Which coordinate space do you want to get your geometry in?
Vertex programs produce vertices in clip coordinates (after the
modelview and projection transformations). So even if you could
capture coords immediately after the vertex program, you may have to
apply an inverse transformation to get what you want.
If you're not sure about coordinate spaces, see section 2.10 of the
OpenGL specification.
Another possibility that occurs to me would be to write a new
extension to the feedback mechanism that returns coordinates in clip
space, before clipping and perspective division.
-Brian
Michael Frumin wrote:
you're right. that worked, but it turns out the FeedbackBuffer is not
the approach I'm looking for. there's no Z-depth because its in screen
coordinates, and it clips everything to the viewing frustum, as opposed
to giving me polygons _before_ clipping and flattening.
will maybe pursue the re-use of Mesa vertex program processing.
thanks,
mike
On 1/17/06, *Brian Paul* < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Michael Frumin wrote:
>
>
> On 1/17/06, *Brian Paul* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>
> <mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> >> wrote:
>
> Michael Frumin wrote:
> > I am attempting to capture 3D geometries from OpenGL
applications for
> >
>
> Have you looked at OpenGL's feedback feature? It lets you
capture
> OpenGL geometry after it's been transformed to screen space,
before
> rasterization.
>
>
>
> Wow, I wish I had known about that earlier. That's a great idea, in
> fact it was super easy to rig something up to capture the whole
buffer.
> Any suggestions as to how to easily build a parser for the binary
string
> returned in the buffer, that is structured according to the
grammar at:
>
http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/feedbackbuffer.html
> (preferable in windows, but *nix would be fine just to see how
it works)?
You don't really need a parser. I think that a switch statement with
some loops (over the polygon vertices) would suffice.
-Brian
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