jCanvas上的globalCompositeOperation

时间:2013-01-30 20:20:44

标签: javascript jquery canvas jcanvas globalcompositeoperation

如何将globalCompositeOperation(或任何其他会给我'multiply'颜色操作的插件)集成到jCanvas jQuery插件中?

// How do I get this working? //
var ctx = document.getElementById('canvas').getContext('2d');
ctx.globalCompositeOperation = 'darker';

// With this - //
$("canvas").drawArc({
  fillStyle: "#c7302a",
  x: 100, y: 100,
  radius: 50
});

$("canvas").drawArc({
  fillStyle: "#395797",
  x: 170, y: 100,
  radius: 50,
  opacity: 1
});

2 个答案:

答案 0 :(得分:2)

对于记录,jCanvas有一个compositing属性,其值映射到ctx.globalCompositeOperation

$("canvas").drawArc({
  fillStyle: "#c7302a",
  x: 100, y: 100,
  radius: 50,
  compositing: 'darker'
});

-Caleb

答案 1 :(得分:1)

好的,我解决了。经过几个小时的努力,这太简单了: 我使用了context blender插件。

JS代码:

$("#canvasReal").drawArc({ // Draw on the real canvas
  fillStyle: "#c7302a",
  x: 100, y: 100,
  radius: 50
});

$("#canvasOff").drawArc({ // Draw on the off screen canvas
  fillStyle: "#395797",
  x: 150, y: 100,
  radius: 50
});

// Blend off-screen canvas onto the real canvas
    var over = canvasOff.getContext('2d'); 
    var under = canvasReal.getContext('2d');
    over.blendOnto(under,'multiply'); 

HTML code:

<canvas width="500" height="250" id="canvasReal"></canvas>
<canvas width="500" height="250"id="canvasOff" style="display:none;"></canvas>