绘制canvas彩色泡泡小球碰撞

墨蓝 2021-09-11 07:54 350阅读 0赞

globalCompositeOperation带来的不一样的烟花

![20170224163016894][]

一.知识点

1.动画：

setInterval(  
            function()\{  
                draw(context);  
                update(canvas.width,canvas.height);  
            \},  
            50  
        );

2.小球碰撞的状态：

ctx.globalCompositeOperation="xor";//lighter

二.代码

<!DOCTYPE html>
    <html>
    <head lang="en">
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
    <canvas id="canvas" style="border:1px solid #aaa;display:block;margin:50px auto;">
        当前浏览器不支持Canvas，请更换浏览器后再试
    </canvas>
    
    <script>
        var balls = [];
        window.onload = function(){
            var canvas = document.getElementById("canvas");
            var  context=canvas.getContext('2d');
            canvas.width = 1200;
            canvas.height = 800;
            for(var i=0;i<100;i++){
                var R=Math.floor(Math.random()*255);//可对一个数进行下舍入。0.1就是0    0.9就是1
                var G=Math.floor(Math.random()*255);
                var B=Math.floor(Math.random()*255);
                var radius=Math.random()*50+20;
                aBall={
                    color:"rgb("+R+","+G+","+B+")",
                    radius:radius,
                    x:Math.random()*(canvas.width-2*radius)+radius,
                    y:Math.random()*(canvas.height-2*radius)+radius,
                    vx:(Math.random()*5+5)*Math.pow(-1,Math.floor(Math.random()*100)),//pow() 方法可返回 x 的 y 次幂的值。
                    vy:(Math.random()*5+5)*Math.pow(-1,Math.floor(Math.random()*100))
                }
                balls[i]=aBall;
            }
            setInterval(
                function(){
                    draw(context);
                    update(canvas.width,canvas.height);
                },
                50
            );  
        } 
        function draw(ctx){
            var canvas = ctx.canvas;
            ctx.clearRect(0,0,canvas.width,canvas.height);
            for( var i = 0 ; i < balls.length ; i ++ ){
                ctx.globalCompositeOperation="xor";//lighter
                ctx.fillStyle=balls[i].color;
                ctx.beginPath();
                ctx.arc(balls[i].x,balls[i].y,balls[i].radius,0,2*Math.PI);
                ctx.closePath();
                ctx.fill();
            }
        }
        function update(canvasWidth, canvasHight){
            for( var i = 0 ; i < balls.length ; i ++ ){
    
                balls[i].x += balls[i].vx;
                balls[i].y += balls[i].vy;
    
                if( balls[i].x - balls[i].radius<=0 ){
                    balls[i].vx = -balls[i].vx;
                    balls[i].x = balls[i].radius;
                }
                if( balls[i].x + balls[i].radius>=canvasWidth ){
                    balls[i].vx = -balls[i].vx;
                    balls[i].x = canvasWidth-balls[i].radius;
                }
                if( balls[i].y - balls[i].radius<=0 ){
                    balls[i].vy = -balls[i].vy;
                    balls[i].y = balls[i].radius;
                }
                if( balls[i].y + balls[i].radius>=canvasHight ){
                    balls[i].vy = -balls[i].vy;
                    balls[i].y = canvasHight-balls[i].radius;
                }
            }
        }
    </script>
    </body>
    </html>

[20170224163016894]: /images/20210813/5097d20a64a84858b7d9831b90f4c608.png