feat: Add --seek command line option for fast-forward debugging

This feature allows developers to jump to a specific time in the demo sequence (e.g., './demo64k --seek 10.5'). It simulates the game logic, audio state (rendering silent buffers), and visual physics (compute shaders) from t=0 up to the target time before starting real-time playback. Audio initialization is refactored to separate device init and start.

8 files changed, 101 insertions, 8 deletions

diff --git a/src/audio/audio.cc b/src/audio/audio.cc
index 6249479..517e376 100644
--- a/src/audio/audio.cc
+++ b/src/audio/audio.cc
@@ -38,7 +38,9 @@ void audio_init() {
     printf("Failed to open playback device.\n");
     return;
   }
+}
 
+void audio_start() {
   if (ma_device_start(&g_device) != MA_SUCCESS) {
     printf("Failed to start playback device.\n");
     ma_device_uninit(&g_device);
@@ -46,6 +48,19 @@ void audio_init() {
   }
 }
 
+void audio_render_silent(float duration_sec) {
+  const int sample_rate = 32000;
+  const int chunk_size = 512;
+  int total_frames = (int)(duration_sec * sample_rate);
+  float buffer[chunk_size * 2]; // Stereo
+
+  while (total_frames > 0) {
+    int frames_to_render = (total_frames > chunk_size) ? chunk_size : total_frames;
+    synth_render(buffer, frames_to_render);
+    total_frames -= frames_to_render;
+  }
+}
+
 void audio_update() {
 }
 
diff --git a/src/audio/audio.h b/src/audio/audio.h
index dd43d97..67c83c2 100644
--- a/src/audio/audio.h
+++ b/src/audio/audio.h
@@ -5,5 +5,7 @@
 #pragma once
 
 void audio_init();
+void audio_start(); // Starts the audio device callback
+void audio_render_silent(float duration_sec); // Fast-forwards audio state
 void audio_update();
 void audio_shutdown();
diff --git a/src/gpu/effect.cc b/src/gpu/effect.cc
index cfef7f9..040b523 100644
--- a/src/gpu/effect.cc
+++ b/src/gpu/effect.cc
@@ -195,6 +195,44 @@ void MainSequence::render_frame(float global_time, float beat, float peak,
   wgpuTextureRelease(surface_texture.texture);
 }
 
+void MainSequence::simulate_until(float target_time, float step_rate) {
+#ifndef STRIP_ALL
+  // Assuming 128 BPM as per main.cc.
+  // Ideally this should be passed in or shared.
+  const float bpm = 128.0f;
+  const float aspect_ratio = 16.0f / 9.0f; // Dummy aspect
+
+  for (float t = 0.0f; t < target_time; t += step_rate) {
+    WGPUCommandEncoderDescriptor encoder_desc = {};
+    WGPUCommandEncoder encoder = wgpuDeviceCreateCommandEncoder(device, &encoder_desc);
+
+    float beat = fmodf(t * bpm / 60.0f, 1.0f);
+
+    // Update active lists
+    for (auto &entry : sequences_) {
+      if (t >= entry.start_time) {
+        entry.seq->update_active_list(t - entry.start_time);
+      }
+    }
+
+    // Dispatch compute
+    for (auto &entry : sequences_) {
+      if (t >= entry.start_time) {
+        // peak = 0.0f during simulation (no audio analysis)
+        entry.seq->dispatch_compute(encoder, t - entry.start_time, beat, 0.0f, aspect_ratio);
+      }
+    }
+
+    WGPUCommandBufferDescriptor cmd_desc = {};
+    WGPUCommandBuffer commands = wgpuCommandEncoderFinish(encoder, &cmd_desc);
+    wgpuQueueSubmit(queue, 1, &commands);
+  }
+#else
+  (void)target_time;
+  (void)step_rate;
+#endif
+}
+
 void MainSequence::shutdown() {
     for (auto &entry : sequences_) {
         entry.seq->reset();
diff --git a/src/gpu/effect.h b/src/gpu/effect.h
index 50b2d72..f92e3ef 100644
--- a/src/gpu/effect.h
+++ b/src/gpu/effect.h
@@ -105,6 +105,10 @@ public:
   void render_frame(float global_time, float beat, float peak,
                     float aspect_ratio, WGPUSurface surface);
 
+  // Fast-forwards the simulation (updates & compute) without rendering.
+  // Used for seeking/debugging.
+  void simulate_until(float target_time, float step_rate);
+
   void shutdown();
 
 private:
diff --git a/src/gpu/gpu.cc b/src/gpu/gpu.cc
index 0655bb3..e68b84d 100644
--- a/src/gpu/gpu.cc
+++ b/src/gpu/gpu.cc
@@ -425,6 +425,10 @@ void gpu_draw(float audio_peak, float aspect_ratio, float time, float beat) {
   g_main_sequence.render_frame(time, beat, audio_peak, aspect_ratio, g_surface);
 }
 
+void gpu_simulate_until(float time) {
+  g_main_sequence.simulate_until(time, 1.0f / 60.0f);
+}
+
 void gpu_shutdown() {
   g_main_sequence.shutdown();
 }
\ No newline at end of file
diff --git a/src/gpu/gpu.h b/src/gpu/gpu.h
index f9c322c..1d79781 100644
--- a/src/gpu/gpu.h
+++ b/src/gpu/gpu.h
@@ -33,6 +33,7 @@ struct RenderPass {
 
 void gpu_init(GLFWwindow *window);
 void gpu_draw(float audio_peak, float aspect_ratio, float time, float beat);
+void gpu_simulate_until(float time);
 void gpu_shutdown();
 
 // Helper functions (exposed for internal/future use)
diff --git a/src/main.cc b/src/main.cc
index fb0b412..75143c0 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -130,12 +130,15 @@ float* generate_tone(float *buffer, float freq) {
 
 int main(int argc, char **argv) {
   bool fullscreen_enabled = false;
+  double seek_time = 0.0;
 
 #ifndef STRIP_ALL
   for (int i = 1; i < argc; ++i) {
     if (strcmp(argv[i], "--fullscreen") == 0) {
       fullscreen_enabled = true;
-      break;
+    } else if (strcmp(argv[i], "--seek") == 0 && i + 1 < argc) {
+      seek_time = atof(argv[i + 1]);
+      i++;
     }
   }
 #else
@@ -166,12 +169,9 @@ int main(int argc, char **argv) {
   double last_beat_time = 0.0;
   int beat_count = 0;
 
-  while (!platform_should_close()) {
-    platform_poll();
-
-    double current_time = platform_get_time();
-    if (current_time - last_beat_time > SECONDS_PER_BEAT / 2.0) { // 8th notes
-      last_beat_time = current_time;
+  auto update_game_logic = [&](double t) {
+    if (t - last_beat_time > SECONDS_PER_BEAT / 2.0) { // 8th notes
+      last_beat_time = t; // Sync to t
 
       const int step = beat_count % 16;
 
@@ -203,6 +203,34 @@ int main(int argc, char **argv) {
 
       ++beat_count;
     }
+  };
+
+#ifndef STRIP_ALL
+  if (seek_time > 0.0) {
+    printf("Seeking to %.2f seconds...\n", seek_time);
+    
+    // Simulate audio/game logic
+    // We step at ~60hz
+    const double step = 1.0/60.0;
+    for (double t = 0.0; t < seek_time; t += step) {
+      update_game_logic(t);
+      audio_render_silent((float)step);
+    }
+    
+    // Simulate Visuals
+    gpu_simulate_until((float)seek_time);
+  }
+#endif
+
+  // Start real audio
+  audio_start();
+
+  while (!platform_should_close()) {
+    platform_poll();
+
+    double current_time = platform_get_time() + seek_time; // Offset logic time
+    
+    update_game_logic(current_time);
 
     int width, height;
     glfwGetFramebufferSize(platform_get_window(), &width, &height);
@@ -221,4 +249,4 @@ int main(int argc, char **argv) {
   gpu_shutdown();
   platform_shutdown();
   return 0;
-}
+}
\ No newline at end of file
diff --git a/tools/spectool.cc b/tools/spectool.cc
index d9b58be..663056d 100644
--- a/tools/spectool.cc
+++ b/tools/spectool.cc
@@ -133,6 +133,7 @@ int play_spec(const char *in_path) {
 
   platform_init_window(false);
   audio_init();
+  audio_start();
   Spectrogram spec;
   spec.spectral_data_a = spec_data.data();
   spec.spectral_data_b =