video texturing -- how are fields re-interlaced?

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Chris Malley (cmalley++at++evt.com)
Thu, 16 Jul 1998 12:25:21 -0600

I've been looking at dmvtO2.c, the Performer example that shows
how to most effectively do video texturing on O2. I believe that
I understand the basic concepts of the example. In a nutshell:
A pfTexture is created whose load source is the current OpenGL
readable. A VL video-to-memory path is set up so that each field
is delivered in a separate DMbuffer. As each DMbuffer arrives,
it is associated with a compatible DMPbuffer. This DMPbuffer
is made the current readable, and the DMbuffer becomes the current
texture (via a copy-by-reference) when the pfTexture is applied.

What I don't understand is how the fields get re-interlaced
when they're rendered. If I were rendering fields in OpenGL, I'd
expect to have to use glCopyTexSubImageEXT (varying y by 1) and the
SGIX_interlace extension. How does Performer know if a DMbuffer
contains a field or a frame? How does it correctly interlace fields?

The answer is probably staring me in the face...

-Chris

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