canvas探照灯效果的示例代码

</iframe><button id="btn">变换</button><button id="con">暂停</button><canvas id="canvas" width="400" height="290" style="border:1px solid black">当前浏览器不支持canvas，请更换浏览器后再试</canvas><script> btn.onclick = function(){history.go();}con.onclick = function(){ if(this.innerHTML == '暂停'){ this.innerHTML = '恢复';        clearInterval(oTimer);    }else{ this.innerHTML = '暂停';         oTimer = setInterval(fnInterval,50);    }} var canvas = document.getElementById('canvas'); //存储画布宽高var H=290,W=400; //存储探照灯var ball = {}; //存储照片var IMG; //存储照片地址var URL = 'http://sandbox.runjs.cn/uploads/rs/26/ddzmgynp/chunfen.jpg'; function initial(){ if(canvas.getContext){ var cxt = canvas.getContext('2d'); var tempR = Math.floor(Math.random()*30+20); var tempX = Math.floor(Math.random()*(W-tempR) + tempR); var tempY = Math.floor(Math.random()*(H-tempR) + tempR)                ball = {            x:tempX,            y:tempY,            r:tempR,            stepX:Math.floor(Math.random() * 21 -10),            stepY:Math.floor(Math.random() * 21 -10)        };        IMG = document.createElement('img');        IMG.src=URL;        IMG.onload = function(){            cxt.drawImage(IMG,0,0);    　　}//欢迎加入全栈开发交流圈一起学习交流：582735936  　　]//面向1-3年前端人员　　}   //帮助突破技术瓶颈，提升思维能力        }       }    } function update(){    ball.x += ball.stepX;    ball.y += ball.stepY;     bumpTest(ball);} function bumpTest(ele){ //左侧    if(ele.x <= ele.r){        ele.x = ele.r;        ele.stepX = -ele.stepX;    } //右侧    if(ele.x >= W - ele.r){        ele.x = W - ele.r;        ele.stepX = -ele.stepX;    } //上侧    if(ele.y <= ele.r){        ele.y = ele.r;        ele.stepY = -ele.stepY;    } //下侧    if(ele.y >= H - ele.r){        ele.y = H - ele.r;        ele.stepY = -ele.stepY;    }} function render(){ //重置画布高度，达到清空画布的效果 canvas.height = H; if(canvas.getContext){ var cxt = canvas.getContext('2d');        cxt.save(); //将画布背景涂黑 cxt.beginPath();        cxt.fillStyle = '#000';        cxt.fillRect(0,0,W,H); //渲染探照灯 cxt.beginPath();        cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);        cxt.fillStyle = '#000';        cxt.fill();         cxt.clip(); //由于使用了clip()，画布背景图片会出现在clip()区域内 cxt.drawImage(IMG,0,0);        cxt.restore();    　　}//欢迎加入全栈开发交流圈一起学习交流：582735936  　　]//面向1-3年前端人员　　}   //帮助突破技术瓶颈，提升思维能力    }}initial();clearInterval(oTimer); function fnInterval(){ //更新运动状态 update(); //渲染 render();    } var oTimer = setInterval(fnInterval,50); </script>