refactor(shaders): extract oct-normal encode/decode into math/normal snippet

New src/shaders/math/normal.wgsl: oct_encode, oct_decode, oct_encode_unorm,
oct_decode_unorm. Registered in InitShaderComposer as "math/normal".
Removed inline copies from gbuf_raster.wgsl and gbuf_pack.wgsl.
18/18 tests passing.

1 files changed, 2 insertions, 10 deletions

diff --git a/cnn_v3/shaders/gbuf_pack.wgsl b/cnn_v3/shaders/gbuf_pack.wgsl
index 71d8471..333589c 100644
--- a/cnn_v3/shaders/gbuf_pack.wgsl
+++ b/cnn_v3/shaders/gbuf_pack.wgsl
@@ -1,4 +1,5 @@
 // G-buffer pack compute shader for CNN v3
+#include "math/normal"
 // Pass 4: Pack all G-buffer channels into two rgba32uint feature textures (32 bytes/pixel)
 // Output feat_tex0 holds 8×f16 geometric channels; feat_tex1 holds 12×u8 context channels.
 
@@ -44,15 +45,6 @@ fn box4(tl: vec2i) -> vec3f {
     return acc * (1.0 / 16.0);
 }
 
-// Decode oct-normal from [0,1] storage → [-1,1] encoded xy → reconstruct z.
-fn decode_oct_normal(rg: vec2f) -> vec3f {
-    let f = rg * 2.0 - vec2f(1.0);
-    var n = vec3f(f.x, f.y, 1.0 - abs(f.x) - abs(f.y));
-    let t = max(-n.z, 0.0);
-    n.x += select(t, -t, n.x >= 0.0);
-    n.y += select(t, -t, n.y >= 0.0);
-    return normalize(n);
-}
 
 @compute @workgroup_size(8, 8)
 fn pack_features(@builtin(global_invocation_id) id: vec3u) {
@@ -73,7 +65,7 @@ fn pack_features(@builtin(global_invocation_id) id: vec3u) {
 
     // Normal: stored as oct-encoded [0,1] in RG; extract just the encoded xy for feat_tex0
     let normal_enc = nm.rg; // already in [0,1] — decode to get the xy for CNN input
-    let n3         = decode_oct_normal(normal_enc);
+    let n3         = oct_decode_unorm(normal_enc);
     // Store oct-encoded in [-1,1] remapped back to what CNN expects (the [-1,1] oct xy)
     let oct_xy     = normal_enc * 2.0 - vec2f(1.0); // remap [0,1] → [-1,1]