<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<style>
#buttons{width: 1200px;margin: 10px auto;clear:both;}
#buttons a{font-size: 18px;display: block;float:left;margin-right: 14px;}
</style>
<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>
<div id="buttons">
<a href="">source-over</a>
<a href="">source-atop</a>
<a href="">source-in</a>
<a href="">source-out</a>
<a href="">destination-over</a>
<a href="">destination-atop</a>
<a href="">destination-in</a>
<a href="">destination-out</a>
<a href="">lighter</a>
<a href="">copy</a>
<a href="">xor</a>
</div>
<script>
window.onload = function(){
draw("source-over");
var buttons = document.getElementById("buttons").getElementsByTagName("a");
for(var i=0;i<buttons.length;i++){
buttons[i].onclick = function(){
draw(this.text);
return false;
}
}
}
function draw(compositeStyle){
var canvas = document.getElementById('canvas');
canvas.width = 1024;
canvas.height = 768;
if(canvas.getContext('2d')){
var context = canvas.getContext('2d');
context.clearRect(0,0,canvas.width,canvas.height);
// draw title
context.font = "bold 40 Arial";
context.textAlign = "center";
context.textBaseline = "#058";
context.fillStyle = "#058";
context.fillText("globalCompositeOperation =" + compositeStyle,canvas.width/2,60);
// draw a rect
context.fillStyle = "blue";
context.fillRect(300,150,500,500);
// draw a triangle
context.globalCompositeOperation = compositeStyle;
context.fillStyle = "red";
context.beginPath();
context.moveTo(700,250);
context.lineTo(1000,750);
context.lineTo(400,750);
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>
