JavaScript图像放大镜效果实现方法详解

Z时代
2024-01-10
分类：综合

1. 基本四瓣花型图案

根据四瓣花卉线的参数方程：

t= r*(1+sin(12*θ)/5)*(0.5+sin(4*θ)/2);
x=t*cos(θ));
y=t*sin(θ));

编写如下的HTML文件。


<!DOCTYPE html>
<head>
	<title>基本的四瓣花型图案</title>
	<script type="text/javascript">
		function draw(id)
		{
			var canvas = document.getElementById(
				id);
			if (canvas == null)
				return false;
			var context = canvas.getContext('2d');
			context.fillStyle = "#EEEEFF";
			context.fillRect(0, 0, 320, 320);
			context.strokeStyle = "blue";
			context.lineWidth = 1;
			var dig = Math.PI / 64;
			context.beginPath();
			for (var i = 0; i <= 128; i++)
			{
				d = 120 * (1 + Math.sin(12 * i *
					dig) / 5);
				t = d * (0.5 + Math.sin(4 * i * dig) /
					2);
				x = (160 + t * Math.cos(i * dig));
				y = (160 + t * Math.sin(i * dig));
				if (i == 0)
					context.moveTo(x, y);
				else
					context.lineTo(x, y);
			}
			context.stroke();
		}
	</script>
</head>
<body onload="draw('myCanvas');">
	<canvas id="myCanvas" width="320" height="320"></canvas>
</body>
</html>

在浏览器中打开包含这段HTML代码的html文件，可以看到在画布中绘制出如图1所示的四瓣花卉线图案。

图1 四瓣花卉线图案

2．平铺的100朵四瓣花

用一个二重循环将图1的四瓣花卉绘制10行10列共100朵。编写的HTML文件内容如下。


<!DOCTYPE html>
<head>
	<title>平铺的100朵四瓣花</title>
	<script type="text/javascript">
		function draw(id)
		{
			var canvas = document.getElementById(
				id);
			if (canvas == null)
				return false;
			var context = canvas.getContext('2d');
			context.fillStyle = "#EEEEFF";
			context.fillRect(0, 0, 320, 320);
			context.strokeStyle = "blue";
			context.lineWidth = 1;
			var dig = Math.PI / 64;
			context.beginPath();
			for (px = 20; px < 320; px += 30)
				for (py = 20; py < 320; py += 30)
			{
				for (var i = 0; i <= 128; i++)
				{
					d = 20 * (1 + Math.sin(12 * i *
						dig) / 5);
					t = d * (0.5 + Math.sin(4 * i *
						dig) / 2);
					x = px + t * Math.cos(i * dig);
					y = py + t * Math.sin(i * dig);
					if (i == 0)
						context.moveTo(x, y);
					else
						context.lineTo(x, y);
				}
				context.stroke();
			}
		}
	</script>
</head>
<body onload="draw('myCanvas');">
	<canvas id="myCanvas" width="320" height="320"></canvas>
</body>
</html>

在浏览器中打开包含这段HTML代码的html文件，可以看到在画布中绘制出如图2所示的平铺的100朵四瓣花卉图案。

图2 平铺的100朵四瓣花卉图案

3．放大镜看平铺的四瓣花

将图2图形中位于中心点周围100以内的点的坐标进行球面镜反射变换，可以实现放大镜效果。编写的HTML文件内容如下。


<!DOCTYPE html>
<head>
	<title>球面镜反射变换</title>
	<script type="text/javascript">
		function draw(id)
		{
			var canvas = document.getElementById(
				id);
			if (canvas == null)
				return false;
			var context = canvas.getContext('2d');
			context.fillStyle = "#EEEEFF";
			context.fillRect(0, 0, 320, 320);
			context.strokeStyle = "blue";
			context.lineWidth = 1;
			var dig = Math.PI / 64;
			context.beginPath();
			var r = 140;
			var x0 = 160;
			var y0 = 160;
			for (px = 20; px < 320; px += 30)
				for (py = 20; py < 320; py += 30)
			{
				for (var i = 0; i <= 128; i++)
				{
					d = 20 * (1 + Math.sin(12 * i *
						dig) / 5);
					t = d * (0.5 + Math.sin(4 * i *
						dig) / 2);
					x = px + t * Math.cos(i * dig);
					y = py + t * Math.sin(i * dig);
					l = Math.sqrt((x - x0) * (x - x0) +
						(y - y0) * (y - y0));
					if (l < r)
					{ // 圆心为（160,160），半径为140的圆内各点进行球面镜反射变换
						s = x - x0 < 0 ? -1 : 1;
						if (x - x0 == 0) x = x0 + 0.1;
						bt = 2 * Math.atan(l / r);
						th = Math.atan((y - y0) / (x - x0));
						m = r * Math.sin(bt);
						x = s * m * Math.cos(th) + x0;
						y = s * m * Math.sin(th) + y0;
					}
					if (i == 0)
						context.moveTo(x, y);
					else
						context.lineTo(x, y);
				}
				context.stroke();
			}
		}
	</script>
</head>
<body onload="draw('myCanvas');">
	<canvas id="myCanvas" width="320" height="320"></canvas>
</body>
</html>