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G-Engine

G-Engine is a C++ game engine that can parse and use the data files from the classic 3D adventure game Gabriel Knight 3: Blood of the Sacred, Blood of the Damned (GK3), developed and published by Sierra Studios in 1999.

The goal of this project is to create a cross-platform game engine capable of playing GK3. The original game only supported Windows, and it's also a bit buggy on modern hardware. Since GK3 is heavily data-driven, the idea is to build a newer, more modern engine that can use the original's data files. Completely new features can also be implemented!

See my blog post introducing the project for more in-depth info!

Getting Started

Currently, the project builds and runs on Mac or Windows. Here are some instructions to get up and running.

GK3 Data Files

This repository does not contain the data files from the game, since those are copyrighted material. You will need to obtain a copy of GK3 (available on Steam or GOG) to get the data files.

Copy the entire contents of the game's Data folder into the Data folder before building/running. This includes all Barn (.brn) asset bundles and all video files (.bik and .avi).

After building, you can also add data files. On Windows, copy them to the Data folder in the exe directory. On Mac, copy them to Gabriel Knight 3.app/Contents/Resources/Data.

Build File Generation

The project uses CMake, which means the definitions of what targets to create, which source files to include, and which libraries to link against are defined in CMakeLists.txt in the project root. Using CMake, you can generate the project files for your preferred IDE.

I've only tested Xcode and Visual Studio 2019 at this point, but it'll likely work with other build systems with a bit of effort.

Mac (Xcode)

Make sure Xcode and CMake are installed. Then, use terminal to execute the script at Build/GenerateMac.sh. The Xcode project will be generated at Build/Mac. Build and run the gk3 target.

Windows (Visual Studio 2019)

Install Visual Studio 2019 and CMake. When you install CMake, I'd recommend adding it to your path.

Then, I'd recommend using Git Bash to execute the Build/GenerateWindows.sh script. This will generate a VS 2019 project at Build/Windows. Build and run the gk3 target.

If you'd prefer to use the native Command Prompt, you'll just need to manually run the CMake command in the bash script file instead.

Platform Support

The engine currently supports Mac and Windows. Most of the engine code is platform-agnostic, but there are some key things that must be taken care of to support a new platform.

Libraries

The engine currently uses the following third-party libraries:

  • ffmpeg
  • fmod
  • GLEW
  • minilzo
  • SDL
  • stb
  • zlib

All library files are included in the repo, so no software need be installed before building and running. To support a new platform, the library files for that platform must be built and added to the appropriate Libraries subdirectory.

CMake

Most of the CMake files probably don't need to change to support a new platform, but there are some platform-specific bits in there. To support a new platform, the CMake file likely needs to be modified.

Platform-Specific Code

A lot of platform-specific code is taken care of by SDL. That being said, because the engine relies on SDL, you can only build and run on a platform that is supported by SDL!

There are also some platform-specific File and System functions that may need to be implemented for a new platform. This includes functionality for loading files from the disk, retrieving the computer name, etc.

Running Tests

This project uses Catch2 for unit tests.

After generating build files with CMake, simply run the tests target to run tests.

Built With

  • SDL - My training wheels for cross-platform OS polling, rendering, and input
  • ffmpeg - Provides AVI and Bink video support. Without this library, I have no idea how I'd ever get video playback working
  • fmod - Made SFX and music way easier than I thought possible
  • zlib - For GK3 asset decompression
  • minilzo - Also for GK3 asset decompression
  • stb - Handy public domain utilities; I'm currently using the image resize algorithms

Contributing

G-Engine is kind of a pet project of mine, and I'm using it primarily as a learning tool. As such, I am not actively looking for contributions.

If you are interested in contributing, you can submit a pull request. However, I request that you do not make pull requests that massively refactor or change how things are implemented. Shoot me an email or open an issue so we can discuss/debate such changes beforehand.

Progress

You may be wondering: what's the status of this project? Is the game playable? Do the graphics work? Here's a screenshot of what the game currently looks like:

Screenshot

(See the "Media" folder for a few more screenshots).

Graphically, the game looks pretty close to the original. You can't tell from the screenshots, but 3D model and face animations are working. A few things that are still missing: lighting on non-BSP models, correct texture filtering, billboard effect on 3D trees, graphical artifacts here and there, etc.

Logically, the game runs, but is definitely not completable. You can walk around, interact with objects, move between rooms, and even talk to NPCs. However, a lot of important internal functions the game relies on to function are not yet implemented, which will likely result in softlocks or crashes in many cases.

Running the Game

From time to time, as new and interesting features are added to the game, I'll package and upload releases here on GitHub. These executables are not "signed" or "notarized", so your OS may complain about files being from an unknown developer. You'll have to use the OS mechanism to bypass such warnings if you want to run the game.

Remember to copy the contents of GK3's "Data" folder to the "Data" folder. If running on Mac, this folder is inside of the .app package - you'll need to right-click on "Gabriel Knight 3.app", select "Show Package Contents", and navigate to the "Content/Resources" folder. If you don't do this, the game will provide an error message about missing "brn" files and fail to run.

As mentioned above, some functionality is implemented, but expect bugs, crashes, poor performance, and missing/incorrect behavior. Do not expect to play the entire game, or even complete a single timeblock!

You can open the developer console using the ~ key, which allows you to enter commands in the Sheep language. For example, try SetLocation("LBY") or PrintString("Hello World"). Check out the GitHub wiki for a list of all Sheep API functions that can be called.

F1, F2, and F3 enable debug visualizations. F4 quits the game.

Authors

License

This project is licensed under the GNU GPLv3 License - see the LICENSE.md file for details.

Acknowledgments

  • Sierra On-Line, who inspired me as a kid and still do today
  • Jane Jensen, for creating and designing the GK series
  • GK3 Tools, which provided guidance on BRN, BSP, and ACT file formats

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A 3D game engine capable of parsing and running data files from the classic Sierra Studio's adventure game Gabriel Knight 3

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