Re: [Mesa3d-users] How to use actual depth when polygon offsetting?

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

Taura M wrote:
> 
> On Tue, 05 Jun 2001 15:35:45 -0600, Brian Paul said:
> 
> >  Doing a clean implementation (as an OpenGL extension) would be some
> >  work but you could hack it into Mesa's software rendering code if you
> >  just wanted to experiment.
> >
> >  Looking at the 3.4 code, in tritemp.h, search for "ctx->PolygonZoffset".
> >  It's added to the vertex Z positions during triangle setup.
> >
> >  Now look at the depth.c file, where the Z test is performed.  You
> >  could add or subtract ctx->PolygonZoffset to the value which is
> >  stored into the Z buffer when the Z test passes.  I think that
> >  would effectively do what you want.
> >
> >  There's a few other places where you'd have to add/subtract
> >  ctx->PolygonZoffset, like the specialized triangle functions in
> >  X/xmesa4.c
> 
> Thanks for the notes, I'll keep them around if having to modify and get
> a special Mesa3D just for this situation comes up. The down side is that
> this modified Mesa3D will have to be compiled as part of the application
> source and I don't know if that's a smart way to do that.
> 
> Isn't there a way to add a few options to glPolgyonOffset? Ie
> GL_OFFSET_DEPTH_PRE
> or something like that. Basically I just want an option that'll write
> the non-offsetted depth value instead of the offsetted depth value.

You'd probably need a new glEnable/Disable() token.  You can't
add new parameters to existing GL functions.

-Brian