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Published 20 hours ago • verified publisher icon AntonioNoack
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OpenSource game engine for Kotlin

Game Engine: Rem's Engine

Parallel to my video editor Rem's Studio, I am developing my own game engine. I have often written the beginnings of small games, but they always had much in common, so I decided to write my own engine.

  • direct Java/Kotlin support
  • usable in my favourite IDE: Intellij Idea
  • completely Open Source
  • no fees
  • fewer annoyances with skeletons than Unreal Engine 4
  • support for all kinds of formats
  • working/loading from inside compressed folders
  • I get to learn even more about game engines <3

This engine does not have the target to offer the best graphics, or be the best performant. Its goal is to be nice and quick to develop in, like a tool box.

What does the engine look like?

Promo Image of Editor

What can you see in this image?

UI Overview

Left is a tree view of the scene, center is the 3d view of the scene, right is the property editor. At the bottom, you can see two file explorers with thumbnail generation: the left one is the project, the right one is my documents-folder.

All UI is part of the engine, so you can create your own components ("Panel"), and your own rendering styles.

Asset Loading

To render assets as thumbnails, or in 3d, they need to be loaded. This scene contains glb/gltf, obj and fbx files, jpegs and webps.

Rendering Debug Modes

Currently, the scene is in "MSAA Deferred" mode, so it renders MSAAx8 with deferred light rendering. There is many more modes. There is also a bit of post-processing: SSR, SSAO, Bloom, outline for selection, refraction for glass. Shadows are conditionally real-time ofc, too.

Skeletal Animations

The woman with the phone is a scene from Mixamo, that I just loaded as a sub-scene. Most file readers export their contents as a ready-to-use sub-scene. It's animated ofc.

Transparency

Transparent objects are currently rendered with an order-independent approach, but it will need a weighting function in the future, so closer panes have more weight on the final color.

Most Relevant Websites

Official Website

Contains most important links (documentation, discord, github), and a tutorial to get started.

Documentation

JavaDoc-like code reference with a handy search bar. Generated by Rem's Docs Generator 😄.

The code is mainly documented within itself, so I recommend you to download the engine source code. Using it, you can easily look up how and where pieces of engine code are being used.

Wiki

Since both projects originate from the same base, the wiki currently is located at Rem's Studio's repository. It contains a bit of information about serialization and the modding/plugin system.

Features

All features can be found in some test in the test folder. Some depend on local files, which you might not have, but most should work, and I try to minimize those.

Architecture

  • entity - component based system like Unity
  • 64-bit fp transformations for universe-scale games
    • on GPU-side, camera is always at origin, FP32
  • AABB optimized scene hierarchy
  • mods / plugins from the start: your game is a mod(ule) for the engine
  • in editor: automatic file reload, on file change
  • heavy operations are cache-based, with automatic free after not-requesting for a set time
    • ImageCache/TextureCache (CPU/GPU)
    • MeshCache, AnimationCache, PrefabCache
    • AudioCache
    • FontManager for textures and sizes
    • PDFCache, VideoCache
    • (File)MetadataCache
  • very basic Lua scripting

File Formats

  • supports loading all kinds of formats
    • Image formats (ffmpeg, ImageIO, Image4j, custom): png, jpg, tga, ico, dds, exr, hdr, svg, pcx, qoi, xcf (Gimp)
    • Video formats (ffmpeg): wav, mp3, mp4, avi, flv, gif
    • Mesh formats (Assimp, custom) obj, fbx, gltf, dae, blend, vox, md2, md5mesh, mitsuba
    • Package formats (Apache Compress, JUnRar): zip, tar, tar.gz, rar, 7z, bz2, lz4, xar, oar
    • Metadata formats (custom): json, csv, yaml, xml
    • Others (Apache PDFBox, custom): pdf, tar/text-based Unity-packages
    • Note: not all are fully supported
  • can load files from compressed folders (recursively as well)
  • files have been abstracted into FileReference, for storage files, web files, files inside zips, in-memory-files, pseudo-files, ...

Graphics

  • pbr workflow
  • pipeline / shader-object abstraction over graphics APIs like OpenGL
  • simple switch between forward- and deferred rendering
    • for beautiful MSAA with a few lights,
    • or thousands of lights without performance hit
    • Note: forward rendering does not support SSR nor SSAO
  • FXAA as cheap anti-aliasing, MSAA as expensive anti-aliasing
  • different light types, with shadow support: directional, spot, point
  • shadows with cascades (directional)
  • planar reflections
  • screen space reflections (SSR)
  • screen space ambient occlusion (SSAO)
  • static, animated and procedural meshes
  • static and animated meshes can be drawn using instanced rendering
    • animation states are stored in 2d texture per skeleton -> instanced meshes can be in different animations, but still be rendered together
  • signed distance functions as mesh replacement
  • bloom to convey brightness
  • AMD FSR: dynamic upscaling and sharpening
    • is used to upscale images in the file explorer as well

UI

  • event based UI library
  • 3d gizmos
  • real-time graph editors
    • materials (shaders)
    • render pipelines (post-processing)
    • animations
  • transparent meshes
    • looks fine until there is dark layers
    • order independent
  • Android-inspired layout system
  • text inputs have integrated spellchecking
  • all kinds of other value inputs
  • rendered on GPU with OpenGL
  • controller support
    • works for UI automatically
    • you can even use your controller in other programs as a mouse, while Rem's Engine/Studio is running :3

Physics

  • Bullet as 3d physics engine
    • running on a separate thread for uninterrupted graphics (optional)
    • running with 64 bit floating precision for accuracy / universe simulations
  • Box2d as 2d physics engine
    • currently a prototype

Planned Features

  • easy local multiplayer
  • usable Multiplayer, local and tcp/udp
  • per-button export to Windows/Linux (currently manual)
  • fully supported Lua scripting
    • LuaAnimTextPanel
    • QuickScriptComponent

Maybe Later Features

  • automatic export to Web
  • automatic export to Android
  • light baking for realistic graphics
  • visual coding? works for some stuff already (pipelines, materials, animation trees)
  • support separate mice / keyboards for local multiplayer?
  • Vulkan backend to support hardware raytracing

Projects using Rem's Engine

Getting Started

  • Download an IDE of your choice. I prefer IntelliJ IDEA, but have worked with Eclipse in the past.
  • Download either the engine source code, and compile it yourself, or download a pre-compiled jar.
    • If there is no release available yet, just ask for a build, and I'll create one :)
  • Add the engine jar as a dependency to your project.
  • Either create an extension (mod), or work directly with the engine.

Samples

Besides my personal projects that use Rem's Engine, there is also quite a few samples within the engine source code. They also function as tests for me.

Some tests, starting the whole engine, like a small game:

  • GFX: MarchingCubes.kt
  • Math: PathfindingAccTest.kt

Some feature tests:

  • Math: SDFColliderTest.kt
  • Internal: Hierarchy.kt
  • GFX: MarchingSquares.kt
  • GFX: MarchingCubes.kt
  • GFX: Reduction.kt
  • GFX: FSR.kt
  • Debug: JsonFormatterTest.kt
  • UI: DrawCurves.kt
  • UI: AnimTest.kt
  • Snake Game, Running Web Demo

You can find most examples in the "tests" folder. In total, there are more than 400 handwritten tests for you to see how the engine works :).

Ports

Build It

All libraries are shipped with the engine :). Use any IDE you want, with Java and Kotlin support. Best use IntelliJ IDEA.

Then run any of the tests you want 😊.

Some parts of the engine have been packed into modules. This is the preferred way to create a game, or library. Currently extracted modules:

  • PDF (pdf document to image converter),
  • SDF (signed distance functions),
  • Bullet (3d physics),
  • Box2d (2d physics),
  • Recast (path finding)
  • Image (image loaders)
  • Mesh (mesh loaders)

So if you need them, don't forget to import them into your project. (either as a compiled artifact = .jar, or as an Intellij module)

Ship It

Linux, Windows

Shipping is easy on Windows and Linux: just export your projects will all dependencies into a .jar file, or download dependencies on the first start (as I do with FFMPEG and spellchecking). To load plugins from your built jar, because your jar won't be scanned at runtime, register them from your main class as internal :).

Android

Shipping to Android is a bit more complicated:

  • download the Android fork as an Android Studio project
  • modify it to your needs
  • libraries can be added just like in IntelliJ IDEA

Web (HTML5, WASM, WebGL)

Note: this is currently broken when using 3d as of 17th March 2024

My JVM->WASM translation is a little slow at the moment, unfortunately. It's fast enough for simple games though. Lots of things haven't been implemented or are half-baked, so be cautious and don't expect too much (e.g., image loading is very limited currently)!

Shipping to web:

  • download JVM2WASM
  • build your game, best as a panel-creating function, into a JAR (don't use sync IO)
  • bind that as the missing VideoStudio/RemsEngine.jar in JVM2WASM
  • run JVM2WASM.kt to create the WASM file and index0.js bindings
  • if needed, implement missing or extra functions from Java

First demo: Snake Game from tests.

Just Try/Use It

If you don't want to compile the engine yourself, and just want to focus on developing games, plugins or mods, you can use pre-built versions. There isn't an official release yet, but you can use the in-official build from my Cellular Automata Demo. A release of Rem's Studio would work as well.

Until I create a release, they might be a bit out of date 😅.

Used libraries

If I forgot something, just write me a message 😄.

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verified publisher icon AntonioNoack

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OpenSource game engine for Kotlin

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