How do I markup a page with an HTML5 canvas such that the canvas
1.) Takes up 80% of the width
2.) Has a corresponding pixel height and width which effectively define the ratio (and are proportionally maintained when the canvas is stretched to 80%)
3.) Is centered both vertically and horizontally
You can assume that the canvas is the only thing on the page, but feel free to encapsulate it in s if necessary.
Given that canvas is nothing without JavaScript, use JavaScript too for sizing and positionning (you know: onresize, position:absolute, etc.)
Tested only on Firefox:
<script>
window.onload = window.onresize = function() {
var C = 0.8; // canvas width to viewport width ratio
var W_TO_H = 2/1; // canvas width to canvas height ratio
var el = document.getElementById("a");
// For IE compatibility http://www.google.com/search?q=get+viewport+size+js
var viewportWidth = window.innerWidth;
var viewportHeight = window.innerHeight;
var canvasWidth = viewportWidth * C;
var canvasHeight = canvasWidth / W_TO_H;
el.style.position = "fixed";
el.setAttribute("width", canvasWidth);
el.setAttribute("height", canvasHeight);
el.style.top = (viewportHeight - canvasHeight) / 2;
el.style.left = (viewportWidth - canvasWidth) / 2;
window.ctx = el.getContext("2d");
ctx.clearRect(0,0,canvasWidth,canvasHeight);
ctx.fillStyle = 'yellow';
ctx.moveTo(0, canvasHeight/2);
ctx.lineTo(canvasWidth/2, 0);
ctx.lineTo(canvasWidth, canvasHeight/2);
ctx.lineTo(canvasWidth/2, canvasHeight);
ctx.lineTo(0, canvasHeight/2);
ctx.fill()
}
</script>
<body>
<canvas id="a" style="background: black">
</canvas>
</body>
Wrapping it with div should work. I tested it in Firefox, Chrome on Fedora 13.
<style type="text/css">
#content {
width: 95%;
height: 95%;
margin: auto;
}
#myCanvas {
width: 100%;
height: 100%;
border: 1px solid black;
}
</style>
And the canvas should be enclosed in tag
<div id="content">
<canvas id="myCanvas">Your browser doesnt support canvas tag</canvas>
</div>
Let me know if it works. Cheers.