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Usagi is a platform independent hierarchical Entity-Component-System based game engine created by Vitei Inc..

In Usagi the entire world is grouped into a hierarchy of entities. These entities are very fine grained, every bone on every character is an entity, with optional additional logical entities where required.

Only components have data, and only systems have code. Entities are a concept to tie together a collection of components and the systems to be run on them; they have neither data nor code.

The systems to be run are determined by the components attatched to an entity. Systems can only act on components from one entity, but they can read from components belonging to parent entities.

For example, the update UpdateSoundActor system will act on any entity with a SoundActorComponent which also has a MatrixComponent in its self or one of its parents. If a RigidBody component exists it will also use that to set a velocity on the SoundActorComponent.

class UpdateSoundActor : public System
{
public:

   struct Inputs
   {
      Required<MatrixComponent, FromSelfOrParents>  mtx;
      Required<SoundActorComponent>                 actor;
      Optional<RigidBody, FromSelfOrParents>	    rigidBody;
   };

   struct Outputs
   {
      Required<SoundActorComponent>	actor;
   };

   DECLARE_SYSTEM(usg::SYSTEM_POST_TRANSFORM)

   static  void	 LateUpdate(const Inputs& inputs, Outputs& outputs, float fDelta)
   {
      SoundActorHandle& actor = outputs.actor.GetRuntimeData().hndl;
      actor.SetPosition(inputs.mtx->matrix.vPos().v3());
      if (inputs.rigidBody.Exists())
      {
         actor.SetVelocity(physics::GetLinearVelocity(inputs.rigidBody));
      }
   }
};

Components of other entities are never directly written to, events are used to communicate between entities

static void OnEvent(const Inputs& inputs, Outputs& outputs, const KillEntityEvent& killEntity)
{
	outputs.state.Modify().current = STATUS_DEAD;
}

By modifying the ECS design pattern to put a hierarchy at its core we believe we have created a paradigm which is far more practical when trying to manage the complex interactions required in a modern game, as well as improving multi-threading potential.

The word Usagi is Japanese for rabbit. Rabbits are quick, nimble and light, and that was our goal for the engine. Vitei was developing games limited in scope but with high technical demands for Nintendo platforms, so we set about creating an engine suited to those titles.

The public release supports Windows, but the currently unmaintained Mac code is also included, both Vulkan and OpenGL versions of the rendering code are publically available - but internally the interface has been proven on everything from 3DS to XBoxOne.

The engine has been proven on a commerical title as well as several internal demos on numerous platforms and APIs.

The open source release is currently in progress, for more details see the introduction and roadmap.

The engine fully supported online multiplayer and more modern shader based platforms; unfortunately these features were not highlighted in its one commercial title.

Progress is likely to be slow, work is being done by ex-staff as Vitei have graciously allowed us to open source this code base. However it is mostly used as a testbed and is no longer being used for commerical projects.

More detailed information is available in the wiki.

Getting up and running

The build process has not been improved or significantly modified and currently has a number of dependencies which can not be directly included in an open source project. Do not clone this project first as it should be checked out to a sub folder of a project which uses the engine.

  1. Install Visual Studio 2022.
    https://www.visualstudio.com/downloads/

  2. Install Ruby 2.3.3.
    Make sure that you select the option to add a path variable
    Note that versions newer than 2.4 will not function with nokogiri
    https://rubyinstaller.org/

  3. Install Python 2.7.14.
    Make sure that you select the option to add a path variable
    https://www.python.org/downloads/

  4. Clone an Usagi based Project
    For example UsagiTest
    Always clone Usagi repos recursively as we make heavy use of submodules
    OR
    Create a new one

  5. Optional Install the FBX SDK 2020.0.1 VS2017.
    Not necessary to run, but required to build the model converter (Ayataka) https://www.autodesk.com/products/fbx/overview

  6. Optional Install and build the Oculus SDK for Windows.
    Not necessary to run, but required if you want to make a VR app
    https://developer.oculus.com/downloads/package/oculus-sdk-for-windows/

  7. From a command window run Setup.bat
    If gems fail to install confirm your ruby version
    If python packages fail to install confirm your python version
    Pay attention to which environmet variables EnvironmentSetup.exe failed to set
    Note you must run environment setup whenever you switch to running a different Usagi project in order to set the correct USAGI_DIR env variable

  8. Optional If you installed the oculus sdk manually add the following environment variable EnvironmentSetup.exe may have been able to automatically find and add them if they were in ../../OculusSDK
    OCULUS_SDK_DIR -> [Oculus SDK directory]

  9. Reset to ensure environment variable changes take effect

  10. Follow the instructions in that projects README.md

Current Version 0.2.5

With v0.2 the engine was switched from OpenGL to Vulkan
v0.2.1 enables Vulkan validation and has addressed the issues that presented. It has also updated the old particle editor to Vulkan as its replacement is not yet ready. v0.2.2 enables per project post process effects v0.2.3 upgrades to PhysX 4.0 and simplifies installation v0.2.5 tackled additional validation issues presented by the latest Vulkan SDK, added effect comprehensive effect definitions and significantly reduced buffer allocations which would present an issue in larger projects. It also dealt with timing issues surrounding releasing assets. Finally it added an implementation of Adaptive Screen Space Ambient Occlusion.

Issues

The current is a list of known issues with Usagi which need to be addressed.

If there is not at least one child entity systems on the root entity will not be run

There is no longer a system other than submodules for linking projects and engine versions

Without a replacement model editor material overrides must be edited in yaml

Resource loading is slow and single threaded

The running of systems is not yet multi-threaded

Spot and projection lights are not properlly culled

The AI would need updating to be able to control flying vehicles

License

Usagi its self is available under the MIT licence (see LICENSE in this repository). We would appreciate you letting us know if you make use of any part of the code or the design; but there is no requirement to do so.
It requires PhysX to run, any project making use of this project will need to be aware of this. Third party software falls under the PhysX, MIT, Modified BSD and zLib licenses, the specifics of which are detailed in Documents/License.md