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11.合成.html
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11.合成.html
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<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<style type="text/css">
canvas{
border:1px solid black;
}
#kno{
width: 500px;
height: auto;
float: left;
font-size: 18px;
}
img{
width: 200px;
height: 200px;
}
</style>
<script type="text/javascript">
window.onload=function(){
//获取元素
var canvas01=document.getElementById("canvas01");
//确定浏览器支持<canvas>元素
if(canvas01.getContext){
//取得上2d下文
var context=canvas01.getContext("2d");
//绘制红色矩形
context.fillStyle="red";
context.fillRect(10,10,100,100);
//修改全局透明度
context.globalAlpha=0.5;
//设置合成操作
context.globalCompositeOperation="destination-over";
//绘制蓝色矩形
context.fillStyle="rgba(0,0,255,1)";
context.fillRect(50,50,100,100);
//重置全局透明度
context.globalAlpha=0;
}
}
</script>
<body>
<!-- canvas元素-->
<canvas id="canvas01" width="200px" height="200px"></canvas>
<!-- 图片资源引入 -->
<img src="./img/img01.jpg" />
<!-- 知识点和问题汇总 -->
<div id="kno">
<b>知识点：</b> <br/>
<strong>1.</strong>两个合成属性：globalAlpha,globalCompositeOperation <br/>
<strong>2.</strong>globalAlpha:表示全局透明度（0~1） <br/>
<strong>3.</strong>globalCompositeOperation：表示后绘制的图形怎样与先绘制的图形结合 <br/>
</div>
</body>
</html>