Develop Reference

How to animate html canvas curve lines?

I have created lines using canvas quadraticCurveTo connecting with each other. My goal is to animate this lines.
I have an example with lineTo method, how to change it for quadraticCurveTo method?
(function () {
var lastTime = 0;
var vendors = ['ms', 'moz', 'webkit', 'o'];
for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] || window[vendors[x] + 'CancelRequestAnimationFrame'];
}
if (!window.requestAnimationFrame) window.requestAnimationFrame = function (callback, element) {
var currTime = new Date().getTime();
var timeToCall = Math.max(0, 16 - (currTime - lastTime));
var id = window.setTimeout(function () {
callback(currTime + timeToCall);
},
timeToCall);
lastTime = currTime + timeToCall;
return id;
};
Example link: http://jsfiddle.net/m1erickson/7faRQ/
What I expected: example image

Animation along a path
To do as the fiddle but with any of the path functions you can use line dash to set the amount of the path that is drawn. This will give you a animation along the path that is at a constant speed.
The only problem with this method is that you do not know how long the path is. To know that involves some rather complicated math (warning some bezier length solutions are approximations).
In this example I used my eye to work out the length.
requestAnimationFrame(loop);
const ctx = canvas.getContext("2d");
ctx.lineCap = "round";
const lines = [[10, 10], [300, 10, 250, 200], [100, 300, 20, 120, 10, 10]];
const render = {
"2"(p) { ctx.lineTo(...p) },
"4"(p) { ctx.quadraticCurveTo(...p) },
"6"(p) { ctx.bezierCurveTo(...p) },
start(width, col) { ctx.lineWidth = width; ctx.strokeStyle = col; ctx.beginPath() }
}
var startTime;
const len = 760;
function loop(time) {
if(startTime === undefined){ startTime = time }
const animTime = time - startTime;
ctx.clearRect(0, 0, 300, 300);
ctx.setLineDash([1, 0]);
render.start(1,"blue")
lines.forEach(l => render[l.length](l));
ctx.stroke();
ctx.setLineDash([(animTime / 10) % len, 10000]);
render.start(8, "red")
lines.forEach(l => render[l.length](l));
ctx.stroke();
requestAnimationFrame(loop);
}
canvas { border : 2px solid black; }
<canvas id="canvas" width = 300 height = 300></canvas>

I know this question is a little old, but SO is filled with bad answers to variations on this question, and until I found this one I found no good solutions. #Blindman67 pointed me in the right direction with setLineDash, and the following works beautifully for me. rnd2() returns a random integer in the range (but you can always just use a constant or a parameter), and curves() calculates a quick rough approximate length of its curve (the average of chord and total segments length), which I multiply by 1.2 to be sure I don't go over. My setLineDash call works with alpha < 1.0 because it doesn't repeatedly overdraw the curve, and it doesn't spend extra time calculating a long invisible blank. raf() is requestAnimationFrame.
var lineLen = 0, delta = rnd2(20, 80);
var approxCurveLen = curves(c0.width, c0.height, ctx, false) * 1.2;
var step = () =>
{
if (lineLen < approxCurveLen)
{
ctx.setLineDash([0, lineLen, delta, approxCurveLen-lineLen]);
ctx.stroke();
lineLen += delta;
raf(step);
}
else
{
ctx.setLineDash([]);
}
};
raf(step);

Acceleration setInterval in Jquery

I am trying to create a bouncing ball (on a canvas). I would love if the ball could accelerate when going up and down. No idea how to do this with setInterval. Here is my code:
setInterval(function animate() {
ctx.clearRect( 0, 0, canvas.width, canvas.height);
if (movement1 === true) {
dotHeight += 1;
if (dotHeight >= 100) movement1 = false;
} else {
dotHeight -= 1;
if (dotHeight <= 0) movement1 = true;
}
ctx.beginPath();
ctx.arc(canvas.width / 2, (canvas.height / 2) + dotHeight, dotSize, 0, 2 * Math.PI);
ctx.fillStyle = "white";
ctx.fill();
}, 4);
This results in a linear movement. I would love to have a natural movement. Basically starting fast and getting slower when reaching the top and vice versa.

You should have both a speed and a gravity (or acceleration) variable:
speed tells you how many units (pixels here) is going to travel your object in the current update.
gravity tells you by how many units is speed increased on each update.
You want a constant gravity so that speed is increasing the same amount of pixels on each update. That will give you a variable speed, so that your object (dot here) is travelling longer or shorter distances on each update, depending on the direction it is travelling.
To make the dot bounce just change the direction of its speed once it reaches the floor. You just need to multiply it by -1 or, instead of that, you could multiply it by a bouncingFactor (-1 < bouncingFactor < 0) so that it loses energy on each bounce:
Here you can see a working example:
var canvas = document.getElementById("canvas");
canvas.width = canvas.offsetWidth;
canvas.height = canvas.offsetHeight;
var ctx = canvas.getContext("2d");
var frames = 0; // Frame counter just to make sure you don't crash your browser while editing code!
// DOT STUFF:
var dotSize = 20;
var dotMinY = 0 + dotSize; // Start position
var dotMaxY = canvas.height - dotSize; // Floor
var dotY = dotMinY;
var dotSpeed = 0;
var dotLastBounceSpeed = 0; // You can use this to determine whether the ball is still bouncing enough to be visible by the user.
var center = canvas.width / 2; // Try to take every operation you can out of the animate function.
var pi2 = 2 * Math.PI;
// WORLD STUFF:
var gravity = .5;
var bounceFactor = .8; // If < 1, bouncing absorbs energy so ball won't go as high as it was before.
// MAIN ANIMATION LOOP:
function animate() {
ctx.clearRect( 0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(center, dotY, dotSize, 0, pi2);
ctx.fillStyle = "red";
ctx.fill();
// First, dotSpeed += gravity is calculated and that returns the new value for dotSpeed
// then, that new value is added to dotY.
dotY += dotSpeed += gravity;
if(dotY >= dotMaxY ) {
dotY = dotMaxY;
dotSpeed *= -bounceFactor;
}
var dotCurrentBounceSpeed = Math.round(dotSpeed * 100); // Takes two decimal digits.
if(frames++ < 5000 && dotLastBounceSpeed != dotCurrentBounceSpeed) {
dotLastBounceSpeed = dotCurrentBounceSpeed;
setTimeout(animate, 16); // 1000/60 = 16.6666...
}
else alert("Animation end. Took " + frames + " frames.");
}
animate();
html, body, #canvas {
position:relative;
width: 100%;
height: 100%;
margin: 0;
overflow:hidden;
}
<canvas id="canvas"></canvas>
You should also consider using requestAnimationFrame insted of setTimeout. From the MDN doc:
The Window.requestAnimationFrame() method tells the browser that you
wish to perform an animation and requests that the browser call a
specified function to update an animation before the next repaint. The
method takes as an argument a callback to be invoked before the
repaint.
The same example with requestAnimationFrame:
var canvas = document.getElementById("canvas");
canvas.width = canvas.offsetWidth;
canvas.height = canvas.offsetHeight;
var ctx = canvas.getContext("2d");
var frames = 0; // Frame counter just to make sure you don't crash your browser while editing code!
// DOT STUFF:
var dotSize = 20;
var dotMinY = 0 + dotSize; // Start position
var dotMaxY = canvas.height - dotSize; // Floor
var dotY = dotMinY;
var dotSpeed = 0;
var dotLastBounceSpeed = 0; // You can use this to determine whether the ball is still bouncing enough to be visible by the user.
var center = canvas.width / 2; // Try to take every operation you can out of the animate function.
var pi2 = 2 * Math.PI;
// WORLD STUFF:
var gravity = .5;
var bounceFactor = .8; // If < 1, bouncing absorbs energy so ball won't go as high as it was before.
// MAIN ANIMATION LOOP:
function animate() {
ctx.clearRect( 0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(center, dotY, dotSize, 0, pi2);
ctx.fillStyle = "red";
ctx.fill();
// First, dotSpeed += gravity is calculated and that returns the new value for dotSpeed
// then, that new value is added to dotY.
dotY += dotSpeed += gravity;
if(dotY >= dotMaxY ) {
dotY = dotMaxY;
dotSpeed *= -bounceFactor;
}
var dotCurrentBounceSpeed = Math.round(dotSpeed * 100); // Takes two decimal digits.
if(frames++ < 5000 && dotLastBounceSpeed != dotCurrentBounceSpeed) {
dotLastBounceSpeed = dotCurrentBounceSpeed;
//setTimeout(animate, 10);
window.requestAnimationFrame(animate); // Better!!
}
else alert("Animation end. Took " + frames + " frames.");
}
animate();
html, body, #canvas {
position:relative;
width: 100%;
height: 100%;
margin: 0;
overflow:hidden;
}
<canvas id="canvas"></canvas>
As you can see, you only need to change one line of code! However, you may need a polyfill so that you fall back to setTimeout if the browser does not support requestAnimationFrame.
You can learn more about requestAnimationFrame in this post. It explains the basics and also how to set a custom frame rate.

The basic principle is to use a velocity variable as opposed to a constant height increment. So instead of dotHeight += 1 or dotHeight -= 1 you would do dotHeight += dotVelocity, where you define dotVelocity, and subtract it by a constant value (gravity) whenever the ball is in the air.
var dotHeight = 0;
var dotVelocity = 3; // start out moving up, like in your example
var gravity = .1; // you can adjust this constant for stronger/weaker gravity
setInterval(function animate() {
ctx.clearRect( 0, 0, canvas.width, canvas.height);
if (dotHeight > 0) { // if it hit the ground, stop movement
dotVelocity -= gravity;
dotHeight += dotVelocity;
}
ctx.beginPath();
ctx.arc(canvas.width / 2, (canvas.height / 2) + dotHeight, dotSize, 0, 2 * Math.PI);
ctx.fillStyle = "white";
ctx.fill();
}, 4);

You could use a speed variable instead of the constant 1 to determine how "far" to move the ball, like this:
var speed = 1;
setInterval(function animate() {
ctx.clearRect( 0, 0, canvas.width, canvas.height);
if (movement1 === true) {
dotHeight += speed;
if (dotHeight >= 100) movement1 = false;
// make it faster
speed += 1;
} else {
dotHeight -= speed;
if (dotHeight <= 0) movement1 = true;
// slow down
speed -= 1;
}
ctx.beginPath();
ctx.arc(canvas.width / 2, (canvas.height / 2) + dotHeight, dotSize, 0, 2 * Math.PI);
ctx.fillStyle = "white";
ctx.fill();
}, 4);

HTML5 Canvas + js game | Reset game on death changes the game speeds up?

I'm trying to make a game using HTML5's canvas and javascript. I believe that I have been doing everything "okay" up until the point where I need to reset the game on death. I'm not really sure what is causing the unexpected behavior but i have thoughts.
Pretty much, the game operates at 'x' speed and then when it resets everything is moving much faster. I have not changed any of the variables for any speed of anything and when debugging and inspecting my code the speeds are the same on the newly created objects as the first time the game is started but they are moving much faster. If you die again it resets again and operates even faster. Die, rinse, repeat and it keeps speeding up until the page would probably hit "not responding" state.
I don't know for sure what I'm doing wrong that is causing the speed difference or at least the illusion of the speed difference. I have an idea that it has something to do with my game loop running multiple times into forever every time it's reset but I don't understand how/why it would do that. any feedback is appreciated.
Also, you can visit my testing page to see all of the code if you need more than I posted below: game test playground
var windowx,
windowy,
canvas,
player,
quadTree,
ctx;
var drawObjects;
var keyState;
var mainloop;
var animFrame;
var ONE_FRAME_TIME;
var reset = function () {
//get canvas and set height and width
canvas = document.getElementById('canvas');
canvas.setAttribute('width', windowx / 2);
canvas.setAttribute('height', windowy / 2);
ctx = canvas.getContext("2d");
drawObjects = [];
keyState = {};
quadTree = new Quadtree(quadTreeBounds);
//make the friendly square
player = new Rectangle(20, 20, 40, 40, 0, 0, XPhysicsBehaviorNormal, YPhysicsBehaviorNormal, XBoundaryBehaviorInCanvas, YBoundaryBehaviorInCanvas, playerObjectType, '#580000', null);
drawObjects.push(player);
drawObjects.push(new Rectangle(40, 100, canvas.width + (distanceOutsideCanvasBeforeDie / 2), canvas.clientHeight - 100, defaultEnemyRectangleVelocity, 0, null, YPhysicsBehaviorNormal, null, YBoundaryBehaviorInCanvas, enemyObjectType, null, OutOfCanvasDieBehavior));
backgroundMusicAudio.play();
//define main loop
mainloop = function () {
buildQuadTree();
updateGame();
drawGame();
};
//define the windowanimationframeobject
animFrame = window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
null;
if (animFrame !== null) {
var recursiveAnim = function () {
mainloop();
animFrame(recursiveAnim, canvas);
};
// start the mainloop
animFrame(recursiveAnim, canvas);
} else {
// fallback to setInterval if the browser doesn't support requestAnimationFrame
ONE_FRAME_TIME = 1000.0 / 60.0;
setInterval(mainloop, ONE_FRAME_TIME);
}
}
$(function () {
//get window width and height;
windowx = window.innerWidth;
windowy = window.innerHeight;
reset();
$(document).on('change', '#sound-enabled-toggle', function() {
var isChecked = $(this).is(':checked');
$('#sound-enabled-toggle').blur();
if (isChecked) {
backgroundMusicAudio.play();
playerJumpAudio = playerJumpMusicAudioSetup();
playerBlinkAudio = playerBlinkMusicAudioSetup();
} else {
backgroundMusicAudio.pause();
playerJumpAudio = new Audio('');
playerBlinkAudio = new Audio('');
}
});
});
//left the function here in case I need to do anything else but for now it's just clearing.
function buildQuadTree() {
quadTree.clear();
}
function updateGame() {
//determine if there are any keys pushed at the current point
keyPressActions();
//loop for calculating and updating all objects positions/values.
for (var i = 0; i < drawObjects.length; i++) {
var object = drawObjects[i];
quadTree.insert(new SimpleRectangle(object.x, object.y, object.width || (object.radius * 2), object.height || (object.radius * 2), object.name));
object.update();
//roundFloatingPoints Numbers to 2 decimal places
roundObjectVelocitiesAndPoints(object);
}
PlayerDeathTrigger(player);
}
function drawGame() {
//clear the canvas
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.font = "20px Verdana";
ctx.fillText("100,000", (canvas.width * .8), (canvas.clientHeight * .1));
ctx.font = "15px Verdana";
ctx.fillText("Temp Score", (canvas.width * .8), (canvas.clientHeight * .05));
//draw all objects in drawObjects
for (var i = 0; i < drawObjects.length; i++) {
var object = drawObjects[i];
object.draw();
}
}

Overall I would recommend re-factoring this code so your reset function doesn't re-create so many objects. Basically the reset function is just re-creating a bulk of the game logic.
The specific issue you identified appears to be coming from the fact that you call setInterval on each reset without clearing the previous interval. See the code below with the minimal changes to prevent this issue.
var windowx,
windowy,
canvas,
player,
quadTree,
ctx,
gameLoop;
var drawObjects;
var keyState;
var mainloop;
var animFrame;
var ONE_FRAME_TIME;
var reset = function() {
// Remove our old game loop
clearInterval(gameLoop);
//get canvas and set height and width
canvas = document.getElementById('canvas');
canvas.setAttribute('width', windowx / 2);
canvas.setAttribute('height', windowy / 2);
ctx = canvas.getContext("2d");
drawObjects = [];
keyState = {};
quadTree = new Quadtree(quadTreeBounds);
//make the friendly square
player = new Rectangle(20, 20, 40, 40, 0, 0, XPhysicsBehaviorNormal, YPhysicsBehaviorNormal, XBoundaryBehaviorInCanvas, YBoundaryBehaviorInCanvas, playerObjectType, '#580000', null);
drawObjects.push(player);
drawObjects.push(new Rectangle(40, 100, canvas.width + (distanceOutsideCanvasBeforeDie / 2), canvas.clientHeight - 100, defaultEnemyRectangleVelocity, 0, null, YPhysicsBehaviorNormal, null, YBoundaryBehaviorInCanvas, enemyObjectType, null, OutOfCanvasDieBehavior));
backgroundMusicAudio.play();
//define main loop
mainloop = function() {
buildQuadTree();
updateGame();
drawGame();
};
//define the windowanimationframeobject
animFrame = window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
null;
if (animFrame !== null) {
var recursiveAnim = function() {
mainloop();
animFrame(recursiveAnim, canvas);
};
// start the mainloop
animFrame(recursiveAnim, canvas);
} else {
// fallback to setInterval if the browser doesn't support requestAnimationFrame
ONE_FRAME_TIME = 1000.0 / 60.0;
gameLoop = setInterval(mainloop, ONE_FRAME_TIME);
}
}
$(function() {
//get window width and height;
windowx = window.innerWidth;
windowy = window.innerHeight;
reset();
$(document).on('change', '#sound-enabled-toggle', function() {
var isChecked = $(this).is(':checked');
$('#sound-enabled-toggle').blur();
if (isChecked) {
backgroundMusicAudio.play();
playerJumpAudio = playerJumpMusicAudioSetup();
playerBlinkAudio = playerBlinkMusicAudioSetup();
} else {
backgroundMusicAudio.pause();
playerJumpAudio = new Audio('');
playerBlinkAudio = new Audio('');
}
});
});
//left the function here in case I need to do anything else but for now it's just clearing.
function buildQuadTree() {
quadTree.clear();
}
function updateGame() {
//determine if there are any keys pushed at the current point
keyPressActions();
//loop for calculating and updating all objects positions/values.
for (var i = 0; i < drawObjects.length; i++) {
var object = drawObjects[i];
quadTree.insert(new SimpleRectangle(object.x, object.y, object.width || (object.radius * 2), object.height || (object.radius * 2), object.name));
object.update();
//roundFloatingPoints Numbers to 2 decimal places
roundObjectVelocitiesAndPoints(object);
}
PlayerDeathTrigger(player);
}
function drawGame() {
//clear the canvas
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.font = "20px Verdana";
ctx.fillText("100,000", (canvas.width * .8), (canvas.clientHeight * .1));
ctx.font = "15px Verdana";
ctx.fillText("Temp Score", (canvas.width * .8), (canvas.clientHeight * .05));
//draw all objects in drawObjects
for (var i = 0; i < drawObjects.length; i++) {
var object = drawObjects[i];
object.draw();
}
}

Creating a stopwatch/timer along with canvas animation at 60fps

I am trying to create a timer alongside some canvas animations. The animation is using a function loop set at 60 fps to refresh the canvas and redraw the objects. The only way I can think of making the stopwatch is by using the same loop to take the milliseconds per frame and add it to the text object. I'm just wondering if there is a more efficient way of doing this?
var frame = 0;
canvas.setLoop(function() {
if(particle.x < 1080 && particle.x > 0){
frame++;
particle.x = 540 + (acc*frame*frame)/120;
gField.t.text = "g = 9.81ms⁻²\nMass = "+particle.mass+"kg\nF = ma\nFrame: " + frame + "\nDistance: " + (particle.x - 540).toFixed(1);
stopwatch();
}else{
canvas.timeline.stop();
}
})
var sec = 0;
var tsec = 0;
var hsec = 0;
function stopwatch(){
hsec+= (5/3);
if(hsec >= 10){
tsec++;
hsec = hsec -10;
}
if(tsec >= 10){
sec++;
tsec = tsec-10;
}
time.text = (sec)+":"+(tsec)+(hsec).toFixed(0);
}
var clicks = 0
control.button.bind("click tap", function() {
clicks++;
if(clicks == 1){
canvas.timeline.start();
}else{
clicks = 0;
canvas.timeline.stop();
}
})
P.s. this is for a dynamics simulation program. I am using the oCanvas library for the canvas animation.

Use requestAnimationFrame as this is the most accurate timer you'll get with JavaScript, and bonus is it will provide you with a high-resolution time-stamp:
var ctx = canvas.getContext('2d'),
startTime = null,
lastTime = null, // for scale
isRunning = false,
FPS = 1000/60,
x = 0,
dx = 4; // ideal frame rate
function loop(timeStamp) {
if (!startTime) startTime = timeStamp;
var timeDiff = lastTime ? timeStamp - lastTime : FPS,
timeElapsed = timeStamp - startTime,
timeScale = timeDiff / FPS; // adjust variations in frame rates
lastTime = timeStamp;
ctx.clearRect(0,0,canvas.width, canvas.height);
// do your stuff using timeScale, ie:
// pos.x += velocity.x * timeScale
x += dx * timeScale;
if (x < 0 || x > canvas.width-1) dx = -dx;
ctx.fillRect(x,0,8,8);
ctx.fillText((timeElapsed*0.001).toFixed(4), 10, 50);
ctx.fillText(timeScale.toFixed(1), 10, 90);
if (isRunning) requestAnimationFrame(loop);
}
ctx.font = "40px sans-serif";
btnToggle.addEventListener("click", function() {
if (isRunning) {
isRunning = false;
this.innerHTML = "Start";
} else {
startTime = lastTime = null;
isRunning = true;
requestAnimationFrame(loop)
this.innerHTML = "Stop";
}
}, false);
<canvas id=canvas width=360 height=100></canvas>
<br><button id="btnToggle">Start</button>
To reset start time initialize it with null (or 0). isRunning is used here just as an example on how you can stop the loop (by setting it to false).
Notice that timeScale is used to compensate for frame rate variations. If the loop is not running at 60 FPS then timeScale will compensate for this, ie. if FPS is 30 timeScale would be 2 and so, so that you can update the parameters correctly based on time.

Resizing an image in an HTML5 canvas

I'm trying to create a thumbnail image on the client side using javascript and a canvas element, but when I shrink the image down, it looks terrible. It looks as if it was downsized in photoshop with the resampling set to 'Nearest Neighbor' instead of Bicubic. I know its possible to get this to look right, because this site can do it just fine using a canvas as well. I've tried using the same code they do as shown in the "[Source]" link, but it still looks terrible. Is there something I'm missing, some setting that needs to be set or something?
EDIT:
I'm trying to resize a jpg. I have tried resizing the same jpg on the linked site and in photoshop, and it looks fine when downsized.
Here is the relevant code:
reader.onloadend = function(e)
{
var img = new Image();
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
};
img.src = reader.result;
}
EDIT2:
Seems I was mistaken, the linked website wasn't doing any better of a job of downsizing the image. I tried the other methods suggested and none of them look any better. This is what the different methods resulted in:
Photoshop:
Canvas:
Image with image-rendering: optimizeQuality set and scaled with width/height:
Image with image-rendering: optimizeQuality set and scaled with -moz-transform:
Canvas resize on pixastic:
I guess this means firefox isn't using bicubic sampling like its supposed to. I'll just have to wait until they actually add it.
EDIT3:
Original Image

So what do you do if all the browsers (actually, Chrome 5 gave me quite good one) won't give you good enough resampling quality? You implement them yourself then! Oh come on, we're entering the new age of Web 3.0, HTML5 compliant browsers, super optimized JIT javascript compilers, multi-core(†) machines, with tons of memory, what are you afraid of? Hey, there's the word java in javascript, so that should guarantee the performance, right? Behold, the thumbnail generating code:
// returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function(x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1;
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
};
}
// elem: canvas element, img: image element, sx: scaled width, lobes: kernel radius
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width : sx,
height : Math.round(img.height * sx / img.width),
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(this.process1, 0, this, 0);
}
thumbnailer.prototype.process1 = function(self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2)
+ Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(self.process1, 0, self, u);
else
setTimeout(self.process2, 0, self);
};
thumbnailer.prototype.process2 = function(self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0, self.dest.width, self.dest.height);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
};
...with which you can produce results like these!
so anyway, here is a 'fixed' version of your example:
img.onload = function() {
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 188, 3); //this produces lanczos3
// but feel free to raise it up to 8. Your client will appreciate
// that the program makes full use of his machine.
document.body.appendChild(canvas);
};
Now it's time to pit your best browsers out there and see which one will least likely increase your client's blood pressure!
Umm, where's my sarcasm tag?
(since many parts of the code is based on Anrieff Gallery Generator is it also covered under GPL2? I don't know)
† actually due to limitation of javascript, multi-core is not supported.

Fast image resize/resample algorithm using Hermite filter with JavaScript. Support transparency, gives good quality. Preview:
Update: version 2.0 added on GitHub (faster, web workers + transferable objects). Finally i got it working!
Git: https://github.com/viliusle/Hermite-resize
Demo: http://viliusle.github.io/miniPaint/
/**
* Hermite resize - fast image resize/resample using Hermite filter. 1 cpu version!
*
* #param {HtmlElement} canvas
* #param {int} width
* #param {int} height
* #param {boolean} resize_canvas if true, canvas will be resized. Optional.
*/
function resample_single(canvas, width, height, resize_canvas) {
var width_source = canvas.width;
var height_source = canvas.height;
width = Math.round(width);
height = Math.round(height);
var ratio_w = width_source / width;
var ratio_h = height_source / height;
var ratio_w_half = Math.ceil(ratio_w / 2);
var ratio_h_half = Math.ceil(ratio_h / 2);
var ctx = canvas.getContext("2d");
var img = ctx.getImageData(0, 0, width_source, height_source);
var img2 = ctx.createImageData(width, height);
var data = img.data;
var data2 = img2.data;
for (var j = 0; j < height; j++) {
for (var i = 0; i < width; i++) {
var x2 = (i + j * width) * 4;
var weight = 0;
var weights = 0;
var weights_alpha = 0;
var gx_r = 0;
var gx_g = 0;
var gx_b = 0;
var gx_a = 0;
var center_y = (j + 0.5) * ratio_h;
var yy_start = Math.floor(j * ratio_h);
var yy_stop = Math.ceil((j + 1) * ratio_h);
for (var yy = yy_start; yy < yy_stop; yy++) {
var dy = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
var center_x = (i + 0.5) * ratio_w;
var w0 = dy * dy; //pre-calc part of w
var xx_start = Math.floor(i * ratio_w);
var xx_stop = Math.ceil((i + 1) * ratio_w);
for (var xx = xx_start; xx < xx_stop; xx++) {
var dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
var w = Math.sqrt(w0 + dx * dx);
if (w >= 1) {
//pixel too far
continue;
}
//hermite filter
weight = 2 * w * w * w - 3 * w * w + 1;
var pos_x = 4 * (xx + yy * width_source);
//alpha
gx_a += weight * data[pos_x + 3];
weights_alpha += weight;
//colors
if (data[pos_x + 3] < 255)
weight = weight * data[pos_x + 3] / 250;
gx_r += weight * data[pos_x];
gx_g += weight * data[pos_x + 1];
gx_b += weight * data[pos_x + 2];
weights += weight;
}
}
data2[x2] = gx_r / weights;
data2[x2 + 1] = gx_g / weights;
data2[x2 + 2] = gx_b / weights;
data2[x2 + 3] = gx_a / weights_alpha;
}
}
//clear and resize canvas
if (resize_canvas === true) {
canvas.width = width;
canvas.height = height;
} else {
ctx.clearRect(0, 0, width_source, height_source);
}
//draw
ctx.putImageData(img2, 0, 0);
}

Try pica - that's a highly optimized resizer with selectable algorythms. See demo.
For example, original image from first post is resized in 120ms with Lanczos filter and 3px window or 60ms with Box filter and 0.5px window. For huge 17mb image 5000x3000px resize takes ~1s on desktop and 3s on mobile.
All resize principles were described very well in this thread, and pica does not add rocket science. But it's optimized very well for modern JIT-s, and is ready to use out of box (via npm or bower). Also, it use webworkers when available to avoid interface freezes.
I also plan to add unsharp mask support soon, because it's very useful after downscale.

I know this is an old thread but it might be useful for some people such as myself that months after are hitting this issue for the first time.
Here is some code that resizes the image every time you reload the image. I am aware this is not optimal at all, but I provide it as a proof of concept.
Also, sorry for using jQuery for simple selectors but I just feel too comfortable with the syntax.
$(document).on('ready', createImage);
$(window).on('resize', createImage);
var createImage = function(){
var canvas = document.getElementById('myCanvas');
canvas.width = window.innerWidth || $(window).width();
canvas.height = window.innerHeight || $(window).height();
var ctx = canvas.getContext('2d');
img = new Image();
img.addEventListener('load', function () {
ctx.drawImage(this, 0, 0, w, h);
});
img.src = 'http://www.ruinvalor.com/Telanor/images/original.jpg';
};
html, body{
height: 100%;
width: 100%;
margin: 0;
padding: 0;
background: #000;
}
canvas{
position: absolute;
left: 0;
top: 0;
z-index: 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<html>
<head>
<meta charset="utf-8" />
<title>Canvas Resize</title>
</head>
<body>
<canvas id="myCanvas"></canvas>
</body>
</html>
My createImage function is called once when the document is loaded and after that it is called every time the window receives a resize event.
I tested it in Chrome 6 and Firefox 3.6, both on the Mac. This "technique" eats processor as it if was ice cream in the summer, but it does the trick.

I've put up some algorithms to do image interpolation on html canvas pixel arrays that might be useful here:
https://web.archive.org/web/20170104190425/http://jsperf.com:80/pixel-interpolation/2
These can be copy/pasted and can be used inside of web workers to resize images (or any other operation that requires interpolation - I'm using them to defish images at the moment).
I haven't added the lanczos stuff above, so feel free to add that as a comparison if you'd like.

This is a javascript function adapted from #Telanor's code. When passing a image base64 as first argument to the function, it returns the base64 of the resized image. maxWidth and maxHeight are optional.
function thumbnail(base64, maxWidth, maxHeight) {
// Max size for thumbnail
if(typeof(maxWidth) === 'undefined') var maxWidth = 500;
if(typeof(maxHeight) === 'undefined') var maxHeight = 500;
// Create and initialize two canvas
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
// Create original image
var img = new Image();
img.src = base64;
// Determine new ratio based on max size
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
// Draw original image in second canvas
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
// Copy and resize second canvas to first canvas
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
return canvas.toDataURL();
}

I'd highly suggest you check out this link and make sure it is set to true.
Controlling image scaling behavior
Introduced in Gecko 1.9.2 (Firefox 3.6
/ Thunderbird 3.1 / Fennec 1.0)
Gecko 1.9.2 introduced the
mozImageSmoothingEnabled property to
the canvas element; if this Boolean
value is false, images won't be
smoothed when scaled. This property is
true by default. view plainprint?
cx.mozImageSmoothingEnabled = false;

If you're simply trying to resize an image, I'd recommend setting width and height of the image with CSS. Here's a quick example:
.small-image {
width: 100px;
height: 100px;
}
Note that the height and width can also be set using JavaScript. Here's quick code sample:
var img = document.getElement("my-image");
img.style.width = 100 + "px"; // Make sure you add the "px" to the end,
img.style.height = 100 + "px"; // otherwise you'll confuse IE
Also, to ensure that the resized image looks good, add the following css rules to image selector:
-ms-interpolation-mode: bicubic: introduce in IE7
image-rendering: optimizeQuality: introduced in FireFox 3.6
As far as I can tell, all browsers except IE using an bicubic algorithm to resize images by default, so your resized images should look good in Firefox and Chrome.
If setting the css width and height doesn't work, you may want to play with a css transform:
-moz-transform: scale(sx[, sy])
-webkit-transform:scale(sx[, sy])
If for whatever reason you need to use a canvas, please note that there are two ways an image can be resize: by resizing the canvas with css or by drawing the image at a smaller size.
See this question for more details.

i got this image by right clicking the canvas element in firefox and saving as.
var img = new Image();
img.onload = function () {
console.debug(this.width,this.height);
var canvas = document.createElement('canvas'), ctx;
canvas.width = 188;
canvas.height = 150;
document.body.appendChild(canvas);
ctx = canvas.getContext('2d');
ctx.drawImage(img,0,0,188,150);
};
img.src = 'original.jpg';
so anyway, here is a 'fixed' version of your example:
var img = new Image();
// added cause it wasnt defined
var canvas = document.createElement("canvas");
document.body.appendChild(canvas);
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
// adding it to the body
document.body.appendChild(canvasCopy);
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
// defining cause it wasnt
var maxWidth = 188,
maxHeight = 150;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
// the line to change
// ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
// the method signature you are using is for slicing
ctx.drawImage(canvasCopy, 0, 0, canvas.width, canvas.height);
};
// changed for example
img.src = 'original.jpg';

For resizing to image with width less that original, i use:
function resize2(i) {
var cc = document.createElement("canvas");
cc.width = i.width / 2;
cc.height = i.height / 2;
var ctx = cc.getContext("2d");
ctx.drawImage(i, 0, 0, cc.width, cc.height);
return cc;
}
var cc = img;
while (cc.width > 64 * 2) {
cc = resize2(cc);
}
// .. than drawImage(cc, .... )
and it works =).

I have a feeling the module I wrote will produce similar results to photoshop, as it preserves color data by averaging them, not applying an algorithm. It's kind of slow, but to me it is the best, because it preserves all the color data.
https://github.com/danschumann/limby-resize/blob/master/lib/canvas_resize.js
It doesn't take the nearest neighbor and drop other pixels, or sample a group and take a random average. It takes the exact proportion each source pixel should output into the destination pixel. The average pixel color in the source will be the average pixel color in the destination, which these other formulas, I think they will not be.
an example of how to use is at the bottom of
https://github.com/danschumann/limby-resize
UPDATE OCT 2018: These days my example is more academic than anything else. Webgl is pretty much 100%, so you'd be better off resizing with that to produce similar results, but faster. PICA.js does this, I believe. –

The problem with some of this solutions is that they access directly the pixel data and loop through it to perform the downsampling. Depending on the size of the image this can be very resource intensive, and it would be better to use the browser's internal algorithms.
The drawImage() function is using a linear-interpolation, nearest-neighbor resampling method. That works well when you are not resizing down more than half the original size.
If you loop to only resize max one half at a time, the results would be quite good, and much faster than accessing pixel data.
This function downsample to half at a time until reaching the desired size:
function resize_image( src, dst, type, quality ) {
var tmp = new Image(),
canvas, context, cW, cH;
type = type || 'image/jpeg';
quality = quality || 0.92;
cW = src.naturalWidth;
cH = src.naturalHeight;
tmp.src = src.src;
tmp.onload = function() {
canvas = document.createElement( 'canvas' );
cW /= 2;
cH /= 2;
if ( cW < src.width ) cW = src.width;
if ( cH < src.height ) cH = src.height;
canvas.width = cW;
canvas.height = cH;
context = canvas.getContext( '2d' );
context.drawImage( tmp, 0, 0, cW, cH );
dst.src = canvas.toDataURL( type, quality );
if ( cW <= src.width || cH <= src.height )
return;
tmp.src = dst.src;
}
}
// The images sent as parameters can be in the DOM or be image objects
resize_image( $( '#original' )[0], $( '#smaller' )[0] );
Credits to this post

So something interesting that I found a while ago while working with canvas that might be helpful:
To resize the canvas control on its own, you need to use the height="" and width="" attributes (or canvas.width/canvas.height elements). If you use CSS to resize the canvas, it will actually stretch (i.e.: resize) the content of the canvas to fit the full canvas (rather than simply increasing or decreasing the area of the canvas.
It'd be worth a shot to try drawing the image into a canvas control with the height and width attributes set to the size of the image and then using CSS to resize the canvas to the size you're looking for. Perhaps this would use a different resizing algorithm.
It should also be noted that canvas has different effects in different browsers (and even different versions of different browsers). The algorithms and techniques used in the browsers is likely to change over time (especially with Firefox 4 and Chrome 6 coming out so soon, which will place heavy emphasis on canvas rendering performance).
In addition, you may want to give SVG a shot, too, as it likely uses a different algorithm as well.
Best of luck!

Fast and simple Javascript image resizer:
https://github.com/calvintwr/blitz-hermite-resize
const blitz = Blitz.create()
/* Promise */
blitz({
source: DOM Image/DOM Canvas/jQuery/DataURL/File,
width: 400,
height: 600
}).then(output => {
// handle output
})catch(error => {
// handle error
})
/* Await */
let resized = await blizt({...})
/* Old school callback */
const blitz = Blitz.create('callback')
blitz({...}, function(output) {
// run your callback.
})
History
This is really after many rounds of research, reading and trying.
The resizer algorithm uses #ViliusL's Hermite script (Hermite resizer is really the fastest and gives reasonably good output). Extended with features you need.
Forks 1 worker to do the resizing so that it doesn't freeze your browser when resizing, unlike all other JS resizers out there.

I converted #syockit's answer as well as the step-down approach into a reusable Angular service for anyone who's interested: https://gist.github.com/fisch0920/37bac5e741eaec60e983
I included both solutions because they both have their own pros / cons. The lanczos convolution approach is higher quality at the cost of being slower, whereas the step-wise downscaling approach produces reasonably antialiased results and is significantly faster.
Example usage:
angular.module('demo').controller('ExampleCtrl', function (imageService) {
// EXAMPLE USAGE
// NOTE: it's bad practice to access the DOM inside a controller,
// but this is just to show the example usage.
// resize by lanczos-sinc filter
imageService.resize($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
// resize by stepping down image size in increments of 2x
imageService.resizeStep($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
})

Thanks #syockit for an awesome answer. however, I had to reformat a little as follows to make it work. Perhaps due to DOM scanning issues:
$(document).ready(function () {
$('img').on("load", clickA);
function clickA() {
var img = this;
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 50, 3);
document.body.appendChild(canvas);
}
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width: sx,
height: Math.round(img.height * sx / img.width)
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(process1, 0, this, 0);
}
//returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function (x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
}
}
process1 = function (self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2) + Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(process1, 0, self, u);
else
setTimeout(process2, 0, self);
};
process2 = function (self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
}
});

I wanted some well defined functions out of answers here so ended up with these which am hoping would be useful for others also,
function getImageFromLink(link) {
return new Promise(function (resolve) {
var image = new Image();
image.onload = function () { resolve(image); };
image.src = link;
});
}
function resizeImageToBlob(image, width, height, mime) {
return new Promise(function (resolve) {
var canvas = document.createElement('canvas');
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
return canvas.toBlob(resolve, mime);
});
}
getImageFromLink(location.href).then(function (image) {
// calculate these based on the original size
var width = image.width / 4;
var height = image.height / 4;
return resizeImageToBlob(image, width, height, 'image/jpeg');
}).then(function (blob) {
// Do something with the result Blob object
document.querySelector('img').src = URL.createObjectURL(blob);
});
Just for the sake of testing this run it on a image opened in a tab.

I just ran a page of side by sides comparisons and unless something has changed recently, I could see no better downsizing (scaling) using canvas vs. simple css. I tested in FF6 Mac OSX 10.7. Still slightly soft vs. the original.
I did however stumble upon something that did make a huge difference and that was using image filters in browsers that support canvas. You can actually manipulate images much like you can in Photoshop with blur, sharpen, saturation, ripple, grayscale, etc.
I then found an awesome jQuery plug-in which makes application of these filters a snap:
http://codecanyon.net/item/jsmanipulate-jquery-image-manipulation-plugin/428234
I simply apply the sharpen filter right after resizing the image which should give you the desired effect. I didn't even have to use a canvas element.

Looking for another great simple solution?
var img=document.createElement('img');
img.src=canvas.toDataURL();
$(img).css("background", backgroundColor);
$(img).width(settings.width);
$(img).height(settings.height);
This solution will use the resize algorith of browser! :)