fix(audio): Remove sample offsets - incompatible with tempo scaling

This fixes the irregular timing caused by mixing music time and physical time.

ROOT CAUSE (THE REAL BUG):
Sample offset calculation was mixing two incompatible time domains:
1. event_trigger_time: in MUSIC TIME (tempo-scaled, can be 2x faster)
2. current_render_time: in PHYSICAL TIME (1:1 with real time, not scaled)

When tempo != 1.0, these diverge dramatically:
  Example at 2.0x tempo:
    - Music time: 10.0s (advanced 2x faster)
    - Physical render time: 5.0s (real time elapsed)
    - Calculated offset: (10.0 - 5.0) * 32000 = 160000 samples = 5 SECONDS!
    - Result: Event triggers 5 seconds late

This caused irregular timing because:
- At tempo 1.0x: offsets were roughly correct (domains aligned)
- At tempo != 1.0x: offsets were wildly wrong (domains diverged)
- Result: Random jitter as tempo changed

WHY WAV DUMP WORKED:
WAV dump doesn't use tempo scaling (g_tempo_scale = 1.0), so music_time ≈
physical_time and the domains stayed aligned by accident.

THE SOLUTION:
Remove sample offsets entirely. Trigger events immediately when music_time
passes their trigger time. Accept ~16ms quantization (one frame at 60fps).

TRADE-OFFS:
- Before: Attempted sample-accurate timing (but broken with tempo scaling)
- After: ~16ms quantization (acceptable for rhythmic events)
- Benefit: Consistent timing across all tempo values
- Benefit: Same behavior in WAV dump and miniaudio playback

CHANGES:
- tracker.cc: Remove offset calculation, always pass offset=0
- Simplify event triggering logic
- Add comment explaining why offsets don't work with tempo scaling

Previous commits (9cae6f1, 7271773) attempted to fix this with render_time
tracking, but missed the fundamental issue: you can't calculate sample offsets
when event times and render times are in different time domains.

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

1 files changed, 7 insertions, 20 deletions

diff --git a/src/audio/tracker.cc b/src/audio/tracker.cc
index 1cccc57..fd25e84 100644
--- a/src/audio/tracker.cc
+++ b/src/audio/tracker.cc
@@ -239,10 +239,10 @@ void tracker_update(float music_time_sec) {
   }
 
   // Step 2: Update all active patterns and trigger individual events
-  // Get current audio RENDER position (write position) for sample-accurate timing
-  // This is where we're currently writing to the ring buffer (~400ms ahead of playback)
-  const float current_render_time = audio_get_render_time();
-  const float SAMPLE_RATE = 32000.0f; // Audio sample rate
+  // NOTE: We trigger events immediately when their time passes (no sample offsets)
+  // This gives ~16ms quantization (60fps) which is acceptable
+  // Sample offsets don't work with tempo scaling because music_time and render_time
+  // are in different time domains (tempo-scaled vs physical)
 
   for (int i = 0; i < MAX_SPECTROGRAMS; ++i) {
     if (!g_active_patterns[i].active)
@@ -262,22 +262,9 @@ void tracker_update(float music_time_sec) {
       if (event.unit_time > elapsed_units)
         break; // This event hasn't reached its time yet
 
-      // Calculate exact trigger time for this event
-      const float event_trigger_time = active.start_music_time +
-                                       (event.unit_time * unit_duration_sec);
-
-      // Calculate sample-accurate offset from current RENDER position (write pos)
-      // This is where we're currently writing to the buffer, not where playback is
-      const float time_delta = event_trigger_time - current_render_time;
-      int sample_offset = (int)(time_delta * SAMPLE_RATE);
-
-      // Clamp to 0 if negative (event is late, play immediately)
-      if (sample_offset < 0) {
-        sample_offset = 0;
-      }
-
-      // Trigger this event as an individual voice with sample-accurate timing
-      trigger_note_event(event, sample_offset);
+      // Trigger this event immediately (no sample offset)
+      // Timing quantization: ~16ms at 60fps, acceptable for rhythm
+      trigger_note_event(event, 0);
 
       active.next_event_idx++;
     }