OGRE  master
Object-Oriented Graphics Rendering Engine
Using the PCZ Scene Manager

The Portal-Connected-Zone Scene Manager (PCZSM) is a plugin for Ogre3D (see www.ogre3d.org for more information about 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 (or Spheres or AAB's).

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

Cheers,

Eric "Chaster" Cha

USING THE PCZ_SCENEMANAGER

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 & 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.

*** 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.

UPDATE as of 3/17/09: Portals can be "closed" (and opened) by calling Portal::setEnable(false) (and Portal::setEnable(false)). Disabling a portal prevents the scene manager from traversing through the portal and also prevents scenenodes & ray queries from crossing the portal. Basically, it turns a portal "off". Disabling an antiportal (see note below about Creating antiportals) prevents the antiportal from blocking scene traversal through regular portals.

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.

It is REQUIRED that a portal be associated with a scene node. 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...)

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.

ANTIPORTALS ** NEW As of 3/17/09 **

Antiportals are a new feature (thanks to Lf3thn4d). Antiportals prevent traversal of portals located behind them (as viewed from the camera). They are created and manipulated the same as regular portals (except you don't need to create them in pairs, since they block scene traversal to other zones instead of connecting them). Only Quad Antiportals are supported.

To Create an antiportal, it's very similar to regular portals. All you need to do is call PCZSceneManager::createAntiPortal("name of the antiportal"), set the corner values, attach it to a node, and add it to the proper 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 can be assigned (by the user) to a zone upon creation of the SceneNode. Use the functions "PCZSceneNode::setHomeZone(PCZone * zone)" followed by "PCZone::_addNode(PCZSceneNode * node)" 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, etc.

KNOWN BUGS:

  • Light traversal is not quite correct. In order to avoid infinite recursion, I had to put in a hack which can potentially result in lighting not traversing into some zones properly. It will probably not be noticeable in most situations, but could potentially show up in very complex portal/zone setups.