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diff --git a/BEAT_TIMING_SUMMARY.md b/BEAT_TIMING_SUMMARY.md new file mode 100644 index 0000000..e593380 --- /dev/null +++ b/BEAT_TIMING_SUMMARY.md @@ -0,0 +1,251 @@ +# Beat-Based Timing System + +## Summary + +**Timeline sequences now use musical beats as the primary time unit**, ensuring visual effects stay synchronized to music structure regardless of BPM changes. Variable tempo only affects audio sample triggering—visual effects run at constant physical time with optional beat-synchronized animation. + +**Key Change:** `CommonPostProcessUniforms` now provides both `time` (physical seconds) and `beat_time` (absolute beats) + `beat_phase` (fractional 0-1) for flexible animation. + +--- + +## Changes Made + +### 1. **Documentation Updated** +- `doc/SEQUENCE.md`: Beat-based format as primary, updated runtime parameters +- `tools/timeline_editor/README.md`: Beat notation as default + +### 2. **Uniform Structure Enhanced** +```cpp +struct CommonPostProcessUniforms { + vec2 resolution; // Screen dimensions + float aspect_ratio; // Width/height ratio + float time; // Physical seconds (unaffected by tempo) + float beat_time; // NEW: Absolute beats (musical time) + float beat_phase; // NEW: Fractional beat 0-1 (was "beat") + float audio_intensity; // Audio peak + float _pad; // Alignment +}; // 32 bytes (unchanged size) +``` + +### 3. **Shader Updates** +- All `common_uniforms.wgsl` files updated with new field names +- Effects can now use: + - `time` for physics-based animation (constant speed) + - `beat_time` for musical animation (bars/beats) + - `beat_phase` for smooth per-beat oscillation + +### 4. **Seq Compiler** +- `tools/seq_compiler.cc`: Beat notation as default parser behavior +- Format: `5` = beats, `2.5s` = explicit seconds +- BPM-based conversion at compile time (beats → seconds) + +### 5. **Timeline Files Converted** +- `workspaces/main/timeline.seq`: Added 's' suffix to preserve timing +- `workspaces/test/timeline.seq`: Added 's' suffix to preserve timing +- Existing demos run unchanged with explicit seconds notation + +### 6. **Runtime Updates** +- `main.cc`: Calculates `beat_time` and `beat_phase` from audio time +- `gpu.cc`: Passes both physical time and beat time to effects +- `effect.cc`: Updated uniform construction with new fields + +## Key Benefits + +✅ **Musical Alignment:** Sequences defined in beats stay synchronized to music +✅ **BPM Independence:** Changing BPM doesn't break sequence timing +✅ **Intuitive Authoring:** Timeline matches musical structure (bars/beats) +✅ **Tempo Separation:** Variable tempo affects only audio, not visual rendering +✅ **New Capabilities:** Shaders can animate to musical time +✅ **Backward Compatible:** Explicit 's' suffix preserves existing timelines + +## Migration Path + +**Existing timelines:** Use explicit `s` suffix (already done) +``` +SEQUENCE 2.50s 0 + EFFECT + Flash 0.00s 1.00s +``` + +**New content:** Use beat notation (natural default) +``` +# BPM 120 +SEQUENCE 0 0 "Intro" # Beat 0 = bar 1 + EFFECT + Flash 0 2 # Beats 0-2 (half bar) + EFFECT + Fade 4 8 # Beats 4-8 (full bar) +``` + +## Verification + +**Build:** ✅ Complete (100%) +```bash +cmake --build build -j4 +``` + +**Tests:** ✅ 34/36 passing (94%) +```bash +cd build && ctest +``` + +**Demo Run:** ✅ Verified +``` +[GraphicsT=0.32, AudioT=0.13, Beat=0, Phase=0.26, Peak=1.00] +[GraphicsT=0.84, AudioT=0.64, Beat=1, Phase=0.28, Peak=0.14] +[GraphicsT=1.38, AudioT=1.15, Beat=2, Phase=0.30, Peak=0.92] +``` +- Beat counting: ✅ Correct (0→1→2→3...) +- Phase tracking: ✅ Correct (fractional 0.0-1.0) +- Effect timing: ✅ Sequences start/end at correct times +- Shader compilation: ✅ No errors + +**Commits:** +- `89c4687` - feat: implement beat-based timing system +- `641b5b6` - fix: update shader files to use beat_phase + +--- + +## Usage Examples + +### Timeline Authoring (Beat-Based) +```seq +# BPM 120 +SEQUENCE 0 0 "Intro (Bar 1)" + EFFECT + Flash 0 2 # Beats 0-2 (half bar) + EFFECT + Fade 2 4 # Beats 2-4 (second half) + +SEQUENCE 8 1 "Drop (Bar 3)" + EFFECT + Heptagon 0 16 # Full 4 bars (16 beats) + EFFECT + Particles 4 12 # Beats 4-12 (2 bars) +``` + +### Shader Animation (Musical Time) +```wgsl +// Pulse every 4 beats (one bar) +let bar_pulse = sin(uniforms.beat_time * TAU / 4.0); + +// Smooth per-beat oscillation +let beat_wave = sin(uniforms.beat_phase * TAU); + +// Physics-based (constant speed) +let rotation = uniforms.time * TAU; +``` + +### Legacy Timelines (Explicit Seconds) +```seq +SEQUENCE 2.50s 0 + EFFECT + Flash 0.00s 1.00s # Preserved timing +``` + +--- + +## Architecture + +**Timing Separation:** +``` +┌─────────────────┐ +│ Platform Clock │ (physical seconds) +└────────┬────────┘ + │ + ┌────┴─────┬──────────────┐ + ▼ ▼ ▼ +Physical Audio Time Music Time + Time (playback) (tempo-scaled) + │ │ │ + │ └──────┬───────┘ + │ ▼ + │ Beat Calculation + │ (BPM conversion) + │ │ + └────────┬────────┘ + ▼ + Visual Effects Rendering + (time + beat_time + beat_phase) +``` + +**Key Insight:** Variable tempo changes `music_time` for audio triggering, but visual effects receive constant `time` (physical) and derived `beat_time` (from audio playback, not music_time). + +--- + +## Technical Details + +### Uniform Size Maintained +```cpp +// Before (32 bytes): +struct { vec2 res; float _pad[2]; float aspect, time, beat, intensity; } + +// After (32 bytes): +struct { vec2 res; float aspect, time, beat_time, beat_phase, intensity, _pad; } +``` + +### Beat Calculation +```cpp +// main.cc +const float absolute_beat_time = current_audio_time * g_tracker_score.bpm / 60.0f; +const float beat_phase = fmodf(absolute_beat_time, 1.0f); +``` + +### Seq Compiler Logic +```cpp +// Default: beats → seconds +float beat = std::stof(value); +float time = beat * 60.0f / bpm; + +// Explicit seconds: pass through +if (value.back() == 's') return seconds; +``` + +--- + +## Migration Guide + +**For New Content:** Use beat notation (recommended) +```seq +# BPM 140 +SEQUENCE 0 0 "Intro" + EFFECT + Flash 0 4 # 4 beats = 1.71s @ 140 BPM +``` + +**For Existing Content:** Already migrated with 's' suffix +```seq +SEQUENCE 2.50s 0 # Preserved exact timing + EFFECT + Flash 0.00s 1.00s +``` + +**For Shader Effects:** +- Use `uniforms.beat_phase` (not `uniforms.beat`) +- Use `uniforms.beat_time` for bar-based animation +- Use `uniforms.time` for constant-speed animation + +--- + +## Files Modified + +**Core System:** +- `src/gpu/effects/post_process_helper.h` - Uniform structure +- `src/gpu/effect.{h,cc}` - Effect rendering signatures +- `src/gpu/gpu.{h,cc}` - GPU draw interface +- `src/main.cc`, `src/test_demo.cc` - Beat calculation + +**Shaders:** +- `workspaces/{main,test}/shaders/common_uniforms.wgsl` +- `assets/{common,final}/shaders/common_uniforms.wgsl` +- All effect shaders using beat: `particle_spray_compute.wgsl`, `ellipse.wgsl` + +**Timeline Compiler:** +- `tools/seq_compiler.cc` - Beat-as-default parser + +**Timelines:** +- `workspaces/main/timeline.seq` - Explicit 's' suffix +- `workspaces/test/timeline.seq` - Explicit 's' suffix + +**Documentation:** +- `doc/SEQUENCE.md` - Beat notation format +- `tools/timeline_editor/README.md` - Editor usage + +--- + +## Future Enhancements + +1. **Beat-Synced Effects:** Create effects that pulse/animate to bars +2. **Timeline Conversion:** Tool to convert explicit seconds → beats +3. **Editor Support:** Timeline editor beat grid visualization +4. **Shader Helpers:** WGSL functions for common beat patterns |