Epysia

A 3D and 2D game engine, written in Java

Epysia builds games as a tree of GameObjects and components, lets you script behaviour in plain Java, and exports a native executable with its own trimmed runtime baked in. Nobody playing your game needs to know or care that a JVM is involved.

Installing

Epysia is an app, not a library. It isn't published to Maven, so don't go looking for it there.

If you're a player or a designer: grab an installer from the releases page. Everything's bundled with a runtime trimmed down by jpackage, so you don't need a JDK on your machine. Windows gets an .exe, Linux gets a .deb and a portable .tar.gz.

If you want to build from source: you'll need JDK 25 and a GPU that can do OpenGL 4.3.

git clone https://github.com/Meekiavelique/Epysia
cd Epysia
./gradlew :epysia-editor:run

To run a scene without opening the editor:

./gradlew runGame -Pscene=/path/to/main.epyscene -PprojectRoot=/path/to/project

Don't forget -PprojectRoot. Without it the runtime has nothing to load from: no asset database, no compiled scripts, no collision matrix, no input map.

What's in it

Scene runtime. Objects made of components, updated on a fixed clock that runs at 60 Hz by default and anywhere from 10 to 480 if you want it. Rendering smooths out the gaps between those updates, so motion stays even whatever the frame rate does.

Rendering. Physically based lighting on OpenGL or Vulkan, with shadows from suns, spots and points, reflections from the environment, and the usual work to keep it fast: only drawing what the camera can see, batching repeated objects, and swapping in simpler meshes at distance. The backend is chosen at launch, and a machine that cannot run Vulkan quietly falls back to OpenGL.

LitMaterial material = new LitMaterial();
material.setBaseColor(0.85f, 0.82f, 0.78f).setRoughness(0.35f);

MeshRenderer renderer = object.addComponent(new MeshRenderer());
renderer.setMeshPath("res://models/rock.epymesh")
        .setMaterial(material)
        .addLevelOfDetailPath("res://models/rock_lod1.epymesh", 25.0f);

Materials and shaders. Material uniforms come straight from annotated Java fields, so you never hand-write the layout. Surface shaders let you override one stage of the standard lit shader and keep shadows, lights and fog for free. They reload while the editor is open.

uniform float waveSpeed = 0.4;

void surfaceVertex(inout vec3 worldPosition, in vec3 localPosition,
                   in vec3 worldNormal, in vec2 uv, in float time) {
    worldPosition.y += sin(worldPosition.x * 2.0 + time * waveSpeed) * 0.1;
}

Post-processing. Ambient occlusion, bloom, fog, vignette and antialiasing, with two places to slot in effects of your own. Pixel art gets its own mode that renders at a fixed resolution and scales up in whole numbers, so nothing smears.

2D. Sprites drawn together in one pass, atlases and flipbook animation, tilemaps with layers, autotiling and per-tile collision, 2D lights, and physics that stays flat.

Physics. Rigid bodies running on native Box3D. Box, sphere, capsule and mesh colliders, triggers, joints, character controllers for 3D and 2D, ray and shape casts, and 16 layers you can decide collide with what.

@Override
public void onUpdate(InputState input, float deltaTimeSeconds) {
    float forward = actions.value(InputActions.MOVE_FORWARD, input);
    float right = actions.value(InputActions.MOVE_RIGHT, input);
    controller.move(new Vector3f(right, 0.0f, -forward).mul(speed));

    if (actions.wasPressed(InputActions.JUMP, input) && controller.isGrounded()) {
        controller.jump();
    }
}

Animation. Skeletons up to 256 joints, .epyclip clips, cross-fade blending, GPU skinning, and joint sockets if you need to bolt something onto a rig.

VFX. Particle systems built as node graphs and run on the GPU, with shapes, noise, curves and gradients, plus bursts for the chaotic stuff.

Visual scripting. One graph format doing five jobs: logic, state machines, surface shaders, post effects and VFX. Any public method on your components turns up as a node on its own.

Audio. Positional sound with a mixer, ducking, streaming and reverb, running on OpenAL.

Navigation. Navmeshes baked from the geometry a surface declares, walked by agents that path around what you put in front of them.

Shipping. An exported game reads epysia-settings.json sitting beside it before the window exists, so a player can change the render backend, adapter, resolution, vsync and frame cap without a rebuild. Saves are written atomically into saves/ so an interrupted write cannot corrupt progress, and an uncaught exception leaves a crash report the next launch can collect.

Steam. Lobbies, achievements, cloud saves, rich presence and the overlay, plus friends, avatars, DLC and the app you were launched as. The app id lives in the project and ships in steam_appid.txt, so a build either identifies itself or carries no Steam dependency at all.

Web requests. services.web() runs a request off the main thread and hands the response back on it, so a script can touch the scene in the callback. Failures arrive as a response rather than an exception.

Navigation. Navmeshes baked from the geometry a surface declares, walked by agents that path around what you put in front of them.

Shipping. An exported game reads epysia-settings.json sitting beside it before the window exists, so a player can change the render backend, adapter, resolution, vsync and frame cap without a rebuild. Saves are written atomically into saves/ so an interrupted write cannot corrupt progress, and an uncaught exception leaves a crash report the next launch can collect.

Steam. Lobbies, achievements, cloud saves, rich presence and the overlay, plus friends, avatars, DLC and the app you were launched as. The app id lives in the project and ships in steam_appid.txt, so a build either identifies itself or carries no Steam dependency at all.

Web requests. services.web() runs a request off the main thread and hands the response back on it, so a script can touch the scene in the callback. Failures arrive as a response rather than an exception.

Scripting. Behaviour subclasses get compiled and hot reloaded while the editor's open. Slap @EpysiaComponent on a class and it shows up in the Add Component menu; @Export puts a field in the inspector and in the scene file.

@EpysiaComponent(name = "Spinner", category = "Gameplay")
public final class Spinner extends Behaviour {

    @Export(label = "Degrees Per Second", min = -720.0f, max = 720.0f, step = 5.0f)
    private float degreesPerSecond = 90.0f;

    private Transform3D transform;

    @Override
    public void onStart(EngineServices services) {
        transform = ownerOrNull().getComponentOrNull(Transform3D.class);
    }

    @Override
    public void onUpdate(InputState input, float deltaTimeSeconds) {
        transform.rotateAxisAngle(0.0f, 1.0f, 0.0f,
                (float) Math.toRadians(degreesPerSecond * deltaTimeSeconds));
    }
}

Editor. A Dear ImGui editor with the scene view, inspector, asset browser, graph canvas, sprite and tilemap authoring, profiler, lighting bakes, and export, all in one place. Code editing highlights Java, Kotlin and GLSL, every action is reachable from one command palette, and the interface scales with Ctrl +/- from 80% to 150%.

Extending it. Subsystems are just EngineModule services discovered through ServiceLoader. They load into both the editor and the standalone runtime, so you can bolt on new features without touching the core.

public final class WeatherModule implements EngineModule {

    @Override
    public int order() {
        return 150;
    }

    @Override
    public void registerSystems(SystemRegistry registry) {
        registry.add(new WeatherSystem());
    }
}

Releases

Push a vX.Y.Z tag and .github/workflows/release.yml takes it from there. It builds on native Windows and Linux runners, publishes editor installers plus the export templates the editor uses to pack games. The Box3D natives get compiled straight from box3d-java in the same workflow, so every release ships with binaries that actually match.

git tag v0.1.0
git push origin v0.1.0

Support and bugs

You found a bug ? You can submit your detailed bug report with the "issues" tab on github or on our discord: https://discord.gg/zHBNkSHkc5

• Choose the "report a bug" tab during onboarding
• Go to the "bugs" channel
• Read the rules and submit the bug!

We will then discuss with you, fix the bug and add you to the credentials ! No bug bounty reward except credit will be offered.

Third-party

• Editor icons are derived from the Godot Engine icon set (MIT).
• Physics runs on Box3D, with vendored FFM bindings under src/main/java/com/meekdev/box3d.
• Built on LWJGL 3, JOML, Dear ImGui, and ClassGraph.

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Copywrite & Licence

This project is brought to you by EPI Studio, a french non-profit development studio. To know more about the non-profit or to join us, check our website: https://epistudio.fr

This project is under the licence MIT. Everyone can copy, modify and distribute the project as long as EPI Studio and Meek are mentionned in your readme.md or LICENCE file.