fix: calculate beat_phase for FlashEffect and refactor uniforms

- seq_compiler.py: Calculate beat_phase from beat_time (was hardcoded 0.0f)
- Refactor: Replace CommonPostProcessUniforms with UniformsSequenceParams
- Remove duplicate struct definition in post_process_helper.h
- Update all CNN effects and tests to use unified uniform struct
- Fixes FlashEffect showing solid white instead of flashing to beat

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

12 files changed, 23 insertions, 31 deletions

diff --git a/cnn_v1/src/cnn_v1_effect.cc b/cnn_v1/src/cnn_v1_effect.cc
index 1f44619..9118831 100644
--- a/cnn_v1/src/cnn_v1_effect.cc
+++ b/cnn_v1/src/cnn_v1_effect.cc
@@ -79,7 +79,7 @@ void CNNv1Effect::resize(int width, int height) {
 }
 
 void CNNv1Effect::render(WGPURenderPassEncoder pass,
-                       const CommonPostProcessUniforms& uniforms) {
+                       const UniformsSequenceParams& uniforms) {
   if (!bind_group_) {
     fprintf(stderr, "CNN render: no bind_group\n");
     return;
diff --git a/cnn_v1/src/cnn_v1_effect.h b/cnn_v1/src/cnn_v1_effect.h
index e820275..6753db8 100644
--- a/cnn_v1/src/cnn_v1_effect.h
+++ b/cnn_v1/src/cnn_v1_effect.h
@@ -26,7 +26,7 @@ class CNNv1Effect : public PostProcessEffect {
   void init(MainSequence* demo) override;
   void resize(int width, int height) override;
   void render(WGPURenderPassEncoder pass,
-              const CommonPostProcessUniforms& uniforms) override;
+              const UniformsSequenceParams& uniforms) override;
   void update_bind_group(WGPUTextureView input_view) override;
 
   // Layer 0 needs framebuffer capture for original input
diff --git a/cnn_v2/src/cnn_v2_effect.cc b/cnn_v2/src/cnn_v2_effect.cc
index 133087a..42aa2bb 100644
--- a/cnn_v2/src/cnn_v2_effect.cc
+++ b/cnn_v2/src/cnn_v2_effect.cc
@@ -377,7 +377,7 @@ void CNNv2Effect::update_bind_group(WGPUTextureView input_view) {
 }
 
 void CNNv2Effect::compute(WGPUCommandEncoder encoder,
-                          const CommonPostProcessUniforms& uniforms) {
+                          const UniformsSequenceParams& uniforms) {
   if (!initialized_ || !static_pipeline_ || !static_bind_group_)
     return;
 
@@ -446,7 +446,7 @@ void CNNv2Effect::compute(WGPUCommandEncoder encoder,
 }
 
 void CNNv2Effect::render(WGPURenderPassEncoder pass,
-                         const CommonPostProcessUniforms& uniforms) {
+                         const UniformsSequenceParams& uniforms) {
   (void)pass;
   (void)uniforms;
   // Compute-only effect, rendering is done by default composite pass
diff --git a/cnn_v2/src/cnn_v2_effect.h b/cnn_v2/src/cnn_v2_effect.h
index 7960b4f..b675736 100644
--- a/cnn_v2/src/cnn_v2_effect.h
+++ b/cnn_v2/src/cnn_v2_effect.h
@@ -19,9 +19,9 @@ class CNNv2Effect : public PostProcessEffect {
   void init(MainSequence* demo) override;
   void resize(int width, int height) override;
   void compute(WGPUCommandEncoder encoder,
-               const CommonPostProcessUniforms& uniforms) override;
+               const UniformsSequenceParams& uniforms) override;
   void render(WGPURenderPassEncoder pass,
-              const CommonPostProcessUniforms& uniforms) override;
+              const UniformsSequenceParams& uniforms) override;
   void update_bind_group(WGPUTextureView input_view) override;
 
   void set_beat_modulation(bool enabled, float scale = 1.0f) {
diff --git a/common/shaders/sequence_uniforms.wgsl b/common/shaders/sequence_uniforms.wgsl
index b302329..be47ad9 100644
--- a/common/shaders/sequence_uniforms.wgsl
+++ b/common/shaders/sequence_uniforms.wgsl
@@ -1,5 +1,5 @@
 // Sequence v2 uniform structure for WGSL shaders
-// Matches UniformsSequenceParams in sequence_v2.h
+// Matches UniformsSequenceParams in sequence.h
 
 struct UniformsSequenceParams {
     resolution: vec2<f32>,
diff --git a/src/app/test_demo.cc b/src/app/test_demo.cc
index cf1a577..83e6f8b 100644
--- a/src/app/test_demo.cc
+++ b/src/app/test_demo.cc
@@ -95,7 +95,7 @@ class PeakMeterEffect : public PostProcessEffectV2 {
   }
 
   void render(WGPURenderPassEncoder pass,
-              const CommonPostProcessUniforms& uniforms) override {
+              const UniformsSequenceParams& uniforms) override {
     uniforms_.update(ctx_.queue, uniforms);
     PostProcessEffect::render(pass, uniforms);
   }
diff --git a/src/gpu/post_process_helper.h b/src/gpu/post_process_helper.h
index 33ef20b..963f671 100644
--- a/src/gpu/post_process_helper.h
+++ b/src/gpu/post_process_helper.h
@@ -4,20 +4,10 @@
 #pragma once
 
 #include "gpu/gpu.h"
+#include "gpu/sequence.h"
 #include "util/mini_math.h"
 
-// Uniform data common to all post-processing effects
-struct CommonPostProcessUniforms {
-  vec2 resolution;       // Screen dimensions
-  float aspect_ratio;    // Width/height ratio
-  float time;            // Physical time in seconds (unaffected by tempo)
-  float beat_time;       // Musical time in beats (absolute, tempo-scaled)
-  float beat_phase;      // Fractional beat (0.0-1.0 within current beat)
-  float audio_intensity; // Audio peak for beat sync
-  float _pad;            // Padding for 16-byte alignment
-};
-static_assert(sizeof(CommonPostProcessUniforms) == 32,
-              "CommonPostProcessUniforms must be 32 bytes for WGSL alignment");
+// Use UniformsSequenceParams (defined in sequence.h) for post-process effects
 
 // Standard post-process bind group layout (group 0):
 #define PP_BINDING_SAMPLER 0       // Sampler for input texture
diff --git a/src/gpu/sdf_effect.h b/src/gpu/sdf_effect.h
index 4f23604..aacea69 100644
--- a/src/gpu/sdf_effect.h
+++ b/src/gpu/sdf_effect.h
@@ -12,7 +12,7 @@
 // Provides CameraParams uniform buffer and helper methods
 //
 // Binding convention:
-//   @group(0) @binding(2): CommonPostProcessUniforms (from Effect base)
+//   @group(0) @binding(2): UniformsSequenceParams (from Effect base)
 //   @group(0) @binding(3): CameraParams
 //   @group(0) @binding(4+): Per-effect custom parameters
 class SDFEffect : public Effect {
diff --git a/src/tests/assets/test_sequence.cc b/src/tests/assets/test_sequence.cc
index edf5c2d..445e44b 100644
--- a/src/tests/assets/test_sequence.cc
+++ b/src/tests/assets/test_sequence.cc
@@ -42,13 +42,13 @@ class DummyEffect : public Effect {
     ++start_calls;
   }
   void render(WGPURenderPassEncoder pass,
-              const CommonPostProcessUniforms& uniforms) override {
+              const UniformsSequenceParams& uniforms) override {
     ++render_calls;
     (void)pass;
     (void)uniforms;
   }
   void compute(WGPUCommandEncoder encoder,
-               const CommonPostProcessUniforms& uniforms) override {
+               const UniformsSequenceParams& uniforms) override {
     (void)encoder;
     (void)uniforms;
   }
@@ -75,7 +75,7 @@ class DummyPostProcessEffect : public PostProcessEffect {
     (void)demo;
   }
   void render(WGPURenderPassEncoder pass,
-              const CommonPostProcessUniforms& uniforms) override {
+              const UniformsSequenceParams& uniforms) override {
     ++render_calls;
     (void)pass;
     (void)uniforms;
diff --git a/tools/cnn_test.cc b/tools/cnn_test.cc
index d88956d..a209cdf 100644
--- a/tools/cnn_test.cc
+++ b/tools/cnn_test.cc
@@ -1332,7 +1332,7 @@ int main(int argc, char** argv) {
   // Create uniform buffers
   const WGPUBufferDescriptor common_uniform_desc = {
       .usage = WGPUBufferUsage_Uniform | WGPUBufferUsage_CopyDst,
-      .size = sizeof(CommonPostProcessUniforms),
+      .size = sizeof(UniformsSequenceParams),
   };
   WGPUBuffer common_uniform_buffer =
       wgpuDeviceCreateBuffer(device, &common_uniform_desc);
@@ -1384,7 +1384,7 @@ int main(int argc, char** argv) {
     printf("Processing layer %d/%d...\n", layer + 1, NUM_LAYERS);
 
     // Update uniforms
-    CommonPostProcessUniforms common_u = {
+    UniformsSequenceParams common_u = {
         .resolution = {static_cast<float>(width), static_cast<float>(height)},
         .aspect_ratio = static_cast<float>(width) / static_cast<float>(height),
         .time = 0.0f,
@@ -1410,7 +1410,7 @@ int main(int argc, char** argv) {
         BindGroupBuilder()
             .sampler(0, sampler)
             .texture(1, current_input)
-            .buffer(2, common_uniform_buffer, sizeof(CommonPostProcessUniforms))
+            .buffer(2, common_uniform_buffer, sizeof(UniformsSequenceParams))
             .buffer(3, layer_params_buffer, sizeof(CNNv1LayerParams))
             .texture(4, original_view)
             .build(device, bgl);
diff --git a/tools/seq_compiler.py b/tools/seq_compiler.py
index 6b72ebd..3b8d126 100755
--- a/tools/seq_compiler.py
+++ b/tools/seq_compiler.py
@@ -516,7 +516,8 @@ void RenderTimeline(WGPUCommandEncoder encoder, float time, int width, int heigh
                       float beat_time, float audio_intensity) {
     Sequence* seq = GetActiveSequence(time);
     if (seq) {
-        seq->preprocess(time, beat_time, 0.0f, audio_intensity);
+        float beat_phase = fmodf(beat_time, 1.0f);
+        seq->preprocess(time, beat_time, beat_phase, audio_intensity);
         seq->render_effects(encoder);
     }
 }
@@ -584,7 +585,8 @@ void RenderTimeline(WGPUSurface surface, float time, int width, int height,
     seq->set_sink_view(g_sink_view);
 
     // Update uniforms via preprocess
-    seq->preprocess(time, beat_time, 0.0f, audio_intensity);
+    float beat_phase = fmodf(beat_time, 1.0f);
+    seq->preprocess(time, beat_time, beat_phase, audio_intensity);
 
     WGPUCommandEncoder encoder = wgpuDeviceCreateCommandEncoder(ctx->device, nullptr);
 
diff --git a/tools/shadertoy/template.cc b/tools/shadertoy/template.cc
index 7636c0a..56b4ab5 100644
--- a/tools/shadertoy/template.cc
+++ b/tools/shadertoy/template.cc
@@ -83,7 +83,7 @@ void ShaderToyEffect::init(MainSequence* demo) {
       {.binding = 1, .textureView = prev_view},
       {.binding = 2,
        .buffer = uniforms_.get().buffer,
-       .size = sizeof(CommonPostProcessUniforms)},
+       .size = sizeof(UniformsSequenceParams)},
       {.binding = 3,
        .buffer = params_.get().buffer,
        .size = sizeof(ShaderToyParams)},
@@ -98,7 +98,7 @@ void ShaderToyEffect::init(MainSequence* demo) {
 
 void ShaderToyEffect::render(WGPURenderPassEncoder pass, float time, float beat,
                              float intensity, float aspect_ratio) {
-  const CommonPostProcessUniforms uniforms = {
+  const UniformsSequenceParams uniforms = {
       .resolution = {static_cast<float>(width_), static_cast<float>(height_)},
       .aspect_ratio = aspect_ratio,
       .time = time,