OpenBGI

This project aims to reverse-engineer the Ethornell Buriko General Interpreter (BGI), and create an open source re-implementation of the engine.

We now have a Discord server: https://discord.gg/3zFTJWUNt7

Status

While we're still working on reimplementing opcodes, but it now makes sense to compile a stand-alone program.

It's still early days, but we are able to enter the main menu and settings screen of at least one game by executing Buriko Programs (._bp scripts.)

We're still exploring graphics routines.

Currently, we're only exploring graphics, not sound.

Workflow

Currently, the workflow is to use Ghidra for analysing the engine, and injecting a DLL into the process for live analysis and producing logs.

Using these logs, we implement similar behaviour in OpenBGI.

Milestones reached:

• Reimplemented enough basic opcodes for Tayutama to run.
• Standalone engine is being worked on.

Goals

OpenBGI aims to be a cross-platform, highly portable reimplementation of the BGI engine.

Main platforms we want to support:

• Windows
• macOS
• Linux
• Android
• WASM (browser)
• Haiku

If possible, we'd like to support:

• Switch 1/2
• PSVita
• PS4 / PS3 / PS2

For now, the only realistic targets are Windows and Linux.

We want to include tools for translating games, and upscale old games on-the-fly.

Out-of-Scope

OpenBGI is not a Visual Novel development platform - If you wish to develop a VN on the Ethornell/BGI platform, then you must contact Buriko Co., Ltd.

Building

While cross-platform compatibility is our goal, the build chain currently is only configured for Linux.

Before you do anything else, you need to install the various tools and dependencies needed:

apt install build-essential gcc-mingw-w64-i686

Building the engine is as simple as running:

make

Finally, run the engine in the directory of the game files:

cd /path/to/the/game
/path/to/openbgi

The engine expect all game resources to have been extracted from the game using the unarc tool in the tools directory. In due time we will support loading directly from unmodified game assets, but for now it helps development to have assets extracted.

Ethornell / Buriko General Interpreter

"Ethornell / Buriko General Interpreter" is most commonly referred to as "BGI" or "Ethornell".

BGI consists of a stack-based Virtual Machine (VM) plus subsystems for drawing graphics, synthesising graphical effects, playing sound, and reading/writing files.

The BGI VM consists of two parts:

• Basic opcodes
• Multi-byte extended opcodes

Basic opcodes mainly deal with routine logic, with the multi-byte opcodes deal with system calls, graphics, sound and custom logic.

The BGI engine exclusively executes Buriko Programs (Compiled ._bp files.)

Scenario scripts (what defines the actual story, choices, scenes, and text) are compiled scripts. These scripts are in turn interpreted and executed by the BGI VM (VM in a VM kind of situation.)

OpenBGI aims to execute the lower-level VM execution. By doing thing, we get execution of Scenario scripts "for free", as the Scenario interpreter is defined in a Buriko Program.

Contact

Feel free to join our Discord server: https://discord.gg/3zFTJWUNt7