From 2d49d9db4712ae3cbd604ec7c9f8627e4f74bde6 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Tue, 25 Mar 2025 17:38:45 -0700
Subject: Add shatter wave gimmick

---
 math.cginc | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

(limited to 'math.cginc')

diff --git a/math.cginc b/math.cginc
index f44aa74..78b93ec 100644
--- a/math.cginc
+++ b/math.cginc
@@ -207,4 +207,24 @@ float median(float3 x) {
   return (x.r + x.g + x.b) - (x_min + x_max);
 }
 
+// Quaternions
+float4 qmul(float4 q1, float4 q2)
+{
+  return float4(
+      q2.xyz * q1.w + q1.xyz * q2.w + cross(q1.xyz, q2.xyz),
+      q1.w * q2.w - dot(q1.xyz, q2.xyz));
+}
+
+// Vector rotation with a quaternion
+// http://mathworld.wolfram.com/Quaternion.html
+float3 rotate_vector(float3 v, float4 r)
+{
+  float4 r_c = r * float4(-1, -1, -1, 1);
+  return qmul(r, qmul(float4(v, 0), r_c)).xyz;
+}
+
+float4 get_quaternion(float3 axis_normal, float theta) {
+  return float4(axis_normal * sin(theta / 2), cos(theta / 2));
+}
+
 #endif  // __MATH_INC
-- 
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