2048 Example
A 2048 puzzle game where you slide tiles to combine them and reach 2048. The game features grid rendering, tile values, score tracking, and game over / win states.
On esp32cyd, swipes are detected via onUnconsumedTouchEvent to slide tiles in the swipe direction. On native, use D-pad controls per Game2048Constants.h button IDs.
Requirements (build flags)
PIXELROOT32_ENABLE_TOUCH=1onnativeandesp32cyd(seeplatformio.ini) so touch code paths compile.
PIXELROOT32_ENABLE_UI_SYSTEM defaults to on in the engine (PlatformDefaults.h).
See platformio.ini for native and esp32cyd (CYD uses ILI9341 240×320 + XPT2046 touch — many calibration defines are in the INI).
Platforms
| Environment | Display / input |
|---|---|
native | SDL2, 240×320, simulated touch + keyboard enabled |
esp32cyd | ILI9341 240×320 + resistive touch (XPT2046 GPIO SPI) |
Controls (GPIO / keyboard)
- Arrow keys / D-pad to slide all tiles in the selected direction.
- Play Again: reset button wired in
Game2048Scene::createResetButton()(GPIO or touch widget depending on build).
Touch (CYD)
Swipe gestures are detected in onUnconsumedTouchEvent:
- DragStart / DragMove / DragEnd events track the swipe direction.
- Minimum swipe distance of 30 pixels triggers a move.
- Swipe direction is determined by the major axis (horizontal or vertical).
Features
- Scene lifecycle + UI labels and conditional touch / GPIO buttons
- TouchEvent pipeline for swipe detection
- Game logic: tile sliding, merging, spawning, win/lose detection
- Custom palette in
color_palette.h(PR32-compatible tile colors) - Score tracking displayed in label
- Audio SFX (no background music): spawn (Triangle), merge (double Triangle), move (simple Triangle)
- Fixed merge behavior: correct merge in all 4 directions (left, right, up, down)
- AI Auto-play: expectimax algorithm with depth-3 search and heuristic evaluation
Audio
Audio SFX are defined in src/assets/sfx.h:
playSpawnSound- Triangle wave (A4) - plays when new tile spawnsplayMergeSound- Double Triangle (C5 + E5) - plays when tiles mergeplayMoveSound- Simple Triangle (A3) - plays on move without mergeplayWinSound/playGameOverSound- win/lose feedback
No background music (removed to reduce memory footprint).
AI Auto-play
The AI uses an optimized Expectimax algorithm with adaptive depth search and intelligent state caching:
Algorithm
| Feature | Implementation |
|---|---|
| Search | Expectimax (MAX nodes: player moves, CHANCE nodes: tile spawns) |
| Depth | Adaptive 2-5 based on empty cells (deeper when board is tight) |
| Sampling | Smart: evaluates all cells when ≤8 empty, samples 6 when >8 empty |
| Spawn probability | Spawn-2 (90%) + Spawn-4 (10%) with proper weighting |
| Transposition Table | 8192-entry cache with FNV-1a hashing to avoid recomputing states |
| Probability cutoff | Stops exploring paths with <0.01% cumulative probability |
Heuristic Evaluation
The AI evaluates board states using 6 weighted factors:
| Factor | Weight | Description |
|---|---|---|
| Empty cells | 4K-100K (exponential) | Mobility bonus that increases as board fills up |
| Monotonicity penalty | -100× | Severe penalty for non-monotonic sequences (larger tiles matter more) |
| Smoothness | +100× | Rewards adjacent tiles with similar values (merge potential) |
| Merge bonus | +1000× per merge | Strong incentive for creating merge opportunities |
| Corner bonus | +100× maxTile | Rewards keeping max tile in any corner |
| Corner penalty | -1000× maxTile | Catastrophic penalty if max tile is NOT in a corner |
| Adjacent tiles | +0.5× value | Bonus for tiles adjacent to max tile (builds L-pattern) |
Performance
- Native (PC): Base depth 3, adaptive up to depth 5
- ESP32: Base depth 2, adaptive up to depth 4
- Average decision time: <100ms on native, <500ms on ESP32
- Win rate: Consistently reaches 2048 tile
Controls
- AI is enabled by compile flag
-D GAME2048_AI_MODE=1inplatformio.ini - When enabled, AI automatically makes optimal moves every frame
- AI respects game rules from
game_rules.md
To disable AI, remove -D GAME2048_AI_MODE=1 from build_flags in platformio.ini.
Documentation links
Build
From examples/2048:
pio run -e native
pio run -e esp32cydUpload (ESP32)
pio run -e esp32cyd --target uploadSource code: https://github.com/PixelRoot32-Game-Engine/PixelRoot32-Game-Engine/tree/main/examples/2048