javascript - 具有两条二次曲线的 Canvas 剪辑图像

Question

我只是想以曲线剪裁图像..但没有发生这种情况.. 仅显示图像，但不显示剪辑。

var canvas = document.getElementById('leaf');
var context = canvas.getContext('2d');

/*
 * save() allows us to save the canvas context before
 * defining the clipping region so that we can return
 * to the default state later on
 */

context.save();
context.beginPath();
context.moveTo(188, 150);
context.quadraticCurveTo(288, 0, 388, 150);
context.lineWidth = 10;
context.quadraticCurveTo(288, 288, 188, 150);
context.lineWidth = 10;

context.clip();

context.beginPath();
var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, 10, 50);
};

imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';

/* context.beginPath();
context.arc(x - offset, y - offset, radius, 0, 2 * Math.PI, false);
context.fillStyle = 'yello';
context.fill();
*/

/*
 * restore() restores the canvas context to its original state
 * before we defined the clipping region
 */

context.restore();
context.beginPath();
context.moveTo(188, 150);
context.quadraticCurveTo(288, 0, 388, 150);
context.lineWidth = 10;
context.quadraticCurveTo(288, 288, 188, 150);
context.lineWidth = 10;

context.strokeStyle = 'blue';
context.stroke();

<canvas id="leaf" width="500" height="500" style='left: 0; 
    position: absolute; top: 0;'></canvas>

Answer 1

您必须从 context.save(); 行移动所有内容至 context.clip();在你的 imgObj 的函数对象中的 onload处理程序:

imageObj.onload = function()
{
    context.save();
    context.beginPath();
    context.moveTo(188, 150);
    context.quadraticCurveTo(288, 0, 388, 150);
    context.lineWidth = 10;
    context.quadraticCurveTo(288, 288, 188, 150);
    context.lineWidth = 10;
    context.clip();
    context.drawImage(imageObj, 10, 50);
};

参见 http://jsfiddle.net/CSkP6/1/举个例子。