Castle Game Engine: CastleOctree: Class TOctreeNode

# Class TOctreeNode
Description | Hierarchy | Fields | Methods | Properties
## Unit CastleOctree ## Declaration `type TOctreeNode = class(TObject)` ## Description Octree node. Leaf nodes store a list of indexes in ItemsIndices array. These are usuallly indexes to some array of items on TOctree. For the sake of this unit they are just some integers that uniquely describe items that you want to keep in octree leafs. The base abstract `TOctreeNode` class doesn't clarify what kind of items are actually kept. Not leaf (internal) nodes have 8 children nodes in TreeSubNodes. Each TOctreeNode also has some essential properties like Box, MiddlePoint and ParentTree. ## Hierarchy TObject TOctreeNode ## Overview ### Fields
| `TreeSubNodes: array [boolean, boolean, boolean] of TOctreeNode;`
### Methods
| `function ItemsCount: integer;`
| `procedure AddItem(ItemIndex: integer);`
| `constructor Create(const ABox: TBox3D; AParentTree: TOctree; AParentNode: TOctreeNode; ADepth: integer; AsLeaf: boolean);`
| `destructor Destroy; override;`
| `function SubnodeWithPoint(const P: TVector3Double): TOctreeSubnodeIndex; overload;`
| `function SubnodeWithPoint(const P: TVector3Single): TOctreeSubnodeIndex; overload;`
| `procedure SubnodesWithBox(const ABox: TBox3D; out SubnodeLow, SubnodeHigh: TOctreeSubnodeIndex);`
| `function FrustumCollisionPossible(const Frustum: TFrustum): boolean;`
| `procedure PushChildrenFrontToBack(List: TOrderedList; const Position: TVector3Single);`
| `procedure PushChildrenBackToFront(List: TOrderedList; const Position: TVector3Single);`
| `procedure PushChildren(List: TOrderedList);`
### Properties
| `property ItemsIndices: TIntegerList read FItemsIndices;`
| `property IsLeaf: boolean read fIsLeaf write SetLeaf;`
| `property MiddlePoint: TVector3Single read fMiddlePoint;`
| `property Box: TBox3D read fBox;`
| `property BoundingSphereCenter: TVector3Single read FBoundingSphereCenter;`
| `property BoundingSphereRadiusSqr: Single read FBoundingSphereRadiusSqr;`
| `property Depth: integer read fDepth;`
## Description ### Fields
| `TreeSubNodes: array [boolean, boolean, boolean] of TOctreeNode;`
Child octree nodes, only if this is an internal node (IsLeaf = `False`). When this is a leaf (IsLeaf = `True`), these are all `Nil`. Indexed by booleans, "true" means that given coordinate is >= than corresponding MiddlePoint coordinate. For example `TreeSubNodes`[true, true, true] are coordinates between MiddlePoint and Box[1]. Subnodes class is always the same as our (Self) class. This field is read-only from outside of this unit.
### Methods
| `function ItemsCount: integer;`
Number of items stored here. Same thing as ItemsIndices.Count, but has somewhat nicer name if you have Items[] property defined in a subclass. Use this only when you know that ItemsIndices <> nil.
| `procedure AddItem(ItemIndex: integer);`
Insert an item into this octree node. It takes care of the octree structure properties: Splits a leaf node into non-leaf node if maximum number of items in leaf is exceeded (and Depth < MaxDepth). And when you insert an item into non-leaf node, it correctly puts it into children subnodes too.
| `constructor Create(const ABox: TBox3D; AParentTree: TOctree; AParentNode: TOctreeNode; ADepth: integer; AsLeaf: boolean);`
Simple constructor. Calculates MiddlePoint as a middle of the ABox, or as (0, 0, 0) if ABox is empty.
| `destructor Destroy; override;`
| `function SubnodeWithPoint(const P: TVector3Double): TOctreeSubnodeIndex; overload;`
In which subnode does the given point lie. Decides using MiddlePoint. This is a simple utility, ignores what is our Box (doesn't check is P is inside Box at all), ignores if we're leaf or not.
| `function SubnodeWithPoint(const P: TVector3Single): TOctreeSubnodeIndex; overload;`
| `procedure SubnodesWithBox(const ABox: TBox3D; out SubnodeLow, SubnodeHigh: TOctreeSubnodeIndex);`
| `function FrustumCollisionPossible(const Frustum: TFrustum): boolean;`
Simple check for frustum collision.
| `procedure PushChildrenFrontToBack(List: TOrderedList; const Position: TVector3Single);`
Push children nodes (use this only for non-leafs) into the List.
| `procedure PushChildrenBackToFront(List: TOrderedList; const Position: TVector3Single);`
| `procedure PushChildren(List: TOrderedList);`
### Properties
| `property ItemsIndices: TIntegerList read FItemsIndices;`
Items stored at the octree node. Items are stored here (and `ItemsIndices` <> nil) only when this is a leaf item (IsLeaf = `True`) or when ParentTree.ItemsInNonLeafNodes is `True`. In the latter case, we store items even in internal nodes, see TOctree.ItemsInNonLeafNodes. Never put any items in the octree node by direct ItemsIndices.Add. Instead you must use AddItem method.
| `property IsLeaf: boolean read fIsLeaf write SetLeaf;`
Is this a leaf node. Changing this property rearranges items correctly. If you change this from `False` to `True` then all items from subnodes are correctly gathered and stored in our ItemsIndices. If you change this from `True` to `False` then subnodes are created and we insert to them our items, following the MiddlePoint rule.
| `property MiddlePoint: TVector3Single read fMiddlePoint;`
Middle point of the octree node, determines how our subnodes divide the space. This is defined for leaf nodes too, since leaf nodes may have to be converted into internal nodes at some point. Note that `MiddlePoint` does not need to be exactly in the middle of the octree node. This is it's default value (if you called constructor without explicitly providing `MiddlePoint` value), but it's not a requirement. `MiddlePoint` may be anywhere inside Box. This way you can explicitly specify some `MiddlePoint` if you know that if will yield better hierarchical division of your scene. When Box is empty, then value of `MiddlePoint` is undefined.
| `property Box: TBox3D read fBox;`
Axis-aligned box in the 3D space that contains all items within this node. It's allowed that some items are actually larger and go (partially) outside of this box too (so you don't have to split one triangle into many when it doesn't fit perfectly into octree node), but it's undefined if the parts that go outside will be detected by collision routines of this node. Special case: when this is empty, then MiddlePoint has undefined value and IsLeaf must be true.
| `property BoundingSphereCenter: TVector3Single read FBoundingSphereCenter;`
Bounding sphere of this box. Right now simply calculated as the smallest possible sphere enclosing Box. So they are only a bad approximation of bounding Box, but they can be sometimes useful in stuations when detecting collision versus bounding sphere is much faster than detecting them versus bounding box. BoundingSphereRadiusSqr = 0 and `BoundingSphereCenter` is undefined if Box is empty.
| `property BoundingSphereRadiusSqr: Single read FBoundingSphereRadiusSqr;`
| `property Depth: integer read fDepth;`
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