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canvas 图形的组合方式

2017-12-28  本文已影响219人  雅玲哑铃

一、所有组合方式概览

globalCompositeOperation 的所有属性值

source-over 默认。在目标图像上(先画的)显示源图像(后画的)
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。
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。
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。
destination-over 在源图像上方显示目标图像。
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。
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
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。
lighter 显示源图像 + 目标图像。
copy 显示源图像。忽略目标图像。
source-over 使用异或操作对源图像与目标图像进行组合。

我们先解释一下目标图和原图你就明白表格中的内容了

目标图：先画在画布上的图形
原图 ：后画在画布上的图形

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "source-over";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

通俗的说：先画的上面显示后画的

source-over.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "source-atop";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

通俗的说：在先画的上面显示后画的，但是后画的在先画的图形区域之外的隐藏

source-atop.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "source-in";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

通俗的说：在先画的上面显示后画的，但是只有先画的图形内的后画图形才显示，其他都隐藏

source-in.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "source-out";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

只显示先画的图形之外的后画图像

source-out.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "destination-over";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

先画的在上面，后画的在下面

destination-over.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "destination-atop";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

后画的图形之外的先画的图形都不会被显示

destination-atop.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "destination-in";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

只有后画的图形上面的先画的图形才被显示

destination-in.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "destination-out";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

只有后画的图形之外的先画的图形才被显示

destination-out.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "lighter";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

先画的+后画的，并且重叠部分颜色不同

lighter.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "copy";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

只显示后画的，忽略先画的

copy.png 
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            canvas{
                border:1px solid red;
            }
        </style>
    </head>
    <body>
        <canvas id="mycanvas" width="800" height="800"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById("mycanvas");
        var context = canvas.getContext("2d");
        //目标图：先画在画布上的图形，
        context.beginPath();
        context.arc(100,100,100,0,Math.PI*2);
        context.fillStyle = "palevioletred";
        context.fill();
        context.globalCompositeOperation = "source-over";
        //原图：后画在画布上的图形
        context.beginPath();
        context.fillStyle = "deepskyblue";
        context.fillRect(50,50,200,200);
        context.fill();
    </script>
</html>

使用异或操作对源图像与目标图像进行组合。

source-over.png

最后我们说一下，我们的 context.globalCompositeOperation 语句最好写在画两个图形的中间，也可以写在上面，不能两个图形的后面

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