js+html5实现canvas绘制椭圆形图案的方法

核心实现步骤与代码示例

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>测试颜色背景</title>
<script>
var ticker=0;
var col = new Array("#000000","#A52A2A","#B8860B","pink","green","yellow","red","orange","#BB008B","#8B0000");
 
function drawBackground(){
var canvasHide=document.getElementById("hide"); //隐藏的画布
var g=canvasHide.getContext("2d"); //找出隐藏画布 hide 的画笔 g 
g.clearRect(0,0,1200,800); //清理隐藏画布
var i=0;
do { //画 不同颜色 依次同心发散的园
g.beginPath();
var grd=g.createRadialGradient(300,300,300-i*25, 300,300,265-i*25);
grd.addColorStop(0,col[(0+i+ticker)%col.length]);
grd.addColorStop(1,col[(1+i+ticker)%col.length]);
g.fillStyle=grd;
g.arc(300,300,300-i*25,0,2*Math.PI);
g.fill();
i++;
} while(i<11);
 
//找出显式画布 myCanvas 的画笔 gg 
var gg=document.getElementById("myCanvas").getContext("2d");
gg.clearRect(0,0,myCanvas.width,myCanvas.height); //清理显式画布
 
/* 将隐式画布 hide 的园形图像，
 * 以 宽 600, 高 300 的比例,
 * 画到显式画布 myCanvas,
 * 结果，隐式画布 hide 的园形图像，在显式画布 myCanvas 上 成了椭圆
 */
gg.drawImage(canvasHide,0,0,600,300); 
ticker++;
}
 
function preperation(){
setInterval('drawBackground()',1000);
 }
</script>
<style>
#myCanvas{
 position:absolute;
 left:0px;
 top:0px;
}
#hide{
 display:none;
}
</style>
</head>
 
<body onLoad="preperation()">
<canvas id="myCanvas" width="600" height="400" ></canvas>
<canvas id="hide" width="600" height="600" ></canvas>
 
</body>
</html>