RE: [Plib-users] clipping performance question.

[Dave M. <Dav...@dy...>]

If you are doing bounding sphere checks for each line segment, it might be
better to hand it all to opengl because it's roughly the same amount of
work.  but if, as you say, the strips contain 100s to 1000s of points then
view frustum culling on each strip is probably worth it  regardless of how
the opengl implementation handles it.  the number of computations is of a
different magnitude.

it also depends on where your viewpoint is.  if you have a god view where
everything is in view and nothing is view frustum culled, then you won't see
improvement.  but if you are inside a _room_ then view frustum culling makes
a big impact.

we've actually tested this on game console where we thought that perhaps an
uber display list (with all geometry) would be _a good thing_ since the main
CPU is a dog and the 3d processor is very fast.  we would eliminate the
overhead for many (several hundred) display lists and pass a single DMA
packet to the 3d processor.  but we found that view frustum culling (ssg
style) is very well worth it, even there.

-- Dave McClurg

-----Original Message-----
From: pli...@li...
[mailto:pli...@li...]On Behalf Of Gouthas,
Themie
Sent: Wednesday, May 30, 2001 10:40 PM
To: 'pli...@li...'
Subject: [Plib-users] clipping performance question.

Just an optimization question for frustrum clipping, which would better be
directed to an OpenGL format, but this forum is more convenient at this
point in time.. 

For basic line strips, say of 100's to 1000's of points. Is it worthwhile
going to the trouble of calculating a bounding spehere  for clipping to the
view frustrum, or is line clipping pretty efficient. You would think that an
intelligent implementation would check the end points of a line segment
first and not attempt to draw it if both were out of the clipping rectangle.
Anyone have an idea what OpenGL does? 
 
Thanks, Themie