We Keep Coding

How to add paint bucket fill in HTML5 canvas [duplicate]

Has anyone implemented a flood fill algorithm in javascript for use with HTML Canvas?
My requirements are simple: flood with a single color starting from a single point, where the boundary color is any color greater than a certain delta of the color at the specified point.
var r1, r2; // red values
var g1, g2; // green values
var b1, b2; // blue values
var actualColorDelta = Math.sqrt((r1 - r2)*(r1 - r2) + (g1 - g2)*(g1 - g2) + (b1 - b2)*(b1 - b2))
function floodFill(canvas, x, y, fillColor, borderColorDelta) {
...
}
Update:
I wrote my own implementation of flood fill, which follows. It is slow, but accurate. About 37% of the time is taken up in two low-level array functions that are part of the prototype framework. They are called by push and pop, I presume. Most of the rest of the time is spent in the main loop.
var ImageProcessing;
ImageProcessing = {
/* Convert HTML color (e.g. "#rrggbb" or "#rrggbbaa") to object with properties r, g, b, a.
* If no alpha value is given, 255 (0xff) will be assumed.
*/
toRGB: function (color) {
var r, g, b, a, html;
html = color;
// Parse out the RGBA values from the HTML Code
if (html.substring(0, 1) === "#")
{
html = html.substring(1);
}
if (html.length === 3 || html.length === 4)
{
r = html.substring(0, 1);
r = r + r;
g = html.substring(1, 2);
g = g + g;
b = html.substring(2, 3);
b = b + b;
if (html.length === 4) {
a = html.substring(3, 4);
a = a + a;
}
else {
a = "ff";
}
}
else if (html.length === 6 || html.length === 8)
{
r = html.substring(0, 2);
g = html.substring(2, 4);
b = html.substring(4, 6);
a = html.length === 6 ? "ff" : html.substring(6, 8);
}
// Convert from Hex (Hexidecimal) to Decimal
r = parseInt(r, 16);
g = parseInt(g, 16);
b = parseInt(b, 16);
a = parseInt(a, 16);
return {r: r, g: g, b: b, a: a};
},
/* Get the color at the given x,y location from the pixels array, assuming the array has a width and height as given.
* This interprets the 1-D array as a 2-D array.
*
* If useColor is defined, its values will be set. This saves on object creation.
*/
getColor: function (pixels, x, y, width, height, useColor) {
var redIndex = y * width * 4 + x * 4;
if (useColor === undefined) {
useColor = { r: pixels[redIndex], g: pixels[redIndex + 1], b: pixels[redIndex + 2], a: pixels[redIndex + 3] };
}
else {
useColor.r = pixels[redIndex];
useColor.g = pixels[redIndex + 1]
useColor.b = pixels[redIndex + 2];
useColor.a = pixels[redIndex + 3];
}
return useColor;
},
setColor: function (pixels, x, y, width, height, color) {
var redIndex = y * width * 4 + x * 4;
pixels[redIndex] = color.r;
pixels[redIndex + 1] = color.g,
pixels[redIndex + 2] = color.b;
pixels[redIndex + 3] = color.a;
},
/*
* fill: Flood a canvas with the given fill color.
*
* Returns a rectangle { x, y, width, height } that defines the maximum extent of the pixels that were changed.
*
* canvas .................... Canvas to modify.
* fillColor ................. RGBA Color to fill with.
* This may be a string ("#rrggbbaa") or an object of the form { r: red, g: green, b: blue, a: alpha }.
* x, y ...................... Coordinates of seed point to start flooding.
* bounds .................... Restrict flooding to this rectangular region of canvas.
* This object has these attributes: { x, y, width, height }.
* If undefined or null, use the whole of the canvas.
* stopFunction .............. Function that decides if a pixel is a boundary that should cause
* flooding to stop. If omitted, any pixel that differs from seedColor
* will cause flooding to stop. seedColor is the color under the seed point (x,y).
* Parameters: stopFunction(fillColor, seedColor, pixelColor).
* Returns true if flooding shoud stop.
* The colors are objects of the form { r: red, g: green, b: blue, a: alpha }
*/
fill: function (canvas, fillColor, x, y, bounds, stopFunction) {
// Supply default values if necessary.
var ctx, minChangedX, minChangedY, maxChangedX, maxChangedY, wasTested, shouldTest, imageData, pixels, currentX, currentY, currentColor, currentIndex, seedColor, tryX, tryY, tryIndex, boundsWidth, boundsHeight, pixelStart, fillRed, fillGreen, fillBlue, fillAlpha;
if (Object.isString(fillColor)) {
fillColor = ImageProcessing.toRGB(fillColor);
}
x = Math.round(x);
y = Math.round(y);
if (bounds === null || bounds === undefined) {
bounds = { x: 0, y: 0, width: canvas.width, height: canvas.height };
}
else {
bounds = { x: Math.round(bounds.x), y: Math.round(bounds.y), width: Math.round(bounds.y), height: Math.round(bounds.height) };
}
if (stopFunction === null || stopFunction === undefined) {
stopFunction = new function (fillColor, seedColor, pixelColor) {
return pixelColor.r != seedColor.r || pixelColor.g != seedColor.g || pixelColor.b != seedColor.b || pixelColor.a != seedColor.a;
}
}
minChangedX = maxChangedX = x - bounds.x;
minChangedY = maxChangedY = y - bounds.y;
boundsWidth = bounds.width;
boundsHeight = bounds.height;
// Initialize wasTested to false. As we check each pixel to decide if it should be painted with the new color,
// we will mark it with a true value at wasTested[row = y][column = x];
wasTested = new Array(boundsHeight * boundsWidth);
/*
$R(0, bounds.height - 1).each(function (row) {
var subArray = new Array(bounds.width);
wasTested[row] = subArray;
});
*/
// Start with a single point that we know we should test: (x, y).
// Convert (x,y) to image data coordinates by subtracting the bounds' origin.
currentX = x - bounds.x;
currentY = y - bounds.y;
currentIndex = currentY * boundsWidth + currentX;
shouldTest = [ currentIndex ];
ctx = canvas.getContext("2d");
//imageData = ctx.getImageData(bounds.x, bounds.y, bounds.width, bounds.height);
imageData = ImageProcessing.getImageData(ctx, bounds.x, bounds.y, bounds.width, bounds.height);
pixels = imageData.data;
seedColor = ImageProcessing.getColor(pixels, currentX, currentY, boundsWidth, boundsHeight);
currentColor = { r: 0, g: 0, b: 0, a: 1 };
fillRed = fillColor.r;
fillGreen = fillColor.g;
fillBlue = fillColor.b;
fillAlpha = fillColor.a;
while (shouldTest.length > 0) {
currentIndex = shouldTest.pop();
currentX = currentIndex % boundsWidth;
currentY = (currentIndex - currentX) / boundsWidth;
if (! wasTested[currentIndex]) {
wasTested[currentIndex] = true;
//currentColor = ImageProcessing.getColor(pixels, currentX, currentY, boundsWidth, boundsHeight, currentColor);
// Inline getColor for performance.
pixelStart = currentIndex * 4;
currentColor.r = pixels[pixelStart];
currentColor.g = pixels[pixelStart + 1]
currentColor.b = pixels[pixelStart + 2];
currentColor.a = pixels[pixelStart + 3];
if (! stopFunction(fillColor, seedColor, currentColor)) {
// Color the pixel with the fill color.
//ImageProcessing.setColor(pixels, currentX, currentY, boundsWidth, boundsHeight, fillColor);
// Inline setColor for performance
pixels[pixelStart] = fillRed;
pixels[pixelStart + 1] = fillGreen;
pixels[pixelStart + 2] = fillBlue;
pixels[pixelStart + 3] = fillAlpha;
if (minChangedX < currentX) { minChangedX = currentX; }
else if (maxChangedX > currentX) { maxChangedX = currentX; }
if (minChangedY < currentY) { minChangedY = currentY; }
else if (maxChangedY > currentY) { maxChangedY = currentY; }
// Add the adjacent four pixels to the list to be tested, unless they have already been tested.
tryX = currentX - 1;
tryY = currentY;
tryIndex = tryY * boundsWidth + tryX;
if (tryX >= 0 && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX;
tryY = currentY + 1;
tryIndex = tryY * boundsWidth + tryX;
if (tryY < boundsHeight && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX + 1;
tryY = currentY;
tryIndex = tryY * boundsWidth + tryX;
if (tryX < boundsWidth && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX;
tryY = currentY - 1;
tryIndex = tryY * boundsWidth + tryX;
if (tryY >= 0 && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
}
}
}
//ctx.putImageData(imageData, bounds.x, bounds.y);
ImageProcessing.putImageData(ctx, imageData, bounds.x, bounds.y);
return { x: minChangedX + bounds.x, y: minChangedY + bounds.y, width: maxChangedX - minChangedX + 1, height: maxChangedY - minChangedY + 1 };
},
getImageData: function (ctx, x, y, w, h) {
return ctx.getImageData(x, y, w, h);
},
putImageData: function (ctx, data, x, y) {
ctx.putImageData(data, x, y);
}
};
BTW, when I call this, I use a custom stopFunction:
stopFill : function (fillColor, seedColor, pixelColor) {
// Ignore alpha difference for now.
return Math.abs(pixelColor.r - seedColor.r) > this.colorTolerance || Math.abs(pixelColor.g - seedColor.g) > this.colorTolerance || Math.abs(pixelColor.b - seedColor.b) > this.colorTolerance;
},
If anyone can see a way to improve performance of this code, I would appreciate it. The basic idea is:
1) Seed color is the initial color at the point to start flooding.
2) Try four adjacent points: up, right, down and left one pixel.
3) If point is out of range or has been visited already, skip it.
4) Otherwise push point onto to the stack of interesting points.
5) Pop the next interesting point off the stack.
6) If the color at that point is a stop color (as defined in the stopFunction) then stop processing that point and skip to step 5.
7) Otherwise, skip to step 2.
8) When there are no more interesting points to visit, stop looping.
Remembering that a point has been visited requires an array with the same number of elements as there are pixels.

To create a flood fill you need to be able to look at the pixels that are there already and check they aren't the color you started with so something like this.
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255]);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b) {
return a[0] === b[0] && a[1] === b[1] && a[2] === b[2] && a[3] === b[3];
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
fillPixel(imageData, x, y, targetColor, fillColor);
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
function fillPixel(imageData, x, y, targetColor, fillColor) {
const currentColor = getPixel(imageData, x, y);
if (colorsMatch(currentColor, targetColor)) {
setPixel(imageData, x, y, fillColor);
fillPixel(imageData, x + 1, y, targetColor, fillColor);
fillPixel(imageData, x - 1, y, targetColor, fillColor);
fillPixel(imageData, x, y + 1, targetColor, fillColor);
fillPixel(imageData, x, y - 1, targetColor, fillColor);
}
}
<canvas></canvas>
There's at least 2 problems with this code though.
It's deeply recursive.
So you might run out of stack space
It's slow.
No idea if it's too slow but JavaScript in the browser is mostly single threaded so while this code is running the browser is frozen. For a large canvas that frozen time might make the page really slow and if it's frozen too long the browser will ask if the user wants to kill the page.
The solution to running out of stack space is to implement our own stack. For example instead of recursively calling fillPixel we could keep an array of positions we want to look at. We'd add the 4 positions to that array and then pop things off the array until it's empty
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255]);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b) {
return a[0] === b[0] && a[1] === b[1] && a[2] === b[2] && a[3] === b[3];
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(imageData, x, y);
if (colorsMatch(currentColor, targetColor)) {
setPixel(imageData, x, y, fillColor);
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
The solution to it being too slow is either to make it run a little at a time OR to move it to a worker. I think that's a little too much to show in the same answer though here's an example.
I tested the code above on a 4096x4096 canvas and it took 16 seconds to fill a blank canvas on my machine so yes it's arguably too slow but putting it in a worker brings new problems which is that the result will be asynchronous so even though the browser wouldn't freeze you'd probably want to prevent the user from doing something until it finishes.
Another issue is you'll see the lines are antialiased and so filling with a solid color fills close the the line but not all the way up to it. To fix that you can change colorsMatch to check for close enough but then you have a new problem that if targetColor and fillColor are also close enough it will keep trying to fill itself. You could solve that by making another array, one byte or one bit per pixel to track places you've ready checked.
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255], 128);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b, rangeSq) {
const dr = a[0] - b[0];
const dg = a[1] - b[1];
const db = a[2] - b[2];
const da = a[3] - b[3];
return dr * dr + dg * dg + db * db + da * da < rangeSq;
}
function floodFill(ctx, x, y, fillColor, range = 1) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// flags for if we visited a pixel already
const visited = new Uint8Array(imageData.width, imageData.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
const rangeSq = range * range;
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(imageData, x, y);
if (!visited[y * imageData.width + x] &&
colorsMatch(currentColor, targetColor, rangeSq)) {
setPixel(imageData, x, y, fillColor);
visited[y * imageData.width + x] = 1; // mark we were here already
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
Note that this version of colorsMatch is kind of naive. It might be better to convert to HSV or something or maybe you want to weight by alpha. I don't know what a good metric is for matching colors.
Update
Another way to speed things up is of course to just optimize the code. Kaiido pointed out an obvious speedup which is to use a Uint32Array view on the pixels. That way looking up a pixel and setting a pixel there's just one 32bit value to read or write. Just that change makes it about 4x faster. It still takes 4 seconds to fill a 4096x4096 canvas though. There might be other optimizations like instead of calling getPixels make that inline but don't push a new pixel on our list of pixels to check if they are out of range. It might be 10% speed up (no idea) but won't make it fast enough to be an interactive speed.
There are other speedups like checking across a row at a time since rows are cache friendly and you can compute the offset to a row once and use that while checking the entire row whereas now for every pixel we have to compute the offset multiple times.
Those will complicate the algorithm so they are best left for you to figure out.
Let me also add, given the answer above freezes the browser while the fill is happening and that on a larger canvas that freeze could be too long, you can easily make the algorithm span over time using ES6 async/await. You need to choose how much work to give each segment of time. Choose too small and it will take a long time to fill. Choose too large and you'll get jank as the browser freezes.
Here's an example. Set ticksPerUpdate to speed up or slow down the fill rate
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
async function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const ticksPerUpdate = 50;
let tickCount = 0;
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(pixelData, x, y);
if (currentColor === targetColor) {
pixelData.data[y * pixelData.width + x] = fillColor;
// put the data back
ctx.putImageData(imageData, 0, 0);
++tickCount;
if (tickCount % ticksPerUpdate === 0) {
await wait();
}
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
}
}
function wait(delay = 0) {
return new Promise((resolve) => {
setTimeout(resolve, delay);
});
}
<canvas></canvas>
update update
Instead of setTimeout which is throttled by the browser, you can abuse postMessage which is not
function makeExposedPromise() {
let resolve;
let reject;
const promise = new Promise((_resolve, _reject) => {
resolve = _resolve;
reject = _reject;
});
return { promise, resolve, reject };
}
const resolveFns = [];
window.addEventListener('message', (e) => {
const resolve = resolveFns.shift();
resolve();
});
function wait() {
const {resolve, promise} = makeExposedPromise();
resolveFns.push(resolve);
window.postMessage('');
return promise;
}
If you use that it there's less need to choose a number of operations. Also note: the slowest part is calling putImageData. The reason it's inside the loop above is only so we can see the progress. Move that to the end and it will run much faster
function makeExposedPromise() {
let resolve;
let reject;
const promise = new Promise((_resolve, _reject) => {
resolve = _resolve;
reject = _reject;
});
return { promise, resolve, reject };
}
const resolveFns = [];
window.addEventListener('message', (e) => {
const resolve = resolveFns.shift();
resolve();
});
function wait() {
const {resolve, promise} = makeExposedPromise();
resolveFns.push(resolve);
window.postMessage('');
return promise;
}
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
async function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(pixelData, x, y);
if (currentColor === targetColor) {
pixelData.data[y * pixelData.width + x] = fillColor;
await wait();
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
It's still better to choose a number of operations per call to wait
There are also faster algorithms. The issue with the one above is there is for every pixel that matches, 4 are added to the stack of things to pixels to check. That's lots of allocations and multiple checking. A faster way is to it by span.
For a given span, check as far left as you can, then as far right as you can, now fill that span. Then, check the pixels above and/or below the span you just found and add the spans you find to your stack. Pop the top span off, and try to expand it left and right. There's no need to check the pixels in the middle since you already checked them. Further, if this span was generated from one below then you don't need to check the pixels below the starting sub-span of this span since you know that area was already filled. Similarly if this pan was generated from one above then you don't need to check the pixels above the starting sub-span of this span for the same reason.
function main() {
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
}
main();
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const spansToCheck = [];
function addSpan(left, right, y, direction) {
spansToCheck.push({left, right, y, direction});
}
function checkSpan(left, right, y, direction) {
let inSpan = false;
let start;
let x;
for (x = left; x < right; ++x) {
const color = getPixel(pixelData, x, y);
if (color === targetColor) {
if (!inSpan) {
inSpan = true;
start = x;
}
} else {
if (inSpan) {
inSpan = false;
addSpan(start, x - 1, y, direction);
}
}
}
if (inSpan) {
inSpan = false;
addSpan(start, x - 1, y, direction);
}
}
addSpan(x, x, y, 0);
while (spansToCheck.length > 0) {
const {left, right, y, direction} = spansToCheck.pop();
// do left until we hit something, while we do this check above and below and add
let l = left;
for (;;) {
--l;
const color = getPixel(pixelData, l, y);
if (color !== targetColor) {
break;
}
}
++l
let r = right;
for (;;) {
++r;
const color = getPixel(pixelData, r, y);
if (color !== targetColor) {
break;
}
}
const lineOffset = y * pixelData.width;
pixelData.data.fill(fillColor, lineOffset + l, lineOffset + r);
if (direction <= 0) {
checkSpan(l, r, y - 1, -1);
} else {
checkSpan(l, left, y - 1, -1);
checkSpan(right, r, y - 1, -1);
}
if (direction >= 0) {
checkSpan(l, r, y + 1, +1);
} else {
checkSpan(l, left, y + 1, +1);
checkSpan(right, r, y + 1, +1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
Note: I didn't test this well, there might be an off by 1 error or other issue. I'm 99% sure I wrote the span method in 1993 for My Paint but don't remember if I have the source. But in any case, it's fast enough there's no need for wait

Here's an implementation that I've been working on. It can get really slow if the replacement color is too close to the original color. It's quite a bit faster in Chrome than Firefox (I haven't tested it in any other browsers).
I also haven't done exhaustive testing yet, so there may be edge cases where it doesn't work.
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return NaN;
}
var pixels = pixelData.data;
var i = (y * pixelData.width + x) * 4;
return ((pixels[i + 0] & 0xFF) << 24) |
((pixels[i + 1] & 0xFF) << 16) |
((pixels[i + 2] & 0xFF) << 8) |
((pixels[i + 3] & 0xFF) << 0);
}
function setPixel(pixelData, x, y, color) {
var i = (y * pixelData.width + x) * 4;
var pixels = pixelData.data;
pixels[i + 0] = (color >>> 24) & 0xFF;
pixels[i + 1] = (color >>> 16) & 0xFF;
pixels[i + 2] = (color >>> 8) & 0xFF;
pixels[i + 3] = (color >>> 0) & 0xFF;
}
function diff(c1, c2) {
if (isNaN(c1) || isNaN(c2)) {
return Infinity;
}
var dr = ((c1 >>> 24) & 0xFF) - ((c2 >>> 24) & 0xFF);
var dg = ((c1 >>> 16) & 0xFF) - ((c2 >>> 16) & 0xFF);
var db = ((c1 >>> 8) & 0xFF) - ((c2 >>> 8) & 0xFF);
var da = ((c1 >>> 0) & 0xFF) - ((c2 >>> 0) & 0xFF);
return dr*dr + dg*dg + db*db + da*da;
}
function floodFill(canvas, x, y, replacementColor, delta) {
var current, w, e, stack, color, cx, cy;
var context = canvas.getContext("2d");
var pixelData = context.getImageData(0, 0, canvas.width, canvas.height);
var done = [];
for (var i = 0; i < canvas.width; i++) {
done[i] = [];
}
var targetColor = getPixel(pixelData, x, y);
delta *= delta;
stack = [ [x, y] ];
done[x][y] = true;
while ((current = stack.pop())) {
cx = current[0];
cy = current[1];
if (diff(getPixel(pixelData, cx, cy), targetColor) <= delta) {
setPixel(pixelData, cx, cy, replacementColor);
w = e = cx;
while (w > 0 && diff(getPixel(pixelData, w - 1, cy), targetColor) <= delta) {
--w;
if (done[w][cy]) break;
setPixel(pixelData, w, cy, replacementColor);
}
while (e < pixelData.width - 1 && diff(getPixel(pixelData, e + 1, cy), targetColor) <= delta) {
++e;
if (done[e][cy]) break;
setPixel(pixelData, e, cy, replacementColor);
}
for (cx = w; cx <= e; cx++) {
if (cy > 0) {
color = getPixel(pixelData, cx, cy - 1);
if (diff(color, targetColor) <= delta) {
if (!done[cx][cy - 1]) {
stack.push([cx, cy - 1]);
done[cx][cy - 1] = true;
}
}
}
if (cy < canvas.height - 1) {
color = getPixel(pixelData, cx, cy + 1);
if (diff(color, targetColor) <= delta) {
if (!done[cx][cy + 1]) {
stack.push([cx, cy + 1]);
done[cx][cy + 1] = true;
}
}
}
}
}
}
context.putImageData(pixelData, 0, 0, 0, 0, canvas.width, canvas.height);
}

I would not treat the canvas as a bitmap image.
Instead I would keep a collection of painting-objects and modify that collection.
Then for example you can fill a path or shape or add a new shape that has the boundaries of the objects you are trying to fill.
I can't see how "normal" floodFill makes sense in vector drawing..

How to shift pixel value to the next mousemove position in canvas?

I am creating a smudging tool with HTML5 canvas. Now I have to shift the pixel color at the point of mouse pointer to the next position where mouse pointer moves. Is it possible to do with javascript?
<canvas id="canvas"><canvas>
var canvas = document.getElementById("canvas");
var context = canvas.getContext('2d');
var url = 'download.jpg';
var imgObj = new Image();
imgObj.src = url;
imgObj.onload = function(e) {
context.drawImage(imgObj, 0, 0);
}
function findPos(obj) {
var curleft = 0,
curtop = 0;
if (obj.offsetParent) {
do {
curleft += obj.offsetLeft;
curtop += obj.offsetTop;
} while (obj = obj.offsetParent);
return {
x: curleft,
y: curtop
};
}
return undefined;
}
function rgbToHex(r, g, b) {
if (r > 255 || g > 255 || b > 255)
throw "Invalid color component";
return ((r << 16) | (g << 8) | b).toString(16);
}
$('#canvas').mousemove(function(e) {
var pos = findPos(this);
var x = e.pageX - pos.x;
var y = e.pageY - pos.y;
console.log(x, y);
var c = this.getContext('2d');
var p = c.getImageData(x, y, 1, 1).data;
var hex = "#" + ("000000" + rgbToHex(p[0], p[1], p[2])).slice(-6);
console.log(hex)
});

I am very short on time ATM so code only.
Uses an offscreen canvas brush to get a copy of the background canvas background where the mouse was last frame. Then use a radial gradient to feather the brush using ctx.globalCompositeOperation = "destination-in". Then draw the updated brush at the next mouse position.
The main canvas is use just to display, the canvas being smeared is called background You can put whatever content you want on that canvas (eg image) and it can be any size, and you can zoom, pan, rotate the background though you will have to convert the mouse coordinates to match the background coordinates
Click drag mouse to smear colours.
const ctx = canvas.getContext("2d");
const background = createCanvas(canvas.width,canvas.height);
const brushSize = 64;
const bs = brushSize;
const bsh = bs / 2;
const smudgeAmount = 0.25; // values from 0 none to 1 full
// helpers
const doFor = (count, cb) => { var i = 0; while (i < count && cb(i++) !== true); }; // the ; after while loop is important don't remove
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
// 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));
// brush gradient for feather
const grad = ctx.createRadialGradient(bsh,bsh,0,bsh,bsh,bsh);
grad.addColorStop(0,"black");
grad.addColorStop(1,"rgba(0,0,0,0)");
const brush = createCanvas(brushSize)
// creates an offscreen canvas
function createCanvas(w,h = w){
var c = document.createElement("canvas");
c.width = w;
c.height = h;
c.ctx = c.getContext("2d");
return c;
}
// get the brush from source ctx at x,y
function brushFrom(ctx,x,y){
brush.ctx.globalCompositeOperation = "source-over";
brush.ctx.globalAlpha = 1;
brush.ctx.drawImage(ctx.canvas,-(x - bsh),-(y - bsh));
brush.ctx.globalCompositeOperation = "destination-in";
brush.ctx.globalAlpha = 1;
brush.ctx.fillStyle = grad;
brush.ctx.fillRect(0,0,bs,bs);
}
// short cut vars
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
var globalTime;
var lastX;
var lastY;
// update background is size changed
function createBackground(){
background.width = w;
background.height = h;
background.ctx.fillStyle = "white";
background.ctx.fillRect(0,0,w,h);
doFor(64,()=>{
background.ctx.fillStyle = `rgb(${randI(255)},${randI(255)},${randI(255)}`;
background.ctx.fillRect(randI(w),randI(h),randI(10,100),randI(10,100));
});
}
// main update function
function update(timer){
globalTime = timer;
ctx.setTransform(1,0,0,1,0,0); // reset transform
ctx.globalAlpha = 1; // reset alpha
if(w !== innerWidth || h !== innerHeight){
cw = (w = canvas.width = innerWidth) / 2;
ch = (h = canvas.height = innerHeight) / 2;
createBackground();
}else{
ctx.clearRect(0,0,w,h);
}
ctx.drawImage(background,0,0);
// if mouse down then do the smudge for all pixels between last mouse and mouse now
if(mouse.button){
brush.ctx.globalAlpha = smudgeAmount;
var dx = mouse.x - lastX;
var dy = mouse.y - lastY;
var dist = Math.sqrt(dx*dx+dy*dy);
for(var i = 0;i < dist; i += 1){
var ni = i / dist;
brushFrom(background.ctx,lastX + dx * ni,lastY + dy * ni);
ni = (i+1) / dist;
background.ctx.drawImage(brush,lastX + dx * ni - bsh,lastY + dy * ni - bsh);
}
}else{
brush.ctx.clearRect(0,0,bs,bs); /// clear brush if not used
}
lastX = mouse.x;
lastY = mouse.y;
requestAnimationFrame(update);
}
requestAnimationFrame(update);
canvas { position : absolute; top : 0px; left : 0px; }
<canvas id="canvas"></canvas>

Drawing a nice looking Laser (Star Wars) on the canvas

Im currently in the process of animation some laser effects on the canvas for the purpose of making my game a bit more enjoyable.
For the purpose of that, i require the drawing and animation of "laser" weapons fire, something along the lines of Star Wars.
So far, im basicly only drawing a short line in red or blue and then drawing a thinner, white, line on top of it, so it gives the impression of a gradient.
I also use linecap = "round";
my current code:
function drawProjectile(weapon, ox, oy, x, y){
var trailEnd = getPointInDirection(weapon.projSize*-2, getAngleFromTo({x: ox, y: oy}, {x: x, y: y}), x, y);
fxCtx.lineCap = "round";
fxCtx.beginPath(); //the background, wider beam
fxCtx.moveTo(x+cam.o.x, y+cam.o.y);
fxCtx.lineTo(trailEnd.x+cam.o.x, trailEnd.y+cam.o.y);
fxCtx.closePath();
fxCtx.strokeStyle = weapon.animColor //blue or red
fxCtx.lineWidth = weapon.projSize;
fxCtx.stroke();
fxCtx.globalAlpha = 0.5; // the inner, thin, white beam
fxCtx.strokeStyle = "white";
fxCtx.lineWidth = 2;
fxCtx.stroke();
fxCtx.globalAlpha = 1;
fxCtx.lineCap = "butt";
}
Can someone advice how to improve my laser beam effect ?

Using canvas as images, glows, and more.
The demo below creates all the graphics it needs as offscreen canvases. The background is also drawn on to leave a burn mark when a laser hits the ground.
Lasers
Laser shots are 3 layered ctx.drawImage calls. The first 2 are glow with ctx.globalCompositeOperation = "lighter" . One has fixed alpha, the second has a random alpha. The last is drawn ctx.globalCompositeOperation = "source-over" and is just an image of a line.
There are 4 images (canvas) for the laaser called laserRed, laserGRed, laserGreen, and laserGGreen. the ones with the extra G are the laser glow.
When the laser shot is at the end I draw 4 frames of expanding glow from pre- rendered image. In the first of the 4 frames I draw to the background canvas leaving a burn mark.
Pre rendered images
All the graphics used are rendered in the function onResize which is called on resize from the boilerplate code.
The function display is called once every frame and handles all the animation.
There is an object called imageTools that has some helper functions to make the coding a little simplier. var image = imageTools.createImage(width,height) creates a canvas. The image has the context attached image.ctx so you can draw to it just like any canvas. You can then draw that image onto the global canvas with imageTools.drawImage(image,x,y,scale,rotation,alpha) The image is drawn at it center point with a scale, rotation, and alpha.
The bullets use an object pool so that the GC (Garbage collection) does not interfere to much.
I did not set any limits so those with high res devices or those with low end machines may see some slowdown. If its a problem OP you can reduce the bullet count by making them go a little faster, you can also reduce the rendering to just two or one layer. But this is a lot faster than if you were rendering with canvas vector calls, shadows, etc...
I will leave the rest for you to work out. Its a bit sparse in the comments but I did not have much time.
There is also some boilerplate at the bottom that is not very readable.
Left click to start the war.
/*************************************************************************************
* Called from boilerplate code and is debounced by 100ms
* Creates all the images used in the demo.
************************************************************************************/
var onResize = function(){
// create a background as drawable image
background = imageTools.createImage(canvas.width,canvas.height);
// create tile image
tile = imageTools.createImage(64,64);
tile.ctx.fillStyle = imageTools.createGradient(ctx,"linear",0,0,64,64,["#555","#666"]);
tile.ctx.fillRect(0,0,64,64);
tile.ctx.fillStyle = "#333"; // add colour
tile.ctx.globalCompositeOperation = "lighter";
tile.ctx.fillRect(0,0,62,2);
tile.ctx.fillRect(0,0,2,62);
tile.ctx.fillStyle = "#AAA"; // multiply colour to darken
tile.ctx.globalCompositeOperation = "multiply";
tile.ctx.fillRect(62,1,2,62);
tile.ctx.fillRect(1,62,62,2);
for(var y = -32; y < canvas.height; y += 64 ){
for(var x = -32; x < canvas.width; x += 64 ){
background.ctx.drawImage(tile,x,y);
}
}
background.ctx.globalCompositeOperation = "multiply"; // setup for rendering burn marks
burn = imageTools.createImage(flashSize/2,flashSize/2);
burn.ctx.fillStyle = imageTools.createGradient(ctx,"radial",flashSize/4,flashSize/4,0,flashSize/4,["#444","#444","#333","#000","#0000"]);
burn.ctx.fillRect(0,0,flashSize/2,flashSize/2);
glowRed = imageTools.createImage(flashSize,flashSize);
glowRed.ctx.fillStyle = imageTools.createGradient(ctx,"radial",flashSize/2,flashSize/2,0,flashSize/2,["#855F","#8000"]);
// #855F is non standard colour last digit is alpha
// 8,8 is ceneter 0 first radius 8 second
glowRed.ctx.fillRect(0,0,flashSize,flashSize);
glowGreen = imageTools.createImage(flashSize,flashSize);
glowGreen.ctx.fillStyle = imageTools.createGradient(ctx,"radial",flashSize/2,flashSize/2,0,flashSize/2,["#585F","#0600"]);
// #855F is non standard colour last digit is alpha
// 8,8 is ceneter 0 first radius 8 second
glowGreen.ctx.fillRect(0,0,flashSize,flashSize);
// draw the laser
laserLen = 32;
laserWidth = 4;
laserRed = imageTools.createImage(laserLen,laserWidth);
laserGreen = imageTools.createImage(laserLen,laserWidth);
laserRed.ctx.lineCap = laserGreen.ctx.lineCap = "round";
laserRed.ctx.lineWidth = laserGreen.ctx.lineWidth = laserWidth;
laserRed.ctx.strokeStyle = "#F33";
laserGreen.ctx.strokeStyle = "#3F3";
laserRed.ctx.beginPath();
laserGreen.ctx.beginPath();
laserRed.ctx.moveTo(laserWidth/2 + 1,laserWidth/2);
laserGreen.ctx.moveTo(laserWidth/2 + 1,laserWidth/2);
laserRed.ctx.lineTo(laserLen - (laserWidth/2 + 1),laserWidth/2);
laserGreen.ctx.lineTo(laserLen - (laserWidth/2 + 1),laserWidth/2);
laserRed.ctx.stroke();
laserGreen.ctx.stroke();
// draw the laser glow FX
var glowSize = 8;
laserGRed = imageTools.createImage(laserLen + glowSize * 2,laserWidth + glowSize * 2);
laserGGreen = imageTools.createImage(laserLen + glowSize * 2,laserWidth + glowSize * 2);
laserGRed.ctx.lineCap = laserGGreen.ctx.lineCap = "round";
laserGRed.ctx.shadowBlur = laserGGreen.ctx.shadowBlur = glowSize;
laserGRed.ctx.shadowColor = "#F33"
laserGGreen.ctx.shadowColor = "#3F3";
laserGRed.ctx.lineWidth = laserGGreen.ctx.lineWidth = laserWidth;
laserGRed.ctx.strokeStyle = "#F33";
laserGGreen.ctx.strokeStyle = "#3F3";
laserGRed.ctx.beginPath();
laserGGreen.ctx.beginPath();
laserGRed.ctx.moveTo(laserWidth/2 + 1 + glowSize,laserWidth/2 + glowSize);
laserGGreen.ctx.moveTo(laserWidth/2 + 1 + glowSize,laserWidth/2 + glowSize);
laserGRed.ctx.lineTo(laserLen + glowSize * 2 - (laserWidth/2 + 1 + glowSize),laserWidth/2 + glowSize);
laserGGreen.ctx.lineTo(laserLen + glowSize * 2 - (laserWidth/2 + 1 + glowSize),laserWidth/2 + glowSize);
laserGRed.ctx.stroke();
laserGGreen.ctx.stroke();
readyToRock = true;
}
var flashSize = 16;
const flashBrightNorm = 4 * (flashSize/2) * (flashSize/2) * Math.PI; // area of the flash
var background,tile,glowRed,glowGreen,grad, laserGreen,laserRed,laserGGreen,laserGRed,readyToRock,burn;
readyToRock = false;
/*************************************************************************************
* create or reset a bullet
************************************************************************************/
function createShot(x,y,xx,yy,speed,type,bullet){ // create a bullet object
if(bullet === undefined){
bullet = {};
}
var nx = xx-x; // normalise
var ny = yy-y;
var dist = Math.sqrt(nx*nx+ny*ny);
nx /= dist;
ny /= dist;
bullet.x = x;
bullet.y = y;
bullet.speed = speed;
bullet.type = type;
bullet.xx = xx;
bullet.yy = yy;
bullet.nx = nx; // normalised vector
bullet.ny = ny;
bullet.rot = Math.atan2(ny,nx); // will draw rotated so get the rotation
bullet.life = Math.ceil(dist/speed); // how long to keep alive
return bullet;
}
// semi static array with object pool.
var bullets=[]; // array of bullets
var bulletPool=[]; // array of used bullets. Use to create new bullets this stops GC messing with frame rate
const BULLET_TYPES = {
red : 0,
green : 1,
}
/*************************************************************************************
* Add a bullet to the bullet array
************************************************************************************/
function addBullet(xx,yy,type){
var bullet,x,y;
if(bulletPool.length > 0){
bullet = bulletPool.pop(); // get bullet from pool
}
if(type === BULLET_TYPES.red){
x = canvas.width + 16 + 32 * Math.random();
y = Math.random() * canvas.height;
}else if(type === BULLET_TYPES.green){
x = - 16 - 32 * Math.random();
y = Math.random() * canvas.height;
}
// randomise shoot to position
var r = Math.random() * Math.PI * 2;
var d = Math.random() * 128 + 16;
xx += Math.cos(r)* d;
yy += Math.sin(r)* d;
bullets[bullets.length] = createShot(x,y,xx,yy,16,type,bullet);
}
/*************************************************************************************
* update and draw bullets
************************************************************************************/
function updateDrawAllBullets(){
var i,img,imgGlow;
for(i = 0; i < bullets.length; i++){
var b = bullets[i];
b.life -= 1;
if(b.life <= 0){ // bullet end remove it and put it in the pool
bulletPool[bulletPool.length] = bullets.splice(i,1)[0];
i--; // to stop from skipping a bullet
}else{
if(b.life < 5){
if(b.life===4){
b.x += b.nx * b.speed * 0.5; // set to front of laser
b.y += b.ny * b.speed * 0.5;
var scale = 0.9 + Math.random() *1;
background.ctx.setTransform(scale,0,0,scale,b.x,b.y);
background.ctx.globalAlpha = 0.1 + Math.random() *0.2;;
background.ctx.drawImage(burn,-burn.width /2 ,-burn.height/2);
}
if(b.type === BULLET_TYPES.red){
img = glowRed;
}else{
img = glowGreen;
}
ctx.globalCompositeOperation = "lighter";
imageTools.drawImage(img,b.x,b.y,(4-b.life)*(4-b.life),b.rot,1);//b.life/4);
imageTools.drawImage(img,b.x,b.y,4,b.rot,b.life/4);
ctx.globalCompositeOperation = "source-over";
}else{
b.x += b.nx * b.speed;
b.y += b.ny * b.speed;
if(b.type === BULLET_TYPES.red){
img = laserRed;
imgGlow = laserGRed;
}else{
img = laserGreen;
imgGlow = laserGGreen;
}
ctx.globalCompositeOperation = "lighter";
imageTools.drawImage(imgGlow,b.x,b.y,1,b.rot,1);
imageTools.drawImage(imgGlow,b.x,b.y,2,b.rot,Math.random()/2);
ctx.globalCompositeOperation = "source-over";
imageTools.drawImage(img,b.x,b.y,1,b.rot,1);
}
}
}
}
/*************************************************************************************
* Main display loop
************************************************************************************/
function display() {
if(readyToRock){
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transform
ctx.globalAlpha = 1; // reset alpha
ctx.drawImage(background,0,0);
ctx.globalCompositeOperation = "source-over";
if(mouse.buttonRaw & 1){
addBullet(mouse.x,mouse.y,BULLET_TYPES.red);
addBullet(mouse.x,mouse.y,BULLET_TYPES.green);
}
updateDrawAllBullets();
}
}
/*************************************************************************************
* Tools for creating canvas images and what not
************************************************************************************/
var imageTools = (function () {
// This interface is as is. No warenties no garenties, and NOT to be used comercialy
var workImg,workImg1,keep; // for internal use
var xdx,xdy,spr; // static vars for drawImage and drawSprite
keep = false;
var tools = {
canvas : function (width, height) { // create a blank image (canvas)
var c = document.createElement("canvas");
c.width = width;
c.height = height;
return c;
},
createImage : function (width, height) {
var i = this.canvas(width, height);
i.ctx = i.getContext("2d");
return i;
},
drawImage : function(image, x, y, scale, ang, alpha) {
ctx.globalAlpha = alpha;
xdx = Math.cos(ang) * scale;
xdy = Math.sin(ang) * scale;
ctx.setTransform(xdx, xdy, -xdy, xdx, x, y);
ctx.drawImage(image, -image.width/2,-image.height/2);
},
hex2RGBA : function(hex){ // Not CSS colour as can have extra 2 or 1 chars for alpha
// #FFFF & #FFFFFFFF last F and FF are the alpha range 0-F & 00-FF
if(typeof hex === "string"){
var str = "rgba(";
if(hex.length === 4 || hex.length === 5){
str += (parseInt(hex.substr(1,1),16) * 16) + ",";
str += (parseInt(hex.substr(2,1),16) * 16) + ",";
str += (parseInt(hex.substr(3,1),16) * 16) + ",";
if(hex.length === 5){
str += (parseInt(hex.substr(4,1),16) / 16);
}else{
str += "1";
}
return str + ")";
}
if(hex.length === 7 || hex.length === 8){
str += parseInt(hex.substr(1,2),16) + ",";
str += parseInt(hex.substr(3,2),16) + ",";
str += parseInt(hex.substr(5,2),16) + ",";
if(hex.length === 5){
str += (parseInt(hex.substr(7,2),16) / 255).toFixed(3);
}else{
str += "1";
}
return str + ")";
}
return "rgba(0,0,0,0)";
}
},
createGradient : function(ctx, type, x, y, xx, yy, colours){ // Colours MUST be array of hex colours NOT CSS colours
// See this.hex2RGBA for details of format
var i,g,c;
var len = colours.length;
if(type.toLowerCase() === "linear"){
g = ctx.createLinearGradient(x,y,xx,yy);
}else{
g = ctx.createRadialGradient(x,y,xx,x,y,yy);
}
for(i = 0; i < len; i++){
c = colours[i];
if(typeof c === "string"){
if(c[0] === "#"){
c = this.hex2RGBA(c);
}
g.addColorStop(Math.min(1,i / (len -1)),c); // need to clamp top to 1 due to floating point errors causes addColorStop to throw rangeError when number over 1
}
}
return g;
},
};
return tools;
})();
// CODE FROM HERE DOWN IS SUPPORT CODE AN HAS LITTLE TO DO WITH THE ANSWER
//==================================================================================================
// The following code is support code that provides me with a standard interface to various forums.
// It provides a mouse interface, a full screen canvas, and some global often used variable
// like canvas, ctx, mouse, w, h (width and height), globalTime
// This code is not intended to be part of the answer unless specified and has been formated to reduce
// display size. It should not be used as an example of how to write a canvas interface.
// By Blindman67
if(typeof onResize === "undefined"){
window["onResize"] = undefined; // create without the JS parser knowing it exists.
// this allows for it to be declared in an outside
// modal.
}
const RESIZE_DEBOUNCE_TIME = 100;
var w, h, cw, ch, canvas, ctx, mouse, createCanvas, resizeCanvas, setGlobals, globalTime = 0, resizeCount = 0;
createCanvas = function () {
var c,
cs;
cs = (c = document.createElement("canvas")).style;
cs.position = "absolute";
cs.top = cs.left = "0px";
cs.zIndex = 1000;
document.body.appendChild(c);
return c;
}
resizeCanvas = function () {
if (canvas === undefined) {
canvas = createCanvas();
}
canvas.width = window.innerWidth-2;
canvas.height = window.innerHeight-2;
ctx = canvas.getContext("2d");
if (typeof setGlobals === "function") {
setGlobals();
}
if (typeof onResize === "function") {
resizeCount += 1;
setTimeout(debounceResize, RESIZE_DEBOUNCE_TIME);
}
}
function debounceResize() {
resizeCount -= 1;
if (resizeCount <= 0) {
onResize();
}
}
setGlobals = function () {
cw = (w = canvas.width) / 2;
ch = (h = canvas.height) / 2;
mouse.updateBounds();
}
mouse = (function () {
function preventDefault(e) {
e.preventDefault();
}
var mouse = {
x : 0,
y : 0,
w : 0,
alt : false,
shift : false,
ctrl : false,
buttonRaw : 0,
over : false,
bm : [1, 2, 4, 6, 5, 3],
active : false,
bounds : null,
crashRecover : null,
mouseEvents : "mousemove,mousedown,mouseup,mouseout,mouseover,mousewheel,DOMMouseScroll".split(",")
};
var m = mouse;
function mouseMove(e) {
var t = e.type;
m.x = e.clientX - m.bounds.left;
m.y = e.clientY - m.bounds.top;
m.alt = e.altKey;
m.shift = e.shiftKey;
m.ctrl = e.ctrlKey;
if (t === "mousedown") {
m.buttonRaw |= m.bm[e.which - 1];
} else if (t === "mouseup") {
m.buttonRaw &= m.bm[e.which + 2];
} else if (t === "mouseout") {
m.buttonRaw = 0;
m.over = false;
} else if (t === "mouseover") {
m.over = true;
} else if (t === "mousewheel") {
m.w = e.wheelDelta;
} else if (t === "DOMMouseScroll") {
m.w = -e.detail;
}
if (m.callbacks) {
m.callbacks.forEach(c => c(e));
}
if ((m.buttonRaw & 2) && m.crashRecover !== null) {
if (typeof m.crashRecover === "function") {
setTimeout(m.crashRecover, 0);
}
}
e.preventDefault();
}
m.updateBounds = function () {
if (m.active) {
m.bounds = m.element.getBoundingClientRect();
}
}
m.addCallback = function (callback) {
if (typeof callback === "function") {
if (m.callbacks === undefined) {
m.callbacks = [callback];
} else {
m.callbacks.push(callback);
}
} else {
throw new TypeError("mouse.addCallback argument must be a function");
}
}
m.start = function (element, blockContextMenu) {
if (m.element !== undefined) {
m.removeMouse();
}
m.element = element === undefined ? document : element;
m.blockContextMenu = blockContextMenu === undefined ? false : blockContextMenu;
m.mouseEvents.forEach(n => {
m.element.addEventListener(n, mouseMove);
});
if (m.blockContextMenu === true) {
m.element.addEventListener("contextmenu", preventDefault, false);
}
m.active = true;
m.updateBounds();
}
m.remove = function () {
if (m.element !== undefined) {
m.mouseEvents.forEach(n => {
m.element.removeEventListener(n, mouseMove);
});
if (m.contextMenuBlocked === true) {
m.element.removeEventListener("contextmenu", preventDefault);
}
m.element = m.callbacks = m.contextMenuBlocked = undefined;
m.active = false;
}
}
return mouse;
})();
// Clean up. Used where the IDE is on the same page.
var done = function () {
window.removeEventListener("resize", resizeCanvas)
mouse.remove();
document.body.removeChild(canvas);
canvas = ctx = mouse = undefined;
}
resizeCanvas();
mouse.start(canvas, true);
mouse.crashRecover = done;
window.addEventListener("resize", resizeCanvas);
function update(timer) { // Main update loop
globalTime = timer;
display(); // call demo code
requestAnimationFrame(update);
}
requestAnimationFrame(update);
/** SimpleFullCanvasMouse.js end **/

You can add a shadow for a glowing effect
fxCtx.shadowBlur = 10;
fxCtx.shadowColor = '#FD0100';
but i think thats all, bacause your laser is so small that a real gradient would not make sense.
Use some nice colors like #FEF1BA insted of white for the red laser and thats it

Filling in certain pixels on an HTML canvas

First off, sorry about the bad title, I couldn't think of a better way to describe what I was trying to do. I have an HTML canvas, which, for argument's sake, is x pixels wide and y pixels tall. I have been trying to write a code that takes the location in the array of the canvas' image data of two pixels that are on lines z and z + 1 and fill in all the pixels in the higher row between the two pixels a certain color. I'm afraid I may not have made much sense, so here's a diagram:
Sorry about the poor graphics, but assume each rectangle is a pixel. The program should take in the first value for each of the black pixels (each is stored as r,g,b,a, the program gets the location of the r in the array representing the canvas' image data), and stores the r value for the lower pixel as bottomPixel and the higher one as topPixel. In this case, bottomPixel = 124 and topPixel = 112 It should use this to fill all pixels between the two base pixels a certain color. For example, using the previous pixel locations, the red pixels in the following picture should be colored in, but the blue one should not.
Here is the code I have: (Assume that the canvas has an Id "Canvas" and is 6px wide by 10px tall)
var cnvs = document.getElementById("Canvas");
cnvs.height = 10; //This height and width is here as an example.
cnvs.width = 6;
var cont = cnvs.getContext("2d");
var environment = cont.getImageData(0,0,6,10);
var bottomPixel = 124;//Not neccesarily 124 or 112, just example values
var topPixel = 112;
if ( bottomPixel - topPixel > 6*4 ) //If bottomPixel is to the right of topPixel
{
for ( var i = 0 ; i < ((bottomPixel-6*4)-topPixel)/4 ; i++ )
{
var index = topPixel + i * 4;
environment.data[index] = 0;
environment.data[index + 1 ] = 255;
environment.data[index + 2 ] = 0;
environment.data[index + 3 ] = 255;
}
}
if ( bottomPixel - topPixel > 6*4 ) //If bottomPixel is to the left of topPixel
{
for ( var i = 0 ; i < (topPixel-(bottomPixel-6*4))/4; i++ )
{
var index = topPixel - i * 4;
environment.data[index] = 0;
environment.data[index + 1 ] = 255;
environment.data[index + 2 ] = 0;
environment.data[index + 3 ] = 255;
}
}
I'd like to know why my code isn't doing what I previously described. If anything here needs clarification, please leave a comment. Thanks!

This is a method that works on the point coordinates and uses a the setPixel function to modify imageData. I'm using blue for start and black for end. You'll need to adjust for your exact condition but you can use setPixel to allow for direct x and y edits on the imageData.
update
I've included an alternate line method and your line method. There is also an animation that will help you find errors.
function ptIndex(p, w) {
return ((p.x|0) + ((p.y|0) * w)) * 4;
}
function setPixel(p, w, d, rgba) {
var i = ptIndex(p, w);
d[i] = rgba.r;
d[i + 1] = rgba.g;
d[i + 2] = rgba.b;
d[i + 3] = rgba.a;
}
function yourLine(p1, p2, w, d, rgba) {
var cnvs = document.getElementById("Canvas");
var bottomPixel = ptIndex(p1, w);
var topPixel = ptIndex(p2, w)
if (bottomPixel - topPixel > w * 4) //If bottomPixel is to the right of topPixel
{
for (var i = 0; i < ((bottomPixel - w * 4) - topPixel) / 4; i++) {
var index = topPixel + i * 4;
d[index] = rgba.r;
d[index + 1] = rgba.g;
d[index + 2] = rgba.b;
d[index + 3] = rgba.a
}
}
if (bottomPixel - topPixel > w * 4) //If bottomPixel is to the left of topPixel
{
for (var i = 0; i < (topPixel - (bottomPixel - w * 4)) / 4; i++) {
var index = topPixel - i * 4;
d[index] = rgba.r;
d[index + 1] = rgba.g;
d[index + 2] = rgba.b;
d[index + 3] = rgba.a
}
}
}
function drawRandPoints() {
var cnvs = document.getElementById("Canvas");
var cont = cnvs.getContext("2d");
// ghost last draw
cont.fillStyle = "white";
cont.fillRect(0, 0, cnvs.width, cnvs.height);
// get image data
var environment = cont.getImageData(0, 0, cnvs.width, cnvs.height);
var d = environment.data, w = cnvs.width;
// create colors
var black = {
r: 0,
g: 0,
b: 0,
a: 255
};
var red = {
r: 255,
g: 0,
b: 0,
a: 255
};
var blue = {
r: 0,
g: 0,
b: 255,
a: 255
};
var frames = 0;
var p1 = {x: ((cnvs.width / 2|0)), y: 0, sx: 1, sy:0};
var p2 = {x: cnvs.width, y: ((cnvs.height / 2)|0), sx: -1, sy: 0};
function step(p) {
if (p.x > cnvs.width) {
p.x = cnvs.width;
p.sx = 0;
p.sy = 1;
}
if (p.y > cnvs.height) {
p.y = cnvs.height;
p.sy = 0;
p.sx = -1;
}
if (p.x < 0) {
p.x = 0;
p.sx = 0;
p.sy = -1;
}
if (p.y < 0) {
p.y = 0;
p.sy = 0;
p.sx = 1;
}
}
function ani() {
cont.fillStyle = "white";
cont.fillRect(0, 0, cnvs.width, cnvs.height);
environment = cont.getImageData(0, 0, cnvs.width, cnvs.height);
d = environment.data;
step(p1);
step(p2);
var p3 = {
x: cnvs.width - p1.x,
y: cnvs.height - p2.y
};
var p4 = {
x: cnvs.width - p2.x,
y: cnvs.height - p1.y
};
yourLine(p1, p2, w, d, {r:0,g:255,b:0,a:255});
myDrawLine(p1, p2, w, d, red);
drawLineNoAliasing(p3, p4, w, d, blue);
setPixel(p1, w, d, black);
setPixel(p2, w, d, black);
frames %= 12;
p1.x += p1.sx;
p1.y += p1.sy;
p2.x += p2.sx;
p2.y += p2.sy;
// Put the pixel data on the canvas.
cont.putImageData(environment, 0, 0);
requestAnimationFrame(ani);
}
ani();
}
function myDrawLine(p1, p2, w, d, rgba) {
// Get the max length between x or y
var lenX = Math.abs(p1.x - p2.x);
var lenY = Math.abs(p1.y - p2.y);
var len = Math.sqrt(Math.pow(lenX,2) + Math.pow(lenY,2));
// Calculate the step increment between points
var stepX = lenX / len;
var stepY = lenY / len;
// If the first x or y is greater then make step negetive.
if (p2.x < p1.x) stepX *= -1;
if (p2.y < p1.y) stepY *= -1;
// Start at the first point
var x = p1.x;
var y = p1.y;
for (var i = 0; i < len; i++) {
x += stepX;
y += stepY;
// Make a point from new x and y
var p = {
x: x,
y: y
};
// Draw pixel on data
setPixel(p, w, d, rgba);
// reached goal (removes extra pixel)
if (Math.abs(p.x - p2.x) <= 1 && Math.abs(p.y - p2.y) <= 1) {
break;
}
}
// Draw start and end pixels. (might draw over line start and end)
setPixel(p1, w, d, rgba);
setPixel(p2, w, d, rgba);
}
// alternate from http://stackoverflow.com/questions/4261090/html5-canvas-and-anti-aliasing answer
// some helper functions
// finds the distance between points
function DBP(x1, y1, x2, y2) {
return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
}
// finds the angle of (x,y) on a plane from the origin
function getAngle(x, y) {
return Math.atan(y / (x == 0 ? 0.01 : x)) + (x < 0 ? Math.PI : 0);
}
// the function
function drawLineNoAliasing(p1, p2, w, d, rgba) {
var dist = DBP(p1.x, p1.y, p2.x, p2.y); // length of line
var ang = getAngle(p2.x - p1.x, p2.y - p1.y); // angle of line
var cos = Math.cos(ang);
var sin = Math.sin(ang);
for (var i = 0; i < dist; i++) {
// for each point along the line
var pt = {
x: p1.x + cos * i,
y: p1.y + sin * i
};
setPixel(pt, w, d, rgba);
}
}
// end alt
drawRandPoints();
#Canvas {
border: 1px solid red image-rendering: optimizeSpeed;
/* Older versions of FF */
image-rendering: -moz-crisp-edges;
/* FF 6.0+ */
image-rendering: -webkit-optimize-contrast;
/* Safari */
image-rendering: -o-crisp-edges;
/* OS X & Windows Opera (12.02+) */
image-rendering: pixelated;
/* Awesome future-browsers */
image-rendering: optimize-contrast;
/* CSS3 Proposed */
-ms-interpolation-mode: nearest-neighbor;
/* IE */
}
<canvas id="Canvas" width="128" height="64" style="width:320px"></canvas>

How can I perform flood fill with HTML Canvas?

Has anyone implemented a flood fill algorithm in javascript for use with HTML Canvas?
My requirements are simple: flood with a single color starting from a single point, where the boundary color is any color greater than a certain delta of the color at the specified point.
var r1, r2; // red values
var g1, g2; // green values
var b1, b2; // blue values
var actualColorDelta = Math.sqrt((r1 - r2)*(r1 - r2) + (g1 - g2)*(g1 - g2) + (b1 - b2)*(b1 - b2))
function floodFill(canvas, x, y, fillColor, borderColorDelta) {
...
}
Update:
I wrote my own implementation of flood fill, which follows. It is slow, but accurate. About 37% of the time is taken up in two low-level array functions that are part of the prototype framework. They are called by push and pop, I presume. Most of the rest of the time is spent in the main loop.
var ImageProcessing;
ImageProcessing = {
/* Convert HTML color (e.g. "#rrggbb" or "#rrggbbaa") to object with properties r, g, b, a.
* If no alpha value is given, 255 (0xff) will be assumed.
*/
toRGB: function (color) {
var r, g, b, a, html;
html = color;
// Parse out the RGBA values from the HTML Code
if (html.substring(0, 1) === "#")
{
html = html.substring(1);
}
if (html.length === 3 || html.length === 4)
{
r = html.substring(0, 1);
r = r + r;
g = html.substring(1, 2);
g = g + g;
b = html.substring(2, 3);
b = b + b;
if (html.length === 4) {
a = html.substring(3, 4);
a = a + a;
}
else {
a = "ff";
}
}
else if (html.length === 6 || html.length === 8)
{
r = html.substring(0, 2);
g = html.substring(2, 4);
b = html.substring(4, 6);
a = html.length === 6 ? "ff" : html.substring(6, 8);
}
// Convert from Hex (Hexidecimal) to Decimal
r = parseInt(r, 16);
g = parseInt(g, 16);
b = parseInt(b, 16);
a = parseInt(a, 16);
return {r: r, g: g, b: b, a: a};
},
/* Get the color at the given x,y location from the pixels array, assuming the array has a width and height as given.
* This interprets the 1-D array as a 2-D array.
*
* If useColor is defined, its values will be set. This saves on object creation.
*/
getColor: function (pixels, x, y, width, height, useColor) {
var redIndex = y * width * 4 + x * 4;
if (useColor === undefined) {
useColor = { r: pixels[redIndex], g: pixels[redIndex + 1], b: pixels[redIndex + 2], a: pixels[redIndex + 3] };
}
else {
useColor.r = pixels[redIndex];
useColor.g = pixels[redIndex + 1]
useColor.b = pixels[redIndex + 2];
useColor.a = pixels[redIndex + 3];
}
return useColor;
},
setColor: function (pixels, x, y, width, height, color) {
var redIndex = y * width * 4 + x * 4;
pixels[redIndex] = color.r;
pixels[redIndex + 1] = color.g,
pixels[redIndex + 2] = color.b;
pixels[redIndex + 3] = color.a;
},
/*
* fill: Flood a canvas with the given fill color.
*
* Returns a rectangle { x, y, width, height } that defines the maximum extent of the pixels that were changed.
*
* canvas .................... Canvas to modify.
* fillColor ................. RGBA Color to fill with.
* This may be a string ("#rrggbbaa") or an object of the form { r: red, g: green, b: blue, a: alpha }.
* x, y ...................... Coordinates of seed point to start flooding.
* bounds .................... Restrict flooding to this rectangular region of canvas.
* This object has these attributes: { x, y, width, height }.
* If undefined or null, use the whole of the canvas.
* stopFunction .............. Function that decides if a pixel is a boundary that should cause
* flooding to stop. If omitted, any pixel that differs from seedColor
* will cause flooding to stop. seedColor is the color under the seed point (x,y).
* Parameters: stopFunction(fillColor, seedColor, pixelColor).
* Returns true if flooding shoud stop.
* The colors are objects of the form { r: red, g: green, b: blue, a: alpha }
*/
fill: function (canvas, fillColor, x, y, bounds, stopFunction) {
// Supply default values if necessary.
var ctx, minChangedX, minChangedY, maxChangedX, maxChangedY, wasTested, shouldTest, imageData, pixels, currentX, currentY, currentColor, currentIndex, seedColor, tryX, tryY, tryIndex, boundsWidth, boundsHeight, pixelStart, fillRed, fillGreen, fillBlue, fillAlpha;
if (Object.isString(fillColor)) {
fillColor = ImageProcessing.toRGB(fillColor);
}
x = Math.round(x);
y = Math.round(y);
if (bounds === null || bounds === undefined) {
bounds = { x: 0, y: 0, width: canvas.width, height: canvas.height };
}
else {
bounds = { x: Math.round(bounds.x), y: Math.round(bounds.y), width: Math.round(bounds.y), height: Math.round(bounds.height) };
}
if (stopFunction === null || stopFunction === undefined) {
stopFunction = new function (fillColor, seedColor, pixelColor) {
return pixelColor.r != seedColor.r || pixelColor.g != seedColor.g || pixelColor.b != seedColor.b || pixelColor.a != seedColor.a;
}
}
minChangedX = maxChangedX = x - bounds.x;
minChangedY = maxChangedY = y - bounds.y;
boundsWidth = bounds.width;
boundsHeight = bounds.height;
// Initialize wasTested to false. As we check each pixel to decide if it should be painted with the new color,
// we will mark it with a true value at wasTested[row = y][column = x];
wasTested = new Array(boundsHeight * boundsWidth);
/*
$R(0, bounds.height - 1).each(function (row) {
var subArray = new Array(bounds.width);
wasTested[row] = subArray;
});
*/
// Start with a single point that we know we should test: (x, y).
// Convert (x,y) to image data coordinates by subtracting the bounds' origin.
currentX = x - bounds.x;
currentY = y - bounds.y;
currentIndex = currentY * boundsWidth + currentX;
shouldTest = [ currentIndex ];
ctx = canvas.getContext("2d");
//imageData = ctx.getImageData(bounds.x, bounds.y, bounds.width, bounds.height);
imageData = ImageProcessing.getImageData(ctx, bounds.x, bounds.y, bounds.width, bounds.height);
pixels = imageData.data;
seedColor = ImageProcessing.getColor(pixels, currentX, currentY, boundsWidth, boundsHeight);
currentColor = { r: 0, g: 0, b: 0, a: 1 };
fillRed = fillColor.r;
fillGreen = fillColor.g;
fillBlue = fillColor.b;
fillAlpha = fillColor.a;
while (shouldTest.length > 0) {
currentIndex = shouldTest.pop();
currentX = currentIndex % boundsWidth;
currentY = (currentIndex - currentX) / boundsWidth;
if (! wasTested[currentIndex]) {
wasTested[currentIndex] = true;
//currentColor = ImageProcessing.getColor(pixels, currentX, currentY, boundsWidth, boundsHeight, currentColor);
// Inline getColor for performance.
pixelStart = currentIndex * 4;
currentColor.r = pixels[pixelStart];
currentColor.g = pixels[pixelStart + 1]
currentColor.b = pixels[pixelStart + 2];
currentColor.a = pixels[pixelStart + 3];
if (! stopFunction(fillColor, seedColor, currentColor)) {
// Color the pixel with the fill color.
//ImageProcessing.setColor(pixels, currentX, currentY, boundsWidth, boundsHeight, fillColor);
// Inline setColor for performance
pixels[pixelStart] = fillRed;
pixels[pixelStart + 1] = fillGreen;
pixels[pixelStart + 2] = fillBlue;
pixels[pixelStart + 3] = fillAlpha;
if (minChangedX < currentX) { minChangedX = currentX; }
else if (maxChangedX > currentX) { maxChangedX = currentX; }
if (minChangedY < currentY) { minChangedY = currentY; }
else if (maxChangedY > currentY) { maxChangedY = currentY; }
// Add the adjacent four pixels to the list to be tested, unless they have already been tested.
tryX = currentX - 1;
tryY = currentY;
tryIndex = tryY * boundsWidth + tryX;
if (tryX >= 0 && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX;
tryY = currentY + 1;
tryIndex = tryY * boundsWidth + tryX;
if (tryY < boundsHeight && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX + 1;
tryY = currentY;
tryIndex = tryY * boundsWidth + tryX;
if (tryX < boundsWidth && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
tryX = currentX;
tryY = currentY - 1;
tryIndex = tryY * boundsWidth + tryX;
if (tryY >= 0 && ! wasTested[tryIndex]) {
shouldTest.push(tryIndex);
}
}
}
}
//ctx.putImageData(imageData, bounds.x, bounds.y);
ImageProcessing.putImageData(ctx, imageData, bounds.x, bounds.y);
return { x: minChangedX + bounds.x, y: minChangedY + bounds.y, width: maxChangedX - minChangedX + 1, height: maxChangedY - minChangedY + 1 };
},
getImageData: function (ctx, x, y, w, h) {
return ctx.getImageData(x, y, w, h);
},
putImageData: function (ctx, data, x, y) {
ctx.putImageData(data, x, y);
}
};
BTW, when I call this, I use a custom stopFunction:
stopFill : function (fillColor, seedColor, pixelColor) {
// Ignore alpha difference for now.
return Math.abs(pixelColor.r - seedColor.r) > this.colorTolerance || Math.abs(pixelColor.g - seedColor.g) > this.colorTolerance || Math.abs(pixelColor.b - seedColor.b) > this.colorTolerance;
},
If anyone can see a way to improve performance of this code, I would appreciate it. The basic idea is:
1) Seed color is the initial color at the point to start flooding.
2) Try four adjacent points: up, right, down and left one pixel.
3) If point is out of range or has been visited already, skip it.
4) Otherwise push point onto to the stack of interesting points.
5) Pop the next interesting point off the stack.
6) If the color at that point is a stop color (as defined in the stopFunction) then stop processing that point and skip to step 5.
7) Otherwise, skip to step 2.
8) When there are no more interesting points to visit, stop looping.
Remembering that a point has been visited requires an array with the same number of elements as there are pixels.

To create a flood fill you need to be able to look at the pixels that are there already and check they aren't the color you started with so something like this.
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255]);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b) {
return a[0] === b[0] && a[1] === b[1] && a[2] === b[2] && a[3] === b[3];
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
fillPixel(imageData, x, y, targetColor, fillColor);
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
function fillPixel(imageData, x, y, targetColor, fillColor) {
const currentColor = getPixel(imageData, x, y);
if (colorsMatch(currentColor, targetColor)) {
setPixel(imageData, x, y, fillColor);
fillPixel(imageData, x + 1, y, targetColor, fillColor);
fillPixel(imageData, x - 1, y, targetColor, fillColor);
fillPixel(imageData, x, y + 1, targetColor, fillColor);
fillPixel(imageData, x, y - 1, targetColor, fillColor);
}
}
<canvas></canvas>
There's at least 2 problems with this code though.
It's deeply recursive.
So you might run out of stack space
It's slow.
No idea if it's too slow but JavaScript in the browser is mostly single threaded so while this code is running the browser is frozen. For a large canvas that frozen time might make the page really slow and if it's frozen too long the browser will ask if the user wants to kill the page.
The solution to running out of stack space is to implement our own stack. For example instead of recursively calling fillPixel we could keep an array of positions we want to look at. We'd add the 4 positions to that array and then pop things off the array until it's empty
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255]);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b) {
return a[0] === b[0] && a[1] === b[1] && a[2] === b[2] && a[3] === b[3];
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(imageData, x, y);
if (colorsMatch(currentColor, targetColor)) {
setPixel(imageData, x, y, fillColor);
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
The solution to it being too slow is either to make it run a little at a time OR to move it to a worker. I think that's a little too much to show in the same answer though here's an example.
I tested the code above on a 4096x4096 canvas and it took 16 seconds to fill a blank canvas on my machine so yes it's arguably too slow but putting it in a worker brings new problems which is that the result will be asynchronous so even though the browser wouldn't freeze you'd probably want to prevent the user from doing something until it finishes.
Another issue is you'll see the lines are antialiased and so filling with a solid color fills close the the line but not all the way up to it. To fix that you can change colorsMatch to check for close enough but then you have a new problem that if targetColor and fillColor are also close enough it will keep trying to fill itself. You could solve that by making another array, one byte or one bit per pixel to track places you've ready checked.
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, [255, 0, 0, 255], 128);
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b, rangeSq) {
const dr = a[0] - b[0];
const dg = a[1] - b[1];
const db = a[2] - b[2];
const da = a[3] - b[3];
return dr * dr + dg * dg + db * db + da * da < rangeSq;
}
function floodFill(ctx, x, y, fillColor, range = 1) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// flags for if we visited a pixel already
const visited = new Uint8Array(imageData.width, imageData.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
const rangeSq = range * range;
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(imageData, x, y);
if (!visited[y * imageData.width + x] &&
colorsMatch(currentColor, targetColor, rangeSq)) {
setPixel(imageData, x, y, fillColor);
visited[y * imageData.width + x] = 1; // mark we were here already
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
Note that this version of colorsMatch is kind of naive. It might be better to convert to HSV or something or maybe you want to weight by alpha. I don't know what a good metric is for matching colors.
Update
Another way to speed things up is of course to just optimize the code. Kaiido pointed out an obvious speedup which is to use a Uint32Array view on the pixels. That way looking up a pixel and setting a pixel there's just one 32bit value to read or write. Just that change makes it about 4x faster. It still takes 4 seconds to fill a 4096x4096 canvas though. There might be other optimizations like instead of calling getPixels make that inline but don't push a new pixel on our list of pixels to check if they are out of range. It might be 10% speed up (no idea) but won't make it fast enough to be an interactive speed.
There are other speedups like checking across a row at a time since rows are cache friendly and you can compute the offset to a row once and use that while checking the entire row whereas now for every pixel we have to compute the offset multiple times.
Those will complicate the algorithm so they are best left for you to figure out.
Let me also add, given the answer above freezes the browser while the fill is happening and that on a larger canvas that freeze could be too long, you can easily make the algorithm span over time using ES6 async/await. You need to choose how much work to give each segment of time. Choose too small and it will take a long time to fill. Choose too large and you'll get jank as the browser freezes.
Here's an example. Set ticksPerUpdate to speed up or slow down the fill rate
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
async function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const ticksPerUpdate = 50;
let tickCount = 0;
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(pixelData, x, y);
if (currentColor === targetColor) {
pixelData.data[y * pixelData.width + x] = fillColor;
// put the data back
ctx.putImageData(imageData, 0, 0);
++tickCount;
if (tickCount % ticksPerUpdate === 0) {
await wait();
}
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
}
}
function wait(delay = 0) {
return new Promise((resolve) => {
setTimeout(resolve, delay);
});
}
<canvas></canvas>
update update
Instead of setTimeout which is throttled by the browser, you can abuse postMessage which is not
function makeExposedPromise() {
let resolve;
let reject;
const promise = new Promise((_resolve, _reject) => {
resolve = _resolve;
reject = _reject;
});
return { promise, resolve, reject };
}
const resolveFns = [];
window.addEventListener('message', (e) => {
const resolve = resolveFns.shift();
resolve();
});
function wait() {
const {resolve, promise} = makeExposedPromise();
resolveFns.push(resolve);
window.postMessage('');
return promise;
}
If you use that it there's less need to choose a number of operations. Also note: the slowest part is calling putImageData. The reason it's inside the loop above is only so we can see the progress. Move that to the end and it will run much faster
function makeExposedPromise() {
let resolve;
let reject;
const promise = new Promise((_resolve, _reject) => {
resolve = _resolve;
reject = _reject;
});
return { promise, resolve, reject };
}
const resolveFns = [];
window.addEventListener('message', (e) => {
const resolve = resolveFns.shift();
resolve();
});
function wait() {
const {resolve, promise} = makeExposedPromise();
resolveFns.push(resolve);
window.postMessage('');
return promise;
}
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
async function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(pixelData, x, y);
if (currentColor === targetColor) {
pixelData.data[y * pixelData.width + x] = fillColor;
await wait();
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
It's still better to choose a number of operations per call to wait
There are also faster algorithms. The issue with the one above is there is for every pixel that matches, 4 are added to the stack of things to pixels to check. That's lots of allocations and multiple checking. A faster way is to it by span.
For a given span, check as far left as you can, then as far right as you can, now fill that span. Then, check the pixels above and/or below the span you just found and add the spans you find to your stack. Pop the top span off, and try to expand it left and right. There's no need to check the pixels in the middle since you already checked them. Further, if this span was generated from one below then you don't need to check the pixels below the starting sub-span of this span since you know that area was already filled. Similarly if this pan was generated from one above then you don't need to check the pixels above the starting sub-span of this span for the same reason.
function main() {
const ctx = document.querySelector("canvas").getContext("2d");
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(100, 145);
ctx.lineTo(110, 105);
ctx.lineTo(130, 125);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
floodFill(ctx, 40, 50, 0xFF0000FF);
}
main();
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return -1; // impossible color
} else {
return pixelData.data[y * pixelData.width + x];
}
}
function floodFill(ctx, x, y, fillColor) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// make a Uint32Array view on the pixels so we can manipulate pixels
// one 32bit value at a time instead of as 4 bytes per pixel
const pixelData = {
width: imageData.width,
height: imageData.height,
data: new Uint32Array(imageData.data.buffer),
};
// get the color we're filling
const targetColor = getPixel(pixelData, x, y);
// check we are actually filling a different color
if (targetColor !== fillColor) {
const spansToCheck = [];
function addSpan(left, right, y, direction) {
spansToCheck.push({left, right, y, direction});
}
function checkSpan(left, right, y, direction) {
let inSpan = false;
let start;
let x;
for (x = left; x < right; ++x) {
const color = getPixel(pixelData, x, y);
if (color === targetColor) {
if (!inSpan) {
inSpan = true;
start = x;
}
} else {
if (inSpan) {
inSpan = false;
addSpan(start, x - 1, y, direction);
}
}
}
if (inSpan) {
inSpan = false;
addSpan(start, x - 1, y, direction);
}
}
addSpan(x, x, y, 0);
while (spansToCheck.length > 0) {
const {left, right, y, direction} = spansToCheck.pop();
// do left until we hit something, while we do this check above and below and add
let l = left;
for (;;) {
--l;
const color = getPixel(pixelData, l, y);
if (color !== targetColor) {
break;
}
}
++l
let r = right;
for (;;) {
++r;
const color = getPixel(pixelData, r, y);
if (color !== targetColor) {
break;
}
}
const lineOffset = y * pixelData.width;
pixelData.data.fill(fillColor, lineOffset + l, lineOffset + r);
if (direction <= 0) {
checkSpan(l, r, y - 1, -1);
} else {
checkSpan(l, left, y - 1, -1);
checkSpan(right, r, y - 1, -1);
}
if (direction >= 0) {
checkSpan(l, r, y + 1, +1);
} else {
checkSpan(l, left, y + 1, +1);
checkSpan(right, r, y + 1, +1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
Note: I didn't test this well, there might be an off by 1 error or other issue. I'm 99% sure I wrote the span method in 1993 for My Paint but don't remember if I have the source. But in any case, it's fast enough there's no need for wait

Here's an implementation that I've been working on. It can get really slow if the replacement color is too close to the original color. It's quite a bit faster in Chrome than Firefox (I haven't tested it in any other browsers).
I also haven't done exhaustive testing yet, so there may be edge cases where it doesn't work.
function getPixel(pixelData, x, y) {
if (x < 0 || y < 0 || x >= pixelData.width || y >= pixelData.height) {
return NaN;
}
var pixels = pixelData.data;
var i = (y * pixelData.width + x) * 4;
return ((pixels[i + 0] & 0xFF) << 24) |
((pixels[i + 1] & 0xFF) << 16) |
((pixels[i + 2] & 0xFF) << 8) |
((pixels[i + 3] & 0xFF) << 0);
}
function setPixel(pixelData, x, y, color) {
var i = (y * pixelData.width + x) * 4;
var pixels = pixelData.data;
pixels[i + 0] = (color >>> 24) & 0xFF;
pixels[i + 1] = (color >>> 16) & 0xFF;
pixels[i + 2] = (color >>> 8) & 0xFF;
pixels[i + 3] = (color >>> 0) & 0xFF;
}
function diff(c1, c2) {
if (isNaN(c1) || isNaN(c2)) {
return Infinity;
}
var dr = ((c1 >>> 24) & 0xFF) - ((c2 >>> 24) & 0xFF);
var dg = ((c1 >>> 16) & 0xFF) - ((c2 >>> 16) & 0xFF);
var db = ((c1 >>> 8) & 0xFF) - ((c2 >>> 8) & 0xFF);
var da = ((c1 >>> 0) & 0xFF) - ((c2 >>> 0) & 0xFF);
return dr*dr + dg*dg + db*db + da*da;
}
function floodFill(canvas, x, y, replacementColor, delta) {
var current, w, e, stack, color, cx, cy;
var context = canvas.getContext("2d");
var pixelData = context.getImageData(0, 0, canvas.width, canvas.height);
var done = [];
for (var i = 0; i < canvas.width; i++) {
done[i] = [];
}
var targetColor = getPixel(pixelData, x, y);
delta *= delta;
stack = [ [x, y] ];
done[x][y] = true;
while ((current = stack.pop())) {
cx = current[0];
cy = current[1];
if (diff(getPixel(pixelData, cx, cy), targetColor) <= delta) {
setPixel(pixelData, cx, cy, replacementColor);
w = e = cx;
while (w > 0 && diff(getPixel(pixelData, w - 1, cy), targetColor) <= delta) {
--w;
if (done[w][cy]) break;
setPixel(pixelData, w, cy, replacementColor);
}
while (e < pixelData.width - 1 && diff(getPixel(pixelData, e + 1, cy), targetColor) <= delta) {
++e;
if (done[e][cy]) break;
setPixel(pixelData, e, cy, replacementColor);
}
for (cx = w; cx <= e; cx++) {
if (cy > 0) {
color = getPixel(pixelData, cx, cy - 1);
if (diff(color, targetColor) <= delta) {
if (!done[cx][cy - 1]) {
stack.push([cx, cy - 1]);
done[cx][cy - 1] = true;
}
}
}
if (cy < canvas.height - 1) {
color = getPixel(pixelData, cx, cy + 1);
if (diff(color, targetColor) <= delta) {
if (!done[cx][cy + 1]) {
stack.push([cx, cy + 1]);
done[cx][cy + 1] = true;
}
}
}
}
}
}
context.putImageData(pixelData, 0, 0, 0, 0, canvas.width, canvas.height);
}

I would not treat the canvas as a bitmap image.
Instead I would keep a collection of painting-objects and modify that collection.
Then for example you can fill a path or shape or add a new shape that has the boundaries of the objects you are trying to fill.
I can't see how "normal" floodFill makes sense in vector drawing..