Re: [Algorithms] Fast Collision Queries - compression

[Landa B. U. <una...@er...>]

=3E =3E
=3E =3E Then=2C the triangles - 3 nibbles each=2E
=3E
=3E Hm=2C that looks pretty nice=2E

Yes=2C that aproach is nice=2C at the moment I=27m not storing the geomet=
ry inside
the tree so is not applicable for me at the moment=2E

=3E
=3E We=27re currently not that smart about leaves=2C but maybe we will tr=
y
=3E that=2E  Anyway=2C I think our kdtree is interesting=2E  It=27s sort =
of a
=3E cross between AABB and kdtree=2E  Each node stores a splitting axis a=
nd
=3E *two* splitting plane offsets=2E  So the child nodes are AABB=27s=2C =
like a
=3E normal kdtree=2C but they may overlap or be disjoint=2C depending on
=3E what=27s inside=2E  Unlike a conventional kdtree=2C there=27s no need=
 to
=3E duplicate primitives that straddle a splitting plane (which made some=

=3E pretty heavy overhead in our tests)=2E  Unlike an AABB tree=2C we onl=
y
=3E store 2 extent bytes=2C not 6=2E  So our node is 6 bytes=3A
=3E
=3E     byte  flags
=3E     byte  offset=5B2=5D // child splitting plane offsets
=3E     int24 child1 // offsets to child1 data=2C if present

I=27m ussig the same concept but ussing a K-dops=2C that means a cross be=
twen a
Kdop and a kd-tree =3A-)

This is my node=3A
struct Node
=7B
  union
  =7B
    struct node
    =7B
      uint16  uFlags=3B
      uint8   rngNode =5B2=5D=3B
      uint16  idxChild=3B
      uint8   rngSplit=5B2=5D=3B
    =7Dnode=3B
    struct leaf
    =7B
      uint16  uFlags=3B
      uint8   rngNode=5B2=5D=3B
      uint16  idxFirst=3B
      uint16  idxLast=3B
    =7Dleaf=3B
  =7D=3B
=7D=3B



These is 8 bytes per node=2C on the  uFlags variable I=27m only ussing 4 =
bits to
store the plane directions=2C I can select the amunt of directions from 3=
 to
13 so in fact I have 1 byte free at the moment=2E

I=27m storing two ranges=2C one the external range ( rngNode ) that is va=
lid for
internal nodes and leafs and the other is the =22loose=22 range (rngSplit=
) thas
is valid only for internal nodes=2C this leads to very acurate mesh
representation=2E

On the internal nodes idxChild stores the index to the lesf child and
idxchid+1 is the right child=2E

On the leafts I only store the first and the last index inside a face lis=
t
varing from 8 to 32 faces per leaf=2E

Unai Landa=2E


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