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DESIGN.md
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DESIGN.md
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# Jump 'n Run - Game Design Document
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## Concept
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2D side-scrolling platformer with run-and-gun combat.
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Inspired by **Jazz Jackrabbit 2**, **Metal Slug**, **Mega Man**, and classic 90s side-scrollers.
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**Theme:** Sci-fi / space western (think *Cowboy Bebop*).
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The player is a bounty hunter traveling between planets and space stations,
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taking on jobs that play out as platformer levels.
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---
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## Game Structure
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### Two Main Modes
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**1. World Map (Spacecraft Navigation)**
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- Top-down or side-view map showing planets, stations, asteroids
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- Player pilots a spacecraft between locations
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- Each location is a level (or hub with multiple levels)
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- Map could be a simple node graph or free-flight between points
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- Unlocking new areas as the story progresses
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- Ship could have upgrades (fuel range, shields, scanner)
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**2. Platformer Levels**
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- Core gameplay: run, jump, shoot, explore
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- Each level is a self-contained planet/station/ship with its own atmosphere
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- Levels end with reaching an exit zone (or defeating a boss)
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- Collectibles: currency (bounty credits), health pickups, weapon upgrades
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- Optional objectives for bonus rewards
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---
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## Atmosphere System
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Each level defines its own atmosphere, affecting gameplay feel:
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| Property | Effect | Example Values |
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|----------------|---------------------------------------------|-------------------------|
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| `GRAVITY` | Fall speed and jump arc | 980 (earth), 400 (moon) |
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| `WIND` | Constant horizontal force on entities | -50 to 50 px/s^2 |
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| `STORM` | Visual effect + periodic strong wind gusts | 0 (calm) to 3 (severe) |
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| `DRAG` | Air resistance (underwater, thick atmo) | 0.0 (none) to 0.9 |
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| `BG_COLOR` | Background clear color | hex color |
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| `PARALLAX_FAR` | Far background image path | assets/bg/stars.png |
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| `PARALLAX_NEAR`| Near background image path | assets/bg/nebula.png |
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| `MUSIC` | Level music track | assets/music/level1.ogg |
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| `PALETTE` | Color mood (warm, cold, toxic, void) | tint/filter values |
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Already implemented: `GRAVITY`, `BG_COLOR`, `MUSIC`, `PARALLAX_FAR`, `PARALLAX_NEAR` (all per-level). Parallax backgrounds are procedurally generated (starfield + nebula) when no image path is specified.
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---
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## Player
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- **Size:** 12x16 px hitbox, 16x16 sprite
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- **Movement:** Run, jump (variable height, coyote time, jump buffer)
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- **Dash:** C key, directional (horizontal, up, diagonal, down while airborne).
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Brief i-frames during dash. 0.15s duration, 0.4s cooldown.
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- **Combat:** Shoot projectiles (X or Space), directional aiming with UP key
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(straight up, or diagonal when combined with LEFT/RIGHT)
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- **Camera:** Holding UP while standing still pans the camera upward
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- **Health:** 3 HP (expandable), invincibility frames + knockback on hit
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- **Death / Respawn:** Death animation plays, then 1s delay before respawning at level spawn with full HP, charges, and brief invincibility. Falling off the level kills instantly with 0.3s delay.
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- **Future abilities:**
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- Wall slide / wall jump
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- Weapon switching (multiple projectile types from the def system)
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- Double jump (upgrade)
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- Melee attack (close range, stronger)
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---
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## Enemies
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### Implemented
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- **Grunt** — Red spiky ground patrol. Walks back and forth, turns at edges/walls. 2 HP.
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- **Flyer** — Purple bat-like. Bobs in air, chases player when close, shoots fireballs. 1 HP.
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### Planned
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- **Turret** — Stationary, rotates to aim at player, fires periodically
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- **Charger** — Detects player at range, charges in a straight line at high speed
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- **Shielder** — Has a directional shield, must be hit from behind or above
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- **Spawner** — Stationary, periodically spawns smaller enemies
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- **Boss** — Large, multi-phase encounters. One per world area.
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---
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## Weapons / Projectiles
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Data-driven system: each weapon type is a `ProjectileDef` struct describing speed,
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damage, lifetime, hitbox, behavior flags, and animations. Adding a new weapon =
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adding a new def. See `src/game/projectile.h` for the full definition.
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### Behavior flags
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- `PROJ_PIERCING` — Passes through enemies (up to `pierce_count` times)
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- `PROJ_BOUNCY` — Ricochets off walls (up to `bounce_count` times)
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- `PROJ_GRAVITY` — Affected by level gravity (scaled by `gravity_scale`)
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- `PROJ_HOMING` — Steers toward nearest valid target
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### Implemented weapon defs
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| Weapon | Speed | Damage | Special | Owner |
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|-----------------|-------|--------|--------------------------|--------|
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| `WEAPON_PLASMA` | 400 | 1 | Default player weapon | Player |
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| `WEAPON_SPREAD` | 350 | 1 | Short range, fan pattern | Player |
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| `WEAPON_LASER` | 600 | 1 | Pierces 3 enemies | Player |
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| `WEAPON_ROCKET` | 200 | 3 | Slight gravity drop | Player |
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| `WEAPON_BOUNCE` | 300 | 1 | 3 wall bounces + gravity | Player |
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| `WEAPON_ENEMY_FIRE` | 180 | 1 | Enemy fireball | Enemy |
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### Directional aiming
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- Forward (default) — shoots horizontally in facing direction
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- Up — hold UP to shoot straight up
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- Diagonal up — hold UP + LEFT/RIGHT to shoot at 45 degrees
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---
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## Levels
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### Format (.lvl)
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Current directives: `TILESET`, `SIZE`, `SPAWN`, `GRAVITY`, `BG_COLOR`, `MUSIC`, `PARALLAX_FAR`, `PARALLAX_NEAR`, `TILEDEF`, `ENTITY`, `LAYER`
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**Needed additions:**
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- `EXIT <tile_x> <tile_y> <next_level>` — Level exit zone
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- `WIND`, `STORM`, `DRAG` — Atmosphere settings
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### Level Ideas
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1. **Derelict Station** — Low gravity, dark, flickering lights, abandoned corridors
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2. **Desert Planet** — High gravity, sand storm wind, bright orange palette
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3. **Gas Giant Moon** — Very low gravity, floating platforms, toxic atmosphere
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4. **Asteroid Belt** — Zero-G sections, small disconnected platforms
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5. **Space Freighter** — Normal gravity, tight corridors, turret enemies
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6. **Volcanic World** — Normal gravity, rising lava hazard, fire enemies
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---
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## World Map
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### Structure
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- Graph of nodes (planets/stations) connected by routes
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- Player selects destination, spacecraft flies there (short animation or instant)
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- Some routes may require fuel/upgrades to unlock
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- Map reveals new nodes as levels are completed
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### Implementation Notes
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- Separate game state from the platformer (own update/render)
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- Needs: node data structure, spacecraft position, route rendering
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- Could start simple: linear level select, evolve into open map
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---
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## Technical TODO
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### High Priority
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- [x] Entity spawn directives in .lvl format (`ENTITY` directive)
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- [ ] Level exit zones and level transitions
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- [x] Dash mechanic
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- [ ] Wall slide / wall jump
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- [x] Particle system (death puffs, landing dust, projectile impact sparks, wall slide dust)
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- [x] Screen shake on damage / enemy kills
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- [x] Sound effects (jump, shoot, hit, enemy death, dash)
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- [x] Basic HUD (health hearts + jetpack charges)
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### Medium Priority
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- [ ] Wind / drag atmosphere properties
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- [x] Parallax scrolling backgrounds (procedural stars + nebula, or from image files)
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- [x] Per-level background color (`BG_COLOR` directive)
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- [x] Music playback per level (`MUSIC` directive)
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- [ ] Weapon switching system
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- [ ] Pickup entities (health, ammo, credits)
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- [ ] Better tileset art (space-themed)
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- [ ] Player sprite polish (more animation frames)
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- [x] Death / respawn system
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- [ ] Pause menu
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### Low Priority (Future)
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- [ ] World map mode
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- [ ] Spacecraft navigation
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- [ ] Boss encounters
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- [ ] Dialogue / mission briefing system
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- [ ] Save system
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- [ ] Controller support (SDL_GameController is initialized)
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- [ ] Multiple playable characters
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---
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## Art Direction
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- Pixel art, 16x16 tile grid
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- Logical resolution: 640x360 (rendered at 2x = 1280x720)
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- Nearest-neighbor scaling for crisp pixels
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- Dark, moody color palettes with bright projectile/effect accents
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- Inspired by: Cowboy Bebop color grading, retro sci-fi, neon-on-dark
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---
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## Controls
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| Action | Key | Status |
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|-----------|--------------|---------------|
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| Move | Arrow keys | Implemented |
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| Jump | Z | Implemented |
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| Shoot | X / Space | Implemented |
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| Aim up | UP (+ shoot) | Implemented |
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| Aim diag | UP+LEFT/RIGHT (+ shoot) | Implemented |
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| Dash | C | Implemented |
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| Look up | UP (stand still) | Implemented |
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| Pause | Escape | Quits game |
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---
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## Reference Games
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- Jazz Jackrabbit 2 (movement feel, weapon variety, level design)
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- Metal Slug (run-and-gun, enemy variety, visual flair)
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- Mega Man X (wall jump, dash, tight controls)
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- Cave Story (atmosphere, exploration, story integration)
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- Cowboy Bebop (aesthetic, tone, music style)
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