html5 canvas简单的直线路径

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>简单直线路径</title>
<script src="js/modernizr.js"></script>
</head>

<body>
<script type="text/javascript">
window.addEventListener('load',eventWindowLoaded,false);
function eventWindowLoaded(){
	canvasApp();
}
function canvasSupport(){
	return Modernizr.canvas;
}
function canvasApp(){
	if(!canvasSupport()){
		return;
	}else{
		var theCanvas = document.getElementById('canvas')
		var context = theCanvas.getContext("2d")

	}
	drawScreen();
    function drawScreen(){
	context.strokeStyle='#ff00ff'    
	context.lineWidth=10;
        context.lineGap='square';
        context.beginPath();
        context.moveTo(20,0);
        context.lineTo(100,0);
        context.stroke();
        context.closePath();
}
	
}


</script>
<canvas id="canvas" width="500" height="500">
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</canvas>
</body>
</html>

写到这篇的时候莫名有种大学里面上计算图形学第一张如何画一个直线（DDA算法）

设直线通过点