# Endless Runner

A 2D side-scrolling endless runner built with Rust and [raylib](https://www.raylib.com/).

![Rust](https://img.shields.io/badge/Rust-2024-orange)

## Gameplay

Run as far as you can on procedurally generated platforms. The world scrolls faster the longer you survive. Stomp enemies for bonus points, collect power-ups, and don't fall off the screen.

**Controls**

| Action | Keys |
|--------|------|
| Jump | `Space` / `W` / `↑` |
| Restart | `Space` / `R` / `Enter` |

### Power-ups

| Icon | Name | Effect |
|------|------|--------|
| I | **Invincible** | Immune to side hits for 5 s |
| J | **Jump Boost** | 1.45× jump height for 6 s |
| 2 | **2× Score** | Double score gain for 8 s |

### Scoring

- Passive: 80 pts/s (multiplied by any active score effect)
- Stomp: 100 pt bonus per enemy (also multiplied)

## Building

**Prerequisites:** Rust toolchain, raylib system library, a Wayland compositor.

```sh
# debug
cargo run

# release (LTO + stripped)
cargo run --release
```

**Web (WebAssembly)**

Prerequisites: [Emscripten SDK](https://emscripten.org/docs/getting_started/downloads.html) activated in your shell.

```sh
./build_web.sh           # produces web/*.js + web/*.wasm
./build_web.sh --serve   # build then serve at http://localhost:8080
```

The web build uses ASYNCIFY so the main game loop requires no changes between native and browser targets.

**Tests**

```sh
cargo test
```

42 unit tests covering physics, collision, effects, and level generation.

## Architecture

```
src/
  main.rs       — entry point, 60 fps cap, dt capped at 0.05 s
  config.rs     — Config struct (all tunable parameters)
  player.rs     — vertical physics, coyote-time jump window
  platform.rs   — scrolling platforms
  enemy.rs      — scrolling enemies with stomp detection
  pickup.rs     — PickupDef (data) + in-world Pickup instance
  effects.rs    — ActiveEffect trait + three concrete impls
  level_gen.rs  — procedural generation (StdRng, scrolling frontier)
  world.rs      — simulation loop, collision resolution, rendering
  game.rs       — state machine (Playing / GameOver), HUD
```

**Key design decisions**

- Player x is fixed; only the world scrolls.
- Speed follows `initial + factor × ln(1 + elapsed / time_scale)` — fast early ramp, logarithmic plateau.
- Landing detection uses the previous and current bottom-y crossing the platform surface, making it tunnelling-safe at high speeds.
- Coyote time: the jump window stays open for 120 ms after leaving a platform edge.
- Power-ups are fully data-driven via `Config::pickup_defs`; adding a new type requires one `PickupDef` entry and one `ActiveEffect` impl.

## Tuning

All gameplay parameters live in `Config::default()` in `src/config.rs` — no recompilation of other modules needed when tweaking values.

```rust
initial_speed: 280.0,       // px/s at t=0
speed_log_factor: 150.0,    // how much speed grows
speed_time_scale: 30.0,     // seconds before growth slows
gravity: 1900.0,            // px/s²
jump_velocity: -800.0,      // px/s (negative = up)
coyote_time: 0.12,          // seconds
enemy_spawn_chance: 0.35,   // per platform
pickup_spawn_chance: 0.28,  // per platform
```