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【HTML5】Canvas之globalCompositeOperation属性详解

globalCompositeOperation即Canvas中的合成操作。

1、source-over

这是默认值，他表示绘制的图形将画在现有画布之上

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="source-over"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

2、destination-over

这个操作的值与前一个值相反，所以现在目标绘制在源之上

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="destination-over"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

3、source-atop

这个操作会将源绘制在目标之上，但是在重叠区域上两者都是不透明的。绘制在其他位置的目标是不透明的，但源是透明的。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="source-atop"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

4、destination-atop

这个操作与source-atop相反，目标绘制在源之上

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="destination-atop"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

5、source-in

在源于目标重叠的区域只绘制源，而不重叠的部分编程透明的。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="source-in"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

6、destination-in

这个操作与source-in相反，在源于目标重叠的区域保留目标。而不重叠的部分都变成透明的。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="destination-in"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

7、source-out

在与目标不重叠的区域上绘制源，其他部分都变成透明的。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="source-out"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

8、destination-out

在与源不重叠的区域上保留目标。其他部分都变成透明的。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="destination-out"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

9、lighter

这个值与顺序无关，如果源与目标重叠，就将两者的颜色值相加。得到的颜色值的最大取值为255。如下例中，红色的rgb值为rgb（255,0,0），绿色的rgb值为rgb（0,128,0），两者相加为rgb（255,128,0），即为图中橘色。如果一个rgb值为rgb（63,169,245），另一个rgb值为rgb（255,123,172），两者相加取最大值255，即rgb（255,255,255）为白色。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="lighter"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

10、copy

这个值与顺序无关，只绘制源，覆盖掉目标。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="copy"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

11、xor

这个值与顺序无关，只绘制出不重叠的源与目标区域。所有重叠的部分都变成透明的

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script type="text/javascript" src="http://www.jq22.com/jquery/jquery-2.1.1.js"></script>
        <script type="text/javascript">
        $(document).ready(function(){
            var canvas=document.getElementById("myCanvas");
            var context=canvas.getContext("2d");
            context.fillStyle="red";
            context.fillRect(50,50,100,100);
            context.globalCompositeOperation="xor"
            context.fillStyle="green";
            context.fillRect(100,100,100,100);
        });
        </script>
    </head>
    <body>
        <canvas id="myCanvas" width="1000" height="1000"></canvas>
    </body>
</html>

注：图中“看不见的区域”为透明的源。

参考网站：https://blog.csdn.net/laijieyao/article/details/41862473

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原文地址：https://www.cnblogs.com/jmwlhj/p/9579000.html