# Sequence System Documentation

This document describes the `.seq` file format used to define demo timelines.

## Overview

Sequence files (`.seq`) define the timeline and layering of visual effects in the demo. They are compiled by `seq_compiler` into C++ code at build time.

## File Location

- Demo sequence: `assets/demo.seq`
- Compiler: `tools/seq_compiler.cc`
- Generated output: `src/generated/timeline.cc`

## Command Line Usage

### Basic Compilation
```bash
./build/seq_compiler assets/demo.seq src/generated/timeline.cc
```

### Validation Only
```bash
./build/seq_compiler assets/demo.seq
```
Validates syntax without generating code.

### Gantt Chart Visualization

**ASCII Gantt Chart:**
```bash
./build/seq_compiler assets/demo.seq --gantt=timeline.txt
```

**HTML/SVG Gantt Chart (Recommended):**
```bash
./build/seq_compiler assets/demo.seq --gantt-html=timeline.html
```
Open `timeline.html` in browser for interactive visualization with hover tooltips.

**Combined Modes:**
```bash
./build/seq_compiler assets/demo.seq timeline.cc --gantt=t.txt --gantt-html=t.html
```

---

## Syntax Reference

### BPM Declaration
```
# BPM 120
```
Specifies beats per minute for the demo. Used to convert beat notation to seconds.

### END_DEMO Directive
```
END_DEMO <time>
```
Specifies when the demo should automatically exit (optional).
- If not specified, demo runs indefinitely until user closes window
- Supports beat notation (e.g., `64b`) or seconds (e.g., `32.0`)

### SEQUENCE Declaration
```
SEQUENCE <global_start> <priority> [optional_end]
  EFFECT <EffectClassName> <local_start> <local_end> <priority> [constructor_args...]
```

**Parameters:**
- `global_start`: When this sequence starts (beats or seconds)
- `priority`: Render order between sequences (higher = rendered later/on top)
  - Use 0-9 for scene effects
  - Use 10+ for post-processing
- `[optional_end]`: Optional end time in brackets (e.g., `[30.0]`)
  - If specified, all effects in the sequence will be forcefully ended at this time
  - Time is relative to the sequence start
  - If omitted, effects run until their individual end times

### EFFECT Declaration
```
EFFECT <+|=|-> <EffectClassName> <local_start> <local_end> [constructor_args...]
```

**Parameters:**
- Priority modifier (one of):
  - `+`: Increment priority (or start at 0 if first effect)
  - `=`: Keep same priority as previous effect
  - `-`: Decrement priority (or start at -1 if first effect, for background layers)
- `EffectClassName`: C++ class name (must be declared in `demo_effects.h`)
- `local_start`: Start time relative to sequence start (beats or seconds)
- `local_end`: End time relative to sequence start (beats or seconds)
- `constructor_args`: Optional additional parameters (rarely used)

**Priority System:**
- Effects are assigned priorities based on their order in the file
- First effect: `+` starts at 0, `-` starts at -1, `=` starts at 0
- Subsequent effects: `+` increments, `=` keeps same, `-` decrements
- Priorities determine render order (lower = drawn first/background)
- Effects should be listed in desired priority order within each sequence

---

## Time Notation

The sequence file supports flexible time notation:

| Notation | Example | Description |
|----------|---------|-------------|
| Integer beats | `0`, `64`, `128` | No decimal point = beats |
| Explicit beats | `0b`, `64b`, `128b` | Suffix 'b' = beats |
| Decimal seconds | `0.0`, `32.0`, `64.0` | Decimal point = seconds |
| Explicit seconds | `32.0s`, `64.0s` | Suffix 's' = seconds |

**Examples at 120 BPM:**
- Beat 0 = 0.0 seconds
- Beat 64 = 32.0 seconds
- Beat 120 = 60.0 seconds

---

## Effect System

### Constructor Parameters

**Standard Parameters (ALL effects receive these automatically):**
- `WGPUDevice device`: WebGPU device handle
- `WGPUQueue queue`: Command queue for GPU operations
- `WGPUTextureFormat format`: Surface texture format

Most effects only use these standard parameters. If an effect needs custom initialization, parameters are specified after the priority field.

**Example (hypothetical custom effect):**
```
EFFECT CustomEffect 0 10 0 1.5 "param"
```
Translates to:
```cpp
std::make_shared<CustomEffect>(device, queue, format, 1.5, "param")
```

### Runtime Parameters

All effects receive these dynamic parameters every frame in their `render()` method:

| Parameter | Type | Description |
|-----------|------|-------------|
| `time` | float | Global time in seconds (from demo start) |
| `beat` | float | Current beat fraction (0.0 to 1.0 within each beat) |
| `intensity` | float | Audio peak intensity (0.0 to 1.0, for beat detection) |
| `aspect_ratio` | float | Screen width/height ratio |

---

## Available Effects

### Scene Effects
Render 3D geometry to the framebuffer with depth testing.

#### HeptagonEffect
Animated geometric heptagon shape.
- **Uses:** `time` (animation), `beat` (rotation), `aspect_ratio` (projection)

#### ParticlesEffect
GPU-simulated particle system.
- **Uses:** `time` (physics), `intensity` (emission rate)

#### Hybrid3DEffect
3D objects with camera movement.
- **Uses:** `time` (camera paths), `beat` (object animation), `aspect_ratio`

#### FlashCubeEffect
Large background cube with Perlin noise texture.
- **Uses:** `time` (rotation), `intensity` (flash trigger on beat hits)
- **Note:** Typically used with priority -1 for background layer

### Post-Process Effects
Full-screen shaders applied in priority order after scene rendering.

#### GaussianBlurEffect
Gaussian blur with beat pulsation.
- **Uses:** `intensity` (blur size pulsates 0.5x-2.5x based on audio peak)

#### SolarizeEffect
Color inversion with alternating red/blue tints.
- **Uses:** `time` (alternates every 2 seconds between color schemes)

#### ChromaAberrationEffect
RGB channel separation effect.
- **Uses:** `time` (animation), `intensity` (separation amount)

#### ThemeModulationEffect
Brightness cycling (bright/dark alternation).
- **Uses:** `time` (cycles every 8 seconds: 1.0 bright to 0.35 dark)

#### FadeEffect
Fade to/from black.
- **Uses:** `time` (fades in first 2s, fades out after 36s - hardcoded timing)

#### FlashEffect
White flash on strong beat hits.
- **Uses:** `intensity` (triggers flash when > 0.7, exponential decay)

---

## Tips & Best Practices

### Layering
- Scene effects render to framebuffer with depth testing
- Post-processing effects are full-screen shaders applied in sequence priority order
- Use negative priority for background elements (skybox, far objects)
- Higher sequence priority = later in post-process chain (rendered on top)

### Priority Guidelines
- **Scene Effects:** priority 0-9
  - Background: -1 (e.g., skybox, distant objects)
  - Midground: 0-5 (main geometry)
  - Foreground: 6-9 (overlays, particles)
- **Post-Process:** priority 10+
  - Apply in order: blur → distortion → color grading

### Timing
- Use beat notation for music-synchronized effects
- Use seconds for absolute timing
- Keep effect durations reasonable (avoid very short < 0.1s unless intentional)
- Use sequence `[end_time]` to forcefully terminate long-running effects

---

## Examples

### Basic Sequence
```
SEQUENCE 0 0
  EFFECT + FlashEffect 0.0 0.5     # Priority 0 (first with +)
  EFFECT + HeptagonEffect 0.2 10   # Priority 1 (increment)
```

### Same Priority (Layered Effects)
```
SEQUENCE 0 0
  EFFECT + Flash 0.0 0.5           # Priority 0
  EFFECT = Fade 0.1 0.3            # Priority 0 (same as Flash)
  EFFECT + Other 0.2 3             # Priority 1 (increment)
```

### Background Elements
```
SEQUENCE 0 0
  EFFECT - FlashCube 0 10          # Priority -1 (background)
  EFFECT = BgEffect 0 5            # Priority -1 (same layer)
  EFFECT + MainEffect 0 10         # Priority 0 (foreground)
```

### Sequence with Explicit End Time
```
SEQUENCE 8b 0 [5.0]
  EFFECT + Particles 0 120         # Would run 120s, but sequence ends at 5s
```

### Post-Processing Chain
```
SEQUENCE 0 10
  EFFECT + GaussianBlur 0 60       # Priority 0 (applied first)
  EFFECT + ChromaAberration 0 60   # Priority 1 (applied second)
  EFFECT + Solarize 0 60           # Priority 2 (applied last)
```

### Music-Synchronized Effects
```
# BPM 120
SEQUENCE 0b 0      # Start at beat 0 (0.0s)
  EFFECT + Flash 0b 1b             # Flash from beat 0 to beat 1 (0-0.5s)
  EFFECT + Heptagon 4b 8b          # Main effect from beat 4 to 8 (2-4s)
```

---

## Debugging & Visualization

### Gantt Charts

Gantt charts help visualize the timeline structure:

**ASCII Chart (Terminal-Friendly):**
```
Time (s): 0    5    10   15   20
          |----|----|----|----|----|

SEQ@0s [pri=0]
          ████████████████████████  (0-20s)
  FlashEffect [pri=1]
          ▓▓··················  (0-1s)
  HeptagonEffect [pri=0]
          ▓▓▓▓▓▓▓▓▓▓▓▓········  (0-10s)
```

**HTML/SVG Chart (Interactive):**
- Color-coded sequences and effects
- Hover tooltips with full details
- Invalid time ranges highlighted in red
- Professional dark theme
- Zoom/pan support
- Easy to share or present

### Validation

Run validation without code generation to catch syntax errors:
```bash
./build/seq_compiler assets/demo.seq
# Output: "Validation successful: 14 sequences, explicit end time."
```

### Common Issues Caught by Validation
- Invalid time ranges (end < start)
- Missing effect classes
- Syntax errors
- Malformed time notation

---

## Integration with Build System

The sequence compiler is automatically invoked during build via CMake:

```cmake
add_custom_command(
  OUTPUT ${GENERATED_DIR}/timeline.cc
  COMMAND seq_compiler assets/demo.seq ${GENERATED_DIR}/timeline.cc
  DEPENDS assets/demo.seq
  COMMENT "Compiling demo sequence..."
)
```

Editing `assets/demo.seq` triggers automatic recompilation and rebuilds affected targets.

---

## See Also

- `doc/HOWTO.md` - Building and running the demo
- `doc/CONTRIBUTING.md` - Coding guidelines
- `assets/demo.seq` - Current demo timeline
- `src/gpu/demo_effects.h` - Available effect classes