United Godot - Cross Engine Development

! EXPERIMENTAL !

This is a small experiment / POC, aimed at C# and Shader dev, which can be built with both Unity and Godot.

The repo contains a Godot project. The folder UnitedGodotProject contains Unity-compatible scripts:

• AutoRotate.cs - very simple
• UnitedGodotTest.cs - More advanced...

To try in Unity, copy UnitedGodot / UnitedGodotProject folders into Assets, and attach UnitedGodotTest.cs to a GameObject...

Background

• Relying on Unity is becoming increasingly untenable
• I mostly need Unity for cross-platform/hardware support
• I generally don't use fancy features or heavy editor integration
• It's probably faster to port a small subset of Unity to Godot, than to port all my code...

Mapped functionality

Classes / structs and their Godot mapping, see details in the source

MonoBehaviour  - inherits from Godot.Node
GameObject     - has a reference to a Godot.Node3D or UnitedGodot.UGGameObject
Mesh           - creates/owns a Godot.ArrayMesh
MeshFilter     - has a (nullable) reference to a Mesh
MeshRenderer   - creates/owns a Godot.MeshInstance3D
Vector3        - owns Godot.Vector3 (same for vec2/vec4/color)
Resources.Load - calls Godot.GD.Load
Material       - Godot.ShaderMaterial
Shader         - Godot.Shader
Texture2D      - Godot.Texture2D

Shader

The basic shader set-up is using three files per shader

.shader      - Unity template (+config of culling/blending etc)
.gdshader    - Godot template (+config of culling/blending etc)
.gdshaderinc - The main (shared) shader code

Goals

• Investigate if this is a useful way to reduce Unity dependency
• Learn a bit about Godot

Non-Goals

• Making a complete Unity API adapter
• Making even a semi-complete Unity API adapter

Problems & Misc Chaotic Notes

• For Unity-style scripts to work, they need to use partial class
• Only the functionality inside UnitedGodotTest.cs was tested, and not much more was implemented
• I don't know why I have to flip the uv coords on Godot
• There's probably unnecessary overhead using the Godot spatial pbr shading system to render plain unlit stuff (at least the fog seems to always on), but I did not find any alternative
• The mapped abstraction don't do anything about the handedness difference (currently handled manually in the UnitedGodotTest.cs), is there a good way to do this?
• Only single kind of textures supported (jpg currently), would be easy to add a function UnitedGodot.Load() which supports extension, or use loop through image types and check if available.
• No mapping of delete/destruction was done
• Mappings of Vector/Color structs means Godot inspection UI don't work for these types, anyone know a way to solve this?
• Mappings of Vector/Color structs means arrays have to be copied, not really acceptable for larger data!
• In Unity, if textures are added to the *.gdshaderinc file, they also need to be added to the Properties section of the .shader file in order to work
• Godot don't yet support building C# projects for Mobile etc
• Godot C# support for new projects: You have to manually click Menu->Tools->C#->Create C# Solution
• Godot Editor: Scenes easily break if you move around or rename folder/files
• Godot C#: Reloading of source code feels shaky, unload assemblies sometimes fails and script properties are set to zero (even though this is not even the default)
• Godot Editor: gdshaderinc files often don't refesh properly, and when exiting the editor, any changes (edited in external editor) are erased as an older version is written to disk