canvas-star4.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <canvas id="canvas" style="margin:0 auto;">
        The current browser does not support Canvas, can replace the browser a try!
    </canvas>

    <script>

        window.onload = function(){
            var canvas = document.getElementById('canvas');

            canvas.width = 1200;
            canvas.height = 800;

            if(canvas.getContext('2d')){
                var context = canvas.getContext('2d');

                // context.fillStyle = "#000";
                var skyStyle = context.createRadialGradient(canvas.width/2,canvas.height,0,canvas.width/2,canvas.height,canvas.height);
                skyStyle.addColorStop(0.0,'#035');
                skyStyle.addColorStop(1.0,'black');
                context.fillStyle = skyStyle;
                
                context.fillRect(0,0,canvas.width,canvas.height)

                for(var i=0;i<200;i++){
                    var r = Math.random() * 5 + 5;
                    var x = Math.random() * canvas.width;
                    var y = Math.random() * canvas.height * 0.65;
                    var a = Math.random() * 360;

                    drawStar(context , x , y , r , a )
                }

            }else{
                alert('当前游览器不支持Canvas，请更换游览器后再试！');
            }
        }

        function drawStar(cxt,x,y,R,rot){
            cxt.save();

                cxt.translate(x,y);
                cxt.rotate(rot/180*Math.PI);
                cxt.scale(0.05*R,0.05*R)

                starPath(cxt);

                cxt.fillStyle = "#fb3";
                cxt.strokeStyle = "#fd5";
                cxt.lineWidth = 3;
                cxt.lineJoin = "round";

                cxt.fill();
                cxt.stroke();

            cxt.restore()
        }

    
        function starPath(cxt){
        
            cxt.beginPath();
            for(var i=0;i<5;i++){
                cxt.lineTo(Math.cos( (18+i*72) / 180 * Math.PI )*20,
                                -Math.sin( (18+i*72) / 180 * Math.PI )*20);
                cxt.lineTo(Math.cos( (54+i*72) / 180 * Math.PI )*0.5*20,
                                -Math.sin( (54+i*72) / 180 * Math.PI )*0.5*20);
            }
            cxt.closePath();
        }
    </script>
</body>
<script>
    /*图形变换

        位移 translate(x,y)

        旋转 rotate(deg)

        缩放 scale(sx,sy)

    */
</script>
</html>

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原文地址：https://www.cnblogs.com/cynthia-wuqian/p/4981611.html