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index.html
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<!DOCTYPE html>
<html>
<head lang="zh-hans">
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<meta name="renderer" content="webkit" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<title>刮刮乐</title>
<style>
.lottery-block{
width: 700px;
height: 500px;
margin: 20px auto;
border: 1px solid #ccc;
}
.lottery-box-gift{
background: url("http://www.helloweba.com/demo/guaguaka/p_1.jpg") no-repeat;
background-size: cover;
width: 640px;
height: 320px;
}
</style>
<script type="text/javascript" src="http://t5.zbjimg.com/c/base/jquery.js"></script>
</head>
<body class="yahei">
<div class="main-block">
<div class="lottery-block">
<div class="lottery-box-gift"></div>
</div>
</div>
<script>
function MakeCanvas($parent, bgColor, radius, callback) {
try { //避免日后取消掉callee
if (!(this instanceof arguments.callee)) { //直接MakeCanvas时自动加上new
return new arguments.callee($parent, bgColor);
}
} catch (e) {
console.log(e.message);
}
$parent.val || ($parent = $($parent)); //转成JQ对象方便些
if ($parent.length > 1) { //传人一堆对象时，一个个执行构造函数，最终返回生成的对象集合
var _arrayObj = [];
[].forEach.call($parent, function (item) {
_arrayObj.push(new MakeCanvas(item));
});
return _arrayObj;
}
if ($parent.css('position') !== 'absolute') { //让生成的canvas，的父级为相对定位
$parent.css('position', 'relative');
}
var _canvas = document.createElement('canvas');
$.extend(this, {
parent: $parent,
width: $parent.width(),
height: $parent.height(),
bgColor: bgColor || '#ccc',
radius: radius || 20,
canvas: _canvas,
ctx: _canvas.getContext('2d'),
x1: 0,
y1: 0,
callback: callback || null
});
this.init();
}
MakeCanvas.prototype = (function () {
var isMouseDown = false; //私有静态变量，保存全局点击状态
var selectable = true;
document.addEventListener('selectstart', function (e) { //防止选中效果，绑定在document上避免超出可视区后再进入时可选中的
!selectable && e.preventDefault();
});
function init() { //创建多个对象时可能会执行多次，此处不能放执行某些全局的操作
var _canvas = this.canvas;
var _ctx = this.ctx;
var _parent = this.parent;
_canvas.style.position = 'absolute';
_canvas.style.cursor = 'pointer';
_canvas.style.zIndex = '99';
_canvas.style.left = '0';
_canvas.style.transition = 'opacity 1s';
_canvas.width = this.width;
_canvas.height = this.height;
_ctx.fillStyle = this.bgColor;
_ctx.fillRect(0, 0, _canvas.width, _canvas.height);
_ctx.globalCompositeOperation = "destination-out"; //在已有图像区域再绘制时会clip & clearRect
_ctx.lineCap = "round"; //设置线条两端为圆弧
_ctx.lineJoin = "round"; //设置线条转折为圆弧
_ctx.lineWidth = this.radius * 2;
_parent.prepend(_canvas);
_parent.bind('dragstart', function () { //避免超出canvas区域时选中拖动导致打开新标签
return false;
});
bindEvents.call(this);
}
function bindEvents() {
var _obj = this;
var _canvas = _obj.canvas;
var _ctx = _obj.ctx;
var _body = document.body;
//为了避免event被jQuery包装，还是用原生addEventListener绑定canvas
_body.addEventListener('mousedown', function (e) {
isMouseDown = true;
startOrEnd(e);
});
_body.addEventListener('touchstart', function (e) {
isMouseDown = true;
startOrEnd(e);
});
_body.addEventListener('mouseup', function (e) {
isMouseDown = false;
if(calcPixel()){
_canvas.style.opacity = '0';
_obj.callback && _obj.callback();
}
});
_body.addEventListener('touchend', function (e) {
isMouseDown = false;
});
_canvas.addEventListener('mouseenter', function (e) { //重新计算出发点以防止超出边界后再进入时起始点错误
if (!isMouseDown) {
return false;
}
startOrEnd(e);
});
_canvas.addEventListener('mousedown', function () { //防止选中效果
selectable = false;
});
_canvas.addEventListener('mousemove', function (e) {
if (!isMouseDown) {
return false;
}
e.preventDefault();
move(e);
});
_canvas.addEventListener('touchmove', function (e) {
if (!isMouseDown) {
return false;
}
e.preventDefault();
move(e);
});
function move(e) {
var _x = getPointX.call(_obj, e);
var _y = getPointY.call(_obj, e);
eraser.apply(_obj, [_ctx, _x, _y, _obj.radius]);
}
function calcPixel() {
var _count = 0;
var _cvsData = _ctx.getImageData(0,0,_canvas.width,_canvas.height);
var _len = _cvsData.width * _cvsData.height;
for(var i =0;i<_len;i++){
if(_cvsData.data[4*i+3] === 0){
_count++;
}
}
return _count*2>_len;
}
function startOrEnd(e) {
_obj.x1 = getPointX.call(_obj, e);
_obj.y1 = getPointY.call(_obj, e);
}
}
function getPointX(e) {
var _obj = this;
if(e.changedTouches){
return e.changedTouches[e.changedTouches.length - 1].clientX - _obj.parent[0].offsetLeft;
}
else{
return e.offsetX ? e.offsetX : e.layerX;
}
}
function getPointY(e) {
var _obj = this;
if(e.changedTouches){
return e.changedTouches[e.changedTouches.length - 1].clientY - _obj.parent[0].offsetTop;
}
else{
return e.offsetY ? e.offsetY : e.layerY;
}
}
function makeCircle(ctx, x , y) {
var _obj = this;
ctx.save();
ctx.beginPath();
ctx.arc(x, y, _obj.radius, 0, 2 * Math.PI);
ctx.fill();
ctx.restore();
}
function eraser(ctx, x, y) {
var _obj = this;
ctx.beginPath();
ctx.moveTo(_obj.x1, _obj.y1);
ctx.lineTo(x,y);
ctx.stroke();
_obj.x1 = x;
_obj.y1 = y;
}
return {
init: init,
makeCircle: makeCircle,
makeLine: eraser
}
})();
new MakeCanvas($('.lottery-box-gift'),null,30,function () {
alert('假吧意思的回调一下嘛');
});
</script>
</body>
</html>