<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<canvas id="canvas" style="margin:0 auto;border:1px #ddd solid">
The current browser does not support Canvas, can replace the browser a try!
</canvas>
<script>
window.onload = function(){
var canvas = document.getElementById('canvas');
canvas.width = 1024;
canvas.height = 768;
if(canvas.getContext('2d')){
var context = canvas.getContext('2d');
context.fillStyle = "blue";
context.fillRect(100,200,400,400);
context.globalCompositeOperation = "sourse-over";
context.fillStyle = "red";
context.beginPath();
context.moveTo(400,300);
context.lineTo(650,700);
context.lineTo(150,700);
context.closePath();
context.fill();
}else{
alert('当前游览器不支持Canvas，请更换游览器后再试！');
}
}
</script>
</body>
<script>
/*global
globalAlpha
globalCompositeOperation = "source-over"(default)
sourse-atop
sourse-in
sourse-out
destination-over //前面绘制的覆盖了后面绘制的图形
destination-atop
destination-in
destination-out
lighter
copy
xor
*/
</script>
</html>
