• Next, use the clip() method to achieve a searchlight effect

</iframe>
<button id="btn">Transformation</button>
<button id="con">suspend</button>
<canvas id="canvas" width="400" height="290" style="border:1px solid black">Current browser does not support canvas，Please change your browser and try again</canvas>
<script> btn.onclick = function(){history.go();}
con.onclick = function(){ if(this.innerHTML == 'suspend'){ this.innerHTML = 'recovery';
        clearInterval(oTimer);
    }else{ this.innerHTML = 'suspend'; 
        oTimer = setInterval(fnInterval,50);
    }
} var canvas = document.getElementById('canvas'); //Storage canvas width and height
var H=290,W=400; //Storage searchlight
var ball = {}; //Store photos
var IMG; //Store photo address
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);
    　　}//Welcome to the full stack development exchange circle to learn and exchange: 582735936
  　　]//For front-end personnel for 1-3 years
　　}   //Help to break through technical bottleneck and improve thinking ability
        }   
    }    
} function update(){
    ball.x += ball.stepX;
    ball.y += ball.stepY; 
    bumpTest(ball);
} function bumpTest(ele){ //Left
    if(ele.x <= ele.r){
        ele.x = ele.r;
        ele.stepX = -ele.stepX;
    } //Right
    if(ele.x >= W - ele.r){
        ele.x = W - ele.r;
        ele.stepX = -ele.stepX;
    } //Upper side
    if(ele.y <= ele.r){
        ele.y = ele.r;
        ele.stepY = -ele.stepY;
    } //Underside
    if(ele.y >= H - ele.r){
        ele.y = H - ele.r;
        ele.stepY = -ele.stepY;
    }
} function render(){ //Reset the height of canvas to empty the canvas
 canvas.height = H; if(canvas.getContext){ var cxt = canvas.getContext('2d');
        cxt.save(); //Black the canvas background
 cxt.beginPath();
        cxt.fillStyle = '#000';
        cxt.fillRect(0,0,W,H); //Rendering searchlights
 cxt.beginPath();
        cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
        cxt.fillStyle = '#000';
        cxt.fill(); 
        cxt.clip(); //Because of the use of clip(), the canvas background image will appear in the clip() area
 cxt.drawImage(IMG,0,0);
        cxt.restore();
    　　}//Welcome to the full stack development exchange circle to learn and exchange: 582735936
  　　]//For front-end personnel for 1-3 years
　　}   //Help to break through technical bottleneck and improve thinking ability
    }

}
initial();
clearInterval(oTimer); function fnInterval(){ //Update motion state
 update(); //Rendering
 render();    
} var oTimer = setInterval(fnInterval,50); 
</script> 
 </pre>