js uses canvas to draw five-pointed stars and gradient colors, blindly drawing

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<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>星云图</title>
	</head>
	<body>
		<canvas id="canvas" style="border: 1px solid black; margin: 20px auto;"></canvas>
	</body>
	<script type="text/javascript">
		var canvas = document.getElementById("canvas")
		canvas.width = 1400
		canvas.height = 700
		var a1 = canvas.getContext("2d")
		a1.beginPath()
		a1.fillStyle="#000020"
		a1.fillRect(0,0,1400,700)
		a1.stroke()
		for(var i=0;i<600;i++){
    
    
			var banjing = Math.random()*5+5
			var heng = Math.random()*canvas.width
			var zong = Math.random()*canvas.height
			var dushu = Math.random()*360
			star(a1,1,2,heng,zong,'yellow',"white",dushu)
		}
		function star(a,r,R,x,y,color,bgcolor,du){
    
    
			a.beginPath()
			for(var i=0;i<5;i++){
    
    
				a.lineTo(Math.cos((18+72*i-du)/180*Math.PI)*R+x,
						 -Math.sin((18+72*i-du)/180*Math.PI)*R+y,
				)
				a.lineTo(Math.cos((54+72*i-du)/180*Math.PI)*r+x,
						 -Math.sin((54+72*i-du)/180*Math.PI)*r+y,
				)
			}
			a.strokeStyle = color
			a.fillStyle = bgcolor
			a.fill()
			a.shadowOffsetX = 0
			a.shadowOffsetY = 0
			a.shadowBlur = 20
			a.shadowColor = "rgb(0,0,0)"
			a.closePath()
			a.stroke()
		}
		a1.beginPath()
		a1.arc(1250,1650,1500,0,2*Math.PI,false)
		a1.strokeStyle="#000030"
		var jianbian = a1.createRadialGradient(700,450,0,700,200,700)
		jianbian.addColorStop(0.0,"#fbe3e3")
		jianbian.addColorStop(0.1,"#4f1603")
		jianbian.addColorStop(0.2,"#a25d56")
		jianbian.addColorStop(0.3,"#431000")
		jianbian.addColorStop(0.45,"#662414")
		jianbian.addColorStop(0.55,"#a67a6d")
		jianbian.addColorStop(0.6,"#5a2211")
		jianbian.addColorStop(0.65,"#a67a6d")
		jianbian.addColorStop(0.75,"#4f1603")
		jianbian.addColorStop(0.9,"#280a00")
		jianbian.addColorStop(1,"#431000")
		a1.fillStyle = jianbian
		a1.fill()
		a1.stroke()
	</script>
</html>
js uses canvas to draw five-pointed stars and gradient colors, blindly drawing

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