Engine Integration

How Galaxy Eggbert uses Urho3D, U3D, and Nova3D.

The Engine Abstraction Strategy

Galaxy Eggbert targets the Urho3D C++ API exclusively. There are no #ifdef GE_ENGINE_* guards in the C++ source. Two pre-built implementations of the Urho3D API exist:

• U3D — the u3d-community fork of Urho3D. Stable; used for Linux and Windows builds.
• Nova3D — Robert Vokac's own Urho3D fork with CNA/SDL3 backend support. Used for Web (Emscripten) and Android targets once it matures.

Switching engines requires only a CMake flag: -DGALAXY_EGGBERT_ENGINE=U3D or =NOVA3D. If Nova3D fails to compile Galaxy Eggbert, Nova3D must fix itself — not Galaxy Eggbert.

The GEEngine.hpp Header

All engine usage flows through a single include:

// src/GalaxyEggbert/GEEngine.hpp
#pragma once
#include <Urho3D/Urho3DAll.h>

This is the only place the engine is included. Every other source file that needs the engine includes GEEngine.hpp.

Urho3D Concepts Used

Entry Point Macro

// src/GalaxyEggbert/Program.cpp
#include "GalaxyEggbertApp.hpp"
URHO3D_DEFINE_APPLICATION_MAIN(GalaxyEggbertApp)

This Urho3D macro expands to the correct main() signature for the target platform (standard main on desktop, SDL_main on Android/Emscripten, etc.) and creates + runs a GalaxyEggbertApp instance.

Event Loop Integration

// GalaxyEggbertApp::Start()
SubscribeToEvent(E_UPDATE, URHO3D_HANDLER(GalaxyEggbertApp, HandleUpdate));

// GalaxyEggbertApp::HandleUpdate()
void GalaxyEggbertApp::HandleUpdate(StringHash, VariantMap& eventData) {
    using namespace Update;
    GameUpdate(eventData[P_TIMESTEP].GetFloat());
}

The update loop is driven by Urho3D's E_UPDATE event which fires every frame. The timestep (dt) comes from the engine's time subsystem. Galaxy Eggbert does not manage its own game loop.

Resource Loading

Resources are loaded through Urho3D::ResourceCache:

auto* cache = context_->GetSubsystem<ResourceCache>();
auto* tex = cache->GetResource<Texture2D>("icons/blupi.png");
auto* tech = cache->GetResource<Technique>("Techniques/Diff.xml");
auto* sound = cache->GetResource<Sound>("sounds/sound001.wav");

Resource paths are relative to the search paths set in GalaxyEggbertApp::Setup(): Data;CoreData;Content. Data and CoreData are from the U3D/Nova3D engine distribution. Content is the game's own asset directory.

U3D vs Nova3D Differences