# Ogre::BspNode Class Reference

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

`#include <OgreBspNode.h>`

List of all members.

## Public Types

typedef std::set< const MovableObject * > | IntersectingObjectSet
typedef std::vector< Brush * > | NodeBrushList

## Public Member Functions

| BspNode (BspLevel *owner, bool isLeaf)
| Constructor, only to be used by BspLevel.
| BspNode ()
| ~BspNode ()
bool | isLeaf (void) const
| Returns true if this node is a leaf (i.e.
BspNode * | getFront (void) const
| Returns a pointer to a BspNode containing the subspace on the positive side of the splitting plane.
BspNode * | getBack (void) const
| Returns a pointer to a BspNode containing the subspace on the negative side of the splitting plane.
Plane::Side | getSide (const Vector3 &point) const
| Determines which side of the splitting plane a worldspace point is.
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.
const Plane & | getSplitPlane (void) const
| Returns details of the plane which is used to subdivide the space of his node's children.
const AxisAlignedBox & | getBoundingBox (void) const
| Returns the axis-aligned box which contains this node if it is a leaf.
int | getNumFaceGroups (void) const
| Returns the number of faces contained in this leaf node.
int | getFaceGroupStart (void) const
| Returns the index to the face group index list for this leaf node.
bool | isLeafVisible (const BspNode *leaf) const
| Determines if the passed in node (must also be a leaf) is visible from this leaf.
void | _addMovable (const MovableObject *mov)
| Internal method for telling the node that a movable intersects it.
void | _removeMovable (const MovableObject *mov)
| Internal method for telling the node that a movable no longer intersects it.
Real | getDistance (const Vector3 &pos) const
| Gets the signed distance to the dividing plane.
const NodeBrushList & | getSolidBrushes (void) const
| Get the list of solid Brushes for this node.
const IntersectingObjectSet & | getObjects (void) const

## Protected Attributes

BspLevel * | mOwner
bool | mIsLeaf
Plane | mSplitPlane
| The plane which splits space in a non-leaf node.
BspNode * | mFront
| Pointer to the node in front of this non-leaf node.
BspNode * | mBack
| Pointer to the node behind this non-leaf node.
int | mVisCluster
| The cluster number of this leaf.
AxisAlignedBox | mBounds
| The axis-aligned box which bounds node if it is a leaf.
int | mNumFaceGroups
| Number of face groups in this node if it is a leaf.
int | mFaceGroupStart
| Index to the part of the main leaf facegroup index buffer(held in BspLevel) for this leaf.
IntersectingObjectSet | mMovables
NodeBrushList | mSolidBrushes

## 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.

Definition at line 48 of file OgreBspNode.h.

## Member Typedef Documentation

typedef std::set<const MovableObject*> Ogre::BspNode::IntersectingObjectSet

| Definition at line 142 of file OgreBspNode.h. Referenced by getObjects().

typedef std::vector<Brush*> Ogre::BspNode::NodeBrushList

| Definition at line 149 of file OgreBspNode.h.

## 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

void Ogre::BspNode::_addMovable | ( | const MovableObject * | mov | ) |

| Internal method for telling the node that a movable intersects it.

void Ogre::BspNode::_removeMovable | ( | const MovableObject * | mov | ) |

| Internal method for telling the node that a movable no longer intersects it.

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.

const AxisAlignedBox& Ogre::BspNode::getBoundingBox | ( | void |  | ) | const

| 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.

Real Ogre::BspNode::getDistance | ( | const Vector3 & | pos | ) | const

| Gets the signed distance to the dividing plane.

int Ogre::BspNode::getFaceGroupStart | ( | void |  | ) | const

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 |  | ) | const

| Returns the number of faces contained in this leaf node. Should only be called on a leaf node.

const IntersectingObjectSet& Ogre::BspNode::getObjects | ( | void |  | ) | const

| Definition at line 201 of file OgreBspNode.h. References IntersectingObjectSet, and mMovables.

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.

const NodeBrushList& Ogre::BspNode::getSolidBrushes | ( | void |  | ) | const

Get the list of solid Brushes for this node.

Remarks:
  Only applicable for leaf nodes.

const Plane& Ogre::BspNode::getSplitPlane | ( | void |  | ) | const

| 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 | ) | const

| 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]`

| Definition at line 50 of file OgreBspNode.h.

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. Definition at line 168 of file OgreBspNode.h.

AxisAlignedBox Ogre::BspNode::mBounds `[protected]`

| The axis-aligned box which bounds node if it is a leaf. Definition at line 185 of file OgreBspNode.h.

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.

Definition at line 195 of file OgreBspNode.h.

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

| Pointer to the node in front of this non-leaf node. Definition at line 166 of file OgreBspNode.h.

bool Ogre::BspNode::mIsLeaf `[protected]`

| Definition at line 157 of file OgreBspNode.h.

IntersectingObjectSet Ogre::BspNode::mMovables `[protected]`

| Definition at line 197 of file OgreBspNode.h. Referenced by getObjects().

int Ogre::BspNode::mNumFaceGroups `[protected]`

| Number of face groups in this node if it is a leaf. Definition at line 187 of file OgreBspNode.h.

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

| Definition at line 156 of file OgreBspNode.h.

NodeBrushList Ogre::BspNode::mSolidBrushes `[protected]`

| Definition at line 199 of file OgreBspNode.h.

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. Definition at line 164 of file OgreBspNode.h.

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.

Definition at line 182 of file OgreBspNode.h.

The documentation for this class was generated from the following file:

- OgreBspNode.h

Copyright © 2000-2005 by The OGRE Team
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License.
Last modified Sun Feb 12 13:05:20 2006