Viewer Architecture

The Second Life client (also known as the "viewer") is a complex piece of software. It can be visualized as a streaming media client like RealPlayer, a game engine like Quake 3, or a web browser.

First you'll need to learn some Second Life Terminology, like "agent", "sim", and "region".

If you like to learn by example, you can learn about:

If you prefer a more hierarchical approach, the viewer is built from:

Message System - reliable and unreliable transport over UDP
Image System - prioritizes and decodes JPEG2000 images into OpenGL textures
Viewer Object System - objects in scene for rendering and editing
Rendering System - from viewer object to drawable to face to vertices to graphics card
Culling - octree and occlusion based culling to speed rendering
UI Widgets - cross platform buttons, scroll bars, etc.
UI Floaters - dialogs and windows built from XML files
Asset System - transport for animations, sounds, notecards, scripts, etc.
Inventory - server-side storage of assets for each user
Sound System - cross platform audio based on FMOD
Movie System - QuickTime-based video on object surfaces
VFS - cached data is held in two "virtual file systems" in large files on the client
Selection Manager - holds extended information for selected objects and allows editing
Avatar Appearance - appearance is constructed from a mesh, parameters to deform the mesh, and textures to describe clothing
Avatar Profiles
Groups
Money

Threads

The viewer is a single process with a few threads:

Main thread -- The input/output main program function.
VFS Thread -- Thread responsible for reading/writing to the virtual file system.
LFS Thread -- Thread responsible for some reading/writing to the local file system. Not sure if this is actually used anywhere.

Program Flow

Initialize
Loop
- Gathers input
- Pumps the TCP i/o
- Render the frame
Shutdown

Viewer Architecture

Threads

Program Flow

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