キャンバスサーチライトエフェクトのサンプルコード

</iframe>
<button id="btn">transform</button>
<button id="con">pause</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 == 'pause'){ this.innerHTML = 'resume';
        clearInterval(oTimer);
    }else{ this.innerHTML = 'pause'; 
        oTimer = setInterval(fnInterval,50);
    }
} var canvas = document.getElementById('canvas'); //store the canvas width and height
var H=290,W=400; //store the searchlight
var ball = {}; //store the photo
var IMG; //store the 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 join the full-stack development exchange circle together to learn and exchange: 582735936
  　　]//For 1-3 years front-end personnel
　　} //Help break through technical bottlenecks and improve thinking skills
        }   
    }    
} 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 side
    if(ele.x >= W - ele.r){
        ele.x = W - ele.r;
        ele.stepX = -ele.stepX;
    } // top side
    if(ele.y <= ele.r){
        ele.y = ele.r;
        ele.stepY = -ele.stepY;
    } // lower side
    if(ele.y >= H - ele.r){
        ele.y = H - ele.r;
        ele.stepY = -ele.stepY;
    }
} function render(){ //reset the height of the canvas to clear it
 canvas.height = H; if(canvas.getContext){ var cxt = canvas.getContext('2d');
        cxt.save(); // black out the background of the canvas
 cxt.beginPath();
        cxt.fillStyle = '#000';
        cxt.fillRect(0,0,W,H); //render the searchlight
 cxt.beginPath();
        cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
        cxt.fillStyle = '#000';
        cxt.fill(); 
        cxt.clip(); //as a result of using clip(), the background image of the canvas will appear in the clip() area
 cxt.drawImage(IMG,0,0);
        cxt.restore();
    　　}//Welcome to join the full-stack development exchange circle to learn together: 582735936
  　　]//For 1-3 years front-end personnel
　　} //Help break through technical bottlenecks and improve thinking skills
    }

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