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:
- Adding a menu item
- Adding a dialog
- How movement works
- How the camera works
- How login works
- How keyboard processing works
- How scripts work
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.
- Image Thread -- Currently unused.
Program Flow
- Initialize - newview/viewer.cpp :: main()
- Loop - newview/viewer.cpp :: main_loop()
- Gathers input
- Pumps the TCP i/o
- Render the frame
- idle()
- everything
- Shutdown
Sources of Input
- The Message System.
- Assets through the Asset System, transmitted using the Transfer Manager and extracted from the VFS.
- Files through Xfer Manager.
- Files copied out of the VFS into local file store and read through c/c++/ll file API.
- XMLRPC calls such as login and buying currency/land.
- HTTP GET/POST to the Backbone.
- Streaming music and videos.
- The web browser.