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Ogre::BspNode Class Reference

Encapsulates a node in a BSP tree. More...

#include <OgreBspNode.h>

List of all members.

Public Methods

 BspNode (BspLevel *owner, bool isLeaf)
 Constructor, only to be used by BspLevel. More...

 BspNode ()
 ~BspNode ()
bool isLeaf (void) const
 Returns true if this node is a leaf (i.e. More...

BspNode * getFront (void) const
 Returns a pointer to a BspNode containing the subspace on the positive side of the splitting plane. More...

BspNode * getBack (void) const
 Returns a pointer to a BspNode containing the subspace on the negative side of the splitting plane. More...

Plane::Side getSide (const Vector3 &point) const
 Determines which side of the splitting plane a worldspace point is. More...

BspNode * getNextNode (const Vector3 &point) const
 Gets the next node down in the tree, with the intention of locating the leaf containing the given point. More...

Plane getSplitPlane (void)
 Returns details of the plane which is used to subdivide the space of his node's children. More...

AxisAlignedBoxgetBoundingBox (void)
 Returns the axis-aligned box which contains this node if it is a leaf. More...

int getNumFaceGroups (void)
 Returns the number of faces contained in this leaf node. More...

int getFaceGroupStart (void)
 Returns the index to the face group index list for this leaf node. More...

bool isLeafVisible (const BspNode *leaf)
 Determines if the passed in node (must also be a leaf) is visible from this leaf. More...


Protected Attributes

BspLevelmOwner
bool mIsLeaf
Plane mSplitPlane
 The plane which splits space in a non-leaf node. More...

BspNode * mFront
 Pointer to the node in front of this non-leaf node. More...

BspNode * mBack
 Pointer to the node behind this non-leaf node. More...

int mVisCluster
 The cluster number of this leaf. More...

AxisAlignedBox mBounds
 The axis-aligned box which bounds node if it is a leaf. More...

int mNumFaceGroups
 Number of face groups in this node if it is a leaf. More...

int mFaceGroupStart
 Index to the part of the main leaf facegroup index buffer(held in BspLevel) for this leaf. More...


Friends

class BspLevel
std::ostream & operator<< (std::ostream &o, BspNode &n)


Detailed Description

Encapsulates a node in a BSP tree.

A BSP tree represents space partitioned by planes . The space which is partitioned is either the world (in the case of the root node) or the space derived from their parent node. Each node can have elements which are in front or behind it, which are it's children and these elements can either be further subdivided by planes, or they can be undivided spaces or 'leaf nodes' - these are the nodes which actually contain objects and world geometry.The leaves of the tree are the stopping point of any tree walking algorithm, both for rendering and collision detection etc. Ogre chooses not to represent splitting nodes and leaves as separate structures, but to merge the two for simplicity of the walking algorithm. If a node is a leaf, the isLeaf() method returns true and both getFront() and getBack() return null pointers. If the node is a partitioning plane isLeaf() returns false and getFront() and getBack() will return the corresponding BspNode objects.


Constructor & Destructor Documentation

Ogre::BspNode::BspNode BspLevel   owner,
bool    isLeaf
 

Constructor, only to be used by BspLevel.

Ogre::BspNode::BspNode  
 

Ogre::BspNode::~BspNode  
 


Member Function Documentation

BspNode * Ogre::BspNode::getBack void    const
 

Returns a pointer to a BspNode containing the subspace on the negative side of the splitting plane.

This method should only be called on a splitting node, i.e. where isLeaf() returns false. Calling this method on a leaf node will throw an exception.

AxisAlignedBox & Ogre::BspNode::getBoundingBox void   
 

Returns the axis-aligned box which contains this node if it is a leaf.

This method should only be called on a leaf node. It returns a box which can be used in calls like Camera::isVisible to determine if the leaf node is visible in the view.

int Ogre::BspNode::getFaceGroupStart void   
 

Returns the index to the face group index list for this leaf node.

The contents of this buffer is a list of indexes which point to the actual face groups held in a central buffer in the BspLevel class (in actual fact for efficency the indexes themselves are also held in a single buffer in BspLevel too). The reason for this indirection is that the buffer of indexes to face groups is organised in chunks relative to nodes, whilst the main buffer of face groups may not be. Should only be called on a leaf node.

BspNode * Ogre::BspNode::getFront void    const
 

Returns a pointer to a BspNode containing the subspace on the positive side of the splitting plane.

This method should only be called on a splitting node, i.e. where isLeaf() returns false. Calling this method on a leaf node will throw an exception.

BspNode * Ogre::BspNode::getNextNode const Vector3   point const
 

Gets the next node down in the tree, with the intention of locating the leaf containing the given point.

This method should only be called on a splitting node, i.e. where isLeaf() returns false. Calling this method on a leaf node will throw an exception.

int Ogre::BspNode::getNumFaceGroups void   
 

Returns the number of faces contained in this leaf node.

Should only be called on a leaf node.

Plane::Side Ogre::BspNode::getSide const Vector3   point const
 

Determines which side of the splitting plane a worldspace point is.

This method should only be called on a splitting node, i.e. where isLeaf() returns false. Calling this method on a leaf node will throw an exception.

Plane Ogre::BspNode::getSplitPlane void   
 

Returns details of the plane which is used to subdivide the space of his node's children.

This method should only be called on a splitting node, i.e. where isLeaf() returns false. Calling this method on a leaf node will throw an exception.

bool Ogre::BspNode::isLeaf void    const
 

Returns true if this node is a leaf (i.e.

contains geometry) or false if it is a splitting plane. A BspNode can either be a splitting plane (the typical representation of a BSP node) or an undivided region contining geometry (a leaf node). Ogre represents both using the same class for simplicity of tree walking. However it is important that you use this method to determine which type you are dealing with, since certain methods are only supported with one of the subtypes. Details are given in the individual methods. Note that I could have represented splitting / leaf nodes as a class hierarchy but the virtual methods / run-time type identification would have a performance hit, and it would not make the code much (any?) simpler anyway. I think this is a fair trade-off in this case.

bool Ogre::BspNode::isLeafVisible const BspNode *    leaf
 

Determines if the passed in node (must also be a leaf) is visible from this leaf.

Must only be called on a leaf node, and the parameter must also be a leaf node. If this method returns true, then the leaf passed in is visible from this leaf. Note that internally this uses the Potentially Visible Set (PVS) which is precalculated and stored with the BSP level.


Friends And Related Function Documentation

friend class BspLevel [friend]
 

std::ostream& operator<< std::ostream &    o,
BspNode &    n
[friend]
 


Member Data Documentation

BspNode* Ogre::BspNode::mBack [protected]
 

Pointer to the node behind this non-leaf node.

AxisAlignedBox Ogre::BspNode::mBounds [protected]
 

The axis-aligned box which bounds node if it is a leaf.

int Ogre::BspNode::mFaceGroupStart [protected]
 

Index to the part of the main leaf facegroup index buffer(held in BspLevel) for this leaf.

This leaf uses mNumFaceGroups from this pointer onwards. From here you use the index in this buffer to look up the actual face. Note that again for simplicity and bulk memory allocation the face group list itself is allocated by the BspLevel for all nodes, and each leaf node is given a section of it to work on. This saves lots of small memory allocations / deallocations which limits memory fragmentation.

BspNode* Ogre::BspNode::mFront [protected]
 

Pointer to the node in front of this non-leaf node.

bool Ogre::BspNode::mIsLeaf [protected]
 

int Ogre::BspNode::mNumFaceGroups [protected]
 

Number of face groups in this node if it is a leaf.

BspLevel* Ogre::BspNode::mOwner [protected]
 

Plane Ogre::BspNode::mSplitPlane [protected]
 

The plane which splits space in a non-leaf node.

Note that nodes do not allocate the memory for other nodes - for simplicity and bulk-allocation of memory the BspLevel is responsible for assigning enough memory for all nodes in one go.

int Ogre::BspNode::mVisCluster [protected]
 

The cluster number of this leaf.

Leaf nodes are assigned to 'clusters' of nodes, which are used to group nodes together for visibility testing. There is a lookup table which is used to determine if one cluster of leaves is visible from another cluster. Whilst it would be possible to expand all this out so that each node had a list of pointers to other visible nodes, this would be very expensive in terms of storage (using the cluster method there is a table which is 1-bit squared per cluster, rounded up to the nearest byte obviously, which uses far less space than 4-bytes per linked node per source node). Of course the limitation here is that you have to each leaf in turn to determine if it is visible rather than just following a list, but since this is only done once per frame this is not such a big overhead.

Copyright © 2002 by The OGRE Team