add seashell

examples/seashell.scad

@@ -0,0 +1,85 @@
+use <surface/sf_thickenT.scad>;
+
+alpha = 85; 
+beta = 5;
+phi = 0;
+omega = 0;
+mu = 1;
+a = 2;
+b = 3;
+
+theta_s = -2400;
+theta_step = 20;
+theta_e = 720;
+
+s_s = -150;
+s_step = 20;
+s_e = 90;
+
+thickness = .2;
+
+seashell();
+
+module seashell() {
+    e =  2.71828;
+    real_e = e / 2.74;
+	pow_a = (a / 10) ^ 2;
+	pow_b = (b / 10) ^ 2;
+
+	function cot(degree) = 1 / tan(degree);
+
+	function radius(theta) = 
+		real_e ^ (theta * cot(alpha));
+
+	function x(theta, s) = 
+		let(r = radius(theta))
+		r * (    
+			(cos(theta + omega) * cos(s + phi) - sin(mu) * sin(theta + omega) * sin(s + phi)) / 
+			sqrt((cos(s) ^ 2) / pow_a + (sin(s) ^ 2) / pow_b)
+			 + sin(beta) * cos(theta)
+		);
+
+	function y(theta, s) = 
+		let(r = radius(theta))
+		r * (    
+			(sin(mu) * cos(theta + omega) * sin(s + phi) + sin(theta + omega) * cos(s + phi)) / 
+			sqrt((cos(s) ^ 2) / pow_a + (sin(s) ^ 2) / pow_b)
+			+ sin(beta) * sin(theta)
+		);
+
+	function z(theta, s) = 
+		let(r = radius(theta))
+		r * (    
+			(cos(mu) * sin(s + phi)) / 
+			sqrt((cos(s) ^ 2) / pow_a + (sin(s) ^ 2) / pow_b)
+			- cos(beta)
+		);
+
+	points = [
+		for(s = [s_s:s_step:s_e])
+			for(theta = [theta_s:theta_step:theta_e])
+			let(
+				x = x(theta, s),
+				y = y(theta, s),
+				z = z(theta, s)
+			)
+			[x, y, z]
+	];
+
+	slen = floor((s_e - s_s) / s_step);
+	thetalen = floor((theta_e - theta_s) / theta_step);
+
+	c = thetalen + 1;
+	triangles = [
+		for(s = [0:slen - 1])
+			for(theta = [0:thetalen - 1])
+			each [
+				[theta + s * c, theta + 1 + s * c, theta + (s + 1) * c], 
+				[theta + 1 + s * c, theta + 1 + (s + 1) * c, theta + (s + 1) * c]
+			]
+	];
+
+
+
+	sf_thickenT(points, thickness, triangles);
+}