fix(tools/shadertoy): fix Next Steps instructions and update EFFECT_WORKFLOW.md

- Fix assets.txt path: shaders/xxx.wgsl (not ../../src/shaders/)
- Fix shader output path to workspaces/main/shaders/
- Step 5: reference cmake/DemoSourceLists.cmake COMMON_GPU_EFFECTS (not CMakeLists.txt GPU_SOURCES)
- Add step for test_demo_effects.cc

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

5 files changed, 75 insertions, 0 deletions

diff --git a/src/effects/scene2_effect.cc b/src/effects/scene2_effect.cc
new file mode 100644
index 0000000..b1b9975
--- /dev/null
+++ b/src/effects/scene2_effect.cc
@@ -0,0 +1,47 @@
+// This file is part of the 64k demo project.
+// Scene2 effect - ShaderToy conversion (scene)
+// Generated by convert_shadertoy.py
+
+#include "effects/scene2_effect.h"
+#include "effects/shaders.h"
+#include "gpu/gpu.h"
+#include "gpu/post_process_helper.h"
+#include "util/fatal_error.h"
+
+Scene2Effect::Scene2Effect(const GpuContext& ctx,
+                            const std::vector<std::string>& inputs,
+                            const std::vector<std::string>& outputs,
+                            float start_time, float end_time)
+    : Effect(ctx, inputs, outputs, start_time, end_time) {
+  HEADLESS_RETURN_IF_NULL(ctx_.device);
+  create_nearest_sampler();
+  create_dummy_scene_texture();
+  pipeline_.set(create_post_process_pipeline(
+      ctx_.device, WGPUTextureFormat_RGBA8Unorm, scene2_shader_wgsl));
+}
+
+void Scene2Effect::render(WGPUCommandEncoder encoder,
+                           const UniformsSequenceParams& params,
+                           NodeRegistry& nodes) {
+  WGPUTextureView output_view = nodes.get_view(output_nodes_[0]);
+
+  // uniforms_buffer_ auto-updated by base class dispatch_render()
+  pp_update_bind_group(ctx_.device, pipeline_.get(), bind_group_.get_address(),
+                       dummy_texture_view_.get(), uniforms_buffer_.get(),
+                       {nullptr, 0});
+
+  WGPURenderPassColorAttachment color_attachment = {};
+  gpu_init_color_attachment(color_attachment, output_view);
+
+  WGPURenderPassDescriptor pass_desc = {};
+  pass_desc.colorAttachmentCount = 1;
+  pass_desc.colorAttachments = &color_attachment;
+
+  WGPURenderPassEncoder pass =
+      wgpuCommandEncoderBeginRenderPass(encoder, &pass_desc);
+  wgpuRenderPassEncoderSetPipeline(pass, pipeline_.get());
+  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_.get(), 0, nullptr);
+  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
+  wgpuRenderPassEncoderEnd(pass);
+  wgpuRenderPassEncoderRelease(pass);
+}
diff --git a/src/effects/scene2_effect.h b/src/effects/scene2_effect.h
new file mode 100644
index 0000000..effc19f
--- /dev/null
+++ b/src/effects/scene2_effect.h
@@ -0,0 +1,24 @@
+// This file is part of the 64k demo project.
+// Scene2 effect - ShaderToy conversion (scene)
+// Generated by convert_shadertoy.py
+
+#pragma once
+
+#include "gpu/effect.h"
+#include "gpu/wgpu_resource.h"
+
+class Scene2Effect : public Effect {
+ public:
+  Scene2Effect(const GpuContext& ctx,
+               const std::vector<std::string>& inputs,
+               const std::vector<std::string>& outputs,
+               float start_time, float end_time);
+
+  void render(WGPUCommandEncoder encoder,
+              const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+ private:
+  RenderPipeline pipeline_;
+  BindGroup bind_group_;
+};
diff --git a/src/effects/shaders.cc b/src/effects/shaders.cc
index 7e32aa6..c6a81d0 100644
--- a/src/effects/shaders.cc
+++ b/src/effects/shaders.cc
@@ -96,6 +96,7 @@ const char* rotating_cube_wgsl =
     SafeGetAsset(AssetId::ASSET_SHADER_ROTATING_CUBE_V2);
 const char* flash_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_FLASH);
 const char* scene1_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_SCENE1);
+const char* scene2_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_SCENE2);
 
 // Compute shaders
 const char* gen_noise_compute_wgsl =
diff --git a/src/effects/shaders.h b/src/effects/shaders.h
index ee6c65e..5fc442a 100644
--- a/src/effects/shaders.h
+++ b/src/effects/shaders.h
@@ -15,6 +15,7 @@ extern const char* particle_render_wgsl;
 extern const char* rotating_cube_wgsl;
 extern const char* flash_shader_wgsl;
 extern const char* scene1_shader_wgsl;
+extern const char* scene2_shader_wgsl;
 
 // Compute shaders
 extern const char* gen_noise_compute_wgsl;
diff --git a/src/gpu/demo_effects.h b/src/gpu/demo_effects.h
index f746326..e1a9c17 100644
--- a/src/gpu/demo_effects.h
+++ b/src/gpu/demo_effects.h
@@ -27,6 +27,8 @@
 #include "effects/placeholder_effect.h"
 #include "effects/rotating_cube_effect.h"
 #include "effects/scene1_effect.h"
+#include "effects/scene2_effect.h"
+
 // TODO: Port CNN effects
 // #include "../../cnn_v1/src/cnn_v1_effect.h"
 // #include "../../cnn_v2/src/cnn_v2_effect.h"