canvas之刮刮乐

效果图:

代码:

  1 <!DOCTYPE html>
  2 <html lang="en">
  3 
  4 <head>
  5     <meta charset="UTF-8">
  6     <meta name="viewport" content="width=device-width, initial-scale=1.0">
  7     <meta http-equiv="X-UA-Compatible" content="ie=edge">
  8     <title>刮刮乐</title>
  9     <style>
 10         .canvasBox {
 11              400px;
 12             height: 200px;
 13             margin: 100px auto;
 14         }
 15 
 16         #canvas1 {
 17             background-repeat: no-repeat;
 18             background-position: center;
 19             background-size: 300px 180px;
 20         }
 21     </style>
 22 </head>
 23 
 24 <body>
 25     <div class="canvasBox">
 26         <canvas width="400" height=200 id="canvas1"></canvas>
 27     </div>
 28     <script>
 29         var oCanvas = document.getElementById('canvas1');
 30         var ctx = oCanvas.getContext('2d');
 31         var w = oCanvas.width;
 32         var h = oCanvas.height;
 33         var lastPoint = {};
 34         var nowPoint = {};
 35         var lastPointX, lastPointY;
 36         var nowPointX, nowPointY;
 37 
 38         function init() {
 39             ctx.fillStyle = '#ccc';
 40             ctx.fillRect(0, 0, w, h);
 41 
 42             var r = Math.random(),
 43                 oImg = new Image();
 44 
 45             if (r < 0.5) {
 46                 oImg.src = './1.png';
 47             } else {
 48                 oImg.src = './2.jpg';
 49             }
 50             oImg.onload = function () {
 51                 oCanvas.style.backgroundImage = 'url(' + oImg.src + ')';
 52                 ctx.globalCompositeOperation = 'destination-out';
 53                 document.addEventListener('mousedown', downFun, false);
 54             }
 55         }
 56         init();
 57 
 58         function downFun(e) {
 59             lastPointX = e.clientX - oCanvas.offsetLeft;
 60             lastPointY = e.clientY - oCanvas.offsetTop;
 61             oCanvas.addEventListener('mousemove', moveFun, false);
 62             document.addEventListener('mouseup', upFun, false);
 63         }
 64 
 65         function moveFun(e) {
 66             nowPointX = e.clientX - oCanvas.offsetLeft;
 67             nowPointY = e.clientY - oCanvas.offsetTop;
 68 
 69             ctx.beginPath();
 70             ctx.fillStyle = 'transpatent';
 71 
 72             ctx.lineWidth = 20;
 73             ctx.moveTo(lastPointX, lastPointY);
 74             ctx.lineTo(nowPointX, nowPointY);
 75             ctx.stroke();
 76 
 77             ctx.arc(nowPointX, nowPointY, 10, 0, Math.PI * 2, 0);
 78             ctx.closePath();
 79             ctx.fill();
 80 
 81             lastPointX = nowPointX;
 82             lastPointY = nowPointY;
 83         }
 84 
 85         function upFun() {
 86             oCanvas.removeEventListener('mousemove', moveFun, false);
 87             document.removeEventListener('mouseup', upFun, false);
 88             clearAll();
 89         }
 90 
 91         function clearAll() {
 92             var d = ctx.getImageData(0, 0, w, h),
 93                 c = 0,
 94                 len = d.data.length;
 95             for (var i = 0; i < len; i += 4) {
 96                 if (d.data[i] === 0) {
 97                     c++;
 98                 }
 99             }
100             if (c > w * h * 0.7) {
101                 ctx.clearRect(0, 0, w, h);
102             }
103         }
104     </script>
105 </body>
106 
107 </html>

一开始鼠标滑动太快会导致两点之间产生空白,后面通过记录鼠标移动前后两点的位置,使用stroke画线即可

 ctx.lineWidth = 20;
 ctx.moveTo(lastPointX, lastPointY);
 ctx.lineTo(nowPointX, nowPointY);
 ctx.stroke();
当刮开一定的面积时就自动全部展示出来

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原文地址：https://www.cnblogs.com/freefy/p/9359448.html