; //pixel size
console.log("Start");
for (let m of hslGen(color.h)){
canvasContext.fillStyle = m;
canvasContext.fillRect(100 + x, 175 + y, pix, pix); //Need to made this a 2d saturation, light graph
console.log(m, x, y);
x += pix;
x = x % (pix * 101);
if (!x)
y += pix;
}
console.log("End");
});
console.log(color);
}, []);
return (
<>
<canvas
ref={canvRef}
height={window.innerHeight}
width={window.innerWidth}
></canvas>
<span>HSL: {col.hsl}</span>
<span>RGB: {col.rgb}</span>
</>
);
};
ReactDOM.render(, document.getElementById("colorCanvas"));
https://codepen.io/vanowm/pen/JjWgJOO

If you're set on using the generator you can do something like so:
const scale = 4; // likely don't want the user to have to click on a single pixel so need some kind of scale factor
const hueInput = document.getElementById('hue');
const canvas = document.getElementById('color-picker');
canvas.width = 100 * scale;
canvas.height = 100 * scale;
canvas.style.width = canvas.width + 'px';
canvas.style.height = canvas.height + 'px';
const context = canvas.getContext('2d');
function * hslGen(hue){
for(let s = 0; s < 100; s++){
for(let l = 100; l > 0; l--){
yield `hsl(${hue}, ${s}%, ${l}%)`;}
}
}
function updateColorPicker() {
const hue = hueInput.value;
// need to keep track of both x and y as it's two dimensional
let y = 0, x = 0;
for (const m of hslGen(hue)) {
context.fillStyle = m; //HSL Generator string
context.fillRect(x * scale, y * scale, scale, scale);
// iterator is doing saturation then lightness so we populate y first then x
y++;
if (y >= 100) {
y = 0;
x++;
}
}
}
hueInput.addEventListener('change', updateColorPicker);
updateColorPicker();
<label> HUE <input type="number" id="hue" value="5"></label>
<br>
<canvas id="color-picker"></canvas>
Because the expected output is 2 dimensional you need both an x and y component. Because of this, the generator in it's current form doesn't seem to make much sense.
A better approach would be to either remove the generator altogether, or make it fit the problem better. Here's an example without the generator :
const scale = 4; // likely don't want the user to have to click on a single pixel so need some kind of scale factor
const hueInput = document.getElementById('hue');
const canvas = document.getElementById('color-picker');
canvas.width = 100 * scale;
canvas.height = 100 * scale;
canvas.style.width = canvas.width + 'px';
canvas.style.height = canvas.height + 'px';
const context = canvas.getContext('2d');
function updateColorPicker() {
const hue = hueInput.value;
// need to keep track of both x and y as it's two dimensional
for(let x = 0; x < 100; x++) {
for(let y = 0; y < 100; y++) {
var m = `hsl(${hue}, ${x}%, ${100-y}%)`;
context.fillStyle = m; //HSL Generator string
context.fillRect(x * scale, y * scale, scale, scale);
}
}
}
hueInput.addEventListener('change', updateColorPicker);
updateColorPicker();
<label> HUE <input type="number" id="hue" value="5"></label>
<br>
<canvas id="color-picker"></canvas>

hyperdrive effect in canvas across randomly placed circles

I'm trying to create a hyperdrive effect, like from Star Wars, where the stars have a motion trail. I've gotten as far as creating the motion trail on a single circle, it still looks like the trail is going down in the y direction and not forwards or positive in the z direction.
Also, how could I do this with (many) randomly placed circles as if they were stars?
My code is on jsfiddle (https://jsfiddle.net/5m7x5zxu/) and below:
var canvas = document.querySelector("canvas");
var context = canvas.getContext("2d");
var xPos = 180;
var yPos = 100;
var motionTrailLength = 16;
var positions = [];
function storeLastPosition(xPos, yPos) {
// push an item
positions.push({
x: xPos,
y: yPos
});
//get rid of first item
if (positions.length > motionTrailLength) {
positions.pop();
}
}
function update() {
context.clearRect(0, 0, canvas.width, canvas.height);
for (var i = positions.length-1; i > 0; i--) {
var ratio = (i - 1) / positions.length;
drawCircle(positions[i].x, positions[i].y, ratio);
}
drawCircle(xPos, yPos, "source");
var k=2;
storeLastPosition(xPos, yPos);
// update position
if (yPos > 125) {
positions.pop();
}
else{
yPos += k*1.1;
}
requestAnimationFrame(update);
}
update();
function drawCircle(x, y, r) {
if (r == "source") {
r = 1;
} else {
r*=1.1;
}
context.beginPath();
context.arc(x, y, 3, 0, 2 * Math.PI, true);
context.fillStyle = "rgba(255, 255, 255, " + parseFloat(1-r) + ")";
context.fill();
}

Canvas feedback and particles.
This type of FX can be done many ways.
You could just use a particle systems and draw stars (as lines) moving away from a central point, as the speed increase you increase the line length. When at low speed the line becomes a circle if you set ctx.lineWidth > 1 and ctx.lineCap = "round"
To add to the FX you can use render feedback as I think you have done by rendering the canvas over its self. If you render it slightly larger you get a zoom FX. If you use ctx.globalCompositeOperation = "lighter" you can increase the stars intensity as you speed up to make up for the overall loss of brightness as stars move faster.
Example
I got carried away so you will have to sift through the code to find what you need.
The particle system uses the Point object and a special array called bubbleArray to stop GC hits from janking the animation.
You can use just an ordinary array if you want. The particles are independent of the bubble array. When they have moved outside the screen they are move to a pool and used again when a new particle is needed. The update function moves them and the draw Function draws them I guess LOL
The function loop is the main loop and adds and draws particles (I have set the particle count to 400 but should handle many more)
The hyper drive is operated via the mouse button. Press for on, let go for off. (It will distort the text if it's being displayed)
The canvas feedback is set via that hyperSpeed variable, the math is a little complex. The sCurce function just limits the value to 0,1 in this case to stop alpha from going over or under 1,0. The hyperZero is just the sCurve return for 1 which is the hyper drives slowest speed.
I have pushed the feedback very close to the limit. In the first few lines of the loop function you can set the top speed if(mouse.button){ if(hyperSpeed < 1.75){ Over this value 1.75 and you will start to get bad FX, at about 2 the whole screen will just go white (I think that was where)
Just play with it and if you have questions ask in the comments.
const ctx = canvas.getContext("2d");
// very simple mouse
const mouse = {x : 0, y : 0, button : false}
function mouseEvents(e){
mouse.x = e.pageX;
mouse.y = e.pageY;
mouse.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : mouse.button;
}
["down","up","move"].forEach(name => document.addEventListener("mouse"+name,mouseEvents));
// High performance array pool using buubleArray to separate pool objects and active object.
// This is designed to eliminate GC hits involved with particle systems and
// objects that have short lifetimes but used often.
// Warning this code is not well tested.
const bubbleArray = () => {
const items = [];
var count = 0;
return {
clear(){ // warning this dereferences all locally held references and can incur Big GC hit. Use it wisely.
this.items.length = 0;
count = 0;
},
update() {
var head, tail;
head = tail = 0;
while(head < count){
if(items[head].update() === false) {head += 1 }
else{
if(tail < head){
const temp = items[head];
items[head] = items[tail];
items[tail] = temp;
}
head += 1;
tail += 1;
}
}
return count = tail;
},
createCallFunction(name, earlyExit = false){
name = name.split(" ")[0];
const keys = Object.keys(this);
if(Object.keys(this).indexOf(name) > -1){ throw new Error(`Can not create function name '${name}' as it already exists.`) }
if(!/\W/g.test(name)){
let func;
if(earlyExit){
func = `var items = this.items; var count = this.getCount(); var i = 0;\nwhile(i < count){ if (items[i++].${name}() === true) { break } }`;
}else{
func = `var items = this.items; var count = this.getCount(); var i = 0;\nwhile(i < count){ items[i++].${name}() }`;
}
!this.items && (this.items = items);
this[name] = new Function(func);
}else{ throw new Error(`Function name '${name}' contains illegal characters. Use alpha numeric characters.`) }
},
callEach(name){var i = 0; while(i < count){ if (items[i++][name]() === true) { break } } },
each(cb) { var i = 0; while(i < count){ if (cb(items[i], i++) === true) { break } } },
next() { if (count < items.length) { return items[count ++] } },
add(item) {
if(count === items.length){
items.push(item);
count ++;
}else{
items.push(items[count]);
items[count++] = item;
}
return item;
},
getCount() { return count },
}
}
// Helpers rand float, randI random Int
// doFor iterator
// sCurve curve input -Infinity to Infinity out -1 to 1
// randHSLA creates random colour
// CImage, CImageCtx create image and image with context attached
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const rand = (min = 1, max = min + (min = 0)) => Math.random() * (max - min) + min;
const doFor = (count, cb) => { var i = 0; while (i < count && cb(i++) !== true); }; // the ; after while loop is important don't remove
const sCurve = (v,p) => (2 / (1 + Math.pow(p,-v))) -1;
const randHSLA = (h, h1, s = 100, s1 = 100, l = 50, l1 = 50, a = 1, a1 = 1) => { return `hsla(${randI(h,h1) % 360},${randI(s,s1)}%,${randI(l,l1)}%,${rand(a,a1)})` }
const CImage = (w = 128, h = w) => (c = document.createElement("canvas"),c.width = w,c.height = h, c);
const CImageCtx = (w = 128, h = w) => (c = CImage(w,h), c.ctx = c.getContext("2d"), c);
// create image to hold text
var textImage = CImageCtx(1024, 1024);
var c = textImage.ctx;
c.fillStyle = "#FF0";
c.font = "64px arial black";
c.textAlign = "center";
c.textBaseline = "middle";
const text = "HYPER,SPEED FX,VII,,Battle of Jank,,Hold the mouse,button to increase,speed.".split(",");
text.forEach((line,i) => { c.fillText(line,512,i * 68 + 68) });
const maxLines = text.length * 68 + 68;
function starWarIntro(image,x1,y1,x2,y2,pos){
var iw = image.width;
var ih = image.height;
var hh = (x2 - x1) / (y2 - y1); // Slope of left edge
var w2 = iw / 2; // half width
var z1 = w2 - x1; // Distance (z) to first line
var z2 = (z1 / (w2 - x2)) * z1 - z1; // distance (z) between first and last line
var sk,t3,t3a,z3a,lines, z3, dd = 0, a = 0, as = 2 / (y2 - y1);
for (var y = y1; y < y2 && dd < maxLines; y++) { // for each line
t3 = ((y - y1) * hh) + x1; // get scan line top left edge
t3a = (((y+1) - y1) * hh) + x1; // get scan line bottom left edge
z3 = (z1 / (w2 - t3)) * z1; // get Z distance to top of this line
z3a = (z1 / (w2 - t3a)) * z1; // get Z distance to bottom of this line
dd = ((z3 - z1) / z2) * ih; // get y bitmap coord
a += as;
ctx.globalAlpha = a < 1 ? a : 1;
dd += pos; // kludge for this answer to make text move
// does not move text correctly
lines = ((z3a - z1) / z2) * ih-dd; // get number of lines to copy
ctx.drawImage(image, 0, dd , iw, lines, t3, y, w - t3 * 2, 1.5);
}
}
// canvas settings
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
// diagonal distance used to set point alpha (see point update)
var diag = Math.sqrt(w * w + h * h);
// If window size is changed this is called to resize the canvas
// It is not called via the resize event as that can fire to often and
// debounce makes it feel sluggish so is called from main loop.
function resizeCanvas(){
points.clear();
canvas.width = innerWidth;
canvas.height = innerHeight;
w = canvas.width;
h = canvas.height;
cw = w / 2; // center
ch = h / 2;
diag = Math.sqrt(w * w + h * h);
}
// create array of points
const points = bubbleArray();
// create optimised draw function itterator
points.createCallFunction("draw",false);
// spawns a new star
function spawnPoint(pos){
var p = points.next();
p = points.add(new Point())
if (p === undefined) { p = points.add(new Point()) }
p.reset(pos);
}
// point object represents a single star
function Point(pos){ // this function is duplicated as reset
if(pos){
this.x = pos.x;
this.y = pos.y;
this.dead = false;
}else{
this.x = 0;
this.y = 0;
this.dead = true;
}
this.alpha = 0;
var x = this.x - cw;
var y = this.y - ch;
this.dir = Math.atan2(y,x);
this.distStart = Math.sqrt(x * x + y * y);
this.speed = rand(0.01,1);
this.col = randHSLA(220,280,100,100,50,100);
this.dx = Math.cos(this.dir) * this.speed;
this.dy = Math.sin(this.dir) * this.speed;
}
Point.prototype = {
reset : Point, // resets the point
update(){ // moves point and returns false when outside
this.speed *= hyperSpeed; // increase speed the more it has moved
this.x += Math.cos(this.dir) * this.speed;
this.y += Math.sin(this.dir) * this.speed;
var x = this.x - cw;
var y = this.y - ch;
this.alpha = (Math.sqrt(x * x + y * y) - this.distStart) / (diag * 0.5 - this.distStart);
if(this.alpha > 1 || this.x < 0 || this.y < 0 || this.x > w || this.h > h){
this.dead = true;
}
return !this.dead;
},
draw(){ // draws the point
ctx.strokeStyle = this.col;
ctx.globalAlpha = 0.25 + this.alpha *0.75;
ctx.beginPath();
ctx.lineTo(this.x - this.dx * this.speed, this.y - this.dy * this.speed);
ctx.lineTo(this.x, this.y);
ctx.stroke();
}
}
const maxStarCount = 400;
const p = {x : 0, y : 0};
var hyperSpeed = 1.001;
const alphaZero = sCurve(1,2);
var startTime;
function loop(time){
if(startTime === undefined){
startTime = time;
}
if(w !== innerWidth || h !== innerHeight){
resizeCanvas();
}
// if mouse down then go to hyper speed
if(mouse.button){
if(hyperSpeed < 1.75){
hyperSpeed += 0.01;
}
}else{
if(hyperSpeed > 1.01){
hyperSpeed -= 0.01;
}else if(hyperSpeed > 1.001){
hyperSpeed -= 0.001;
}
}
var hs = sCurve(hyperSpeed,2);
ctx.globalAlpha = 1;
ctx.setTransform(1,0,0,1,0,0); // reset transform
//==============================================================
// UPDATE the line below could be the problem. Remove it and try
// what is under that
//==============================================================
//ctx.fillStyle = `rgba(0,0,0,${1-(hs-alphaZero)*2})`;
// next two lines are the replacement
ctx.fillStyle = "Black";
ctx.globalAlpha = 1-(hs-alphaZero) * 2;
//==============================================================
ctx.fillRect(0,0,w,h);
// the amount to expand canvas feedback
var sx = (hyperSpeed-1) * cw * 0.1;
var sy = (hyperSpeed-1) * ch * 0.1;
// increase alpha as speed increases
ctx.globalAlpha = (hs-alphaZero)*2;
ctx.globalCompositeOperation = "lighter";
// draws feedback twice
ctx.drawImage(canvas,-sx, -sy, w + sx*2 , h + sy*2)
ctx.drawImage(canvas,-sx/2, -sy/2, w + sx , h + sy)
ctx.globalCompositeOperation = "source-over";
// add stars if count < maxStarCount
if(points.getCount() < maxStarCount){
var cent = (hyperSpeed - 1) *0.5; // pulls stars to center as speed increases
doFor(10,()=>{
p.x = rand(cw * cent ,w - cw * cent); // random screen position
p.y = rand(ch * cent,h - ch * cent);
spawnPoint(p)
})
}
// as speed increases make lines thicker
ctx.lineWidth = 2 + hs*2;
ctx.lineCap = "round";
points.update(); // update points
points.draw(); // draw points
ctx.globalAlpha = 1;
// scroll the perspective star wars text FX
var scrollTime = (time - startTime) / 5 - 2312;
if(scrollTime < 1024){
starWarIntro(textImage,cw - h * 0.5, h * 0.2, cw - h * 3, h , scrollTime );
}
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
canvas { position : absolute; top : 0px; left : 0px; }
<canvas id="canvas"></canvas>

Here's another simple example, based mainly on the same idea as Blindman67, concetric lines moving away from center at different velocities (the farther from center, the faster it moves..) also no recycling pool here.
"use strict"
var c = document.createElement("canvas");
document.body.append(c);
var ctx = c.getContext("2d");
var w = window.innerWidth;
var h = window.innerHeight;
var ox = w / 2;
var oy = h / 2;
c.width = w; c.height = h;
const stars = 120;
const speed = 0.5;
const trailLength = 90;
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, w, h);
ctx.fillStyle = "#fff"
ctx.fillRect(ox, oy, 1, 1);
init();
function init() {
var X = [];
var Y = [];
for(var i = 0; i < stars; i++) {
var x = Math.random() * w;
var y = Math.random() * h;
X.push( translateX(x) );
Y.push( translateY(y) );
}
drawTrails(X, Y)
}
function translateX(x) {
return x - ox;
}
function translateY(y) {
return oy - y;
}
function getDistance(x, y) {
return Math.sqrt(x * x + y * y);
}
function getLineEquation(x, y) {
return function(n) {
return y / x * n;
}
}
function drawTrails(X, Y) {
var count = 1;
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, w, h);
function anim() {
for(var i = 0; i < X.length; i++) {
var x = X[i];
var y = Y[i];
drawNextPoint(x, y, count);
}
count+= speed;
if(count < trailLength) {
window.requestAnimationFrame(anim);
}
else {
init();
}
}
anim();
}
function drawNextPoint(x, y, step) {
ctx.fillStyle = "#fff";
var f = getLineEquation(x, y);
var coef = Math.abs(x) / 100;
var dist = getDistance( x, y);
var sp = speed * dist / 100;
for(var i = 0; i < sp; i++) {
var newX = x + Math.sign(x) * (step + i) * coef;
var newY = translateY( f(newX) );
ctx.fillRect(newX + ox, newY, 1, 1);
}
}
body {
overflow: hidden;
}
canvas {
position: absolute;
left: 0;
top: 0;
}

scrambling images on canvas producing whitespace

I'm starting with a canvas element. I'm making the left half red, and the right side blue. Every half second, setInterval calls a function, scramble, which splits both RHS and LHS into pieces, and shuffles them.
Here is a fiddle: https://jsfiddle.net/aeq1g3yb/
The code is below. The reason I'm using window.onload is because this thing is supposed to scramble pictures and I want the pictures to load first. I'm using colors here because of the cross-origin business that I don't know enough about, so this is my accommodation.
var n = 1;
var v = 1;
function scramble() {
//get the canvas and change its width
var c = document.getElementById("myCanvas");
c.width = 600;
var ctx = c.getContext("2d");
//drawing 2 different colors side by side
ctx.fillStyle = "red";
ctx.fillRect(0, 0, c.width/2, c.height);
ctx.fillStyle = "blue";
ctx.fillRect(c.width/2, 0, c.width/2, c.height);
//how big will each shuffled chunk be
var stepsA = (c.width/2) / n;
var stepsB = (c.width/2) / n;
var step = stepsA + stepsB;
var imgDataA = [];
var imgDataB = [];
for (var i = 0; i < n; i++) {
var imgDataElementA = ctx.getImageData(stepsA*i, 0, stepsA, c.height);
var imgDataElementB = ctx.getImageData(c.width/2+stepsB*i, 0, stepsB, c.height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
//clearing out the canvas before laying on the new stuff
ctx.fillStyle = "white";
ctx.fillRect(0, 0, c.width, c.height);
//put the images back
for (var i = 0; i < n; i++) {
ctx.putImageData(imgDataA[i], step*i, 0);
ctx.putImageData(imgDataB[i], step*i+stepsA, 0);
}
//gonna count the steps
var count = document.getElementById("count");
count.innerHTML = n;
n += v;
if (n >= 100 || n <= 1) {
v *= -1;
}
}; //closing function scramble
window.onload = function() { //gotta do this bc code executes before image loads
scramble();
};
window.setInterval(scramble, 500);
More or less, this thing works the way I want it to. But there is one problem: Sometimes there are vertical white lines.
My question is:
Why are there white lines? If you view the fiddle, you will see the degree to which this impairs the effect of the shuffle.

You can`t divide a Pixel
The problem can be solve but will introduce some other artifacts as you can not divide integer pixels into fractions.
Quick solution
The following solution for your existing code rounds down for the start of a section and up for the width.
for (var i = 0; i < n; i++) {
var imgDataElementA = ctx.getImageData(
Math.floor(stepsA * i), 0,
Math.ceil(stepsA + stepsA * i) - Math.floor(stepsA * i), c.height
);
var imgDataElementB = ctx.getImageData(
Math.floor(c.width / 2 + stepsB * i), 0,
Math.ceil(c.width / 2 + stepsB * i + stepsB) - Math.floor(c.width / 2 + stepsB * i), c.height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
Quicker options
But doing this via the pixel image data is about the slowest possible way you could find to do it. You can just use the 2D context.imageDraw function to do the movement for you. Or if you want the best in terms of performance a WebGL solution would be the best with the fragment shader doing the scrambling for you as a parallel solution.
There is no perfect solution
But in the end you can not cut a pixel in half, there are a wide range of ways to attempt to solve this but each method has its own artifacts. Ideally you should only slice an image if the rule image.width % slices === 0 in all other cases you will have one or more slices that will not fit on an integer number of pixels.
Example of 4 rounding methods.
The demo shows 4 different methods and with 2 colors. Mouse over to see a closer view. Each method is separated horizontally with a white line. Hold the mouse button to increase the slice counter.
The top is your original.
The next three are 3 different ways of dealing with the fractional pixel width.
const mouse = {x : 0, y : 0, button : false}
function mouseEvents(e){
const m = mouse;
if(m.element){
m.bounds = m.element.getBoundingClientRect();
m.x = e.pageX - m.bounds.left - scrollX;
m.y = e.pageY - m.bounds.top - scrollY;
m.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : m.button;
}
}
["down","up","move"].forEach(name => document.addEventListener("mouse"+name,mouseEvents));
const counterElement = document.getElementById("count");
// get constants for the demo
const c = document.getElementById("myCanvas");
mouse.element = c;
// The image with the blue and red
const img = document.createElement("canvas");
// the zoom image overlay
const zoom = document.createElement("canvas");
// the scrambled image
const scram = document.createElement("canvas");
// Set sizes and get context
const w = scram.width = zoom.width = img.width = c.width = 500;
const h = scram.height = zoom.height = img.height = c.height;
const dCtx = c.getContext("2d"); // display context
const iCtx = img.getContext("2d"); // source image context
const zCtx = zoom.getContext("2d"); // zoom context
const sCtx = scram.getContext("2d"); // scrambled context
// some constants
const zoomAmount = 4;
const zoomRadius = 60;
const framesToStep = 10;
function createTestPattern(ctx){
ctx.fillStyle = "red";
ctx.fillRect(0, 0, c.width/2, c.height/2);
ctx.fillStyle = "blue";
ctx.fillRect(c.width/2, 0, c.width/2, c.height/2);
ctx.fillStyle = "black";
ctx.fillRect(0, c.height/2, c.width/2, c.height/2);
ctx.fillStyle = "#CCC";
ctx.fillRect(c.width/2, c.height/2, c.width/2, c.height/2);
}
createTestPattern(iCtx);
sCtx.drawImage(iCtx.canvas, 0, 0);
// Shows a zoom area so that blind men like me can see what is going on.
function showMouseZoom(src,dest,zoom = zoomAmount,radius = zoomRadius){
dest.clearRect(0,0,w,h);
dest.imageSmoothingEnabled = false;
if(mouse.x >= 0 && mouse.y >= 0 && mouse.x < w && mouse.y < h){
dest.setTransform(zoom,0,0,zoom,mouse.x,mouse.y)
dest.drawImage(src.canvas, -mouse.x, -mouse.y);
dest.setTransform(1,0,0,1,0,0);
dest.globalCompositeOperation = "destination-in";
dest.beginPath();
dest.arc(mouse.x,mouse.y,radius,0,Math.PI * 2);
dest.fill();
dest.globalCompositeOperation = "source-over";
dest.lineWidth = 4;
dest.strokeStyle = "black";
dest.stroke();
}
}
function scramble(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w/2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
((i / 2) | 0) * steps + (i % 2) * (w / 2)- 0.5, y,
steps + 1, height,
i * steps - 0.5, y,
steps+ 1, height
);
}
}
function scrambleFloor(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w/2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
(((i / 2) | 0) * steps + (i % 2) * (w / 2)- 0.5) | 0, y,
steps + 1, height,
(i * steps - 0.5) | 0, y,
steps + 1, height
);
}
}
function scrambleNoOverlap(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w / 2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
((i / 2) | 0) * steps + (i % 2) * (w / 2), y,
steps, height,
i * steps - 0.5, y,
steps, height
);
}
}
function scrambleOriginal(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
//how big will each shuffled chunk be
var stepsA = (w/2) / slices;
var stepsB = (w/2) / slices;
var step = stepsA + stepsB;
var imgDataA = [];
var imgDataB = [];
for (var i = 0; i < slices; i++) {
var imgDataElementA = src.getImageData(stepsA*i, y, stepsA, height);
var imgDataElementB = src.getImageData(w/2+stepsB*i, y, stepsB, height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
//clearing out the canvas before laying on the new stuff
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
//put the images back
for (var i = 0; i < slices; i++) {
dest.putImageData(imgDataA[i], step*i, y);
dest.putImageData(imgDataB[i], step*i+stepsA, y);
}
}; //closing function scramble
const scrambleMethods = [scrambleOriginal,scramble,scrambleFloor,scrambleNoOverlap];
var frameCount = 0;
var sliceStep = 1;
var slices = 1;
function mainLoop(){
if(mouse.button){
if(frameCount++ % framesToStep === framesToStep-1){ // every 30 Frames
slices += sliceStep;
if(slices > 150 || slices < 2){ sliceStep = -sliceStep }
counterElement.textContent = slices; // Prevent reflow by using textContent
sCtx.clearRect(0,0,w,h);
sCtx.imageSmoothingEnabled = true;
const len = scrambleMethods.length;
for(var i = 0; i < len; i ++){
scrambleMethods[i](iCtx,sCtx,(128/len) * i, 128/len-2);
scrambleMethods[i](iCtx,sCtx,(128/len) * i + 128, 128/len-2);
}
}
}
dCtx.fillStyle = "white";
dCtx.fillRect(0,0,w,h);
dCtx.drawImage(sCtx.canvas,0,0);
showMouseZoom(dCtx,zCtx);
dCtx.drawImage(zCtx.canvas,0,0);
requestAnimationFrame(mainLoop);
}
//scramble(iCtx,sCtx);
requestAnimationFrame(mainLoop);
canvas {
border: 1px solid black;
}
#count {
position : absolute;
top : 0px;
left : 10px;
font-family: monospace;
font-size: 20px;
}
<canvas id="myCanvas" height = "256" title="Hold mouse button to chance slice count"></canvas>
<p id="count"></p>

Create color gradient describing discrete distribution of points

I am making a map that renders position of game objects (Project Zomboid zombies):
As user zooms out, single dots are no longer useful. Instead, I'd like to render distribution of zombies on an area using red color gradient. I tried to loop over all zombies for every rendered pixel and color it reciprocally to the sum of squared distances to the zombies. The result:
That's way too blurry. Also the results are more influenced by the zombies that are AWAY from the points - I need to influence them more by the zombies that are CLOSE. So what this is is just math. Here's the code I used:
var h = canvas.height;
var w = canvas.width;
// To loop over more than 1 pixel (performance)
var tileSize = 10;
var halfRadius = Math.floor(tileSize/2);
var time = performance.now();
// "Squared" because we didnt unsquare it
function distanceSquared(A, B) {
return (A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y);
}
// Loop for every x,y pixel (or region of pixels)
for(var y=0; y<h; y+=tileSize) {
for(var x=0; x<w; x+=tileSize) {
// Time security - stop rendering after 1 second
if(performance.now()-time>1000) {
x=w;y=h;break;
}
// Convert relative canvas offset to absolute point on the map
var point = canvasPixeltoImagePixel(x, y);
// For every zombie add sqrt(distance from this point to zombie)
var distancesRoot = 0;
// Loop over the zombies
var zombieCoords;
for(var i=0; i<zombies_length; i++) {
// Get single zombie coordinates as {x:0, y:0}
if((coords=zombies[i].pixel)==null)
coords = zombies[i].pixel = tileToPixel(zombies[i].coordinates[0], zombies[i].coordinates[1], drawer);
// square root is a) slow and b) probably not what I want anyway
var dist = distanceSquared(coords, point);
distancesRoot+=dist;
}
// The higher the sum of distances is, the more intensive should the color be
var style = 'rgba(255,0,0,'+300000000/distancesRoot+')';
// Kill the console immediatelly
//console.log(style);
// Maybe we should sample and cache the transparency styles since there's limited ammount of colors?
ctx.fillStyle = style;
ctx.fillRect(x-halfRadius,y-halfRadius,tileSize,tileSize);
}
}
I'm pretty fine with theoretical explanation how to do it, though if you make simple canvas example with some points, what would be awesome.

This is an example of a heat map. It's basically gradient orbs over points and then ramping the opacity through a heat ramp. The more orbs cluster together the more solid the color which can be shown as an amplified region with the proper ramp.
update
I cleaned up the variables a bit and put the zeeks in an animation loop. There's an fps counter to see how it's performing. The gradient circles can be expensive. We could probably do bigger worlds if we downscale the heat map. It won't be as smooth looking but will compute a lot faster.
update 2
The heat map now has an adjustable scale and as predicted we get an increase in fps.
if (typeof app === "undefined") {
var app = {};
}
app.zeeks = 200;
app.w = 600;
app.h = 400;
app.circleSize = 50;
app.scale = 0.25;
init();
function init() {
app.can = document.getElementById('can');
app.ctx = can.getContext('2d');
app.can.height = app.h;
app.can.width = app.w;
app.radius = Math.floor(app.circleSize / 2);
app.z = genZ(app.zeeks, app.w, app.h);
app.flip = false;
// Make temporary layer once.
app.layer = document.createElement('canvas');
app.layerCtx = app.layer.getContext('2d');
app.layer.width = Math.floor(app.w * app.scale);
app.layer.height = Math.floor(app.h * app.scale);
// Make the gradient canvas once.
var sCircle = Math.floor(app.circleSize * app.scale);
app.radius = Math.floor(sCircle / 2);
app.gCan = genGradientCircle(sCircle);
app.ramp = genRamp();
// fps counter
app.frames = 0;
app.fps = "- fps";
app.fpsInterval = setInterval(calcFps, 1000);
// start animation
ani();
flicker();
}
function calcFps() {
app.fps = app.frames + " fps";
app.frames = 0;
}
// animation loop
function ani() {
app.frames++;
var ctx = app.ctx;
var w = app.w;
var h = app.h;
moveZ();
//ctx.clearRect(0, 0, w, h);
ctx.fillStyle = "#006600";
ctx.fillRect(0, 0, w, h);
if (app.flip) {
drawZ2();
drawZ();
} else {
drawZ2();
}
ctx.fillStyle = "#FFFF00";
ctx.fillText(app.fps, 10, 10);
requestAnimationFrame(ani);
}
function flicker() {
app.flip = !app.flip;
if (app.flip) {
setTimeout(flicker, 500);
} else {
setTimeout(flicker, 5000);
}
}
function genGradientCircle(size) {
// gradient image
var gCan = document.createElement('canvas');
gCan.width = gCan.height = size;
var gCtx = gCan.getContext('2d');
var radius = Math.floor(size / 2);
var grad = gCtx.createRadialGradient(radius, radius, radius, radius, radius, 0);
grad.addColorStop(1, "rgba(255,255,255,.65)");
grad.addColorStop(0, "rgba(255,255,255,0)");
gCtx.fillStyle = grad;
gCtx.fillRect(0, 0, gCan.width, gCan.height);
return gCan;
}
function genRamp() {
// Create heat gradient
var heat = document.createElement('canvas');
var hCtx = heat.getContext('2d');
heat.width = 256;
heat.height = 5;
var linGrad = hCtx.createLinearGradient(0, 0, heat.width, heat.height);
linGrad.addColorStop(1, "rgba(255,0,0,.75)");
linGrad.addColorStop(0.5, "rgba(255,255,0,.03)");
linGrad.addColorStop(0, "rgba(255,255,0,0)");
hCtx.fillStyle = linGrad;
hCtx.fillRect(0, 0, heat.width, heat.height);
// create ramp from gradient
var ramp = [];
var imageData = hCtx.getImageData(0, 0, heat.width, 1);
var d = imageData.data;
for (var x = 0; x < heat.width; x++) {
var i = x * 4;
ramp[x] = [d[i], d[i + 1], d[i + 2], d[i + 3]];
}
return ramp;
}
function genZ(n, w, h) {
var a = [];
for (var i = 0; i < n; i++) {
a[i] = [
Math.floor(Math.random() * w),
Math.floor(Math.random() * h),
Math.floor(Math.random() * 3) - 1,
Math.floor(Math.random() * 3) - 1
];
}
return a;
}
function moveZ() {
var w = app.w
var h = app.h;
var z = app.z;
for (var i = 0; i < z.length; i++) {
var s = z[i];
s[0] += s[2];
s[1] += s[3];
if (s[0] > w || s[0] < 0) s[2] *= -1;
if (s[1] > w || s[1] < 0) s[3] *= -1;
}
}
function drawZ() {
var ctx = app.ctx;
var z = app.z;
ctx.fillStyle = "#FFFF00";
for (var i = 0; i < z.length; i++) {
ctx.fillRect(z[i][0] - 2, z[i][1] - 2, 4, 4);
}
}
function drawZ2() {
var ctx = app.ctx;
var layer = app.layer;
var layerCtx = app.layerCtx;
var gCan = app.gCan;
var z = app.z;
var radius = app.radius;
// render gradients at coords onto layer
for (var i = 0; i < z.length; i++) {
var x = Math.floor((z[i][0] * app.scale) - radius);
var y = Math.floor((z[i][1] * app.scale) - radius);
layerCtx.drawImage(gCan, x, y);
}
// adjust layer for heat ramp
var ramp = app.ramp;
// apply ramp to layer
var imageData = layerCtx.getImageData(0, 0, layer.width, layer.height);
d = imageData.data;
for (var i = 0; i < d.length; i += 4) {
if (d[i + 3] != 0) {
var c = ramp[d[i + 3]];
d[i] = c[0];
d[i + 1] = c[1];
d[i + 2] = c[2];
d[i + 3] = c[3];
}
}
layerCtx.putImageData(imageData, 0, 0);
// draw layer on world
ctx.drawImage(layer, 0, 0, layer.width, layer.height, 0, 0, app.w, app.h);
}
<canvas id="can" width="600" height="400"></canvas>