There is a group of at least 4 people (including me) working on GTA2 re, in which the main goal is to reimplement the version 10.5 of the PC version of GTA2 (freeloader version).
Github project link: https://github.com/CriminalRETeam/gta2_re
There are almost 1800 functions matched out of 4400. A function is matched when its assembly is reproduced from original gta2.exe with maximum accuracy possible (i.e. it has the exact same instructions with the same CPU registers in the same exact order). The Frontend is very functional (although the sound does not work yet) and we are working to boot into the map. The workflow of matches doesn't follow a specific path or an order. For example, even if we can't enter the game yet, there are a lot of in-game functions matched, such as the script ones.
I think that here is a good place to discuss about this project. You can ask me questions about the project or about the GTA2 behaviour and maybe I can give an answer you (or search for one).
For example, do you know that you can place only 20 phones with a trigger in the game? When I was working on Enhanced Downtown, I wanted to spread many phones across neutral areas of Downtown to create many "neutral missions", but I got only 1 working. It's because there are (6 * 3) + 1 = 19 phones with a trigger in Downtown, 6 for each gang (2 green, 2 yellow, 1 red, 1 info phone) and 1 for the tutorial mission phone. I only understood what was happening when I saw the size of the threads array on the reverse engineering project, which is 20.
Also, the game crashes if you use CHECK_CHAR_CURR_WEAPON on a ped that doesn't exists or if the ped is not a Player because this opcode in particular doesn't check for null pointers for the ped itself or the player associated with the ped, and you can see it explicitly on the code.
The desync behaviour of using SET_ALL_CONTROLS_STATUS on multiplayer (on non-Vike GTA2 version) also can be seen explicitly on the code, in which the player pointer given by the script isn't used at all and thus the command always affects the user (which is different for each player).
Here is a brief summary of the GTA2_RE files:
The relevant folders are:
- 3rdParty:
Compiler & Linker used to build GTA2;
GTA2Hax: a reimplementation of d3ddll and DmaVideo.dll. It's the same project discussed on viewtopic.php?t=829 , but it's completed! This achievment means we are able to use ImGui inside GTA2 to help debug stuff, such as calling functions, changing fields and attributes in runtime etc.
- Scripts: Python scripts to help the reverse engieering. The most useful are: create scratches on decomp.me; and color functions that are matched, so we readily know what function is matched or not.
- Source: Game files source code, both .cpp and .hpp.
I will mention some of them that you may have some interest:
miss2_0x11C.cpp - Script opcodes and other related functions (plenty of them already matched)
frosty_pasteur_0xC1EA8.cpp - .scr related stuff, such as threads, total missions, kill frenzies passed/failed and CMD pointers
Game_0x40.cpp - The main in-game class. It's responsible for game loop, game boot and stores the players pointers.
youthful_einstein.cpp - Kind of Multiplayer class, specially about tag game
winmain.cpp - The functions that are on the top of the hierarchy, and the most interesting function is WinMain_5E53F0, which initializes the game and controls the game loop.
Hud.cpp - HUD stuff: from rendering to the functionality of all interface objects, such as health bar, wanted level heads, zone name, car name etc
Frontend.cpp - Main Menu functions (very functional at this moment)
Draw.cpp - String, Text & Figure drawing. Very used on Frontend and HUD drawing
gbh_graphics & dma_video - Integration with d3ddll and DmaVideo libraries
MapRenderer.cpp - Map rendering stuff: tiles, blocks etc.
Object_5C.cpp:
Object_5C - Not really known but it can be a object in the broader sense (explosions for example)
Object_2C - Objects like the ones created by OBJ_DATA in scripting
Object_3C.cpp - Seems to be the object physics, such as the angle, velocity etc.
Phi_8CA8.cpp - Seems to store all object attributes like friction, weight, if it has shadows etc.
map_0x370.cpp - Map & zone functions (about 85% of them are matched)
Car_BC.cpp - The main car class
Car_B0.cpp - Car physics (involves a lot of processing velocity, angles, and uses model physics like max speed, acceleration, handling etc.)
Car_10.cpp - Car door class
CarInfo_808.cpp - Deal with car properties, such as mass, num of remaps, num of doors etc.
Ped.cpp - The main ped class (managing occupations, objectives etc)
char.cpp:
Char_B4 - The ped as an object (in which may includes ped walking code)
Char_203AC - Ped Pool
Sprite.cpp - The 2D sprites on the game, including peds and cars
Player.cpp - Player class
eager_benz.cpp - Something to do with the player score
thirsty_lamarr.cpp - Something to do with the number of lives and multipliers
Camera.cpp - Camera
Cranes.cpp - Cranes stuff
Gang.cpp - Gangs stuff
PublicTransport.cpp - Buses and trains
Firefighters.cpp - Firetrucks
Ambulance_110.cpp - Ambulances
Police_7B8.cpp - Police main class
Police_38.cpp:
PoliceCrew_38 - Cop crew class, such as cop duos, swat team etc.
PoliceRoadblock_A4 - Police roadblocks
Police_7C - Unknown police class
Kfc_1E0 - Probably "EmergencyUnit" class, in which includes police, ambulance and firefighters
Shooey_CC - Maybe crime
xenodochial_morse & sleepy_stonebraker_0x6C - Something to do with game credits
Fix16 - Fixed Point, very used. It replaces floats on great part of the game, including coordinates. Floats are only used when they are inevitable, such as on the functions that renderize strings on the screen and renderize the map (Vertex stuff).
Ang16 - Angle fixed point. Ranges from 0 to 1439.
Fix16_Point - It's what is called "CVector" on 3D GTA's
Fix16_Rect - Maybe collision boxes
error.cpp - Fatal Error handling
gtx_0x106C - Textures & Sprites loader & managing
magical_germain_0x8EC - Something to do with managing Text & String sprites
lucid_hamilton - A big storage of game variables (such as multiplayer game mode)