Table of Contents
定义和用法
浏览器支持
属性值
Home Web Front-end HTML Tutorial html5中 canvas标签中 2d上下文 globalCompositeOperation属性 - MythMan

html5中 canvas标签中 2d上下文 globalCompositeOperation属性 - MythMan

May 20, 2016 pm 01:49 PM

定义和用法

     globalCompositeOperation 属性设置或返回如何将一个源(新的)图像绘制到目标(已有)的图像上。

 

例:

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;">var</span> c=document.getElementById("myCanvas"<span style="color: #000000;">);
</span><span style="color: #008080;"> 2</span> <span style="color: #0000ff;">var</span> ctx=c.getContext("2d"<span style="color: #000000;">);
</span><span style="color: #008080;"> 3</span> 
<span style="color: #008080;"> 4</span> ctx.fillStyle="red"<span style="color: #000000;">;
</span><span style="color: #008080;"> 5</span> ctx.fillRect(20,20,75,50<span style="color: #000000;">);
</span><span style="color: #008080;"> 6</span><span style="color: #ff0000;"> ctx.globalCompositeOperation="source-over";
</span><span style="color: #008080;"> 7</span> ctx.fillStyle="blue"<span style="color: #000000;">;
</span><span style="color: #008080;"> 8</span> ctx.fillRect(50,50,75,50<span style="color: #000000;">);
</span><span style="color: #008080;"> 9</span> 
<span style="color: #008080;">10</span> ctx.fillStyle="red"<span style="color: #000000;">;
</span><span style="color: #008080;">11</span> ctx.fillRect(150,20,75,50<span style="color: #000000;">);
</span><span style="color: #008080;">12</span> <span style="color: #ff0000;">ctx.globalCompositeOperation="destination-over";
</span><span style="color: #008080;">13</span> ctx.fillStyle="blue"<span style="color: #000000;">;
</span><span style="color: #008080;">14</span> ctx.fillRect(180,50,75,50);
Copy after login

 

浏览器支持

Internet Explorer 9、Firefox、Opera、Chrome 以及 Safari 支持 globalCompositeOperation 属性。

注释:Internet Explorer 8 以及更早的版本不支持 元素。

属性值

蓝色:源图像 = 您打算放置到画布上的绘图。

红色:目标图像 = 您已经放置在画布上的绘图。

1.source-over  默认。在目标图像上显示源图像。
2.source-in  在目标图像中显示源图像。只有目标图像内的源图像部分会显示,目标图像是透明的。

 

3.source-out 在目标图像之外显示源图像。只会显示目标图像之外源图像部分,目标图像是透明的。


4.source-atop 在目标图像顶部显示源图像。源图像位于目标图像之外的部分是不可见的。

5.destination-over 在源图像上方显示目标图像。

6.destination-atop 在源图像顶部显示目标图像。源图像之外的目标图像部分不会被显示。

7.destination-in 在源图像中显示目标图像。只有源图像内的目标图像部分会被显示,源图像是透明的。

8.destination-out 在源图像外显示目标图像。只有源图像外的目标图像部分会被显示,源图像是透明的。

9.lighter 显示源图像 + 目标图像。

10.copy 显示源图像。忽略目标图像。

 

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