HTML5 canvas height and width 100% distorts the game animation

I am not sure, how i can be more specific, but i am putting my best effort to explain it.I am trying to understand, what should i be looking for to be more specific, so this is all i have got at this moment.

I was exploring HTML5 JavaScript games, and I noticed, that making the canvas height and width 100% distorts the animation within. a simple example that i got from here. If i change the canvas size to 100% (in the example I have provided) it breaks the animation of the game(for example the asteroid).

I would like to know, which property of HTML5 is responsible for this behaviour and what should I be looking for to get the HTML5 animation fit the complete screen size?

EDIT
I tried to run cordova to build the game to native platform,but the 1st problem i am encountering is that the canvas was not fitting the screen size. (that’s why i wanted it to completely fit the browser screen, but i see a complete misfit when a canvas made for the browser screen is rendered to the native using cordova).
I explored phaser, about how they are solving this problem, and found this game which is using something called a ScalingManager.
So, my questions are
1. What is scaling a Game?
2. How is the scaling-manager of phaser working
3. without using the scaling manager why will a game not fit the moile screen size even though the canvas height and width are properly mentioned?
4. is there a small experment (without using any phaser or similar javascript game framework) that i can do to understand the need for scaling with simple HTML5 javasctipt and cordova?

Answer

A canvas has two distinct sizes:

the size of the element on the page
the size in pixel of the canvas

To avoid distortion and get a pixel-perfect graphic you need to ensure they end up equal… for example:

function redraw() {
    canvas.width = canvas.offsetWidth;
    canvas.height = canvas.offsetHeight;
    ...
}

For single-page HTML games where you just want to draw everything in a canvas a simple approach is:

<!DOCTYPE html>
<html>
  <head>
    <style type='text/css'>
       * {
          margin: 0;
          padding: 0;
          border: none;
       }

       body,html {
          height: 100%;
          width: 100%;
       }

    </style>
  </head>
  <body>
    <script>
        var canvas = document.createElement('canvas');
        canvas.style.position = 'absolute';
        var body = document.body;
        body.insertBefore(canvas, body.firstChild);
        var context = canvas.getContext('2d');

        var devicePixelRatio = window.devicePixelRatio || 1;
        var backingStoreRatio = context.webkitBackingStorePixelRatio
            || context.mozBackingStorePixelRatio || context.msBackingStorePixelRatio
            || context.oBackingStorePixelRatio || context.backingStorePixelRatio || 1;
         var ratio = devicePixelRatio / backingStoreRatio;

        redraw();
        window.addEventListener('resize', redraw, false);
        window.addEventListener('orientationchange', redraw, false);
        function redraw() {
            width = (window.innerWidth > 0 ? window.innerWidth : screen.width);
            height = (window.innerHeight > 0 ? window.innerHeight : screen.height);
            canvas.style.width = width + 'px';
            canvas.style.height = height + 'px';
            width *= ratio;
            height *= ratio;

            if (canvas.width === width && canvas.height === height) {
              return;
            }

            canvas.width = width;
            canvas.height = height;
        }
        //draw things
    </script>
  </body>
</html>

You will also need to check for changes in innerWidth / innerHeight if your app has parts in which you’re just waiting for user interaction (not looping on calling redraw) and the user instead resizes the browser window or tilts the phone/tab.

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Answer