<!doctype html> <html> <head> <meta charset="utf-8"> <title>无标题文档</title> <meta content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no" /> <style> .content,.cover{width:400px; height:400px; position:absolute; left:50%; top:50%; margin:-200px 0 0 -200px;} .content{ font-size:48px; line-height:400px; text-align:center;} h3{ text-align:center; line-height:200px;} </style> </head> <body> <h3>快来刮开！！！</h3> <div >中奖啦~！</div> <canvas></canvas> </body> <script> var isdown = false, cover = document.getElementById("cover"), covercanvas = cover.getContext("2d"); // covercanvas.fillStyle="transparent"; covercanvas.fillRect(0,0,400,400); function fillter( canvas ){ canvas.fillStyle="#ccc"; canvas.fillRect(0,0,400,400); } function isDown(e){ e.preventDefault(); isdown=true; } function isUp(e){ isdown=false; } function draw( e ){ e.preventDefault(); if(isdown){ if(e.changedTouches){ e=e.changedTouches[e.changedTouches.length-1]; } var _height= parseInt((window.innerHeight-400)/2), _width= parseInt((window.innerWidth-400)/2), touchTop=e.clientY - _height, touchLeft=e.clientX - _width; with(covercanvas){ beginPath(); arc(touchLeft, touchTop, 10, 0, Math.PI * 2); fill(); } } //alert(touchTop); } fillter(covercanvas); covercanvas.globalCompositeOperation = 'destination-out'; cover.addEventListener('touchstart',isDown); cover.addEventListener('touchmove',draw); cover.addEventListener('touchend',isUp); cover.addEventListener('mousemove',draw); cover.addEventListener('mousedown',isDown); cover.addEventListener('mouseup',isUp); </script> </html>
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