Re: reflecting GeoSets causes shading to malfunciton (fwd)

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david.heskamp++at++lmco.com
Thu, 6 Feb 97 09:44:30 EST

Thanks for everyone who responded.

Using glFrontFace (GL_CW) solves the problem globally! But, it causes
non-reflected geometry to behave improperly. How do I selectively change front
face ordering for various Geosets?

--- Begin Included Message ---

   From: swapnil++at++teil.soft.net (SWAPNIL H SHAH)
   Date: Thu, 6 Feb 1997 09:39:52 -0530 (IST)

   The problem might be that, as u r mirroring the X co-ordinates, your
   polygon/face 's front plan goes to back, and so Performer engine HIDES it
   from u and so u see is only BLACK..

Close. The order of the polygon vertices has been changed by the
flip, so front is no longer front. You can either change all the
vertices around in the pfGeoSet, which is a big pain, or you can stick
glFrontFace (GL_CW) in a pre-draw callback to change the vertex order
to clockwise, and glFrontFace (GL_CCW) in a post-draw callback to
reset things for all the other geometry.

I'm not sure what the IrisGL equivalent is, or if there's a Performer
encapsulation of it...

Tim

> To: info-performer++at++sgi.com
> Subject: reflecting GeoSets causes shading to malfunciton

> Hello Performers:
>
> I have a GeoSet with normals bound per vertex. I am trying to reflect the
> GeoSet across the YZ plane by negating the X-component of all the coords and
> negating the X-component of all the normals. Shading does not work after I
> do this. The geometry is located properly, but the surfaces appear black for
> the most part. Anyone know why?
>
>
> Dave Heskamp
>
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Dave Heskamp

Lockheed Martin Tactical Defense Systems
1210 Massillon Road
Akron, Ohio 44315-0001
         
phone: (330) 796 - 5383
fax: (330) 796 - 7009
email: david.heskamp++at++lmco.com

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