Re: [Mesa3d-dev] projection plane

[Brian P. <br...@tu...>]

Ricardo_Rogerio_Gutierrez/FIN/CORP/CF...@cf... wrote:
> hi to all
> 
> well I have a question about the projection plane, specifically is: if is
> there any way to obtain the projection plane? or if I need to do some
> calculation for getting it?
> 
> I say for example if I have
> 
> +    +
>  +     +   +                          these are my objects on my program
> (spheres)
>      +    +
> 
> ----------------                   this is my prejection plane
> 
> 
> how can I get this plane (I say the plane of the user view?)
> 
> 
> well I hope have explained well...
> 
> I hope U can help me
> 
> rick.


It's not exactly clear what you want, but my guess is you want the coordinates
of the four corners of the projection plane in world coordinates.  Is that right?

If so, that's easy.

If you call glFrustum(l, r, b, t, n, f) then the four corners of the projection
plane in eye coordinates are (l, b, n), (r, b, n), (l, t, n) and (r, t, n).

The modelview matrix transforms points from object (world) space to eye
coordinates.  To go backwards (from eye space to object/world space), multiply
those four coordinates by the inverse of the modelview matrix.

Note that the modelview matrix combines the conceptual modelling and viewing
transformations.  You'll need to be careful that the modelview matrix has the
right transformation.

-Brian