update TODO and fix shaders.cc

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diff --git a/TODO.md b/TODO.md
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@@ -19,6 +19,7 @@ This file tracks prioritized tasks with detailed attack plans.
 ## Priority 3: Shader Optimization (Task #21)
 **Goal:** Improve GPU performance and reduce shader source bloat.
 - [ ] **Attack Plan - Normal Factorization:** Create a standard WGSL helper for normal calculation to avoid duplicate code in every effect.
+- [ ] **Tri-planar or bi-planar mapping**: see https://iquilezles.org/articles/biplanar/ for instance
 
 ## Future Goals
 - [ ] **Task #5: Spectrogram Editor**: Web-based visual tool for extreme audio compression.