Ran Yakir (rany++at++sgi.sgi.com)
Wed, 4 Jun 1997 11:19:54 +0000
>
> How about performance?
> What is more realistic?
Both pfLight and pfLightSource encapsulate the functionality of OpenGL (or
IrisGL) lights. Those lights are performed in hardware per vertex.
A pfLight is a libpr object, which defines an OpenGL light when applied. It has
to be applied from within the DRAW process, because it issues GL commands. A
pfLightSource is a libpf node. It is normally added to the scene graph with
pfAddChild. Therefore it is affected by the nodes above it in the scene graph -
DCSs, Switches, etc. So you can animate the position of a light using a DCS
above the pfLightSource.
A pfLightSource also supports some lighting techniques which are not supported
by normal GL lights, like projected texture for spotlights and shadows. These
techniques give you high quality lighting effects but requires multiple passes
when drawing the database. If you use only the normal GL lights, you have no
performance difference between the two, and they both give the same results
quality speaking.
Ran
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