Develop Reference

Canvas - resize image and save to a variable

So, I have a browser game which is run by a canvas with dynamic dimensions(it scales to the user's window's dimensions) which takes images at various sizes, scales them according to the user's window dimensions and draws them:
(example of my resizing algo:)
https://jsfiddle.net/8o3sn9mh/55/
var
canvas = document.getElementById('c'),
ctx = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var flower = new Image();
//the src is actually local, but i put a url for example's sake
flower.src = "http://plainicon.com/dboard/userprod/2803_dd580/prod_thumb/plainicon.com-46129-128px-af2.png"
flower.onload = function(){
ctx.drawImage(flower,0,0,128,128, 0, 0, window.innerWidth / 2, window.innerHeight / 2);
}
as you can see, I am drawing a 128x128px image and I resize it to half's the user's window. So, I was thinking - my game may do this operation every single render execution, and it may take unnecessary resizing time to perform it every time. So:
1) Does performing this resizing take more time since I use it every requestAnimationFrame?
2) Is there a way to resize my image one time, save it into a var and use it in order to save that time?
Regardless I'd like a way to save the resized image into a var in order to fit it inside canvas' createPattern method:
pattern = ctx.createPattern(resizedFlower, 'repeat'); //resizedFlower should be the original flower resized into half's the user's window's width + height
ctx.fillStyle = pattern;
ctx.fillRect(0, 0, 50, 50);

You can save your image to a canvas and then use drawImage with that canvas. For instance:
var canvas = document.getElementById('c'),
ctx = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var flowerCanvas = document.createElement('canvas');
flowerCanvas.width = window.innerWidth;
flowerCanvas.height = window.innerHeight;
flowerCtx = flowerCanvas.getContext('2d');
var flower = new Image();
//the src is actually local, but i put a url for example's sake
flower.src = "http://plainicon.com/dboard/userprod/2803_dd580/prod_thumb/plainicon.com-46129-128px-af2.png"
flower.onload = function(){
flowerCtx.drawImage(flower,0,0,128,128, 0, 0, window.innerWidth / 2, window.innerHeight / 2);
ctx.drawImage(flowerCanvas,0,0);
}
Now you can reuse flowerCanvas and it will be whatever size you initially drew it at. You probably won't see much of a performance gain between resizing vs not resizing, although you should benchmark it to be sure.
Also you shouldn't resize everything everyframe, you can listen for a window resize event, and resize when that event fires.

If I resize my canvas, my createJS text becames blurry

I'm using createJS to drawn inside the canvas. I have my canvas set to occupy the browser window maintaining aspect ratio using the resize() function.
This is the code:
mytext = new createjs.Text("Lorem ipsum dolor sit amet 2","19px Calibri","#073949");
mytext.x = 450
mytext.y = 300;
stage.addChild(mytext);
resize = function() {
var canvas = document.getElementById('canvas');
var canvasRatio = canvas.height / canvas.width;
var windowRatio = window.innerHeight / window.innerWidth;
var width;
var height;
if (windowRatio < canvasRatio) {
height = window.innerHeight - 35;
width = height / canvasRatio;
} else {
width = window.innerWidth;
height = width * canvasRatio;
}
canvas.style.width = width + 'px';
canvas.style.height = height + 'px';
}()
What happens is that the text gets blurry (decrease of quality) when the canvas resizes.
http://i.imgur.com/RQOSajs.png
vs
http://i.imgur.com/Xwhf5c5.png
How can I solve this issue?

Since you are using CreateJS, you can simply resize the canvas, and scale the entire stage to redraw everything at the new size:
// just showing width to simplify the example:
var newWidth = 800;
var scale = newWidth/myCanvas.width;
myCanvas.width = newWidth;
myStage.scaleX = myStage.scaleY = scale;
myStage.update(); // draw at the new size.

#Adam's answer is correct as far as scaling the canvas goes. You do NOT want to scale with CSS, as it will stretch your canvas instead of changing its pixel dimensions. Set the width and height of the canvas using JavaScript instead.
stage.canvas.width = window.innerWidth;
stage.canvas.height = window.innerHeight;
As you stated in your comment, this will only change the canvas size, and not reposition or scale your content. You will have to do this manually. This is fairly simple. Generally, I recommend putting your "resize" listener in the JavaScript in your HTML file, rather than on a frame script.
First, determine the scale, based on the size of the window and the size of your content. You can use the exportRoot.nominalBounds.width and exportRoot.nominalBounds.height which is the bounds of the first frame. If you want to scale something else, use its nominalBounds instead.
Note that nominalBounds is appended to all MovieClips exported from Flash/Animate. If you enable multi-frame bounds, and want to use those, you will have to modify your approach.
The main idea is to use the original, unscaled size of your contents.
var bounds = exportRoot.nominalBounds;
// Uses the larger of the width or height. This will "fill" the viewport.
// Change to Math.min to "fit" instead.
var scale = Math.max(window.innerWidth / bounds.width, window.innerHeight / bounds.height);
exportRoot.scaleX = exportRoot.scaleY = scale;
You can then center it if you want.
exportRoot.x = *window.innerWidth - bounds.width*scale)/2;
exportRoot.y = *window.innerHeight - bounds.height*scale)/2;
Here is a quick sample of a responsive canvas using a simple shape as the scaling contents:
http://jsfiddle.net/lannymcnie/4yy08pax/
Doing this with Flash/Animate CC export has come up a few times, so it is on my list of future EaselJS demos to include on createjs.com, and in the EaselJS GitHub.
I hope this helps.

Take a look at my jsfiddle : https://jsfiddle.net/CanvasCode/ecr7o551/1/
Basically you just store the original canvas size and then use that to work out new positions and sizes
html
<canvas id="canvas" width="400" height="400">
Canvas was unable to start up.
</canvas>
<button onclick="resize()">Click me</button>
javascript
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var originalWidth = canvas.width;
var originalHeight = canvas.height;
render = function()
{
context.fillStyle = "#DDD";
context.fillRect(0,0, originalWidth * (canvas.width / originalWidth), originalHeight * (canvas.height / originalHeight));
context.fillStyle = "#000";
var fontSize = 48 * (canvas.width / originalWidth);
context.font = fontSize+"px serif";
context.fillText("Hello world", 100 * (canvas.width / originalWidth), 200 * (canvas.height / originalHeight));
}
resize = function()
{
canvas.width = 800;
canvas.height = 600;
render();
}
render();

The HTML5 canvas element works with two different sizes
Visual size on screen, controlled via CSS, like you're setting with canvas.style.width/height
Size of pixel buffer for the drawing, controlled via numeric width and height pixel attributes on the canvas element.
The browser will stretch the buffer to fit the size on screen, so if the two values are not 1:1 ratio text will look blurry.
Try adding the following lines to your code
canvas.width = width;
canvas.height = height;

I created a function to resize all the elements on the screen after resizing the canvas. It saves the initial coordinates and scales for the elements with the original width of 900 px and then it changes them according to the current width ratio relative to the original width ratio. The text isn't blurry/bad quality anymore.
resize = function() {
var canvas = document.getElementById('canvas');
var canvasRatio = canvas.height / canvas.width;
var windowRatio = window.innerHeight / window.innerWidth;
var width;
var height;
if (windowRatio < canvasRatio) {
height = window.innerHeight;
width = height / canvasRatio;
} else {
width = window.innerWidth;
height = width * canvasRatio;
}
canvas.width = width;
canvas.height = height;
reziseElements();
};
reziseElements = function()
{
var canvrat = canvas.width / 900;
//Simplified
stage.scaleX = stage.scaleY = canvrat;
//Old Version
/*for (i=0; i<stage.numChildren ;i++)
{
currentChild = stage.getChildAt(i);
if (typeof currentChild.oscaleX == 'undefined')
{
currentChild.oscaleX = currentChild.scaleX;
currentChild.ox = currentChild.x;
currentChild.oy = currentChild.y;
}
}
for (i=0; i<stage.numChildren ;i++)
{
currentChild = stage.getChildAt(i);
currentChild.scaleX = currentChild.scaleY = currentChild.oscaleX * canvrat
currentChild.x = currentChild.ox * canvrat
currentChild.y = currentChild.oy * canvrat
} */
}

Resizing canvas to full browser window width and height

I'm playing around with a node/socket.io Pictionary game. I apologize in advance, I am a designer and not too keen with js.
I'm just trying to re-size the canvas so it will be the entire width and height of a browser window without scaling up the stroke path? Right now, the Javascript sets the canvas to 500px.
Here is the relevant code:
// ================================================
// canvas drawing section
// ================================================
var canvas = $('#canvas'),
context = canvas[0].getContext('2d');
socket.on('drawCanvas', function(canvasToDraw) {
if(canvasToDraw) {
canvas.width(500);
context.lineJoin = 'round';
context.lineWidth = 2;
// ...
}
});

canvas[0].width = $(window).width();
canvas[0].height = $(window).height();
worked great.

You're using jQuery to change the dimensions, and that won't work well with canvas (it will scale the canvas contents too). Set the dimensions directly on the canvas element:
canvas[0].width = 500;
// Or:
canvas.get(0).width = 500;
To set the canvas to the full window dimensions, try this:
canvas[0].width = $(window).width();
canvas[0].height = $(window).height();

Use clientWidth and clientHeight property of canvas
if (canvas[0].width != canvas[0].clientWidth || canvas[0].height != canvas[0].clientHeight) {
canvas[0].width = canvas[0].clientWidth;
canvas[0].height = canvas[0].clientHeight;
}
and set the css for canvas width and height to 100%;

Windows 8 Javascript set Canvas to fill screen

I'm trying to create a HTML5 canvas using Windows 8 / WinJS. Here's what I have:
var body = document.getElementById("body");
var canvas = document.createElement("canvas");
canvas.id = "myCanvas";
body.appendChild(canvas);
var canvasContext = canvas.getContext("2d");
canvas.width = document.width;
canvas.height = document.height;
canvasContext.fillStyle = "#f00";
canvasContext.fillRect(canvas.width - 100, canvas.height - 50, 100, 50);
console.log("canvas width " + canvas.width + ", height " + canvas.height);
Most of this is directly from a tutorial, but for all the tutorials I've seen, the width and height are set to hard coded numbers, for example:
canvas.width = 800;
canvas.height = 600;
Admittedly that does work, but I want the canvas to be as big as the screen, whatever the resolution. How do I achieve this?

You can just use the viewport with and viewport height CSS values to do this (see some information on these here)
In this specific case you could just do:
canvas.style.width = "100vw";
canvas.style.height = "100vh";
The advantage of this solution is that you don't have to load 3rd party libraries, e.g. JQuery to size to the full width / height.

By "screen", do you mean the browser window size?
If so, you can use window.outerWidth and window.outerHeight instead of document.width and document.height. Or if you use jQuery: $(window).width() and $(window).height().
Also, you want to listen to the resize event on the window so that you can reinitialize the canvas when the browser is resized.

HTML canvas - drawing disappear on resizing

I have created a basic shape in HTML canvas element which works fine.
The problem occurs when I resize the canvas, all the drawing in the canvas disappears. Is this the normal behavior? or is there a function that can be used to stop this?
One way to fix this could be to call drawing function again on canvas resize however this may not be very efficient if there is huge content to be drawn.
What's the best way?
Here is the link to sample code https://gist.github.com/2983915

You need to redraw the scene when you resize.
setting the width or height of a canvas, even if you are setting it to the same value as before, not only clears the canvas but resets the entire canvas context. Any set properties (fillStyle, lineWidth, the clipping region, etc) will also be reset.
If you do not have the ability to redraw the scene from whatever data structures you might have representing the canvas, you can always save the entire canvas itself by drawing it to an in-memory canvas, setting the original width, and drawing the in-memory canvas back to the original canvas.
Here's a really quick example of saving the canvas bitmap and putting it back after a resize:
http://jsfiddle.net/simonsarris/weMbr/

Everytime you resize the canvas it will reset itself to transparant black, as defined in the spec.
You will either have to:
redraw when you resize the canvas, or,
don't resize the canvas

One another way is to use the debounce if you are concerned with the performance.
It doesnt resize or redraw every position you are dragging. But it will resize only when the it is resized.
// Assume canvas is in scope
addEventListener.("resize", debouncedResize );
// debounce timeout handle
var debounceTimeoutHandle;
// The debounce time in ms (1/1000th second)
const DEBOUNCE_TIME = 100;
// Resize function
function debouncedResize () {
clearTimeout(debounceTimeoutHandle); // Clears any pending debounce events
// Schedule a canvas resize
debounceTimeoutHandle = setTimeout(resizeCanvas, DEBOUNCE_TIME);
}
// canvas resize function
function resizeCanvas () { ... resize and redraw ... }

I had the same problem. Try following code
var wrapper = document.getElementById("signature-pad");
var canvas = wrapper.querySelector("canvas");
var ratio = Math.max(window.devicePixelRatio || 1, 1);
canvas.width = canvas.offsetWidth * ratio;
canvas.height = canvas.offsetHeight * ratio;
It keeps the drawing as it is

One thing that worked for me was to use requestAnimationFrame().
let height = window.innerHeight;
let width = window.innerWidth;
function handleWindowResize() {
height = window.innerHeight;
width = window.innerWidth;
}
function render() {
// Draw your fun shapes here
// ...
// Keep this on the bottom
requestAnimationFrame(render);
}
// Canvas being defined at the top of the file.
function init() {
ctx = canvas.getContext("2d");
render();
}

I had the same problem when I had to resize the canvas to adjust it to the screen.
But I solved it with this code:
var c = document.getElementById('canvas');
ctx = c.getContext('2d');
ctx.fillRect(0,0,20,20);
// Save canvas settings
ctx.save();
// Save canvas context
var dataURL = c.toDataURL('image/jpeg');
// Resize canvas
c.width = 50;
c.height = 50;
// Restore canvas context
var img = document.createElement('img');
img.src = dataURL;
img.onload=function(){
ctx.drawImage(img,20,20);
}
// Restote canvas settings
ctx.restore();
<canvas id=canvas width=40 height=40></canvas>

I also met this problem.but after a experiment, I found that Resizing the canvas element will automatically clear all drawings off the canvas!
just try the code below
<canvas id = 'canvas'></canvas>
<script>
var canvas1 = document.getElementById('canvas')
console.log('canvas size',canvas1.width, canvas1.height)
var ctx = canvas1.getContext('2d')
ctx.font = 'Bold 48px Arial'
var f = ctx.font
canvas1.width = 480
var f1 = ctx.font
alert(f === f1) //false
</script>