Light & Material's interaction!

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Torres Mario 678-3280 AMSRL-BE-M (mtorres++at++arl.mil)
Thu, 18 May 95 15:05:25 MDT

  I am currently working on quantifying the interaction of Ambient and
Diffuse light and material properties to try and relate them to some
physically correct models that we have. In a perfly hack I've set up a
4 face pyramid with each face having a different color: red, green, blue
and white. I've also setup sliders to change the Materials ambient and
diffuse colors and a toggle to switch between various Material Color
Modes.

  The CONFUSING behavior: When I set the pfMtlColorMode to DIFFUSE and
then vary the Mtl DIFFUSE color I see no apparent effect on the colors of
my pyramid. HOWEVER, if I change the material AMBIENT color (with the
PFMTL_CMODE_DIFFUSE), the pyramid's color are affected and change with
changing of ambient color. Is this behavior normal? correct? Does it
make sense that if the MaterialColorMode is PFMTL_CMODE_DIFFUSE the
AMBIENT material colors are active?

The same behavior is shown when I use the PFMTL_CMODE_AMBIENT. That is
the pyramids colors are changed by changing the diffuse material colors
and not the ambient material colors (as I would expect it).

Another, goody: When I change to this PFMTL_CMODE_DIFFUSE mode from
another mode (like PFMTL_CMODE_AMBIENT) the WHITE face of the pyramid
turns BLACK. (Is there a force of opposites at work here? ;)

 I have many more questions which I can't find answers to, but I will
restrain... I have read all the Performer documentation and only a
couple of many possible ColorModes are briefly mentioned there. GL
documentation was not of much help either. I did read the OpenGL Ch 6 on
Lighting, however, are all the definitions contained therein valid for
Performer? It seems to me that OpenGL is capable of much more than
Performer is, in terms of lighting, shadows, etc. Can I depend on the
lighting and material mathematical definitions given in the OpenGL
literature and considered them to be same for Performer?

  Sorry, for having so many questions, I am hoping for a clue to any
them.
   

  Thanks in advance,

  Mario A. Torres

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