A Gameboy (Color) emulator written in Kotlin, able to run on desktop/JVM (with LibGDX + VisUI) and in browser (with Bootstrap and KorAU).

The emulator is in a good and usable state. Both DMG and CGB emulation is complete and quite accurate, enough to make most commercial games run perfectly.

• Upscaling with HQ2X, HQ3X and HQ4X
• .sav game saving compatible with most other emulators (BGB, VBA, ...)
• Save states with "undo last load" function
• Live rewinding of games for up to 60 seconds
• Fast-forwarding at any integer multiplier (with hold and toggle hotkeys)
• Basic gamepad/controller support
• Debugger with:
  • Emulator halting / Line-by-line debugging
  • PC and write breakpoints
  • Memory, register and stack view
  • Tileset and BG Map Viewers
  • Cartridge Info Viewer
  • Per-instruction CPU/register state logging
  • Instruction Set Viewer

• Entire emulator working fully
• Full game saving and RTC support (into browser local storage)

• Some MBC3 controllers have a built-in RTC for keeping track of time; Gamelin implements it, but in a very simple format incompatible with other emulators that has a high chance of not working with most games (it was tested with Pokemon Crystal and successfully kept time after turning the game off overnight - needs more testing).

Here's a non-exhaustive list of games I've tested. Results might sometimes be outdated. All games that support both DMG/GB and CGB/GBC were tested in GBC mode.

• Pokemon Blue (Global, 1996, Game Freak)
  • Tested until Viridian Forest
• Pokemon Yellow (Global, Game Freak)
  • Played until reaching the end of Route 1
• Pokemon Silver (Global, 2000, Game Freak)
  • Played until first GYM, including Bellsprout Tower
• Pokemon Crystal (Global, 2001, Game Freak)
  • Played until reaching Bellsprout Tower
• Dr. Mario (Global version, 1990, Nintendo)
• Tetris (JP and Global versions, 1989, Nintendo)
• Tetris DX (Global, 1998, Nintendo)
• Pokemon Pinball (Global, 1999, Jupiter)
• Super Mario Land (Global, Nintendo)
  • Played until 2-1
• Super Mario Land 2 (Global, 1992, Nintendo)
  • Played the first level
• Super Mario Bros. Deluxe (Global, 1999, Nintendo)
  • Played until 1-3, other modes also briefly tested
• Wario Land 3 (Global, 2000, Nintendo)
  • Played the first level
• The Legend of Zelda: Link's Awakening (Global, 1993, Nintendo)
  • Played until shortly after obtaining your sword at the shore
• The Legend of Zelda: Link's Awakening DX (Global, 1998, Nintendo)
  • Played until finding the toadstool in the mysterious woods
• The Legend of Zelda: Oracle of Ages (Global, 2001, Nintendo)
  • Played until receiving the wooden sword
• Kirby's Dream Land (Global, Nintendo/HAL)
  • Played until middle of stage 2
• Donkey Kong (Global, 1994, Nintendo)
• Donkey Kong Land (Global, 1995, Nintendo/RARE)
  • Tested for the first 2 levels
• Donkey Kong Country (Global, 2000, RARE)
  • Played the first level
• Yoshi (Global, 1992, Nintendo)
• Tic-Tac-Toe (1996, Norman Nithman)

The main goals of this emulator is to both learn more about emulation of real-world hardware as well as creating a nice-to-use emulator with many comfort features that should be able to run well in the browser. Accuracy is only a goal when it fixes issues encountered by actual games; implementing complex but ultimately useless hardware details that aren't used by games (like the OAM bug or MBC1 multicarts) is not a goal of this emulator, particularly considering the speed requirements needed to make it work in the browser.

# Run on desktop
./gradlew run

# Create jarfile
./gradlew dist

# Create web build in web/
./gradlew distJs

Blargg, mooneye and acid2 ROMs can be run automatically using gradle:

gradle jvmTest

Note that by default, only passing tests are run to allow easily catching regressions. To run all tests, change TEST_ALL in src/jvmTest/xyz/angm/gamelin/tests/ProjectConfig.kt to true.

• cpu_instrs, mem_timing, mem_timing-2, instr_timing, interrupt_time: Pass
• dmg_sound: 8/12 pass (07, 09, 10, 12 fail)
• cgb_sound: 7/12 pass (07, 08, 09, 11, 12 fail)
• oam_bug: Everything but 3 and 6 fail (OAM bug won't be implemented)

• acceptance: 27 out of 75 pass
• emulator-only: All pass (except MBC1 multicart; will not be supported)

Both the dmg-acid2 and cgb-acid2 test written by Matt Currie pass (CGB in DMG mode untested). Thank you to @mattcurrie for creating them!

• Imran Nazar, for their series of blog posts on GB emulation
• Michael Steil, for The Ultimate Game Boy Talk
• kotcrab, for creating the xgbc emulator I often used to confirm/understand fine behavior as well as VisUI
• czyzby, for making the VisUI Tinted skin
• stan-roelofs, for their emulator, which I abridged the sound implementation from
• Megan Sullivan, for her list of GB opcodes
• gbdev.io for a list of useful resources
• metaphore, who made the hqx filter implementation Gamelin uses
• danwsong, whose gemuboi-js emulator inspired gamelin.kjs's design
• blargg, Gekkio and mattcurie for their test ROMs and retrio for hosting blargg's ROMs
• You, for reading this :)