Super Mario World 2: Yoshi's Island Recomp

Super Mario World 2: Yoshi's Island Recomp

A native recompilation of Super Mario World 2: Yoshi's Island (USA), built on snesrecomp.

Yoshi's Island is Nintendo's 1995 platformer for the Super NES: Yoshi carries baby Mario across the island to rescue his brother Luigi from Kamek and Baby Bowser. Its hand-drawn look, with sprites stretched, rotated and morphed on the cartridge's Super FX 2 chip, made it one of the most distinctive games of the console.

You must legally own a copy of the game. No ROM data is distributed with this project, in the repository or in any release. The recompiled C is generated locally from your own copy and is never committed.

☕ Keep the ports coming

This project is free and always will be. Every port in this series, Yoshi's Island included, is built with many hours of AI-assisted reverse engineering, and that AI time is paid. If you enjoy playing it, a coffee at buymeacoffee.com/mpolizel keeps the AI running so more SNES games can be ported to native Recomp. Any amount helps, and thank you!

Download (ready-to-run Windows build)

Get the latest yoshisisland-<version>-windows-x64.zip from the Releases page.

The zip is a setup pack: it contains the launcher, the recompiler and this source tree (with the framework patches already applied), but no game data. On first run:

1. Unzip anywhere and start SuperMarioWorld2YoshisIslandSNESRecomp.exe.
2. Let it download the portable build tools (one time per machine), or point it at a cmake-clang-v1 zip you already have.
3. Pick your own Super Mario World 2 - Yoshi's Island (USA).sfc (CRC32 d138f224; the file name does not matter, the contents are checked).
4. Press Generate & rebuild. The playable game is built into build/ and started; run it from there afterwards.

In the launcher, Settings → Shader lists the scanline, CRT and upscaler presets; choosing one switches the renderer to OpenGL automatically. A fresh install starts with no shader (the plain picture), the lightest option for any graphics card; pick a CRT or upscaler preset there if yours has room. Your choice is saved in config.ini and kept. The upscalers include ScaleFX and the neural NNEDI3 presets.

During play, Ctrl+L (or Select+L3 on a controller) reopens the launcher: shader, window scale, volume and controls apply when you press Resume, without restarting the game. I cycles the audio interpolation between Gaussian (the console's own, the default), Cubic (crisper highs) and Sinc; it only changes what you hear, never the game, and the choice is saved in audio_interpolation.txt.

On laptops with two graphics cards (NVIDIA Optimus, AMD switchable graphics) the game asks the driver for the dedicated one. If it still runs slowly, set the game's executable to High performance in Windows Settings → System → Display → Graphics.

Saves and updates

The game's own save (the three save files on the cartridge's battery) is kept in build\saves\save.srm.

With Check for updates on start ticked (the default; on the launcher's main screen, next to Skip launcher on boot), the game asks GitHub for the latest release when it starts and offers to install a newer one. Accepting closes the game, downloads the new setup pack, copies it over the install folder and reopens the setup window: press Generate & rebuild. Nothing is deleted; build\ (the rebuilt game, saves\, save states, config.ini, keybinds.ini) and rom.cfg are kept. Untick the box to turn the check off (saved in update.ini).

Your saves are never lost or broken by an update. In-game saves and save states made by any release keep working in every later one. Before installing, the updater copies build\saves\ to save-backups\<date>_before_<version>\ and never deletes those copies; save files are left out of the copy, and if they changed anyway the backup is put back. Every release after the first is checked against the one before it with tools/check_update_compat.ps1, which builds the previous release, makes an in-game save and a save state with it, installs the new pack with the previous release's own updater and rebuilds; it fails unless every save file is byte-identical and the new build continues the old save state.

See CHANGELOG.md for what changed in each release.

Status

Boots through the Nintendo logo, the opening story and the title screen into the file select, the intro on Yoshi's Island and the first level, at full speed with the Super FX graphics drawn. The in-game save is written to save.srm. Most code still runs through the snesrecomp interpreter; every world and boss is not yet verified. See Porting from here.

Framework patches

patches/ holds changes to the snesrecomp and recomp-ui submodules. Reapply them after updating the submodules:

git -C snesrecomp apply ../patches/snesrecomp-audio-interpolation.patch
git -C snesrecomp apply ../patches/snesrecomp-glsl-passprev-and-vao.patch
git -C snesrecomp apply ../patches/snesrecomp-mosaic-frame-model.patch
git -C snesrecomp apply ../patches/snesrecomp-nmi-idle-loop-wai.patch
git -C snesrecomp apply ../patches/snesrecomp-nmi-wai-in-handler.patch
git -C snesrecomp apply ../patches/snesrecomp-raster-oam-and-hdma.patch
git -C snesrecomp apply ../patches/snesrecomp-raster-vram-journal.patch
git -C snesrecomp apply ../patches/snesrecomp-resume-state-restart.patch
git -C snesrecomp apply ../patches/snesrecomp-shader-forces-opengl.patch
git -C recomp-ui apply ../patches/recomp-ui-host-toggle.patch

snesrecomp-raster-oam-and-hdma.patch is the renderer fix shared with the other ports: per-line sprite tables, HDMA set up in vblank, and vblank writes kept in their own field. It also counts HDMA's first transfer, made in V=0's H-blank, as a table line, as the hardware does. Yoshi's Island uploads Yoshi's tiles and his sprite table together at line 221; in 0.1.0 the renderer drew every line with the newest tiles, so the per-line sprite table was limited to screen splits (with the older table under the new tiles, Yoshi showed extra heads). Since 0.1.1 the tiles are journaled too (below), and the table and tiles of each line come from the same moment.

snesrecomp-raster-vram-journal.patch makes the renderer draw each line with the video memory, palettes and sprite table it had on hardware. The renderer runs after the CPU half of a frame, so a write made while the picture is drawn (in forced blank at the bottom of the screen) used to reach every line of that frame; it is now journaled and replayed from its own line, and writes made by the next frame's NMI before the render are kept out. It also reads BG mode 2's offset-per-tile rows at BG3VOFS and BG3VOFS+8 (the code read BG3VOFS-1 and +7, a row off when BG3VOFS is a multiple of 8) and drops a +1 on the vertical offset, as bsnes does. Both showed in World 1-7: the stage was assembled from the wrong rows, then shook 8 pixels back and forth while Yoshi walked, because the next frame's offset table, uploaded at line 217, was drawn under this frame's fine scroll. With video memory journaled, the per-line sprite table of snesrecomp-raster-oam-and-hdma.patch applies to every frame that rewrites it again.

snesrecomp-resume-state-restart.patch makes a setting that needs a restart come back to the same moment. The in-game launcher saves saves\resume.sav, restarts and loads it before the first frame, when no session exists yet. A save state holds the machine but not the CPU half's registers or resume point (a load during play keeps the session's own, the game's idle loop), so the frame driver booted from the reset vector over it. The restart file is now written in the rollback format (machine plus execution residue), and the frame driver takes the interpreter's resume point at the start of a frame. Save-state slots keep their format.

snesrecomp-mosaic-frame-model.patch builds the mosaic table on every visible line. The optimized renderer built it only on line 0, which frame-model hosts never render, so every line of a mosaic-enabled layer sampled the layer's first row.

snesrecomp-nmi-idle-loop-wai.patch and snesrecomp-nmi-wai-in-handler.patch make a WAI halt until the next interrupt, as on hardware, in the main loop and inside an interrupt handler; without them the interpreter could spin to its step cap and freeze the screen.

snesrecomp-audio-interpolation.patch adds the Cubic and Sinc audio interpolation (I key). They resample the dry output only; the echo buffer, OUTX, pitch modulation and save states stay those of the console's Gaussian filter, so the game runs identically in every mode.

snesrecomp-glsl-passprev-and-vao.patch fixes two shader bugs: a pass that reads PassPrev<n> back to the game frame got nothing (ScaleFX drew black), and switching to no shader mid-game drew a black screen because the shader path left the plain path's vertex attributes disabled.

snesrecomp-shader-forces-opengl.patch switches the renderer to OpenGL when a shader is picked, since the presets only run there.

recomp-ui-host-toggle.patch lets a title add one checkbox of its own beside "Skip launcher on boot"; this project uses it for the update check.

ROM identity

File	Super Mario World 2 - Yoshi's Island (USA).sfc
Publisher	Nintendo
Developer	Nintendo EAD
Year	1995
Mapping	lorom
Region	USA (North America)
Coprocessor	Super FX 2 (GSU-2)
CRC32	d138f224
SHA-256	9b4957466798bbdb5b43a450bbb60b2591ae81d95b891430f62d53ca62e8bc7b

tools/regen.sh refuses to run against anything else, so a mismatched revision fails immediately instead of producing subtly wrong output.

Build

git submodule update --init --recursive
bash tools/regen.sh --rom "/path/to/Super Mario World 2 - Yoshi's Island (USA).sfc"
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j

The ROM does not have to live in the repository — keeping it on your own drive is the better habit, and SNESRECOMP_ROM sets the path once for a shell. Without either, tools/regen.sh finds Super Mario World 2 - Yoshis Island (USA).sfc at the repo root, then the path the setup wizard recorded in rom.cfg; .gitignore blocks both from ever being committed.

tools/regen.sh verifies the ROM, generates src/gen/*.c, and re-syncs recomp/funcs.h. Re-run it whenever you change anything under recomp/.

The Windows build is a window app: diagnostics go to SuperMarioWorld2YoshisIslandSNESRecomp.log beside the executable. -DSMW2_CONSOLE=ON brings the console back for debugging.

Run

./build/SuperMarioWorld2YoshisIslandSNESRecomp                    # launcher picks the ROM
./build/SuperMarioWorld2YoshisIslandSNESRecomp "/path/to/Super Mario World 2 - Yoshi's Island (USA).sfc"

With no ROM on the command line the build opens the recomp-ui launcher: a ROM picker with a verification badge, plus display / audio / input settings. Your choice is cached in rom.cfg beside the executable, so the next launch opens on it and "Skip launcher on boot" makes it immediate.

Either way the ROM is checked against the digests above before anything boots — a dump that could not have produced this build is refused at the door rather than mis-executing ten frames in.

Layout

Path	What lives there
recomp/	Analysis input: bank*.cfg, symbols.toml, generated funcs.h
rom_identity.txt	ROM digests — read by the build, tools/regen.sh and CI
src/	Host code you own: main.c, game_rtl.c, smw2_update.c
src/gen/	Generated C. Never committed — regenerate locally
assets/shaders/	Scanline, CRT and upscaler presets for the launcher
patches/	Changes to the framework submodules (see above)
snesrecomp/	Framework submodule (owns lib/recomp-net, lib/retcomm-rbengine)
tools/	regen.sh — the ROM → C pipeline; check_update_compat.ps1; import_libretro_shaders.py
scripts/	package_release.sh — player-facing zip
framework_pins.txt	Exact framework commits this project was scaffolded against

Porting from here

The scaffold stops where the game-specific work starts. In rough order:

1. Make it boot. src/game_rtl.c holds the frame driver. It starts on the framework's beam-aligned driver (snesrecomp/runner/src/beam_frame_driver.h): one frame per PPU field, interrupts taken where the beam latches them, the field rasterized from the raster journal.
2. Name things. Add entries to recomp/symbols.toml as you identify routines, then re-run tools/regen.sh. Set emit = true to promote one into ahead-of-time analysis; leave it false to keep it interpreted. See recomp/README.md.
3. Resolve dispatch misses. After every run, deal with unresolved indirect targets before anything else — they are the reason a port diverges, and they are cheap to fix early.
4. Never synthesise a result to get past uncovered code, and never edit src/gen/ by hand. Fix the config or the framework and regenerate.

Multiplayer

Single player.

License

This project's own source is under the MIT license in LICENSE. The framework carries its own terms (PolyForm Noncommercial 1.0.0) — see snesrecomp/LICENSE and snesrecomp/THIRD_PARTY_ATTRIBUTION.md; the changes in patches/ apply to that framework and fall under its terms. The shaders under assets/shaders/_libretro/ come from libretro/glsl-shaders and keep each author's license in their file headers. None of these cover the game data, which is not distributed here.

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