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   源码介绍

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1. 基于JQuery设计,实现图层动态刮卡效果，兼容手机浏览器。

<script>
    (function(bodyStyle) {
        bodyStyle.mozUserSelect = 'none';
        bodyStyle.webkitUserSelect = 'none';

        var img = new Image();
        var canvas = document.querySelector('canvas');
        canvas.style.backgroundColor='transparent';
        canvas.style.position = 'absolute';

        img.addEventListener('load', function(e) {
            var ctx;
            var w = img.width,
                h = img.height;
            var offsetX = canvas.offsetLeft,
                offsetY = canvas.offsetTop;
            var mousedown = false;

            function layer(ctx) {
                ctx.fillStyle = 'gray';
                ctx.fillRect(0, 0, w, h);
            }

            function eventDown(e){
                e.preventDefault();
                mousedown=true;
            }

            function eventUp(e){
                e.preventDefault();
                mousedown = false;
                var data=ctx.getImageData(0,0,w,h).data;
                for(var i=0,j=0;i<data.length;i =4){
                    if(data[i] && data[i 1] && data[i 2] && data[i 3]){
                        j ;
                    }
                }
                if(j<=w*h*0.5){
                    alert('ok');
                }
            }

            function eventMove(e){
                e.preventDefault();
                if(mousedown) {
                    if(e.changedTouches){
                        e=e.changedTouches[e.changedTouches.length-1];
                    }
                    var x = (e.clientX document.body.scrollLeft || touch.pageX) - offsetX || 0,
                        y = (e.clientY document.body.scrollTop || touch.pageY) - offsetY || 0;
                    with(ctx) {
                        beginPath()
                        arc(x, y, 5, 0, Math.PI * 2);
                        fill();
                    }
                }
            }

            canvas.width=w;
            canvas.height=h;
            canvas.style.backgroundImage='url(' img.src ')';
            ctx=canvas.getContext('2d');
            ctx.fillStyle='transparent';
            ctx.fillRect(0, 0, w, h);
            layer(ctx);

            ctx.globalCompositeOperation = 'destination-out';

            canvas.addEventListener('touchstart', eventDown);
            canvas.addEventListener('touchend', eventUp);
            canvas.addEventListener('touchmove', eventMove);
            canvas.addEventListener('mousedown', eventDown);
            canvas.addEventListener('mouseup', eventUp);
            canvas.addEventListener('mousemove', eventMove);
        });
        img.src = 'prize.jpg';    
    })(document.body.style);
</script>