OpenRCT2

An open source clone of RollerCoaster Tycoon 2 built by decompiling the original game one bit at a time.

Screenshot 1, cheat windows
Screenshot 2, large land tool area (up to 64 squares at once)
Screenshot 3, high resolution
Screenshot 4, resizable window

1 Introduction

1.1 Background

OpenRCT2 is an attempt to decompile RollerCoaster Tycoon 2 into C. RollerCoaster Tycoon 2 was originally written in MASM and Visual C++ where functions related to interfacing with the operating system were written in C (supposedly 1%), with the rest of the game being written in pure x86 assembly. For an example of this method, OpenTTD was formed through a similar procedure; the original game, Transport Tycoon Deluxe, was decompiled into C which allowed for the addition of thousands of features to the game. RollerCoaster Tycoon 2 uses the third version of Chris Sawyer's engine, which shares some code with Transport Tycoon. This is reflected in the usage of OpenTTD 0.1 code such as the windowing system and graphics rendering. While the version of the engine used in Chris Sawyer's Locomotion is newer, OpenRCT2 is currently targeting the RollerCoaster Tycoon 2 engine to ease the decompilation process.

1.2 Decompiling the game

In order to decompile the game gradually without introducing new bugs, each procedure in RollerCoaster Tycoon 2 is to be re-written in C on an individual basis. To test the accuracy of the re-written procedures, the decompiled C procedures are compiled into a DLL (openrct2.dll) which exports an entry procedure mimicking the WinMain function in RollerCoaster Tycoon 2. The original executablerct2.exe has been patched so that openrct2.dll and WinMain are in the DLL import table and the WinMain export procedure in openrct2.dll is called at the start of the WinMain procedure in rct2.exebefore returning. With this system implemented, starting rct2.exe calls the new DLL as part of its initialization; the DLL can then run all the decompiled code whilst still being able to read / write to therct2.exe memory model and run rct2.exe procedures.

The project therefore acts as a patch to RollerCoaster Tycoon 2, allowing each procedure to be gradually implemented while simultaneously adding new features where possible. Until all procedures of the original game are re-written in C, the project must remain a DLL which is called from the patchedrct2.exe.

1.3 Progress

Currently, the windowing system, graphics rendering and basic game loop are being decompiled. Decompiling all of the game's procedures is a convenient way of identifying the game's memory structure. SDL2 has been used as a replacement for the operating system calls, allowing for cross-platform support after the dependency on the original game's executable has been removed.

As of 16th August 2014, various UI improvements have already been made, settings are now stored in a local INI file. More drawing functions have now been decompiled but still remain cryptic C, much of the game management have been decompiled (e.g. peep generation, awards, cash out) and almost half of the windows. A rough estimate based on number of functions in the original game and number of functions now in C tells us that the project is approximately 25% complete of its target goal of having the game run on 100% C code. More information can be found in changes to original game andwindow progress.

1.4 Aim

The aim is to completely decompile RollerCoaster Tycoon 2 into C so that cross-platform support, new features, and new gameplay can be added in a similar fashion to OpenTTD. With the addition of SDL2, the game can already be run in a resizeable window (which was not possible originally). Once the game has been fully decompiled, additional gameplay features, gameplay tweaks, and improvements can be introduced. The following is only a brief, non-exhaustive list of the possibilities - there are many more:

Improved peep path-finding
Increased window / ride / object / map / construction limits
More sandbox-friendly gameplay
Editing available objects
Improved title sequence
Translation into more languages
Re-introduction of RollerCoaster Tycoon 1 mechanics:
- Shuttle Loop compatibility
- Have Fun! objective
- Finish building five coasters objective
- Using the mountain tool during the game

2 Downloading the game / Building the source code

A couple of third parties offer downloadable precompiled builds. However, building the project is always recommended

OpenRCT.net

OpenRCT2.com

There is also a Launcher available from OpenRCT.net that will automatically update your build so that you always have the current version as they are released.

3 License

OpenRCT2 is licensed under the GNU General Public License version 3.

4 More information