From 61edcfabd20775828a6c8c321494686b7ccf2bb1 Mon Sep 17 00:00:00 2001
From: xfy <i@rua.plus>
Date: Tue, 14 Jul 2026 14:12:31 +0800
Subject: [PATCH] feat: plumb spin parameter into GPU uniform

---
 assets/shaders/black_hole.wgsl | 2 +-
 src/render/material.rs         | 4 ++--
 src/render/plugin.rs           | 1 +
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/assets/shaders/black_hole.wgsl b/assets/shaders/black_hole.wgsl
index 4b5a112..455e4c6 100644
--- a/assets/shaders/black_hole.wgsl
+++ b/assets/shaders/black_hole.wgsl
@@ -33,7 +33,7 @@ struct BlackHoleUniforms {
     grid_enabled: u32,
     planet_count: u32,
     steps: u32,
-    _pad4: f32,
+    spin: f32,
     _pad5: f32,
 };
 
diff --git a/src/render/material.rs b/src/render/material.rs
index 9fc639f..9d1bc24 100644
--- a/src/render/material.rs
+++ b/src/render/material.rs
@@ -37,7 +37,7 @@ pub struct BlackHoleUniforms {
     pub grid_enabled: u32,
     pub planet_count: u32,
     pub steps: u32,
-    pub _pad4: f32,
+    pub spin: f32,       // Phase 2: dimensionless Kerr spin χ = a/M ∈ [0,1].
     pub _pad5: f32,
 }
 
@@ -69,7 +69,7 @@ impl Default for BlackHoleUniforms {
             grid_enabled: 0,
             planet_count: 0,
             steps: 300,
-            _pad4: 0.0,
+            spin: 0.0,
             _pad5: 0.0,
         }
     }
diff --git a/src/render/plugin.rs b/src/render/plugin.rs
index 69eb9ff..9d05295 100644
--- a/src/render/plugin.rs
+++ b/src/render/plugin.rs
@@ -226,5 +226,6 @@ fn mirror_params(
         u.grid_enabled = params.grid_enabled as u32;
         u.planet_count = params.planet_count;
         u.steps = params.steps;
+        u.spin = params.spin;
     }
 }