From dd632d5845029515492539c2bf461666e4234d0f Mon Sep 17 00:00:00 2001
From: Justin Lin <justin.sdk@gmail.com>
Date: Mon, 24 Jan 2022 18:05:37 +0800
Subject: [PATCH] add reaction_diffusion

---
 src/experimental/reaction_diffusion.scad | 96 ++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 src/experimental/reaction_diffusion.scad

diff --git a/src/experimental/reaction_diffusion.scad b/src/experimental/reaction_diffusion.scad
new file mode 100644
index 00000000..e2970765
--- /dev/null
+++ b/src/experimental/reaction_diffusion.scad
@@ -0,0 +1,96 @@
+function init(x, y, n, ix, iy, in) = 
+    let(
+	    half_x = floor(x / 2),
+		half_y = floor(y / 2),
+		half_ix = floor(ix / 2),
+		half_iy = floor(iy / 2),
+		lowx = half_x - half_ix,
+		highx = half_x + half_ix,
+		lowy = half_y - half_iy,
+		highy = half_y + half_iy
+	)
+	[
+		for(j = [0:y - 1])
+		[
+			for(i = [0:x - 1])
+			i >= lowx && i < highx && j >= lowy && j < highy ?
+				in : n
+		]
+	];
+
+function gray_scott(u, v, feel, kill, Du, Dv, space_x, space_y) =
+    let(
+		nuv = [
+			for(y = [0:space_y - 1])
+			let(
+				uy = (y + 1 + space_y) % space_y,
+				ly = (y - 1 + space_y) % space_y,
+				row_u = u[y],
+				row_v = v[y],
+				row_uu = u[uy],
+				row_ul = u[ly],
+				row_vu = v[uy],
+				row_vl = v[ly]
+			)
+			[
+				for(x = [0:space_x - 1])
+				let(
+					cu = row_u[x],
+					cv = row_v[x],
+					rx = (x + 1 + space_x) % space_x,
+					lx = (x - 1 + space_x) % space_x,
+					reaction = cu * (cv ^ 2)
+				)
+                [
+					Du * (row_uu[x] + row_u[rx] + row_ul[x] + row_u[lx] - 4 * cu) - reaction + feel * (1 - cu), 
+					Dv * (row_vu[x] + row_v[rx] + row_vl[x] + row_v[lx] - 4 * cv) + reaction - (feel + kill) * cv
+				]
+			]
+		]
+	)
+	[
+	    u + [for(row = nuv) [for(uv = row) uv[0]]], 
+		v + [for(row = nuv) [for(uv = row) uv[1]]]
+	];
+	
+function _reaction_diffusion(feel, kill, generation, u, v, Du, Dv, space_x, space_y) = 
+    generation == 0 ? [u, v] :
+	let(nuv = gray_scott(u, v, feel, kill, Du, Dv, space_x, space_y))
+	_reaction_diffusion(feel, kill, generation - 1, nuv[0], nuv[1], Du, Dv, space_x, space_y);
+	
+function reaction_diffusion(
+    feel, kill, generation, space_size = [50, 50], init_size = [10, 10], init_u = 0.5, init_v = 0.25, Du = 0.2, Dv = 0.1) =
+	let(
+		u = init(space_size[0], space_size[1], 1, init_size[0], init_size[1], init_u),
+		v = init(space_size[0], space_size[1], 0, init_size[0], init_size[1], init_v)
+	)
+	_reaction_diffusion(feel, kill, generation, u, v, Du, Dv, space_size[0], space_size[1]);
+
+
+/*
+use <surface/sf_thicken.scad>;
+use <experimental/reaction_diffusion.scad>;
+
+feel = 0.04; 
+kill = 0.06;
+generation = 1000;
+thickness = 0.5;
+altitude_scale = 10;
+space_size = [50, 50];
+init_size = [10, 10];
+
+uv = reaction_diffusion(feel, kill, generation, space_size, init_size);
+
+leng_y = len(uv[0]);
+leng_x = len(uv[0][0]);
+
+points = [
+    for(y = [0:leng_y - 1])
+	[
+	     for(x = [0:leng_x - 1])
+		 [x, y, uv[0][y][x] * altitude_scale]
+	]
+];
+
+sf_thicken(points, thickness);
+*/
\ No newline at end of file