without - resize canvas javascript




Resize HTML5 canvas to fit window (10)

How can I automatically scale the HTML5 <canvas> element to fit the page?

For example, I can get a <div> to scale by setting the height and width properties to 100%, but a <canvas> won't scale, will it?


CSS

body { margin: 0; } 
canvas { display: block; } 

JavaScript

window.addEventListener("load", function()
{
    var canvas = document.createElement('canvas'); document.body.appendChild(canvas);
    var context = canvas.getContext('2d');

    function draw()
    {
        context.clearRect(0, 0, canvas.width, canvas.height);
        context.beginPath();
        context.moveTo(0, 0); context.lineTo(canvas.width, canvas.height); 
        context.moveTo(canvas.width, 0); context.lineTo(0, canvas.height); 
        context.stroke();
    }
    function resize()
    {
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;
        draw();
    }
    window.addEventListener("resize", resize);
    resize();
});

A pure CSS approach adding to solution of @jerseyboy above.
Works in Firefox (tested in v29), Chrome (tested in v34) and Internet Explorer (tested in v11).

<!DOCTYPE html>
<html>
    <head>
    <style>
        html,
        body {
            width: 100%;
            height: 100%;
            margin: 0;
        }
        canvas {
            background-color: #ccc;
            display: block;
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            width: 100%;
            height: 100%;
        }
    </style>
</head>
<body>
    <canvas id="canvas" width="500" height="500"></canvas>
    <script>
        var canvas = document.getElementById('canvas');
        if (canvas.getContext) {
            var ctx = canvas.getContext('2d');
            ctx.fillRect(25,25,100,100);
            ctx.clearRect(45,45,60,60);
            ctx.strokeRect(50,50,50,50);
        }
    </script>
</body>
</html>

Link to the example: http://temporaer.net/open/so/140502_canvas-fit-to-window.html

But take care, as @jerseyboy states in his comment:

Rescaling canvas with CSS is troublesome. At least on Chrome and Safari, mouse/touch event positions will not correspond 1:1 with canvas pixel positions, and you'll have to transform the coordinate systems.


I believe I have found an elegant solution to this:

JavaScript

/* important! for alignment, you should make things
 * relative to the canvas' current width/height.
 */
function draw() {
  var ctx = (a canvas context);
  ctx.canvas.width  = window.innerWidth;
  ctx.canvas.height = window.innerHeight;
  //...drawing code...
}

CSS

html, body {
  width:  100%;
  height: 100%;
  margin: 0px;
}

Hasn't had any large negative performance impact for me, so far.


I think this is what should we exactly do: http://www.html5rocks.com/en/tutorials/casestudies/gopherwoord-studios-resizing-html5-games/

function resizeGame() {
    var gameArea = document.getElementById('gameArea');
    var widthToHeight = 4 / 3;
    var newWidth = window.innerWidth;
    var newHeight = window.innerHeight;
    var newWidthToHeight = newWidth / newHeight;

    if (newWidthToHeight > widthToHeight) {
        newWidth = newHeight * widthToHeight;
        gameArea.style.height = newHeight + 'px';
        gameArea.style.width = newWidth + 'px';
    } else {
        newHeight = newWidth / widthToHeight;
        gameArea.style.width = newWidth + 'px';
        gameArea.style.height = newHeight + 'px';
    }

    gameArea.style.marginTop = (-newHeight / 2) + 'px';
    gameArea.style.marginLeft = (-newWidth / 2) + 'px';

    var gameCanvas = document.getElementById('gameCanvas');
    gameCanvas.width = newWidth;
    gameCanvas.height = newHeight;
}

window.addEventListener('resize', resizeGame, false);
window.addEventListener('orientationchange', resizeGame, false);

If you're interested in preserving aspect ratios and doing so in pure CSS (given the aspect ratio) you can do something like below. The key is the padding-bottom on the ::content element that sizes the container element. This is sized relative to its parent's width, which is 100% by default. The ratio specified here has to match up with the ratio of the sizes on the canvas element.

// Javascript

var canvas = document.querySelector('canvas'),
    context = canvas.getContext('2d');

context.fillStyle = '#ff0000';
context.fillRect(500, 200, 200, 200);

context.fillStyle = '#000000';
context.font = '30px serif';
context.fillText('This is some text that should not be distorted, just scaled', 10, 40);
/*CSS*/

.container {
  position: relative; 
  background-color: green;
}

.container::after {
  content: ' ';
  display: block;
  padding: 0 0 50%;
}

.wrapper {
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  bottom: 0;
}

canvas {
  width: 100%;
  height: 100%;
}
<!-- HTML -->

<div class=container>
  <div class=wrapper>
    <canvas width=1200 height=600></canvas>  
  </div>
</div>

If your div completely filled the webpage then you can fill up that div and so have a canvas that fills up the div.

You may find this interesting, as you may need to use a css to use percentage, but, it depends on which browser you are using, and how much it is in agreement with the spec: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#the-canvas-element

The intrinsic dimensions of the canvas element equal the size of the coordinate space, with the numbers interpreted in CSS pixels. However, the element can be sized arbitrarily by a style sheet. During rendering, the image is scaled to fit this layout size.

You may need to get the offsetWidth and height of the div, or get the window height/width and set that as the pixel value.


The following solution worked for me the best. Since I'm relatively new to coding, I like to have visual confirmation that something is working the way I expect it to. I found it at the following site: http://htmlcheats.com/html/resize-the-html5-canvas-dyamically/

Here's the code:

<!DOCTYPE html>

<head>
    <meta charset="utf-8">
    <title>Resize HTML5 canvas dynamically | www.htmlcheats.com</title>
    <style>
    html, body {
      width: 100%;
      height: 100%;
      margin: 0px;
      border: 0;
      overflow: hidden; /*  Disable scrollbars */
      display: block;  /* No floating content on sides */
    }
    </style>
</head>

<body>
    <canvas id='c' style='position:absolute; left:0px; top:0px;'>
    </canvas>

    <script>
    (function() {
        var
        // Obtain a reference to the canvas element using its id.
        htmlCanvas = document.getElementById('c'),
        // Obtain a graphics context on the canvas element for drawing.
        context = htmlCanvas.getContext('2d');

       // Start listening to resize events and draw canvas.
       initialize();

       function initialize() {
           // Register an event listener to call the resizeCanvas() function 
           // each time the window is resized.
           window.addEventListener('resize', resizeCanvas, false);
           // Draw canvas border for the first time.
           resizeCanvas();
        }

        // Display custom canvas. In this case it's a blue, 5 pixel 
        // border that resizes along with the browser window.
        function redraw() {
           context.strokeStyle = 'blue';
           context.lineWidth = '5';
           context.strokeRect(0, 0, window.innerWidth, window.innerHeight);
        }

        // Runs each time the DOM window resize event fires.
        // Resets the canvas dimensions to match window,
        // then draws the new borders accordingly.
        function resizeCanvas() {
            htmlCanvas.width = window.innerWidth;
            htmlCanvas.height = window.innerHeight;
            redraw();
        }
    })();

    </script>
</body> 
</html>

The blue border shows you the edge of the resizing canvas, and is always along the edge of the window, visible on all 4 sides, which was NOT the case for some of the other above answers. Hope it helps.


Unless you want the canvas to upscale your image data automatically (that's what James Black's answer talks about, but it won't look pretty), you have to resize it yourself and redraw the image. Centering a canvas


(function() {

    // get viewport size
    getViewportSize = function() {
        return {
            height: window.innerHeight,
            width:  window.innerWidth
        };
    };

    // update canvas size
    updateSizes = function() {
        var viewportSize = getViewportSize();
        $('#myCanvas').width(viewportSize.width).height(viewportSize.height);
        $('#myCanvas').attr('width', viewportSize.width).attr('height', viewportSize.height);
    };

    // run on load
    updateSizes();

    // handle window resizing
    $(window).on('resize', function() {
        updateSizes();
    });

}());

function resize() {

    var canvas = document.getElementById('game');
    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.style.width = width + 'px';
    canvas.style.height = height + 'px';
};

window.addEventListener('resize', resize, false);




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