Glossary

SL

Common abbreviation for Second Life

Viewer

Client software, written in C++, that runs on the user’s Windows, Macintosh, or Linux computer. The process is named “newview” for historical reasons.

Simulator

The primary SL server process. Each simulator process simulates one 256x256 meter region. As the viewer moves through the world it is handled off from one simulator to another. Multiple simulator processes run on each server host, currently 2 to 16.

Sim

Server host machine, for example sim1234.agni.lindenlab.com. The SL server grid consists of 2000+ sims. Sometimes “sim” is used incorrectly to mean simulator process or region.

Host

Any server computer, but usually a sim.

Region

Data set for a region of the world, like “Orientation Island” or “Ahern”. A region can be run by any simulator process, and regions move from sim to sim as the hosts are shut down, crash, etc.

Grid

A collection of sims. Linden Lab runs several grids for internal and external testing.

Farm

synonym for grid.

Agni

The primary SL grid to which users connect.

Parcel

An area of land owned by a single user or group. Parcels are composed of square blocks measuring 4x4 meters, but the blocks do not have to be contiguous. Parcels have both an integer local id and a global UUID.

Estate

A collection of regions with a particular set of rules, such as banned users, sun position, etc. Each estate has an owner, either a user or “Governor Linden”. Most privately owned regions are in their own estates. Estates have integer identifiers. The “mainland” is estate id 1.

Avatar

The graphical representation of a user. Implemented in the class LLVOAvatar on the viewer.

Agent

The data representation of the current user. In general “agent” means you and “avatar” means someone else. Identified by a UUID, usually called “agent_id” in the code.

Asset

A data resource such as an image, sound, script, object, etc. Assets can be downloaded to the viewer or uploaded into a central asset store. Assets are identified by UUID and type. Types are in llassettype.h.

Texture

An image applied to the surface of an object.

Floater

A dialog or window appearing in the user interface. Implemented in classes titled “LLFloater*”

Vector

An array of floating point values used to represent positions, colors, etc. Implemented in LLVector3, LLVector4, LLColor4, etc.

Quaternion

Representation of a rotation. SL uses unit quaternions represented in four floats. This allows only three floats to be transmitted and the remaining value reconstructed on the viewer. See GameDev article on quaternions.

Message Template

The protocol description for UDP packet communication between the viewer and servers. Described in the text file app_settings/message_template.msg.

LSL

Linden Scripting Language, a C-like language used for server-side scripting of objects.

Primitive

3D object in the world. Each prim is represented by a set of parameters, including position, scale, rotation, shape, cut, hollow, etc. Prims can be linked together into link sets. They can also be attached to avatars, but this process is separate from linking. Primitives are implemented in LLPrimitive, with vertex generation performed in LLVolume and rendering in LLVOVolume.

Prim

Abbreviation for primitive.

Task

Server-side representation of a primitive or link set. Since primitives can contain scripts or be physically simulated each task adds load to the server process. The agent is also represented as a task on the server, but has extensive additional processing.

FMOD

Cross-platform audio library. Used to play decompressed sound effects and stream MP3 music to users on particular parcels. See FMOD.org.

JPEG2000

Wavelet based image compression format. Inherently progressive, so images can be displayed with only partial data available, without increases in file size. See the Wikipedia entry on JPEG2000.

Kakadu

Cross-platform high-performance JPEG2000 library. Linden Lab does not have redistribution rights to Kakadu so the open source viewer ships with OpenJPEG.

Ogg Vorbis

Open source audio compression library. Sound effects are stored as .ogg files in the asset system. See Ogg Vorbis.

UUID

Globally unique identifier, a 128-bit number represented as a 16-byte binary value or 36-byte hexadecimal string. UUIDs can be generated by any part of the system and are guaranteed to be unique.