带回调函数的Canvas刮奖刮刮卡JQuery插件，支持移动端PC端

Scratch.js 插件 看不懂暂时不管，把代码复制下去，名为为Scratch.js的文件。

var Scratch = (function () {

    /**
     * Merge properties between two objects
     * @param obj1
     * @param obj2
     * @returns {{}}
     */
  function mergeOptions(obj1, obj2){
    var obj3 = {};
    for (var key in obj1) { obj3[key] = obj1[key]; }
    for (var key in obj2) { obj3[key] = obj2[key]; }
    return obj3;
  }

    /**
     * Generate a random number
     * @param min
     * @param max
     * @returns {Number}
     */
  function randomPoint(min, max) {
    var random = Math.abs(Math.random()*(max - min) + min);
    return random = parseInt(random.toFixed(0), 10);
  }

    /**
     * Scratch constructor
     * @param options
     * @constructor
     */
    var Scratch = function(options) {
        this.cursor = {
            png: '', // Modern browsers
            cur: '', // for IE
                x: 0,
                y: 0,
                default: 'auto'
        };
        this.pointSize = {
            x: 5,
            y: 5
        };
    this.defaults = {
        canvasId: '', // Canvas id
      imageBackground: '', // Path [src]
      pictureOver: '', // Path [src]
            cursor: this.cursor, // Custom pointer
      sceneWidth: 250, // Canvas width
      sceneHeight: 250, // Canvas height
      radius: 40, // Radius of scratch zone
      nPoints: 10, // n points for clear canvas
            pointSize: this.pointSize,
            percent: null,
            callback: null
    };

    this.options = mergeOptions(this.defaults, options);
    this.options.cursor = mergeOptions(this.cursor, options.cursor);
    this.options.pointSize = mergeOptions(this.pointSize, options.pointSize);

    // init Scratch
        this.init();
    };

    Scratch.prototype.init = function () {
        var _this = this; // Save the "this" :)
        this.canvas = document.getElementById(this.options.canvasId);
        this.ctx = this.canvas.getContext('2d');
        this.canvas.width = this.options.sceneWidth;
        this.canvas.height = this.options.sceneHeight;
        this.image = new Image();
        this.image.src = this.options.pictureOver;
        this.percent = 0;
        this.zone = null;
        this.pixelRatio = window.devicePixelRatio;

        // Set background after draw the canvas
        this.setBackground();
        this.setCursor();

        var scratchMove = function(e) {
            e.preventDefault();
            _this.scratch(e);
      var clear = _this.clear();
      if (clear) {
        _this.canvas.style.pointerEvents = 'none';
        _this.callback(_this.options.callback);
      }
        };

        window.addEventListener('resize', function() {
            _this.update();
            // Resize the canvas
            _this.redraw();
        });

        window.addEventListener('scroll', function() {
            _this.update();
        });

        // Mouse & Touch events
        this.canvas.addEventListener('mousedown', function(e) {
            _this.canvas.addEventListener('mousemove', scratchMove);

      document.body.addEventListener('mouseup', function _func() {
        _this.canvas.removeEventListener('mousemove', scratchMove);
        this.removeEventListener('mouseup', _func);
      });
        });

        this.canvas.addEventListener('touchstart', function(e) {
            _this.canvas.addEventListener('touchmove', scratchMove);

      document.body.addEventListener('touchend', function _func() {
        _this.canvas.removeEventListener('touchmove', scratchMove);
        this.removeEventListener('touchend', _func);
      });
        });

    };

    Scratch.prototype.setCursor = function() {
        var string = '';

    if (document.documentElement.classList.contains('is-ie') || navigator.userAgent.indexOf('Trident') != -1 || navigator.userAgent.indexOf('Edge') != -1) {
      string += 'url(' + this.options.cursor.cur + '), auto';
    } else {
      string += 'url(' + this.options.cursor.png + ') ' + this.options.cursor.x + ' ' + this.options.cursor.y + ', pointer';
    }

        this.canvas.setAttribute('style', 'cursor:' + string + ';');
    };

    // Update positions etc
    Scratch.prototype.update = function() {
        this.zone = this.canvas.getBoundingClientRect();
    };

    Scratch.prototype.redraw = function () {
        var oldWidth = this.options.sceneWidth;
        var newWidth = this.zone.width;
        if(newWidth < oldWidth) {
            this.ctx.clearRect(0, 0, this.zone.width, this.zone.height);
            this.canvas.width = this.zone.width;
            this.canvas.height = this.zone.height;
            this.ctx.drawImage(this.image, 0, 0, this.zone.width, this.zone.height);
        }
    };

    Scratch.prototype.setBackground = function() {
        var _this = this;
        this.image.onload = function() {
            _this.zone = _this.canvas.getBoundingClientRect();
            // Draw image
            _this.ctx.drawImage(this, 0, 0);
            // When the canvas have been drawn
            var IMG = document.createElement('img');
            IMG.classList.add('scratch_picture-under');
            IMG.src = _this.options.imageBackground;
            _this.canvas.parentElement.insertBefore(IMG, _this.canvas);
        };
    };

    Scratch.prototype.clearPoint = function (x1, y1) {
     var radius = this.options.radius;
     var x = Math.random() * 2 * radius - radius;
     var ylim = Math.sqrt(radius * radius - x * x);
     var y = Math.random() * 2 * ylim - ylim;
     x += radius;
     y += radius;

     x = parseInt(x, 10);
     y = parseInt(y, 10);

     return {
         x: x + x1,
         y: y + y1
     }

    };

    Scratch.prototype.getPosition = function(e) {
        var posX, posY;
        switch (e.type) {
            case 'touchmove':
                posX = e.touches[0].clientX - this.options.radius - window.pageXOffset;
                posY = e.touches[0].clientY - this.options.radius - window.pageYOffset;
                break;
            case 'mousemove':
                posX = e.clientX - this.options.radius - window.pageXOffset;
                posY = e.clientY - this.options.radius - window.pageYOffset;
                break;
        }

        return {
            x: posX,
            y: posY
        }
    };

    Scratch.prototype.scratch = function(e) {
        var position = this.getPosition(e);
        var x = position.x - this.zone.left;
        var y = position.y - this.zone.top + window.pageYOffset;
        var i = 0;
        var len = this.options.nPoints;

        for(i; ivar points = this.clearPoint(x, y);
            this.ctx.clearRect(points.x, points.y, this.options.pointSize.x, this.options.pointSize.y);
        }
        this.percent = this.getPercent();
    };

    Scratch.prototype.getPercent = function() {
        var percent;
      var counter = 0; // number of pixels clear
        var imageData = this.ctx.getImageData(0, 0, this.canvas.width, this.canvas.height);
        var imageDataLength = imageData.data.length;

        for(var i = 0; i < imageDataLength; i += 4) {
      if (imageData.data[i] === 0 && imageData.data[i+1] === 0 && imageData.data[i+2] === 0 && imageData.data[i+3] === 0) {
        counter++;
      }
        }

        if (counter >= 1) {
            percent = (counter / (this.canvas.width * this.canvas.height)) * 100;
        } else {
            percent = 0;
        }
        return percent;
    };

    Scratch.prototype.clear = function() {
        if (this.percent >= this.options.percent) {
            this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
          return true;
        }
    };

    Scratch.prototype.callback = function(callback) {
        if (callback != null && this.percent >= this.options.percent) {
            callback();
        }
    };

    return Scratch;
})();

使用方法
在页面中引入Scratch.js文件。例如：

<script type="text/javascript" src="js/Scratch.js">script>       

HTML结构
使用下面的HTML结构来制作一个刮刮卡：

<div class="scratch_container">
  <div class="scratch_viewport">
    
    <canvas id="js-scratch-canvas">canvas>
  div>
div>   

CSS样式
为刮刮卡添加下面的CSS样式。

.scratch_container {
  position: relative;
  margin: 0 auto;
  max-width: 1024px;
}

.scratch_viewport {
  position: relative;
  width: 250px;
  height: 250px;
  margin: 0 auto;
  z-index: 0;
}

.scratch_picture-under {
  position: absolute;
  top: 0;
  left: 0;
  display: block;
  z-index: -1;
}

.scratch_container canvas {
  position: relative;
  width: 100%;
  height: auto;
  z-index: 1;
}                   

初始化插件
在页面页面底部标记结束之前，使用下面的代码来实例化一个刮刮卡对象。


var scratch = new Scratch({
canvasId: 'js-scratch-canvas',
imageBackground: 'loose.jpg',
pictureOver: 'foreground.jpg',
cursor: {
png: 'piece.png',
cur: 'piece.cur',
x: '20',
y: '17'
},
radius: 20,
nPoints: 100,
percent: 50,
callback: function () {
alert('I am Callback.');
},
pointSize: { x: 3, y: 3}
});
重点内容

配置参数
该Canvas刮刮卡插件的可用配置参数有：
canvasId：canvas的id。
imageBackground：背景图片（刮开后呈现的图片）。
pictureOver：前景图片。
sceneWidth：canvas的宽度。
sceneHeight：canvas的高度。
radius：清除区域的半径。
nPoints：清除区域的杂点数量。
percent：在清除多少区域之后清空canvas。
cursor：光标。
png：png格式的光标。
x：Move position x。
y：Move position y。
cur：cur格式的光标（IE使用）。

本文出自：http://www.htmleaf.com/html5/html5-canvas/201610064070.html
本文只为传播分享技术，版权归原作者所有。