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BSPINFO.DOC
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1995-11-29
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BSPInfo Version 1.01 by Marc Rousseau
During the development of ZenNode, I often wondered what was going on
with the BSP structures that were being built. Was this algorithm doing
better than that one? How balanced is the tree? How deep is it going? ...
BSPInfo grew out of the tool used to see what was going on. It reports
statistics to describe the BSP tree. It can be used to give you a feel of
how particular Node builders are performing.
The following is a brief description of each of the values displayed by
BSPInfo.
Depth The maximum depth of the BSP tree. The deeper the tree, the
more work DOOM has to do to update the display. A smaller
value means that, on average, DOOM will have fewer NODES to
traverse when updating the screen.
FOM ( Figure of Merit ) This is an attempt to measure the
'balance' of the tree. Each node with both a right and left
child or no children is considered balanced. The FOM value
is a ratio of balanced nodes to the overall number of nodes.
An FOM of 1.000 indicates perfect binary tree. This will
*VERY RARELY* occur, since it requires a number of nodes that
is an exact power of 2 and every node being balanced.
Balance The percentage of nodes to the left and right of the root
node. Generally, a more balanced tree is preferable to a less
balanced tree, since, the average depth for any node is likely
to be smaller. ( This actually is an indication of how well
the node builder chose it's first partition. )
Splits How many times the Node builder had to split segments to
fit everything into the tree. There are no hard rules saying
that splits are bad, however fewer is generally better.
Diagonals The number of BSP partition lines chosen that were diagonal.
The DOOM rendering engine runs much faster when the partition
lines are either vertical or horizontal. Generally the fewer
diagonals the better.
Nodes Number of NODES in the map.
Segs Number of SEGS in the map.
IMPORTANT:
None of these figures are meant to imply that one Node builder is better
(or worse) than another. They are simply designed to describe the type of
BSP trees being built. Some favor shallow tree depths, others attempt to
reduce splits, others favor reducing diagonals. No one value should be viewed
as more important than the others. In general, if a Node builder builds a
BSP tree with all values significantly lower, except FOM, than other Node
builders, it most likely means that that level will play slightly faster in
DOOM but is no more or less 'correct' than any other Node builder. Of course
these numbers aren't important. The only thing that is important is that
the BSP tree created works correctly under DOOM.