Whatz PCZSM For?


23-12-2008 17:04:22

Just wanted to ask: What's this SceneManager for? What kinds of scenes does it handle well? How does it do it? etc. I'd seen PCZSM long back, but I didn't get 'what it was all about'. So, I'd really like it if you could explain.

Thanks a lot! :)

ps. I might not reply that soon, I read the Add-Ons forums less often.


26-12-2008 06:53:32

It's a Portal engine. Only the current Zone is rendered plus the zones that can be seen thru any portals in view.


26-12-2008 13:35:27

The Portal-Connected-Zone Scene Manager (PCZSM) is a plugin for Ogre3D which allows traversal of a scene which is non-homogeneous in structure. Specifically, the PCZSM uses "Zones" which have their own hierarchy. Zones are connected to other zones by "Portals" which can be envisioned as 4-point convex planar polygons.

This document gives basic information on the usage of the PCZSceneManager. It is not complete, and will change & expand as needed. Note that as of this writing, the PCZSM has not undergone very extensive testing, nor is it optimized very much. Assistance in these two areas would be greatly appreciated. For support or to report bugs, please see the Developer Forum at Ogre3D.org


Eric "Chaster" Cha

Using the PCZSM

NOTE: For an example of PCZSM usage, see the PCZTestApp Application. It is probably a lot easier to understand than trying to figure it all out from this.

Loading and Initialization

The PCZSM is loaded just like any other Scene Manager plugin. Included in the standard PCZSM plugin is the "default" zone. If the user wishes to utilize the OctreeZone or TerrainZone, the "PLugin_OctreeZone" should be loaded *after* the PCZSM plugin is loaded.

Before using the PCZSM, the PCZSceneManager::init(zoneType) function should be called. During intialization, the user specifies what type of zone (ZoneType_Default, ZoneType_OCtree, ZoneType_Terrain) the PCZSM should use for the default zone. The default zone is the zone where entities are placed if they are not specified to be in other zones.

Creating Zones

Once the PCZSM has been initialized, the user can proceed with creating zones (PCZSceneManager::createZone(zoneType, zoneName)). Zones can be anything from the outdoors (i.e. a Terrain) to a room in a building, or a tunnel in a dungeon. Zones can be of any size or shape, and can move.

NOTE: In the PCZSM, sky rendering (domes, boxes, planes) is associated with a specific zone. For example, if the user has a building on a terrain, the sky could be associated with the terrain (i.e. the "outdoors") using the function PCZSceneManager::setSkyZone(zone). This tells the PCZSM to only draw the sky when the designated zone is visible. (i.e. only draw the sky when the 'outdoor' zone is visible). Usually, the Sky should be associated with the default zone (which is usually used as the "all encompassing exterior zone").

Creating Portals

Once the user has created a zone (in addition to the default zone), they can create portals to attach two zones together. To do this, the user just creates a new Portal instance (i.e. newPortal = new Portal) and sets the portal corner points, attaches it to a node, and then adds it to the zone (see PCZTestApp -> RoomObject.cpp -> createPortals() function).


NEW AS OF 9/25/07:

To create a portal, the user just calls PCZSceneManager::createPortal(). NOTE: The user should NOT just instantiate a portal manually (i.e. portal = new Portal) because the clean up of portals is handled by the scene manager directly. Instantiating portals using the C++ 'new' command will result in memory leaks and errors if the scene is destroyed and recreated.

To destroy a portal use PCZSceneManager::destroyPortal(Portal *p) or PCZSceneManager::destroyPortal(String & portalName).


Then set the portal corner points, attaches it to a node, and then adds it to the zone (see PCZTestApp -> RoomObject.cpp -> createPortals() function).

NOTE: Portals currently only connect different zones. The user can't connect portals to the same zone yet (i.e. no teleporters). This functionality could be added later.

NEW IN VERSION 1.2: Portals can take 3 different forms: quad portals, AAB portals, and Sphere portals. AAB and Sphere portals do not add any culling planes to the frustum, and just serve to serve as enclosures for zones which aren't naturally surrounded by geometry. They function a little different than traditional quad portals in that they are volumetric, instead of planar (crossing is determined by going from "inside" to "outside" or vice versa).

Quad Portals require 4 corner points which are co-planar and form a polygon which is convex. Quad Portal corners are specified in right-handed counter- clockwise winding order so that the norm of the portal would be facing the viewer.

AAB Portals require 2 corner points (minimum & maximum corners) and form an axis- aligned box around the zone. IMPORTANT: The AAB portals that are associated with a node require a node which has the correct size AAB (node->_getWorldAABB()).

Sphere Portals require 2 corner points (center point, and point on the surface of the sphere).

The "direction" norm of AAB and Sphere portals is specified as either Vector3::UNIT_NEGATIVE_Z or Vector3::UNIT_Z. The first corresponds to a portal with norm facing 'inward' and the latter corresponds to a portal with norm facing 'outward'.

NOTE regarding Portal Norms: The Norm of a portal should always point away from the zone the portal leads to. Another way to think of this is a node will only cross a portal if it crosses the portal traveling opposite direction of the norm).

Portals also (currently) require a "matching" portal for proper scene traversal. In other words, portals always exist in pairs - one in each zone connected and co-existing in the same location, but facing in opposite directions.

While it is technically not required that a portal be associated with a scene node, it is STRONGLY recommended. Use Portal::setNode() to associate the portal with a scene node. Once the portal is associated with a scene node, it will move with the scene node (including rotations or translations). Because of this, it is also highly recommended (although not required) that the node a portal is associated with be located at the center of the portal.

NOTE: Scaling of a portal is not yet *tested*. Scaling a node should scale the portal (but don't cry to me if it doesn't work right yet...) Also, if you don't associate the portal with a scene node, you will NOT be able to move it short of redefining the cornerpoints manually (and who wants to do that?).

Once all portals in the scene have been created, the user can either manually assign their zone targets (i.e. the zone which they connect to) or they can call PCZSceneManager::connectPortalsToTargetZonesByLocation() to do it automatically. Note that this function requires all portals to have a matching portal in the target zone.
Creating Objects / Entities

Once the zones and portals have been created, the user can create objects/entities. The user should use SceneManager::createSceneNode() to create all scene nodes.

NOTE: ALL OBJECTS *MUST* BE ATTACHED TO SCENENODES!!! Unlike the other SM's available in Ogre3d, the PCZSM relies on Scene Nodes to determine zone locality of all entities - including cameras and lights. Consequently, when a camera (or light) is created, the user should also attach the camera (or light) to a scene node and use that node to manipulate the object.

SceneNodes should be assigned (by the user) to a zone upon creation of the SceneNode. Use the function "PCZSceneManager::setNodeHomeZone(node, zone)" to do this.

If the user doesn't do this, the PCZSM will try to figure out which zone the node belongs in using volumetric testing, but since there are situations when this can fail, it is highly recommended that the user does so explicitly instead of relying on the SM to figure it out. Note that this only has to be done when adding a node to the scene. Once the node is in the proper zone, the SM will handle moving it to other zones as necessary.

NOTE: In order for the automatic zone assignment function to work, zones must have an "enclosure" object/node assigned to them (using the "PCZone::setEnclosureNode() function). The enclosure node (or more specifically, the object attached to it) supplies the axis-aligned bounding box that determines the bounds of the zone. So for example, the enclosure node/object for a room would be the model of the walls, ceiling, and floor (assuming they are all modeled as one object or at least all attached to the same node). See the PCZTestApp for an example.

Scene Queries

I have implemented Scene Query functions for Default & Octree Zones. In general, they are used the same way as Scene Queries for any other Scene Manager, with one difference. The user must specify the "start zone" for any scene query using XXXSceneQuery::setStartZone(zone) where "XXX" is Ray, Sphere, AxisAlignedBox, et cetera.


26-12-2008 13:36:12

Taken from the PCZSM Wiki page.