</iframe><button id="btn">變換</button><button id="con">暫停</button><canvas id="canvas" width="400" height="290" style="border:1px solid black">當前瀏覽器不支持canvas，請更換瀏覽器后再試</canvas><script> btn.onclick = function(){history.go();}con.onclick = function(){ if(this.innerHTML == '暫停'){ this.innerHTML = '恢復';        clearInterval(oTimer);    }else{ this.innerHTML = '暫停';         oTimer = setInterval(fnInterval,50);    }} var canvas = document.getElementById('canvas'); //存儲畫布寬高var H=290,W=400; //存儲探照燈var ball = {}; //存儲照片var IMG; //存儲照片地址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);    　　}//歡迎加入全棧開發交流圈一起學習交流：582735936  　　]//面向1-3年前端人員　　}   //幫助突破技術瓶頸，提升思維能力        }       }    } function update(){    ball.x += ball.stepX;    ball.y += ball.stepY;     bumpTest(ball);} function bumpTest(ele){ //左側    if(ele.x <= ele.r){        ele.x = ele.r;        ele.stepX = -ele.stepX;    } //右側    if(ele.x >= W - ele.r){        ele.x = W - ele.r;        ele.stepX = -ele.stepX;    } //上側    if(ele.y <= ele.r){        ele.y = ele.r;        ele.stepY = -ele.stepY;    } //下側    if(ele.y >= H - ele.r){        ele.y = H - ele.r;        ele.stepY = -ele.stepY;    }} function render(){ //重置畫布高度，達到清空畫布的效果 canvas.height = H; if(canvas.getContext){ var cxt = canvas.getContext('2d');        cxt.save(); //將畫布背景涂黑 cxt.beginPath();        cxt.fillStyle = '#000';        cxt.fillRect(0,0,W,H); //渲染探照燈 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()，畫布背景圖片會出現在clip()區域內 cxt.drawImage(IMG,0,0);        cxt.restore();    　　}//歡迎加入全棧開發交流圈一起學習交流：582735936  　　]//面向1-3年前端人員　　}   //幫助突破技術瓶頸，提升思維能力    }}initial();clearInterval(oTimer); function fnInterval(){ //更新運動狀態 update(); //渲染 render();    } var oTimer = setInterval(fnInterval,50); </script>