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docs(snake): add complete running guide for SDL3 snake game
- Comprehensive setup and running instructions - Architecture overview of FFI bindings and game logic - Mojo language features demonstrated - Troubleshooting guide - Performance characteristics - Future improvement suggestions Status: Ready to run with integrated Mojo compiler Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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mojo/samples/examples/snake/RUN_GUIDE.md
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mojo/samples/examples/snake/RUN_GUIDE.md
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# SDL3 Snake Game - Running Guide
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## Quick Start
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```bash
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cd mojo/samples/examples/snake
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pixi install
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pixi run run
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```
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## What This Is
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A complete Snake game written in pure Mojo with SDL3 FFI bindings. Features:
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- ✅ Full game mechanics (movement, collision, food)
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- ✅ SDL3 graphics rendering
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- ✅ Keyboard input handling (arrow keys + ESC to quit)
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- ✅ SIMD-optimized structures
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- ✅ Pure Mojo (no C/C++ code needed)
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## Architecture
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**sdl3.mojo** (250+ lines)
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- SDL3 FFI bindings using `sys.ffi`
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- Opaque pointer types (SDL_Window, SDL_Renderer)
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- Event handling (keyboard, quit)
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- Color and rendering calls
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**snake.mojo** (340+ lines)
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- Game state management
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- Snake body tracking (List of positions)
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- Food spawning (random placement)
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- Collision detection
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- Rendering pipeline
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- Event loop
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## Key Mojo Features Demonstrated
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1. **FFI Bindings** - Loading native libraries and calling C functions
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```mojo
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fn load_sdl3() -> SDL3:
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return SDL3(OwnedDLHandle(SDL3_LIB_PATH))
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```
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2. **SIMD Structures** - Using SIMD for efficient storage
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```mojo
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@register_passable("trivial")
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struct SDL_Event:
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var _low: SIMD[DType.uint64, 8] # 64 bytes
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var _high: SIMD[DType.uint64, 8] # 64 bytes
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```
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3. **Unsafe Pointers** - Direct memory access to C structures
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```mojo
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var window: SDL_Window = sdl.create_window()
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var renderer: SDL_Renderer = sdl.create_renderer(window)
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```
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4. **Pattern Matching** - Direction and state handling
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```mojo
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fn get_delta(self) -> (Int, Int):
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if self == Direction.UP:
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return (0, -1)
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...
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```
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## Compilation
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### Development (Interpreter)
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```bash
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pixi run run # Uses Mojo interpreter
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```
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### Production (Native Binary)
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```bash
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pixi run build # Compiles to native binary
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./snake # Run compiled binary
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```
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## Requirements
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- **Mojo Compiler**: `<1.0.0` (from conda.modular.com)
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- **SDL3 Library**: Installed via Conan (in pixi.lock)
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- **Platform**: macOS (arm64), Linux (x86_64, aarch64)
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## Game Controls
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- **Arrow Keys**: Move snake (Up/Down/Left/Right)
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- **ESC**: Quit game
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- **Auto-restart**: Game over → Press any key to restart
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## Gameplay
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1. Snake starts in center
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2. Food appears randomly on grid
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3. Snake eats food to grow
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4. Cannot eat itself
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5. Cannot go off-screen
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6. Game speeds up slightly on each food eaten
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## Performance
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- 60 FPS target (16ms per frame)
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- Game update every 100ms
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- Minimal allocations (snake body uses pre-allocated List)
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- Optimized rendering (dirty region updates)
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## Troubleshooting
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### "libSDL3.dylib not found"
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- Update the path in sdl3.mojo line 8:
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```bash
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find ~/.conan2 -name "libSDL3*"
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```
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### "No window" or "renderer failed"
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- SDL3 initialization error
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- Check SDL3 library is properly installed
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- Verify X11/display server on Linux
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### Compilation errors
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- Ensure Mojo compiler version < 1.0.0
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- Check pixi environment: `pixi install --force`
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## Code Structure
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```
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sdl3.mojo
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├── Constants (SDL init flags, event types, scancodes)
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├── Structs (SDL_FRect, SDL_Event)
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├── FFI bindings (SDL_Init, CreateWindow, PollEvent, etc.)
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└── SDL3 wrapper class
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snake.mojo
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├── Game constants (grid size, speed)
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├── Color definitions
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├── Direction enum
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├── GameState struct
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├── Main game loop
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├── Render functions
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└── Event handling
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```
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## Future Improvements
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- [ ] Score tracking and display
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- [ ] Difficulty levels
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- [ ] Sound effects (using SDL_mixer)
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- [ ] Multiplayer support
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- [ ] Save high scores
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- [ ] Better graphics (sprite sheets)
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## Learning Resources
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See the Mojo compiler documentation for:
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- [FFI Integration](../compiler/examples/snake/)
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- [SIMD Operations](../compiler/examples/operators.mojo)
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- [Memory Management](../../compiler/src/runtime/memory.mojo)
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---
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**Status**: Production Ready ✅
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**Last Updated**: January 23, 2026
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**Author**: MetaBuilder Contributors
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