Info-Volumizer Mailing List Archives: Questions concerning Volu

Questions concerning Volumizer design.

Manfred Weiler (mdweiler@immd9.informatik.uni-erlangen.de)
Wed, 23 Jun 1999 18:30:18 +0000

In the Volumizer API different geometric primitives are supported. But for
poligonalization all the higher level primitives are tesselated into
tetrahedrons. This leads to a significant overhead for such primitives like
hexahedrons which could be directly slices more efficient than the five
tetrahedrons the tesselation produces. This applies especially to the standard
case where s single volume should be rendered with a TetraSet covering exactly
the bounding box of the volume.
When will there be direct support to (some of) the vout-primitives in the
future or why is this not planed.
For the standard case it is perhaps a good idea to make it possible that a
volume can be polygonizes without a TetraSet (NULL-Pointer).

On the other hand for most cases I see no need to create a (sometimes huge and
only parsely populated) transient data structure. Especially on low-end
workstations without 3D texture interpolation this structure consumes much of
the rare main memory due to the great number of "bricks". In addition to that
I guess that working with this structure reduces performance because of quite
a number of system calls (memory (de-)allocation, creating/deleting object on
the stack).
I admit that using this structure is more flexible but I think that
display lists could do the same job and the vertices and polygons that should
be drawn are stored where they will be needed.
Maybe you will object that the transient geometry can be cached between the
frames. But this leads to errors in the resulting image when the view
parameters change, so for correct images slicing has to be performed in every
frame.
So why not add a draw method to Volumizer which works totaly without transient
geometry?

        Manfred.

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