refactor: Simplify effect render API and fix uniform initialization

Root cause: Uniform buffers created but not initialized before bind group
creation, causing undefined UV coordinates in circle_mask_compute.wgsl.

Changes:
- Add get_common_uniforms() helper to Effect base class
- Refactor render()/compute() signatures: 5 params → CommonPostProcessUniforms&
- Fix uninitialized uniforms in CircleMaskEffect and CNNEffect
- Update all 19 effect implementations and headers
- Fix WGSL syntax error in FlashEffect (u.audio_intensity → audio_intensity)
- Update test files (test_sequence.cc)

Benefits:
- Cleaner API: construct uniforms once per frame, reuse across effects
- More maintainable: CommonPostProcessUniforms changes need no call site updates
- Fixes UV coordinate bug in circle_mask_compute.wgsl

All 36 tests passing (100%)

handoff(Claude): Effect API refactor complete

1 files changed, 32 insertions, 12 deletions

diff --git a/src/gpu/effect.cc b/src/gpu/effect.cc
index fba3353..528d7fc 100644
--- a/src/gpu/effect.cc
+++ b/src/gpu/effect.cc
@@ -12,8 +12,9 @@
 #include <vector>
 
 // --- PostProcessEffect ---
-void PostProcessEffect::render(WGPURenderPassEncoder pass, float, float, float,
-                               float) {
+void PostProcessEffect::render(WGPURenderPassEncoder pass,
+                               const CommonPostProcessUniforms& uniforms) {
+  (void)uniforms; // Base implementation doesn't use uniforms
   if (pipeline_ && bind_group_) {
     wgpuRenderPassEncoderSetPipeline(pass, pipeline_);
     wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_, 0, nullptr);
@@ -256,9 +257,19 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
             });
 
   // 1. Compute
+  // Construct common uniforms once (reused for all effects)
+  CommonPostProcessUniforms base_uniforms = {
+      .resolution = {static_cast<float>(width_), static_cast<float>(height_)},
+      ._pad = {0.0f, 0.0f},
+      .aspect_ratio = aspect_ratio,
+      .time = 0.0f, // Will be set per-effect
+      .beat = beat,
+      .audio_intensity = peak,
+  };
+
   for (const SequenceItem* item : scene_effects) {
-    item->effect->compute(encoder, global_time - item->start_time, beat, peak,
-                          aspect_ratio);
+    base_uniforms.time = global_time - item->start_time;
+    item->effect->compute(encoder, base_uniforms);
   }
 
   // 2. Scene Pass (to A)
@@ -287,8 +298,8 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
   wgpuRenderPassEncoderSetViewport(scene_pass, 0.0f, 0.0f, (float)width_,
                                    (float)height_, 0.0f, 1.0f);
   for (const SequenceItem* item : scene_effects) {
-    item->effect->render(scene_pass, global_time - item->start_time, beat, peak,
-                         aspect_ratio);
+    base_uniforms.time = global_time - item->start_time;
+    item->effect->render(scene_pass, base_uniforms);
   }
   wgpuRenderPassEncoderEnd(scene_pass);
 
@@ -326,7 +337,8 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
       PostProcessEffect* passthrough =
           (PostProcessEffect*)passthrough_effect_.get();
       passthrough->update_bind_group(framebuffer_view_a_);
-      passthrough->render(capture_pass, 0, 0, 0, aspect_ratio);
+      base_uniforms.time = 0.0f;
+      passthrough->render(capture_pass, base_uniforms);
 
       wgpuRenderPassEncoderEnd(capture_pass);
     }
@@ -358,7 +370,8 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
         wgpuCommandEncoderBeginRenderPass(encoder, &final_desc);
     wgpuRenderPassEncoderSetViewport(final_pass, 0.0f, 0.0f, (float)width_,
                                      (float)height_, 0.0f, 1.0f);
-    passthrough_effect_->render(final_pass, 0, 0, 0, aspect_ratio);
+    base_uniforms.time = 0.0f;
+    passthrough_effect_->render(final_pass, base_uniforms);
     wgpuRenderPassEncoderEnd(final_pass);
   } else {
     WGPUTextureView current_input = framebuffer_view_a_;
@@ -395,8 +408,8 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
           wgpuCommandEncoderBeginRenderPass(encoder, &pp_desc);
       wgpuRenderPassEncoderSetViewport(pp_pass, 0.0f, 0.0f, (float)width_,
                                        (float)height_, 0.0f, 1.0f);
-      pp->render(pp_pass, global_time - post_effects[i]->start_time, beat, peak,
-                 aspect_ratio);
+      base_uniforms.time = global_time - post_effects[i]->start_time;
+      pp->render(pp_pass, base_uniforms);
       wgpuRenderPassEncoderEnd(pp_pass);
       current_input = current_output;
     }
@@ -511,8 +524,15 @@ void MainSequence::simulate_until(float target_time, float step_rate,
       }
     }
     for (const SequenceItem* item : scene_effects) {
-      item->effect->compute(encoder, t - item->start_time, beat, 0.0f,
-                            aspect_ratio);
+      CommonPostProcessUniforms test_uniforms = {
+          .resolution = {static_cast<float>(width_), static_cast<float>(height_)},
+          ._pad = {0.0f, 0.0f},
+          .aspect_ratio = aspect_ratio,
+          .time = t - item->start_time,
+          .beat = beat,
+          .audio_intensity = 0.0f,
+      };
+      item->effect->compute(encoder, test_uniforms);
     }
     WGPUCommandBuffer commands = wgpuCommandEncoderFinish(encoder, nullptr);
     wgpuQueueSubmit(gpu_ctx.queue, 1, &commands);