image.png
image.png
<!-- test.html -->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Test</title>
</head>
<body>
<h1>adsfasdfasdf</h1>
<div id="div" style="width:300px;height:90px;margin:200px;padding:0;">
</div>
<script src="/utils/scratchcard.js"></script>
<script>
var div = document.getElementById('div');
div.ScratchCard('一等奖');
</script>
</body>
</html>
/**
* scratchcard.js
*/
Element.prototype.ScratchCard = function(t){
var s = this;
if(!s.nodeType || s.nodeType !== 1 || !t || Object.prototype.toString.call(t) !== '[object String]') return;
w = s.clientWidth;
h = s.clientHeight;
var bg = document.createElement('div'),
canvas = document.createElement('canvas'),
context = canvas.getContext("2d"),
touched = false,
page_x = 0,
page_y = 0,
begin = function(e){
touched = true;
page_x = e.pageX-s.offsetLeft;
page_y = e.pageY-s.offsetTop;
},
move = function(e){
e.preventDefault();
if(touched){
context.globalCompositeOperation="destination-out"
context.beginPath();
context.moveTo( page_x,page_y );
var epx = e.pageX || e.touches[0].pageX,
epy = e.pageY || e.touches[0].pageY;
page_x = epx-s.offsetLeft;
page_y = epy-s.offsetTop;
context.lineTo( page_x,page_y );
context.stroke();
context.lineWidth = Math.floor(h / 4);
}
},
end = function(e){
touched = false;
};
s.style.position = 'relative';
bg.innerText = t;
bg.style.fontSize = Math.floor(w / (t.length + 4)) + 'px';
bg.style.textAlign = 'center';
bg.style.width = w + 'px';
bg.style.height = h + 'px';
bg.style.lineHeight = h + 'px';
bg.style.background = 'lightblue';
s.appendChild(bg);
canvas.width = w;
canvas.height = h;
canvas.style.position = 'absolute';
canvas.style.top = '0';
s.appendChild(canvas);
context.lineCap = "round";
context.fillStyle="#ccc";
context.fillRect(0,0,w,h);
//手指放到屏幕上
canvas.addEventListener('touchstart', begin);
canvas.addEventListener('mousedown', begin);
//手指开始移动
canvas.addEventListener('touchmove', move);
canvas.addEventListener('mousemove', move);
//手指离开
canvas.addEventListener('touchend', end);
canvas.addEventListener('mouseup', end);
}
