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我想（我已经完成了1-3）：

  1. 从页面抓取图像
  2. 将其添加到画布元素
  3. 将图像剪辑到蒙版
  4. 在图像周围移动（动画）蒙版

我已经完成了前 3 个，但不知道如何移动面具。请帮忙！

// get the canvas
var canvas = document.getElementById('c');
var context = canvas.getContext('2d');  

// get a div from the page
var stuff = document.getElementsByName('testElem')[0];

// add a class to the div
stuff.setAttribute('class', 'pleaseWork');
var newImage = new Image();

// get the background image of the div
var bgClass = document.getElementsByClassName('pleaseWork')[0].style.backgroundImage;

  var x = canvas.width / 2;
  var y = canvas.height / 2;
  var radius = 75;
  var offset = 50;  

  // clip the context to create a circular clipping mask
  context.save();
  context.beginPath();
  context.arc(x, y, radius, 0, 2 * Math.PI, false);
  context.clip();

// on load put the image into the clipping mask
newImage.onload = function () {
    context.drawImage(newImage,0,0);
}

// put the background image from the div into the canvas (without the url())
newImage.src = bgClass.replace(/^url|[\(\)]/g, '');

如何从画布上移动（动画）剪切蒙版以显示剪切图像的不同部分？

感谢您的任何想法！

4

1 回答 1

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您可以将剪辑+绘图代码放在一个函数中，并在动画循环中调用该函数：

示例代码和演示：http: //jsfiddle.net/m1erickson/07mzbat9/

绘图功能：

function draw(){

    // clear the canvas
    ctx.clearRect(0,0,cw,ch);

    // save the unclipped context
    ctx.save();

    // draw a circular path
    ctx.beginPath();
    ctx.arc(cx,cy,radius,0,PI2);
    ctx.closePath();
    ctx.stroke();

    // create a clipping path from the circular path
    // use the clipping path to restrict drawing 
    ctx.clip();
    ctx.drawImage(img,0,0);

    // restore the unclipped context (to remove clip)
    ctx.restore();
}

动画循环：

var cw=canvas.width;
var ch=canvas.height;
var cx=50;
var cy=50;
var radius=35;
var PI2=Math.PI*2;

// animate the mask across the canvas
function animate(time){
    if(cx-radius>cw || cy-radius>ch){return;}
    requestAnimationFrame(animate);
    cx+=0.2;
    cy+=0.2;
    draw();
}
于 2014-09-02T18:24:48.267 回答