用HTML5 Canvas和JavaScript联手打造生动的动态星空背景效果 - 从代码实现开始

最编程 2024-02-16 15:10:29
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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>星空背景</title>
</head>
<body style="overflow-x:hidden;">
    <canvas id="canvas"></canvas> <!-- 创建一个画布元素 -->
</body>

<script>
    // 获取画布元素和2D上下文
	canvas = document.getElementById('canvas');
	ctx = canvas.getContext('2d'); 
	// 设置画布宽度和高度
	w = canvas.width = window.innerWidth;		
	h = canvas.height = window.innerHeight-50; 
	
	hue = 217; // 设定颜色
	stars = []; // 存储星星的数组
	count = 0,
	maxStars = 1500; // 星星数量

    // 创建用于渲染星星的小画布
	canvas2 = document.createElement('canvas');
	w2 = canvas2.width = 100;
	h2 = canvas2.height = 100;
	ctx2 = canvas2.getContext("2d");
	gradientCache = ctx2.createRadialGradient(w2 / 2, h2 / 2, 0, w2 / 2, h2 / 2, w2 / 2);
	gradientCache.addColorStop(0.025, '#fff');
	gradientCache.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
	gradientCache.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
	gradientCache.addColorStop(1, 'transparent');
	ctx2.fillStyle = gradientCache;
	ctx2.beginPath();
	ctx2.arc(w2 / 2, h2 / 2, w2 / 2, 0, Math.PI * 2);
	ctx2.fill();

    // 生成随机数
	function random(min, max) {
		if (arguments.length < 2) {
			max = min;
			min = 0;
		}
		if (min > max) {
			var hold = max;
			max = min;
			min = hold;
		}
		return Math.floor(Math.random() * (max - min + 1)) + min;
	}

    // 确定星星轨道半径
	function maxOrbit(x, y) {
		var max = Math.max(x, y), diameter = Math.round(Math.sqrt(max * max + max * max));
		return diameter / 2;
	}

    // 构造函数用于创建星星对象
	Star = function() {
		this.orbitRadius = random(maxOrbit(w, h));
		this.radius = random(60, this.orbitRadius) / 10;
		this.orbitX = w / 2;
		this.orbitY = h / 2;
		this.timePassed = random(2, maxStars);	
		this.speed = random(this.orbitRadius) / 120000;
		this.alpha = random(2, 10) / 10;
		count++;
		stars[count] = this;
	}

    // 在画布上绘制星星
	Star.prototype.draw = function() {
		x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX;
		y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY;
		twinkle = random(10);

		if (twinkle === 1 && this.alpha > 0) {
			this.alpha -= 0.05;
		} else if (twinkle === 2 && this.alpha < 1) {
			this.alpha += 0.05;
		}

		ctx.globalAlpha = this.alpha;
		ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
		this.timePassed += this.speed;
	}

    // 创建一定数量的星星对象
	for (var i = 0; i < maxStars; i++) {
		new Star();
	}

    // 开始绘制星空背景
	function start() {
		ctx.globalCompositeOperation = 'source-over';
		ctx.globalAlpha = 1;
		ctx.fillStyle = 'hsla(' + hue + ', 64%,6%,0.2)';
		ctx.fillRect(0, 0, w, h)

		ctx.globalCompositeOperation = 'lighter';
		for (var i = 1, l = stars.length; i < l; i++) {
			stars[i].draw();
		};
		window.requestAnimationFrame(start);
	}

	start(); // 调用开始函数
</script>
</html>
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