Difference between revisions of "AROT (MREA Section)"

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(Completed tables)
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They are structured recursively, starting with a ''root'' node and traversing their way to individual ''leaf'' nodes.
 
They are structured recursively, starting with a ''root'' node and traversing their way to individual ''leaf'' nodes.
 
A full-branch octant will split sub-octants across 3-tiers, one for each dimension of euclidean space.
 
A full-branch octant will split sub-octants across 3-tiers, one for each dimension of euclidean space.
 +
 +
=== Layout ===
 +
 +
{| class="wikitable"
 +
! Data Type
 +
! Element Count
 +
! Description
 +
! Notes
 +
|-
 +
| [[#Header|Header]]
 +
| 1
 +
| Octree Header
 +
|
 +
|-
 +
| long
 +
| round_up(bitmap_bit_count / 32) * bitmap_count
 +
| Mesh Bitmap Array
 +
| An array of word-packed bitmaps relating octant nodes to sets of MREA meshes
 +
|-
 +
| long
 +
| node_count
 +
| Node Indirection Table
 +
| Since nodes use variable-length-encoding, there is an indirection table with byte-offsets (relative to first node)
 +
|-
 +
| [[#Node Entry|Node Entry]]
 +
| node_count
 +
| Node Entry Table
 +
| Tightly-packed blob of nodes
 +
|}
  
 
=== Header ===
 
=== Header ===
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| AABB
 
| AABB
 
| AABB that fully-encloses area and serves as the octree's root-shape
 
| AABB that fully-encloses area and serves as the octree's root-shape
 +
|}
 +
 +
=== Node Entry ===
 +
 +
{| class="wikitable"
 +
! Offset
 +
! Size
 +
! Data Type
 +
! Description
 +
! Notes
 +
|-
 +
| 0x0
 +
| 2
 +
| short
 +
| Bitmap Index
 +
| Index of the mesh bitmap defining a set of MREA meshes for this octant node
 +
|-
 +
| 0x2
 +
| 2
 +
| short
 +
| Additional Child Count
 +
| If non-zero, this counts the octant's child-nodes ''in addition'' to the first child (a value of 0x7 actually indicates 8 child-nodes)
 +
'''If zero, this node-entry ends here'''
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|-
 +
| 0x4
 +
| 2
 +
| long[additional_child_count + 1]
 +
| Node Child Indexes
 +
| Variable-length array of node-entry indices that are children of this node-entry
 
|}
 
|}

Revision as of 14:54, 10 April 2015

File:Octree2.svg
Left: Recursive subdivision of a cube into octants. Right: The corresponding octree.

Within MREA resources, the AROT section stores an octree which is used to accelerate rendering of areas in back-to-front order.

Octrees are a form of BSP tree that subdivide an area in 3-dimensions. They are structured recursively, starting with a root node and traversing their way to individual leaf nodes. A full-branch octant will split sub-octants across 3-tiers, one for each dimension of euclidean space.

Layout

Data Type Element Count Description Notes
Header 1 Octree Header
long round_up(bitmap_bit_count / 32) * bitmap_count Mesh Bitmap Array An array of word-packed bitmaps relating octant nodes to sets of MREA meshes
long node_count Node Indirection Table Since nodes use variable-length-encoding, there is an indirection table with byte-offsets (relative to first node)
Node Entry node_count Node Entry Table Tightly-packed blob of nodes

Header

Offset Size Data Type Description Notes
0x0 4 long Magic AROT
0x4 4 long Version Always 0x1
0x8 4 long Mesh-Bitmap Count Count of mesh-bitmaps
0xC 4 long Mesh-Bitmap Bit-Count Count of bits in each mesh-bitmap (matches MREA's mesh count)
0x10 4 long Node Count Number of octant nodes
0x14 24 float2x3 AABB AABB that fully-encloses area and serves as the octree's root-shape

Node Entry

Offset Size Data Type Description Notes
0x0 2 short Bitmap Index Index of the mesh bitmap defining a set of MREA meshes for this octant node
0x2 2 short Additional Child Count If non-zero, this counts the octant's child-nodes in addition to the first child (a value of 0x7 actually indicates 8 child-nodes)

If zero, this node-entry ends here

0x4 2 long[additional_child_count + 1] Node Child Indexes Variable-length array of node-entry indices that are children of this node-entry
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