Developer Guide

This guide helps you read, navigate, and modify the OpenSimulator source code. It assumes you are comfortable with C# and want to know where things live so you can fix a bug or build a feature without getting lost.

All paths below are relative to the OpenSim/ directory of the source tree (e.g. OpenSim/Region/Application/...).

Quick mental model

OpenSim is two programs that talk over HTTP:

• OpenSim (the simulator) – hosts regions (“scenes”) and talks to viewers.
• Robust (the grid services server) – hosts shared services (assets, inventory, grid map, login, presence, …) as HTTP endpoints.

Both are built from many small .csproj projects (one per folder), orchestrated by prebuild.xml at the repo root – not one giant project.

Sections

1. Architecture overview – entry points, the module system, and how services vs connectors work.
2. Where to look – a “I want to change X → start here” index.
3. Data flow – walkthroughs of login and region teleport/crossing.
4. Sim-to-sim and sim-to-Robust protocols – HTTP methods, paths, and example request/response bodies (local grid and Hypergrid).
5. Region module events – lifecycle methods and the EventManager / IClientAPI events an optional module can hook.

Before you dig in

• Build it first: see the Admin – build from source.
• The code uses Mono.Addins for plugin discovery; modules/plugins are wired through extension points rather than hardcoded new calls.
• scene.RegisterModuleInterface<T>(this) / scene.RequestModuleInterface<T>() is the dependency-injection pattern used everywhere – learn it early.