1 files changed, 105 insertions, 0 deletions
diff --git a/src/effects/theme_modulation_effect.cc b/src/effects/theme_modulation_effect.cc
new file mode 100644
index 0000000..1c81d79
--- /dev/null
+++ b/src/effects/theme_modulation_effect.cc
@@ -0,0 +1,105 @@
+// This file is part of the 64k demo project.
+// It implements theme modulation (bright/dark alternation).
+
+#include "effects/theme_modulation_effect.h"
+#include "gpu/post_process_helper.h"
+#include "gpu/shaders.h"
+#include <cmath>
+
+struct ThemeModulationParams {
+  float theme_brightness;
+  float _pad[3];
+};
+static_assert(sizeof(ThemeModulationParams) == 16, "ThemeModulationParams must be 16 bytes for WGSL alignment");
+
+ThemeModulationEffect::ThemeModulationEffect(const GpuContext& ctx)
+    : PostProcessEffect(ctx) {
+  const char* shader_code = R"(
+    struct VertexOutput {
+      @builtin(position) position: vec4<f32>,
+      @location(0) uv: vec2<f32>,
+    };
+
+    struct CommonUniforms {
+      resolution: vec2<f32>,
+      _pad0: f32,
+      _pad1: f32,
+      aspect_ratio: f32,
+      time: f32,
+      beat: f32,
+      audio_intensity: f32,
+    };
+
+    struct ThemeModulationParams {
+      theme_brightness: f32,
+      _pad0: f32,
+      _pad1: f32,
+      _pad2: f32,
+    };
+
+    @group(0) @binding(0) var inputSampler: sampler;
+    @group(0) @binding(1) var inputTexture: texture_2d<f32>;
+    @group(0) @binding(2) var<uniform> uniforms: CommonUniforms;
+    @group(0) @binding(3) var<uniform> params: ThemeModulationParams;
+
+    @vertex
+    fn vs_main(@builtin(vertex_index) vertexIndex: u32) -> VertexOutput {
+      var output: VertexOutput;
+      // Large triangle trick for fullscreen coverage
+      var pos = array<vec2<f32>, 3>(
+        vec2<f32>(-1.0, -1.0),
+        vec2<f32>(3.0, -1.0),
+        vec2<f32>(-1.0, 3.0)
+      );
+      output.position = vec4<f32>(pos[vertexIndex], 0.0, 1.0);
+      output.uv = pos[vertexIndex] * 0.5 + 0.5;
+      return output;
+    }
+
+    @fragment
+    fn fs_main(input: VertexOutput) -> @location(0) vec4<f32> {
+      let color = textureSample(inputTexture, inputSampler, input.uv);
+      // Apply theme brightness modulation
+      return vec4<f32>(color.rgb * params.theme_brightness, color.a);
+    }
+  )";
+
+  pipeline_ =
+      create_post_process_pipeline(ctx_.device, ctx_.format, shader_code);
+
+  params_buffer_ = gpu_create_buffer(
+      ctx_.device, 16, WGPUBufferUsage_Uniform | WGPUBufferUsage_CopyDst);
+}
+
+void ThemeModulationEffect::update_bind_group(WGPUTextureView input_view) {
+  pp_update_bind_group(ctx_.device, pipeline_, &bind_group_, input_view,
+                       uniforms_.get(), params_buffer_);
+}
+
+void ThemeModulationEffect::render(WGPURenderPassEncoder pass,
+                                   const CommonPostProcessUniforms& uniforms) {
+  uniforms_.update(ctx_.queue, uniforms);
+
+  // Alternate between bright and dark every 4 seconds (2 pattern changes)
+  // Music patterns change every 2 seconds at 120 BPM
+  float cycle_time = fmodf(uniforms.time, 8.0f);        // 8 second cycle (4 patterns)
+  bool is_dark_section = (cycle_time >= 4.0f); // Dark for second half
+
+  // Smooth transition between themes using a sine wave
+  float transition =
+      (std::sin(uniforms.time * 3.14159f / 4.0f) + 1.0f) * 0.5f; // 0.0 to 1.0
+  float bright_value = 1.0f;
+  float dark_value = 0.35f;
+  float theme_brightness =
+      bright_value + (dark_value - bright_value) * transition;
+
+  // Update params buffer
+  ThemeModulationParams params = {theme_brightness, {0.0f, 0.0f, 0.0f}};
+  wgpuQueueWriteBuffer(ctx_.queue, params_buffer_.buffer, 0, &params,
+                       sizeof(params));
+
+  // Render
+  wgpuRenderPassEncoderSetPipeline(pass, pipeline_);
+  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_, 0, nullptr);
+  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
+}