A cross-platform Avalonia-based Game Boy emulator. (Work In Progress)
G33kBoy exists so I can learn Game Boy hardware properly, starting from a clean SM83 CPU implementation.
My ZX Spectrum emulator taught me a lot about emulation, and the Game Boy has a similar CPU – but it also includes a dedicated PPU (video) and sound hardware that need to be emulated too. It is also a playground for some CPU performance techniques I wanted to try.
Global key hooks translate the following keys into the Game Boy joypad:
| Keyboard | Joypad |
|---|---|
| Arrow keys | D-pad |
Z |
B |
X |
A |
C |
Auto-fire A |
| Space | Select |
| Enter/Return | Start |
- ROM loading from ZIPs – Load standard
.gbROMs directly, or from a.ziparchive containing a Game Boy ROM. - Multiple speed modes – Cycle between normal, fast, maximum, and pause to match how you want to play or test.
- On-demand auto-fire – Enable hardware auto-fire (Hardware → Auto-fire) to have
Cpulse the A button. - Ambient blur background – Optional blurred background so the Game Boy screen stands out while the app blends into your desktop.
- Original green display – Toggle a classic four-shade green palette to mimic the original DMG screen.
- LCD emulation – Optional high‑fidelity LCD simulation including pixel‑grid structure, sub‑pixel glow, grain, edge shadowing, and per‑pixel diffusion to closely mimic the look of the original DMG screen.
- Motion blur – Blend frames together for a persistence-of-vision effect that smooths fast movement.
- Screenshot capture – Save the current frame as a TGA screenshot.
- Tile map export – Export the current tile map as a TGA image for debugging graphics or capturing assets.
The Game Boy’s original DMG screen has a distinctive look: soft diffusion, pixel‑grid separation, slight edge‑shadowing, and a subtle shimmer caused by panel grain.
G33kBoy includes an optional LCD emulation mode that reproduces these characteristics without shaders, using a hand‑tuned software renderer.
Techniques used:
- Pixel‑grid outlines for authentic DMG cell structure
- Per‑pixel grain to simulate panel irregularities
- Dynamic edge‑shadowing for a recessed‑screen feel
- Tinted top/bottom/side glow that matches the original greenish bleed
- High‑quality scaling that preserves “LCD softness” without blur
LCD emulation can be toggled at runtime and has very little performance overhead thanks to lookup‑table optimisation.
- ✔ CPU: full instruction set + automated tests
- ✔ PPU: Scanline-based renderer
- ✔ Boot ROM behaviour
- ✔ Battery-backed RAM persistence
- ✔ Zipped ROM loading
- ☐ Audio
- ☐ Cartridge MBCs
- ☐ Gameplay 'roll back'
- ☐ Game Boy Color support
- SM83 accuracy –
DTC.SM83implements the Game Boy CPU, including interrupt handling, prefixed instructions, memory bus, PPU timing, and a mnemonic disassembler to inspect opcode streams. - Shared core utilities –
DTC.Coreprovides reusable commands, extensions, converters, and Avalonia helpers so the emulator and any future UI/drivers share common infrastructure. - Avalonia UI shell –
G33kBoyhosts the emulator in a cross-platform desktop window. - Validation suite –
UnitTeststarget the CPU core via NUnit, ensuring regressions are caught early. - Battery-backed saves – Cartridge RAM is checkpointed every few seconds, compressed, and restored when the ROM loads so in-game progress (scores, unlocks, etc.) persists between sessions.
external/GameboyCPUTests/– CPU tests for regression validation https://github.com/adtennant/GameboyCPUTestsexternal/blargg-test-roms/– Blargg test ROMs to verify accuracy. https://github.com/retrio/gb-test-romsexternal/dmg-acid2.gb– The Acid2 test ported to the DMG; useful for visual and timing verification. https://github.com/mattcurrie/dmg-acid2
- Quality, feedback, and testing – Lavanya
- Artistic input and advice – Sam (aka Doobie)
Licensed under the MIT License. See LICENSE for details.