From 3dcb2fd0e240f3c0141e65c32bc2c4a7f8e9fd20 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Sat, 13 Jul 2024 16:33:25 -0700
Subject: Integration pixellation and trochoid shaders

Trochoid is a WIP. Need to do some magic to make it properly shear. In
short: it's currently implemented as a standalone Mesh Renderer object
which I place on my avatar's neck bone. Since its object origin is not
at the hip bone like everything else, it behaves weirdly when shearing.

Solution is to implement it as a regular skinned mesh renderer. Requires
some careful analysis to get right.
---
 trochoid_math.cginc | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 trochoid_math.cginc

(limited to 'trochoid_math.cginc')

diff --git a/trochoid_math.cginc b/trochoid_math.cginc
new file mode 100644
index 0000000..f116db0
--- /dev/null
+++ b/trochoid_math.cginc
@@ -0,0 +1,90 @@
+#ifndef __TROCHOID_MATH
+#define __TROCHOID_MATH
+
+#if defined(_TROCHOID)
+
+#include "globals.cginc"
+
+#define PI 3.14159265
+#define TAU PI * 2.0
+
+float3 trochoid_map(float theta, float r0, float3 vert_z)
+{
+  r0 *= r0;
+  r0 *= 100;
+
+  float R = _Trochoid_R;
+  float r = _Trochoid_r;
+  float d = _Trochoid_d;
+
+  theta *= max(R, r);
+  float theta_t = theta + _Time[2];
+
+  float x = (R - r) * cos(theta_t) + d * cos((R - r) * theta_t / r);
+  float y = (R - r) * sin(theta_t) - d * sin((R - r) * theta_t / r);
+  float z = vert_z + cos(theta_t * 5) * .1 + theta * .0002;
+
+  float3 result = float3(x, y, z) * r0;
+  result.xy *= 0.1;
+  return result;
+}
+
+float trochoid_normal(float3 objPos, float2 uv)
+{
+  float theta = uv.x * TAU;
+  float r0 = length(objPos.xyz);
+
+  float x = objPos.x;
+  float y = objPos.y;
+  float z = objPos.z;
+
+  float e = 5E-2;
+  float small_step = 1E-2 * e;
+  float du_dt = (trochoid_map(theta + small_step, r0, z) - trochoid_map(theta - small_step, r0, z)) / small_step;
+  small_step = 1E-4 * e;
+  float du_dr = (trochoid_map(theta, r0 + small_step, z) - trochoid_map(theta, r0 - small_step, z)) / small_step;
+  small_step = 1E-5 * e;
+  float du_dz = (trochoid_map(theta, r0, z + small_step) - trochoid_map(theta, r0, z - small_step)) / small_step;
+
+  // U(T(x, y, z), R(x, y, z), Z(x, y, z))
+  // T(x, y, z) = atan2(y, x)
+  // R(x, y, z) = length(float3(x, y, z))
+  // Z(x, y, z) = z
+  // U(a, b, c) = trochoid_map(a, b, c)
+  // dU/dx = dU/dT dT/dx + dU/dR dR/dx + dU/dZ dZ/dx
+  // dU/dy = dU/dT dT/dy + dU/dR dR/dy + dU/dZ dZ/dy
+  // dU/dz = dU/dT dT/dz + dU/dR dR/dz + dU/dZ dZ/dz
+  // dT/dx = d/dx atan2(y, x) = -y / (x**2 + y**2)
+  // dT/dy = d/dx atan2(y, x) = x / (x**2 + y**2)
+  // dT/dz = d/dz atan2(y, x) = 0
+  // dR/dx = d/dx sqrt(x**2 + y**2 + z**2) = x / sqrt(x**2 + y**2 + z**2)
+  // dR/dy = d/dy sqrt(x**2 + y**2 + z**2) = y / sqrt(x**2 + y**2 + z**2)
+  // dR/dz = d/dy sqrt(x**2 + y**2 + z**2) = z / sqrt(x**2 + y**2 + z**2)
+  // dZ/dx = 0
+  // dZ/dy = 0
+  // dZ/dz = 1
+  float xy_norm = sqrt(x * x + y * y);
+  float dt_dx = -y / xy_norm;
+  float dt_dy = x / xy_norm;
+  float dt_dz = 0;
+  float xyz_norm = sqrt(x * x + y * y + z * z);
+  float dr_dx = x / xyz_norm;
+  float dr_dy = y / xyz_norm;
+  float dr_dz = z / xyz_norm;
+  float dz_dx = 0;
+  float dz_dy = 0;
+  float dz_dz = 1;
+
+  float3 normal =
+    normalize(
+        float3(
+          du_dt * dt_dx + du_dr * dr_dx + du_dz * dz_dx,
+          du_dt * dt_dy + du_dr * dr_dy + du_dz * dz_dy,
+          du_dt * dt_dz + du_dr * dr_dz + du_dz * dz_dz));
+  return UnityObjectToWorldNormal(normal);
+}
+
+#endif  // _TROCHOID
+
+#endif  // __TROCHOID_MATH
+
-- 
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