feat: Add --shader-only option to convert_shadertoy.py

Allows regenerating just the .wgsl shader file without touching
.h/.cc files when iterating on shader code.

Usage: ./tools/shadertoy/convert_shadertoy.py shader.txt EffectName --shader-only

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

2 files changed, 15 insertions, 1 deletions

diff --git a/tools/shadertoy/README.md b/tools/shadertoy/README.md
index d12865f..283a65f 100644
--- a/tools/shadertoy/README.md
+++ b/tools/shadertoy/README.md
@@ -19,6 +19,9 @@ EOF
 # Generate effect files
 ./tools/shadertoy/convert_shadertoy.py tunnel.txt Tunnel
 
+# Regenerate only shader (if .h/.cc already exist)
+./tools/shadertoy/convert_shadertoy.py tunnel.txt Tunnel --shader-only
+
 # Follow printed instructions to integrate
 ```
 
diff --git a/tools/shadertoy/convert_shadertoy.py b/tools/shadertoy/convert_shadertoy.py
index 2f402cc..e85f384 100755
--- a/tools/shadertoy/convert_shadertoy.py
+++ b/tools/shadertoy/convert_shadertoy.py
@@ -296,15 +296,17 @@ def generate_shader(effect_name, shadertoy_code, is_post_process=False):
 
 def main():
     if len(sys.argv) < 3:
-        print("Usage: convert_shadertoy.py <shader.txt> <EffectName> [--post-process]")
+        print("Usage: convert_shadertoy.py <shader.txt> <EffectName> [--post-process] [--shader-only]")
         print()
         print("Examples:")
         print("  ./tools/shadertoy/convert_shadertoy.py tunnel.txt Tunnel")
         print("  ./tools/shadertoy/convert_shadertoy.py blur.txt Blur --post-process")
+        print("  ./tools/shadertoy/convert_shadertoy.py tunnel.txt Tunnel --shader-only")
         print()
         print("Options:")
         print("  --post-process  Generate post-process effect (operates on previous frame)")
         print("                  Default: scene effect (renders geometry)")
+        print("  --shader-only   Only regenerate .wgsl shader (skip .h/.cc files)")
         print()
         print("This will generate:")
         print("  src/gpu/effects/<effect>_effect.h")
@@ -315,6 +317,7 @@ def main():
     shader_file = sys.argv[1]
     effect_name = sys.argv[2]
     is_post_process = '--post-process' in sys.argv
+    shader_only = '--shader-only' in sys.argv
 
     # Ensure effect name is CamelCase
     if '_' in effect_name:
@@ -339,6 +342,14 @@ def main():
     shader_path = repo_root / "workspaces" / "main" / "shaders" / f"{snake_name}.wgsl"
 
     # Generate files
+    if shader_only:
+        print(f"Regenerating shader only: {effect_name}")
+        print(f"  Shader:     {shader_path}")
+        print()
+        shader_path.write_text(generate_shader(effect_name, shadertoy_code, is_post_process))
+        print(f"✓ Shader regenerated")
+        return
+
     print(f"Generating effect: {effect_name}")
     print(f"  Header:     {header_path}")
     print(f"  Impl:       {impl_path}")