[转载]刮刮奖效果的简单实现 - ms_config - 博客园

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[转载]刮刮奖效果的简单实现 – ms_config – 博客园.

 

无意中看到个刮刮奖的效果,觉得很有意思.就想自己也做一个,怎样用html5及JavaScript实现呢,回忆以前

 

做报表的时候,用过html5 canvas元素.心里就有思路了.

 

惯例先用关键字在网上搜索了下,发现一些例子,已经做得很不错了,完全可以拿来主义.嘿…

 

自己简单改了下,就发布在runjs上去了.

 

源码如下:
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8" />
    <title>eraser effect</title>
	</head>
<body>
    <div id="canvas"></div>
</body>
</html>

js

(function() {
    // Creates a new canvas element and appends it as a child
    // to the parent element, and returns the reference to
    // the newly created canvas elemen
    function createCanvas(parent, width, height) {
        var canvas = {};
        canvas.node = document.createElement('canvas');
        canvas.context = canvas.node.getContext('2d');
        canvas.node.width = width || 100;
        canvas.node.height = height || 100;
        parent.appendChild(canvas.node);
        return canvas;
    }

    function init(container, width, height, fillColor) {
        var canvas = createCanvas(container, width, height);
        var ctx = canvas.context;
        // define a custom fillCircle method
        ctx.fillCircle = function(x, y, radius, fillColor) {
            this.fillStyle = fillColor;
            this.beginPath();
            this.moveTo(x, y);
            this.arc(x, y, radius, 0, Math.PI * 2, false);
            this.fill();
        };
        ctx.clearTo = function(fillColor) {
            ctx.fillStyle = fillColor;
            ctx.fillRect(0, 0, width, height);
        };
        ctx.clearTo(fillColor || "#ddd");

        // bind mouse events
        canvas.node.onmousemove = function(e) {
            if (!canvas.isDrawing) {
                return;
            }
            var x = e.pageX - this.offsetLeft;
            var y = e.pageY - this.offsetTop;
            var radius = 10; // or whatever
            var fillColor = '#ff0000';
            ctx.globalCompositeOperation = 'destination-out';
            ctx.fillCircle(x, y, radius, fillColor);
        };
        canvas.node.onmousedown = function(e) {
            canvas.isDrawing = true;
        };
        canvas.node.onmouseup = function(e) {
            canvas.isDrawing = false;
        };
    }

    var container = document.getElementById('canvas');
    init(container, 531, 438, '#ddd');

})();
        #canvas {
            background:url(http://www.topscratchcards.com/images/games/888ladies/scratchcard-winning-ticket.jpg);
            width: 531px;
            height: 438px;
        }
    
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