bezzant / zelda3

Zelda3

A reimplementation of Zelda 3.

About

This is a reverse engineered clone of Zelda 3 - A Link to the Past.

It's around 70-80kLOC of C/C++ code, and reimplements all parts of the original game. The game is playable from start to end.

You need a copy of the ROM to extract game resources (levels, images). Then once that's done, the ROM is no longer needed.

It uses the PPU and DSP implementation from LakeSnes. Additionally, it can be configured to also run the original machine code side by side. Then the RAM state is compared after each frame, to verify that the C++ implementation is correct.

I got much assistance from spannierism's Zelda 3 JP disassembly and the other ones that documented loads of function names and variables.

Compiling

Put the ROM in tables/zelda3.sfc

cd tables

Install python dependencies: pip install pillow and pip install pyyaml

Run python extract_resources.py to extract resources from the ROM into a more human readable format.

Run python compile_resources.py to produce .h files that gets included by the C++ code.

Windows

Build the .sln file with Visual Studio

Linux

apt install libsdl2-dev

Make sure you are in the root directory.

clang++ -I/usr/include/SDL2 -lSDL2 -O2 -ozelda3 *.cpp snes/*.cpp

Usage and controls

The game supports snapshots. The joypad input history is also saved in the snapshot. It's thus possible to replay a playthrough in turbo mode to verify that the game behaves correctly.

The game is run with ./zelda3 and takes an optional path to the ROM-file, which will verify for each frame that the C++ code matches the original behavior.

Button	Key
Up	Up arrow
Down	Down arrow
Left	Left arrow
Right	Right arrow
Start	Enter
Select	Right shift
A	X
B	Z
X	S
Y	A
L	D
R	C

Additionally, the following commands are available:

Key	Action
W	Fill health/magic
E	Hard reset
P	Pause
T	Toggle replay turbo
K	Clear all input history from current snapshot
F1-F10	Load snapshot
Shift+F1-F10	Save snapshot
Ctrl+F1-F10	Replay the snapshot

Additionally, there are a bunch of included playthrough snapshots that play all dungeons of the game. You access them with the digit keys. If you want to replay the stage in turbo mode, press Ctrl+Digit (eg Ctrl-5).

License

This project is licensed under the MIT license. See 'LICENSE.txt' for details.