Technical Reference/terms
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This is a glossary of software technical reference terms commonly found in descriptions of how OpenSimulator works from invocation, initialization, main loop and various services.
Definitions of OpenSimulator technical terms
- Region
- A region has an X/Y position in a grid and a regionhandle calculated from the position. A region can also be defined as an IP endpoint that the Viewer can use to establish a client connection. The unique ID of a region is a UUID. This means that a region can change position, and because of that position change, the regionhandle will be recalculated. The regionhandle will uniquely identify a position in a grid.
- A region contains a number of sub components:
- Scene
- Client/Viewer circuits
- Regionhandle
- A regionhandle is a 64-bit number that stores the X/Y location of a place in a grid. The high order 32-bits are the X position, and the bottom 32-bits are the Y position. A region handle can be calculated as follows: ((X * 256 + x_offset) << 32) + (Y * 256 + y_offset). X and Y are the grid location of a region. X_offset and y_offset are the x and y location of a place within a region so their values will be in the range of 0 to 255 (inclusive).
- Scene
- A scene is part of a region, currently there is a one to one relationship, i.e. one region has one scene. A scene contains all the 3d objects, called Entities, entities can either be ScenePresences or SceneObjectGroups. A ScenePresence can be represented by an avatar, if it is a root scene presence. SceneObjectGroups consists of a number of SceneObjectParts.
- Avatar/ScenePresence
- Each viewer is represented by one or more avatars. The Root avatar or ScenePresence functions as a kind of cursor, into the grid. Where the region will keep the viewer updated on the state of the simulation, taking place in the scene. Besides the root presence, a number of child presences will exist in the neighboring regions, enabling the viewer to know what is going on in the neighboring regions.
- Viewer
- An application which is used to view the state of the simulation. Currently only three different viewers are known: the LL viewer, the OpenSL test client and AjaxLife.
- Session
- Each connection between a viewer and a region, regardless if the avatar is the root or a child, is a session.
- Simulator
- A program which can manage several Regions
- OpenSim.cs (OpenSim.cs )
- OpenSim_SwInit (Initialization from Main() )
- OpenSim_SwMainLoopl (After initialization, a main loop waits for connections or commands)
- OpenSim_SwRegionHandshake (How a client connects to the simulator)
- OpenSim_UserService (How the user server works)
- OpenSim_InterRegionCommunications (How the sim communicates with other sims)
- OpenSim_GridService (How the grid server works)
- OpenSim_AssetService (How the asset server works)
- OpenSim_SimService (How the simulator operates after a connection is made)
- Sim_Throttles (How the simulator handles throttling of packets)
