From 0bb7fa35cc340a65c944e546231632379bcfa30c Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Sat, 31 Jan 2026 15:44:30 +0100
Subject: 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.
---
 src/gpu/effect.cc | 38 ++++++++++++++++++++++++++++++++++++++
 src/gpu/effect.h  |  4 ++++
 src/gpu/gpu.cc    |  4 ++++
 src/gpu/gpu.h     |  1 +
 4 files changed, 47 insertions(+)

(limited to 'src/gpu')

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)
-- 
cgit v1.2.3