html5通过canvas实现刮刮卡效果示例分享_html5教程技巧

<script><br /> (function(bodyStyle) {<br /> bodyStyle.mozUserSelect = 'none';<br /> bodyStyle.webkitUserSelect = 'none';<br /> <br /> var img = new Image();<br /> var canvas = document.querySelector('canvas');<br /> canvas.style.backgroundColor='transparent';<br /> canvas.style.position = 'absolute';<br /> <br /> img.addEventListener('load', function(e) {<br /> var ctx;<br /> var w = img.width,<br /> h = img.height;<br /> var offsetX = canvas.offsetLeft,<br /> offsetY = canvas.offsetTop;<br /> var mousedown = false;<br /> <br /> function layer(ctx) {<br /> ctx.fillStyle = 'gray';<br /> ctx.fillRect(0, 0, w, h);<br /> }<br /> <br /> function eventDown(e){<br /> e.preventDefault();<br /> mousedown=true;<br /> }<br /> <br /> function eventUp(e){<br /> e.preventDefault();<br /> mousedown=false;<br /> }<br /> <br /> function eventMove(e){<br /> e.preventDefault();<br /> if(mousedown) {<br /> if(e.changedTouches){<br /> e=e.changedTouches[e.changedTouches.length-1];<br /> }<br /> var x = (e.clientX + document.body.scrollLeft || e.pageX) - offsetX || 0,<br /> y = (e.clientY + document.body.scrollTop || e.pageY) - offsetY || 0;<br /> with(ctx) {<br /> beginPath()<br /> arc(x, y, 5, 0, Math.PI * 2);<br /> fill();<br /> }<br /> }<br /> }<br /> <br /> canvas.width=w;<br /> canvas.height=h;<br /> canvas.style.backgroundImage='url('+img.src+')';<br /> ctx=canvas.getContext('2d');<br /> ctx.fillStyle='transparent';<br /> ctx.fillRect(0, 0, w, h);<br /> layer(ctx);<br /> <br /> ctx.globalCompositeOperation = 'destination-out';<br /> <br /> canvas.addEventListener('touchstart', eventDown);<br /> canvas.addEventListener('touchend', eventUp);<br /> canvas.addEventListener('touchmove', eventMove);<br /> canvas.addEventListener('mousedown', eventDown);<br /> canvas.addEventListener('mouseup', eventUp);<br /> canvas.addEventListener('mousemove', eventMove);<br /> });<br /> img.src = 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';<br /> })(document.body.style);<br /></script>

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