canvas - 剪辑到绘制的路径

Question

我正在尝试绘制一条路径，他们将其用作我 Canvas 的蒙版。

'use strict';

var canvas = new fabric.Canvas('c', {
    hoverCursor: 'pointer',
    isDrawingMode: true
});

canvas.freeDrawingBrush = new fabric.PencilBrush(canvas);
canvas.freeDrawingBrush.color = '#000';
canvas.freeDrawingBrush.width = 100;

fabric.Image.fromURL('http://fabricjs.com/assets/pug_small.jpg', function(img) {

    canvas.add(img);
    canvas.setWidth(img.getWidth());
    canvas.setHeight(img.getHeight());
    canvas.centerObject(img);
    img.selectable = false;
});

canvas.on('path:created', function(data) {

    var path = data.path;

    canvas.remove(path);
    canvas.clipTo = function(context) {
        path.render(context);
    };

    canvas.isDrawingMode = false;
    canvas.renderAll();
});

如何使整个路径成为图像的可见区域？

http://jsfiddle.net/db45yhpo/

编辑

这就是我想要实现的目标，但使用的是 FabricJS。

http://www.createjs.com/demos/easeljs/alphamaskreveal

Answer 1

我没有fabricjs的经验，所以可能有更好的处理方法，但我会:
在隐藏的 Canvas 上重绘你的路径，
然后从这个隐藏的 Canvas 创建一个新的 fabric.Image()，
设置其globalCompositeOperation参数为`"destination-atop"，
在原始 Canvas 上绘制它。

var canvas = new fabric.Canvas('c', {
  hoverCursor: 'pointer',
  isDrawingMode: true
});

canvas.freeDrawingBrush = new fabric.PencilBrush(canvas);
canvas.freeDrawingBrush.color = '#000';
canvas.freeDrawingBrush.width = 100;

fabric.Image.fromURL('http://fabricjs.com/assets/pug_small.jpg', function(img) {
  canvas.add(img);
  canvas.setWidth(img.getWidth());
  canvas.setHeight(img.getHeight());
  canvas.centerObject(img);
  img.selectable = false;
});

canvas.on('path:created', function(data) {
  var clipper = document.createElement('canvas');
  clipper.width = canvas.width;
  clipper.height = canvas.height;
  var ctx = clipper.getContext('2d');
  var path = data.path;
  data.path.render(ctx);
  canvas.remove(path);
  canvas.isDrawingMode = false;
  var oImg = new fabric.Image(clipper)
  oImg.globalCompositeOperation = 'destination-atop';
  canvas.add(oImg);
  canvas.renderAll();
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.5.0/fabric.min.js"></script>
<canvas id="c"></canvas>