canvas探照灯效果

　　也可以在使用clip()方法前通过使用save()方法对当前画布区域进行保存，并在以后的任意时间通过restore()方法对其进行恢复

　　接下来使用clip()方法实现一个探照灯效果

<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://www.gxlcms.com/';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);
 } 
 } 
}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();
 }

}
initial();
clearInterval(oTimer);function fnInterval(){ //更新运动状态 update(); //渲染 render(); 
}var oTimer = setInterval(fnInterval,50);</script>

更多canvas探照灯效果 相关文章请关注PHP中文网！