ALttP Randomizer Bot
The goal is to write a bot that can play Legend of Zelda: A Link to the Past's Randomizer in a similar way that a human would.
Unlike a Tool-Assisted Speedrun (TAS) of the original game, the Randomizer shuffles the locations of items around, so the bot can't blindly follow a script verbatim.
The bot reads out chunks of memory from the emulated SNES to understand what is on-screen: it's not operating on the video/images shown on screen. For fairness, it doesn't use any data that wouldn't be knowable to a human player: e.g. it doesn't peak inside chests before opening them.
Architecture
The bot is written as a library that gets linked into a slightly-modified Snes9x emulator. There are 2 key functions in the interface:
void ap_tick(uint32_t frame, uint16_t * joypad)- This function is called each frame, and blocks emulation until the bot returns. The bot can set the controller state with the
*joypadoutparameter.
- This function is called each frame, and blocks emulation until the bot returns. The bot can set the controller state with the
uint8_t * (*base)(uint32_t addr)onstruct ap_snes9x- This function can be used by the bot to get the memory address for a given SNES virtual memory address.
The overall code quality is pretty bad, and is mostly shaped around rapid iteration.
Videos in action
- 24 minutes of gameplay, from 2020/10/04, sped up 10x
- Randomizer Settings: Open mode, Sword on Uncle, No Glitches, Defeat Ganon
- Cheating: infinite health, bombs, and arrows
- Hits about ~45 checks, clears Eastern Palace
Credits
This wouldn't be possible without the crazy amount of reverse-engineering effort put into this game.
- MathOnNapkin's Zelda 3 RAM/ROM/SRAM documentation
- MathOnNapkin's Zelda 3 Annotated Disassembly
- wiiqwertyuiop's Zelda 3 Annotated Disassembly