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p5.js Flood Fill (bucket tool) works slowly and wierd

So I wrote a flood fill function that works like a paint-app bucket tool: you click inside a closed shape and it'll fill with a color.
I have two problems with it:
performance - let's say my canvas is 600*600 (370,000 pixels) and I draw a big circle in it that for example has about 100K pixels in it, it can take about 40(!!!) seconds to fill this circle! thats insane!
A sqaure of exactly 10,000 pixels takes 0.4-0.5 seconds on average, but (I guess) since the sizes of the arrays used the program are growing so much, a sqaure 10 times the size takes about 100 times the length to fill.
there's something wierd about the filling. I'm not really sure how it happens but it's always leaving a few un-filled pixels. Not much at all, but it's really wierd.
My flood fill function uses 4 helper-functions: get and set pixel color, checking if it's a color to fill, and checking if that's a pixel that has been checked before.
Here are all the functions:
getPixelColor = (x, y) => {
let pixelColor = [];
for (let i = 0; i < pixDens; ++i) {
for (let j = 0; j < pixDens; ++j) {
index = 4 * ((y * pixDens + j) * width * pixDens + (x * pixDens + i));
pixelColor[0] = pixels[index];
pixelColor[1] = pixels[index + 1];
pixelColor[2] = pixels[index + 2];
pixelColor[3] = pixels[index + 3];
}
}
return pixelColor;
};
setPixelColor = (x, y, currentColor) => { //Remember to loadPixels() before using this function, and to updatePixels() after.
for (let i = 0; i < pixDens; ++i) {
for (let j = 0; j < pixDens; ++j) {
index = 4 * ((y * pixDens + j) * width * pixDens + (x * pixDens + i));
pixels[index] = currentColor[0];
pixels[index + 1] = currentColor[1];
pixels[index + 2] = currentColor[2];
pixels[index + 3] = currentColor[3];
}
}
}
isDuplicate = (posHistory, vector) => {
for (let i = 0; i < posHistory.length; ++i) {
if (posHistory[i].x === vector.x && posHistory[i].y === vector.y) {
return true;
}
}
return false;
}
compareColors = (firstColor, secondColor) => {
for (let i = 0; i < firstColor.length; ++i) {
if (firstColor[i] !== secondColor[i]) {
return false;
}
}
return true;
}
floodFill = () => {
loadPixels();
let x = floor(mouseX);
let y = floor(mouseY);
let startingColor = getPixelColor(x, y);
if (compareColors(startingColor, currentColor)) {
return false;
}
let pos = [];
pos.push(createVector(x, y));
let posHistory = [];
posHistory.push(createVector(x, y));
while (pos.length > 0) {
x = pos[0].x;
y = pos[0].y;
pos.shift();
if (x <= width && x >= 0 && y <= height && y >= 0) {
setPixelColor(x, y, currentColor);
let xMinus = createVector(x - 1, y);
if (!isDuplicate(posHistory, xMinus) && compareColors(getPixelColor(xMinus.x, xMinus.y), startingColor)) {
pos.push(xMinus);
posHistory.push(xMinus);
}
let xPlus = createVector(x + 1, y);
if (!isDuplicate(posHistory, xPlus) && compareColors(getPixelColor(xPlus.x, xPlus.y), startingColor)) {
pos.push(xPlus);
posHistory.push(xPlus);
}
let yMinus = createVector(x, y - 1);
if (!isDuplicate(posHistory, yMinus) && compareColors(getPixelColor(yMinus.x, yMinus.y), startingColor)) {
pos.push(yMinus);
posHistory.push(yMinus);
}
let yPlus = createVector(x, y + 1);
if (!isDuplicate(posHistory, yPlus) && compareColors(getPixelColor(yPlus.x, yPlus.y), startingColor)) {
pos.push(yPlus);
posHistory.push(yPlus);
}
}
}
updatePixels();
}
I would really apprciate it if someone could help me solve the problems with the functions.
Thank you very much!!
EDIT: So I updated my flood fill function itself and removed an array of colors that I never used. this array was pretty large and a few push() and a shift() methods called on it on pretty much every run.
UNFORTUNATLY, the execution time is 99.9% the same for small shapes (for example, a fill of 10,000 takes the same 0.5 seconds, but large fills, like 100,000 pixels now takes about 30 seconds and not 40, so that's a step in the right direction.
I guess that RAM usage is down as well since it was a pretty large array but I didn't measured it.
The wierd problem where it leaves un-filled pixels behind is still here as well.

A little suggestion:
You don't actually have to use the posHistory array to determine whether to set color. If the current pixel has the same color as startingColor then set color, otherwise don't set. This would have the same effect.
The posHistory array would grow larger and larger during execution. As a result, a lot of work has to be done just to determine whether to fill a single pixel. I think this might be the reason behind your code running slowly.
As for the "weird thing":
This also happened to me before. I think that's because the unfilled pixels do not have the same color as startingColor. Say you draw a black shape on a white background, you would expect to see some gray pixels (close to white) between the black and white parts somewhere. These pixels play the role of smoothing the shape.

How to Create a Multidimenisonal PRNG?

I am working on a procedural terrain generator, but the 3d Map is constantly morphing and changing, calling for at least 4d noise (5d if I need to make it loop). I haven't found a good perlin/simplex noise library that will work in this many dimensions, so I thought this would be a good time to learn how those algorithms work. After starting to make my own "perlin" noise, I found a large problem. I need to get a psudo random value based on the nD coordinates of that point. So far I have found solutions online that use the dot product of a single point and a vector generated by the inputs, but those became very predictable very fast (I'm not sure why). I then tried a recursive approach (below), and this worked ok, but I got some weird behavior towards the edges.
Recursive 3d randomness attempt:
function Rand(seed = 123456, deg = 1){
let s = seed % 2147483647;
s = s < 1 ? s + 2147483647 : s;
while(deg > 0){
s = s * 16807 % 2147483647;
deg--;
}
return (s - 1) / 2147483646;
}
function DimRand(seed, args){
if(args.length < 2){
return Rand(seed, args[0]);
}else{
let zero = args[0];
args.shift();
return DimRand(Rand(seed, zero), args);
}
}
var T = 1;
var c = document.getElementById('canvas').getContext('2d');
document.getElementById('canvas').height = innerHeight;
document.getElementById('canvas').width = innerWidth;
c.width = innerWidth;
c.height = innerHeight;
var size = 50;
function display(){
for(let i = 0; i < 20; i ++){
for(let j = 0; j < 20; j ++){
var bright = DimRand(89,[i,j])*255
c.fillStyle = `rgb(${bright},${bright},${bright})`
c.fillRect(i*size, j*size, size, size);
}
}
T++;
}
window.onmousedown=()=>{display();}
And here is the result:
The top row was always 1 (White), the 2d row and first column were all 0 (Black), and the 3d row was always very dark (less than ≈ 0.3)
This might just be a bug, or I might have to just deal with it, but I was wondering if there was a better approach.

Natural Movement with Noise

Im creating an object that randomly moves in a natural way using noise like this (works as intended):
The objects encounter a collision and their trajectory is manipulated, the movement path now changes to straight line (words as intended)
thisRabbit.x = _world.width * (noise(thisRabbit.t));
thisRabbit.y = _world.height * (noise(thisRabbit.t+5));
thisRabbit.t += 0.001;
The problem is after this movement , i want the object to start moving in a random direction again as it was initially. If i use the same function, the object jumps to the last location before the trajectory was modified.
let vx = this.acquiredFood[0] - this.x;
let vy = this.acquiredFood[1] - this.y;
let f = (this.genes.speed + 10) / Math.sqrt(vx*vx+vy*vy);
vx = vx * f;
vy = vy * f;
let newX = this.x + vx;
let newY = this.y + vy;
So how do i get the object to move as before, given a starting position
edit: snippet here: https://editor.p5js.org/vince.chinner/sketches/HPFKR8eIw

Your problem is that you used a factor from 0 to 1 generated with noise and an incremented seed to generate the position by multiplying directly the world dimentions. When reaching food, you cannot increment the seed as to be in the exact position where the movement to get your food led you (I found no inverse function for noise to get the seed from the return value).
What you need to do instead is use the noise to increment or decrement the coordinates, so that no matter where the seed is, you don't loose your current position.
Here are the different corrections I applied to the code, as there were also syntax errors, I can't really paste the whole stuff here for copyright reasons (you didn't share the whole code here and the sketch belongs to you)
MAIN CORRECTION:
used a var found because returning from the forEach callback doesn't make you leave the findFood function, but the callback one. And the forEach loop doesn't stop. Using this var prevents the further forEach tests to be made and allows you to return from findFood so that no further move is made after seeing food.
noise is now applied to a value of 4 and I subtract 2, so that x and y now change with a range of -2 to 2 each. Of course, with this method, you need to check against world dimentions or else the rabbit could leave the world. The seed increment has been changed too or else it would vary too slowly (adapt values as you wish)
findFood(){
var thisRabbit = this, found = false;
_world.food.forEach(f => {
if(!found){
let d = int(dist(f[0], f[1], thisRabbit.x, thisRabbit.y));
if(d < (thisRabbit.genes.vision / 2)+3){
thisRabbit.state = "foundFood";
this.acquiredFood = f;
found = true;
}
}
});
if(found){ return; }
thisRabbit.x += (noise(thisRabbit.t) * 4) - 2;
if(thisRabbit.x < 0){ thisRabbit.x = 0; }
if(thisRabbit.x > _world.width){ thisRabbit.x = _world.width; }
thisRabbit.y += (noise(thisRabbit.t + 5) * 4) - 2;
if(thisRabbit.y < 0){ thisRabbit.y = 0; }
if(thisRabbit.y > _world.height){ thisRabbit.y = _world.height; }
thisRabbit.t += 0.01;
}
SYNTAX ERRORS:
lines 23 / 24: assignment should be with a value (null or false)
this.genes = null;
this.acquiredFood = null;
lines 129 to 133: end you instructions with a ; instead of a ,
this.width = w;
this.height = h;
this.foodDensity = foodDensity;
this.food = [];
this.rabits = [];
line 156 to 160: there should be no space between rabbit and .t. Additionnally, because the coordinates are not directly linked to t, I would prefer to use random for starting position:
let x = this.width * random();
let y = this.height * random();
let _rabbit = new rabbit(x, y);
_rabbit.genes = genes;
_rabbit.t = t;

HTML5 Canvas, better pixel control and better speed

I'm trying to create a little simulation with the help of HTML5 and Javascript using a canvas. My problem however is, I can't really think of a way to control the behavior of my pixels, without making every single pixel an object, which leads to an awful slowdown of my simulation.
Heres the code so far:
var pixels = [];
class Pixel{
constructor(color){
this.color=color;
}
}
window.onload=function(){
canv = document.getElementById("canv");
ctx = canv.getContext("2d");
createMap();
setInterval(game,1000/60);
};
function createMap(){
pixels=[];
for(i = 0; i <= 800; i++){
pixels.push(sub_pixels = []);
for(j = 0; j <= 800; j++){
pixels[i].push(new Pixel("green"));
}
}
pixels[400][400].color="red";
}
function game(){
ctx.fillStyle = "white";
ctx.fillRect(0,0,canv.width,canv.height);
for(i = 0; i <= 800; i++){
for(j = 0; j <= 800; j++){
ctx.fillStyle=pixels[i][j].color;
ctx.fillRect(i,j,1,1);
}
}
for(i = 0; i <= 800; i++){
for(j = 0; j <= 800; j++){
if(pixels[i][j].color == "red"){
direction = Math.floor((Math.random() * 4) + 1);
switch(direction){
case 1:
pixels[i][j-1].color= "red";
break;
case 2:
pixels[i+1][j].color= "red";
break;
case 3:
pixels[i][j+1].color= "red";
break;
case 4:
pixels[i-1][j].color= "red";
break;
}
}
}
}
}
function retPos(){
return Math.floor((Math.random() * 800) + 1);
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<script language="javascript" type="text/javascript" src="game.js"></script>
</head>
<body>
<canvas width="800px" height="800px" id="canv"></canvas>
</body>
</html>
So my two big questions are, what better way of controlling those pixels is there? And how can I speed up the pixel generation?
Hope you can help me.

Optimizing pixel manipulation
There are many options to speed up your code
Pixels as 32bit ints
The following will slug most machines with too much work.
// I removed fixed 800 and replaced with const size
for(i = 0; i <= size; i++){
for(j = 0; j <= size; j++){
ctx.fillStyle=pixels[i][j].color;
ctx.fillRect(i,j,1,1);
}
}
Don't write each pixel via a rect. Use the pixel data you can get from the canvas API via createImageData and associated functions. It uses typed arrays that are a little quicker than arrays and can have multiple view on the same content.
You can write all the pixels to the canvas in a single call. Not blindingly fast but a zillion times faster than what you are doing.
const size = 800;
const imageData = ctx.createImageData(size,size);
// get a 32 bit view
const data32 = new Uint32Array(imageData.data.buffer);
// To set a single pixel
data32[x+y*size] = 0xFF0000FF; // set pixel to red
// to set all pixels
data32.fill(0xFF00FF00); // set all to green
To get a pixel at a pixel coord
const pixel = data32[x + y * imageData.width];
See Accessing pixel data for more on using the image data.
The pixel data is not displayed until you put it onto the canvas
ctx.putImageData(imageData,0,0);
That will give you a major improvement.
Better data organization.
When performance is critical you sacrifice memory and simplicity to get more CPU cycles doing what you want and less doing a lot of nothing.
You have red pixels randomly expanding into the scene, you read every pixel and check (via a slow string comparison) if it is red. When you find one you add a random red pixel besides it.
Checking the green pixels is a waste and can be avoided. Expanding red pixels that are completely surrounded by other reds is also pointless. They do nothing.
The only pixels you are interested in are the red pixels that are next to green pixels.
Thus you can create a buffer that holds the location of all active red pixels, An active red has at least one green. Each frame you check all the active reds, spawning new ones if they can, and killing them if they are surrounded in red.
We don't need to store the x,y coordinate of each red, just the memory address so we can use a flat array.
const reds = new Uint32Array(size * size); // max size way over kill but you may need it some time.
You dont want to have to search for reds in your reds array so you need to keep track of how many active reds there are. You want all the active reds to be at the bottom of the array. You need to check each active red only once per frame. If a red is dead than all above it must move down one array index. But you only want to move each red only once per frame.
Bubble array
I dont know what this type of array is called its like a separation tank, dead stuff slowly moves up and live stuff moves down. Or unused items bubble up used items settle to the bottom.
I will show it as functional because it will be easier to understand. but is better implemented as one brute force function
// data32 is the pixel data
const size = 800; // width and height
const red = 0xFF0000FF; // value of a red pixel
const green = 0xFF00FF00; // value of a green pixel
const reds = new Uint32Array(size * size); // max size way over kill but you var count = 0; // total active reds
var head = 0; // index of current red we are processing
var tail = 0; // after a red has been process it is move to the tail
var arrayOfSpawnS = [] // for each neighbor that is green you want
// to select randomly to spawn to. You dont want
// to spend time processing so this is a lookup
// that has all the possible neighbor combinations
for(let i = 0; i < 16; i ++){
let j = 0;
const combo = [];
i & 1 && (combo[j++] = 1); // right
i & 2 && (combo[j++] = -1); // left
i & 4 && (combo[j++] = -size); // top
i & 5 && (combo[j++] = size); // bottom
arrayOfSpawnS.push(combo);
}
function addARed(x,y){ // add a new red
const pixelIndex = x + y * size;
if(data32[pixelIndex] === green) { // check if the red can go there
reds[count++] = pixelIndex; // add the red with the pixel index
data32[pixelIndex] = red; // and set the pixel
}
}
function safeAddRed(pixelIndex) { // you know that some reds are safe at the new pos so a little bit faster
reds[count++] = pixelIndex; // add the red with the pixel index
data32[pixelIndex] = red; // and set the pixel
}
// a frame in the life of a red. Returns false if red is dead
function processARed(indexOfRed) {
// get the pixel index
var pixelIndex = reds[indexOfRed];
// check reds neighbors right left top and bottom
// we fill a bit value with each bit on if there is a green
var n = data32[pixelIndex + 1] === green ? 1 : 0;
n += data32[pixelIndex - 1] === green ? 2 : 0;
n += data32[pixelIndex - size] === green ? 4 : 0;
n += data32[pixelIndex + size] === green ? 8 : 0;
if(n === 0){ // no room to spawn so die
return false;
}
// has room to spawn so pick a random
var nCount = arrayOfSpawnS[n].length;
// if only one spawn point then rather than spawn we move
// this red to the new pos.
if(nCount === 1){
reds[indexOfRed] += arrayOfSpawnS[n][0]; // move to next pos
}else{ // there are several spawn points
safeAddRed(pixelIndex + arrayOfSpawnS[n][(Math.random() * nCount)|0]);
}
// reds frame is done so return still alive to spawn another frame
return true;
}
Now to process all the reds.
This is the heart of the bubble array. head is used to index each active red. tail is the index of where to move the current head if no deaths have been encountered tail is equal to head. If however a dead item is encountered the head move up one while the tail remains pointing to the dead item. This moves all the active items to the bottom.
When head === count all active items have been checked. The value of tail now contains the new count which is set after the iteration.
If you were using an object rather than a Integer, instead of moving the active item down you swap the head and tail items. This effectively creates a pool of available objects that can be used when adding new items. This type of array management incurs not GC or Allocation overhead and is hence very quick when compared to stacks and object pools.
function doAllReds(){
head = tail = 0; // start at the bottom
while(head < count){
if(processARed(head)){ // is red not dead
reds[tail++] = reds[head++]; // move red down to the tail
}else{ // red is dead so this creates a gap in the array
// Move the head up but dont move the tail,
// The tail is only for alive reds
head++;
}
}
// All reads done. The tail is now the new count
count = tail;
}
The Demo.
The demo will show you the speed improvement. I used the functional version and there could be some other tweaks.
You can also consider webWorkers to get event more speed. Web worker run on a separate javascript context and provides true concurrent processing.
For the ultimate speed use WebGL. All the logic can be done via a fragment shader on the GPU. This type of task is very well suited to parallel processing for which the GPU is designed.
Will be back later to clean up this answer (got a little too long)
I have also added a boundary to the pixel array as the reds were spawning off the pixel array.
const size = canvas.width;
canvas.height = canvas.width;
const ctx = canvas.getContext("2d");
const red = 0xFF0000FF;
const green = 0xFF00FF00;
const reds = new Uint32Array(size * size);
const wall = 0xFF000000;
var count = 0;
var head = 0;
var tail = 0;
var arrayOfSpawnS = []
for(let i = 0; i < 16; i ++){
let j = 0;
const combo = [];
i & 1 && (combo[j++] = 1); // right
i & 2 && (combo[j++] = -1); // left
i & 4 && (combo[j++] = -size); // top
i & 5 && (combo[j++] = size); // bottom
arrayOfSpawnS.push(combo);
}
const imageData = ctx.createImageData(size,size);
const data32 = new Uint32Array(imageData.data.buffer);
function createWall(){//need to keep the reds walled up so they dont run free
for(let j = 0; j < size; j ++){
data32[j] = wall;
data32[j * size] = wall;
data32[j * size + size - 1] = wall;
data32[size * (size - 1) +j] = wall;
}
}
function addARed(x,y){
const pixelIndex = x + y * size;
if (data32[pixelIndex] === green) {
reds[count++] = pixelIndex;
data32[pixelIndex] = red;
}
}
function processARed(indexOfRed) {
var pixelIndex = reds[indexOfRed];
var n = data32[pixelIndex + 1] === green ? 1 : 0;
n += data32[pixelIndex - 1] === green ? 2 : 0;
n += data32[pixelIndex - size] === green ? 4 : 0;
n += data32[pixelIndex + size] === green ? 8 : 0;
if(n === 0) { return false }
var nCount = arrayOfSpawnS[n].length;
if (nCount === 1) { reds[indexOfRed] += arrayOfSpawnS[n][0] }
else {
pixelIndex += arrayOfSpawnS[n][(Math.random() * nCount)|0]
reds[count++] = pixelIndex;
data32[pixelIndex] = red;
}
return true;
}
function doAllReds(){
head = tail = 0;
while(head < count) {
if(processARed(head)) { reds[tail++] = reds[head++] }
else { head++ }
}
count = tail;
}
function start(){
data32.fill(green);
createWall();
var startRedCount = (Math.random() * 5 + 1) | 0;
for(let i = 0; i < startRedCount; i ++) { addARed((Math.random() * size-2+1) | 0, (Math.random() * size-2+1) | 0) }
ctx.putImageData(imageData,0,0);
setTimeout(doItTillAllDead,1000);
countSameCount = 0;
}
var countSameCount;
var lastCount;
function doItTillAllDead(){
doAllReds();
ctx.putImageData(imageData,0,0);
if(count === 0 || countSameCount === 100){ // all dead
setTimeout(start,1000);
}else{
countSameCount += count === lastCount ? 1 : 0;
lastCount = count; //
requestAnimationFrame(doItTillAllDead);
}
}
start();
<canvas width="800" height="800" id="canvas"></canvas>

The main cause of your slow down is your assumption that you need to loop over every pixel for every operation. You do not do this, as that would be 640,000 iterations for every operation you need to do.
You also shouldn't be doing any manipulation logic within the render loop. The only thing that should be there is drawing code. So this should be moved out to preferably a separate thread (Web Workers). If unable to use those a setTimeout/Interval call.
So first a couple of small changes:
Make Pixel class contain the pixel's coordinates along with the color:
class Pixel{
constructor(color,x,y){
this.color=color;
this.x = x;
this.y = y;
}
}
Keep an array of pixels that will end up creating new red pixels. And another one to keep track of what pixels have been updated so we know which ones need drawn.
var pixels = [];
var infectedPixesl = [];
var updatedPixels = [];
Now the easiest part of the code to change is the render loop. Since the only thing that it needs to do is draw the pixels it will be only a couple lines.
function render(){
var numUpdatedPixels = updatedPixels.length;
for(let i=0; i<numUpdatedPixels; i++){
let pixel = updatedPixels[i];
ctx.fillStyle = pixel.color;
ctx.fillRect(pixel.x,pixel.y,1,1);
}
//clear out the updatedPixels as they should no longer be considered updated.
updatedPixels = [];
//better method than setTimeout/Interval for drawing
requestAnimationFrame(render);
}
From there we can move on to the logic. We will loop over the infectedPixels array, and with each pixel we decide a random direction and get that pixel. If this selected pixel is red we do nothing and continue on. Otherwise we change it's color and add it to a temporary array affectedPixels. After which we test to see if all the pixels around the original pixel are all red, if so we can remove it from the infectedPixels as there is no need to check it again. Then add all the pixels from affectedPixels onto the infectedPixels as these are now new pixels that need to be checked. And the last step is to also add affectedPixels onto updatedPixels so that the render loop draws the changes.
function update(){
var affectedPixels = [];
//needed as we shouldn't change an array while looping over it
var stillInfectedPixels = [];
var numInfected = infectedPixels.length;
for(let i=0; i<numInfected; i++){
let pixel = infectedPixels[i];
let x = pixel.x;
let y = pixel.y;
//instead of using a switch statement, use the random number as the index
//into a surroundingPixels array
let surroundingPixels = [
(pixels[x] ? pixels[x][y - 1] : null),
(pixels[x + 1] ? pixels[x + 1][y] : null),
(pixels[x] ? pixels[x][y + 1] : null),
(pixels[x - 1] ? pixels[x - 1][y] : null)
].filter(p => p);
//filter used above to remove nulls, in the cases of edge pixels
var rand = Math.floor((Math.random() * surroundingPixels.length));
let selectedPixel = surroundingPixels[rand];
if(selectedPixel.color == "green"){
selectedPixel.color = "red";
affectedPixels.push(selectedPixel);
}
if(!surroundingPixels.every(p=>p.color=="red")){
stillInfectedPixels.push(pixel);
}
}
infectedPixels = stillInfectedPixel.concat( affectedPixels );
updatedPixels.push(...affectedPixels);
}
Demo
var pixels = [],
infectedPixels = [],
updatedPixels = [],
canv, ctx;
window.onload = function() {
canv = document.getElementById("canv");
ctx = canv.getContext("2d");
createMap();
render();
setInterval(() => {
update();
}, 16);
};
function createMap() {
for (let y = 0; y < 800; y++) {
pixels.push([]);
for (x = 0; x < 800; x++) {
pixels[y].push(new Pixel("green",x,y));
}
}
pixels[400][400].color = "red";
updatedPixels = [].concat(...pixels);
infectedPixels.push(pixels[400][400]);
}
class Pixel {
constructor(color, x, y) {
this.color = color;
this.x = x;
this.y = y;
}
}
function update() {
var affectedPixels = [];
var stillInfectedPixels = [];
var numInfected = infectedPixels.length;
for (let i = 0; i < numInfected; i++) {
let pixel = infectedPixels[i];
let x = pixel.x;
let y = pixel.y;
let surroundingPixels = [
(pixels[x] ? pixels[x][y - 1] : null),
(pixels[x + 1] ? pixels[x + 1][y] : null),
(pixels[x] ? pixels[x][y + 1] : null),
(pixels[x - 1] ? pixels[x - 1][y] : null)
].filter(p => p);
var rand = Math.floor((Math.random() * surroundingPixels.length));
let selectedPixel = surroundingPixels[rand];
if (selectedPixel.color == "green") {
selectedPixel.color = "red";
affectedPixels.push(selectedPixel);
}
if (!surroundingPixels.every(p => p.color == "red")) {
stillInfectedPixels.push(pixel);
}
}
infectedPixels = stillInfectedPixels.concat(affectedPixels);
updatedPixels.push(...affectedPixels);
}
function render() {
var numUpdatedPixels = updatedPixels.length;
for (let i = 0; i < numUpdatedPixels; i++) {
let pixel = updatedPixels[i];
ctx.fillStyle = pixel.color;
ctx.fillRect(pixel.x, pixel.y, 1, 1);
}
updatedPixels = [];
requestAnimationFrame(render);
}
<canvas id="canv" width="800" height="800"></canvas>

Simplify table code in EaselJs

I've got a 2x3 table that I'm adding to EaselJS...currently I'm building it like this:
for (var i = 0; i < 6; i++) {
if(i == 1 || i == 3 || i == 5) {
var xPos = playersBoxW;
} else {
var xPos = 0;
}
if(i == 2 || i == 3) {
var yPos = playersBoxH;
} else if (i == 4|| i == 5) {
var yPos = playersBoxH*2;
} else {
var yPos = 0;
}
playerBox[i] = new createjs.Container().set({x: xPos, y: yPos});
}
It just seems a very inefficient way of doing it and not useful if the table grows. Anyone else have an idea to simplify this?

If you are just trying to do row/column math, there is an easier way.
Here is your original example (with some code to make it work) http://jsfiddle.net/u3ds24y5/
You can just derive the column and row with a simple equation. This lets you change the number of columns and total count easily.
var column = i % num_columns;
var row = Math.floor(i / num_columns);
var x = column * column_width;
var y = row * row_height;
Here is an updated fiddle: http://jsfiddle.net/u3ds24y5/1/
Simplified code:
var cols = 2, total = 6; // Change these
for (var i = 0; i < total; i++) {
var xPos = i % cols * playersBoxW,
yPos = Math.floor(i/cols) * playersBoxH;
// Create container, etc
}

Looking at your code I think this algorithm is essentially what it boils down to:
xPos seems to be equal to the integer division of i (by table width) times playersBoxW. e.g if i = 3 and width is 2, then xPos is equal to playersBoxW times int division of 3/2 which is 1.
yPos seems to be equal to the integer division of i (by table height) times playersBoxH. e.g if i = 4 and height = 3, then yPos is equal to playersBoxH times int division of 4/3 which is 1.
function integerDivision(a, b) {
return Math.floor(a / b);
}
function makeTable(width, height, player, arr) {
var xPos, yPos, size = width*height;
for (var i = 0; i < size; i++) {
xPos = player.boxW * integerDivision(i, width);
yPos = player.boxH * integerDivision(i, height);
arr[i] = new createjs.Container().set({x: xPos, y: yPos});
}
return arr;
}
Integer division is like regular division but you throw the remainder away. So in this case we round the number down:
3/2 = 1.5 => floor the result (round down) => 1
Side node: EaslJS containers can be expensive sometimes so be careful with them.
Containers have some overhead, so you generally shouldn't create a Container to hold a single child. [easljs doc]