Jazz Jackrabbit Gg — Development skill for Claude Code

Jazz Jackrabbit — Game Gear port

A Sega Game Gear port of haroldo-ok's Genesis/SGDK homebrew port of Jazz Jackrabbit (episode 1: Diamondus, Tubelectric, Medivo — 7 stages). Background blocks and sprites are drawn at half size (JJ1's 32×32 blocks become 16×16), and the level layouts are unchanged, so the 160×144 screen shows the same area of the level as the Genesis's 320×288.

Controls

Game Gear	Action
D-pad	move (and steer the airboard)
2	jump
1	fire
Up + 1	switch weapon (not while on the airboard)
Start	pause; on the title screen, start (Left/Right picks the level)

Building

Requires SDCC 4.2 and devkitSMS (`DEVKIT`, default `~/.devkitsms`) plus Python 3 with Pillow. The Genesis sources (`res/*.inc`) are read by `tools/convert.py`.

make              # jazz.gg (1 MB, Sega mapper)
make jazz_trace.gg  # differential-test build

Layout

• src/main.c – main loop (fixed timestep: one game frame per elapsed video frame), title, sky gradient (line interrupts)
• src/gg_logic.c – the game simulation, a port of the Genesis game_core.c, run from ROM bank 2
• src/gg_world.c – banked level data access (collision masks, events)
• src/render.c – tile-cache map streaming, sprites, HUD
• src/music.c – music player (frame interrupt)
• src/sound.c – PSG sound effects
• tools/convert.py – converts the Genesis assets into gen/data.bin (halved tiles/sprites, baked collision)

Tests

• tests/diff/run.sh, tests/diff/rom.sh – differential tests: the GG logic (on the host and on the Z80 through the smstest emulator harness) against the Genesis game core, frame by frame
• tests/bgstress.tpl + tools/bgverify.py – random play, then every dumped screen is checked against the level data
• tests/bench.tpl / tests/speed.tpl – cycle profiles and real-time speed
• tests/music/run.sh – the ROM's PSG output against the reference player (title, every song, with effects)

Music

The soundtrack is co