POKéMON SL0P EDITION

A cheeky romhack of Pokémon Yellow, built on the pret/pokeyellow disassembly. All the mods live in a handful of files and are toggled/used entirely in-game — no external cheat device.

Features

⚡ Fastboot

If a save exists, the game skips the GameFreak intro, the title screen, and the CONTINUE menu, and drops you straight into your save. (New game still shows the normal flow.)

• home/init.asm / engine/movie/intro.asm — skip the intro
• engine/movie/title.asm — skip the title
• engine/menus/main_menu.asm — autoload + splash

🎬 Custom intro splash

A brief POKéMON / SL0P / EDITION graphic (a real 2bpp image, not text) is shown for ~2s on boot.

• engine/slop_intro.asm + gfx/slop/intro.png (built with a custom rgbgfx Makefile rule → deduped tiles + tilemap)

🎛️ SL0P MENU — press SELECT in the overworld

A table-driven cheat menu. Cursor + A to pick, B to back out / close.

Everything is in engine/slop_menu.asm. Adding a new entry = add a name to SlopMenuText, a dw Handler to SlopMenuHandlers, and bump SLOP_MENU_COUNT. Handlers return carry set (a warp/exit was started) or clear (back to the menu), and can be submenus or one-shot actions.

Persistent flags (reused unused WRAM): wUnusedFlag (NOWILD), wUnusedCreditsByte aliased as wSlopSaverDir (screensaver: 0 = off, else the current auto-scroll PAD_* direction).

EXPLORE is a self-contained camera loop in engine/slop_menu.asm. It renders straight out of the map block buffer (wOverworldMap): compute a view pointer wOverworldMap + (by+1)*stride + bx (by/bx = player block, stride = width+6), LoadCurrentMapView, push to VRAM, OBJ off. A d-pad press moves the camera coords by ~one screen (SLOP_PAGE_X/Y). Movement is a real hardware smooth-scroll built on the walk engine's own machinery: SlopScroll{Up,Down,Left,Right} ramp hSCX/hSCY SLOP_SCROLL_PX px/frame, advance wMapViewVRAMPointer, and inject the newly exposed edge with the Schedule*Redraw helpers (applied in VBlank). At a map edge it smooth-scrolls the remaining distance up to the boundary, then crosses using that connection's *Alignment offset and LoadMapDatas the neighbour (one unavoidable load), or stops if there's no connection.

SAVER is the same loop with wSlopSaverDir set: instead of reading the d-pad, SlopSaverPickDir synthesises a direction into the normal dispatch (so it inherits smooth scroll + edge crossing), keeping one heading until it's blocked, then turning onto a random still-open direction (never an immediate U-turn). "Open" (SlopValidDirMask) means >= 2 coords of room that way or a connection to cross — the >= 2 matters because moves round to even coords and a map's far edge is always odd, so a plain coord != max test would never register the edge and the wander would freeze one step short of it. Arrows are skipped, and OAM is cleared + frozen right after every LoadMapData so the reloaded player/Pikachu are never drawn. Any real button exits.

Crossing a connection applies its alignment offset blindly, so at an edge the connection doesn't span the camera can land outside the neighbour; SlopClampCoords (run after every entry/cross LoadMapData) clamps the coords back into [0,maxY] x [0,maxX] so the view never reads past wOverworldMap into garbage.

• Direction arrows are 4 OBJ sprites in wShadowOAM using the font's down/ right glyphs ($ee/$ed) plus CGB OBJ X/Y-flip for up/left; set wUpdateSpritesEnabled=$ff after building them so the vblank PrepareOAMData leaves shadow OAM alone. Shown per-direction when a move is possible.
• A warps here: scans wTileMap outward from the view centre (col 8,row 9) for the nearest IsTilePassable tile, sets wYCoord/wXCoord, wDestinationWarpID=$ff, LoadMapData (enters at those coords), returns carry set.

See ~/dev/gbc/tools/render_overworld.py for the ground-truth map that proved connections join maps along shared edges with an offset -- the same math this camera uses to cross seams.

Build

make            # -> pokeyellow.gbc  (rgbds 1.0.1)

The build is reproducible; the intro graphic regenerates from gfx/slop/intro.png.