Re: [Plib-users] Newbie Question: Mixing SSG & OpenGL

[Steve B. <sjb...@ai...>]

Stanford Ng wrote:

> After much digging under the hood of my program, I'm still encountering
> problems with mixing SSG & OpenGL.  I've narrowed it down to the
> ssgCullAndDraw() call influencing the GL state somehow.

It does change state without restoring it - yes.

That's not accidental though - it's very inefficient in OpenGL to keep
setting and restoring state unnecessarily - so we leave it to the
application to save and restore state if it wishes to.

Many applications (all of mine) get away without doing that and are
faster as a result, others can do things like not restoring all of
the detailed texture attributes because they just glDisable texture
globally.  So, it's better to let the application decide.

> When I comment
> out ssgCullAndDraw() in my redraw routine, the draw_water() works fine,
> drawing a blue rectangle.  When I leave the call in there, the rectangle
> is still drawn, but it is very dark and blends right into the
> background.
> 
> I'm trying to puzzle out what ssgCullAndDraw() is doing that would
> affect the standard OpenGL stuff... I'm still quite a novice when it
> comes to these things.  If someone could explain things, I'd much
> appreciate it!  Thanks in advance!

As a first shot at fixing this, you could wrap ssgCullAndDraw with

  glPushAttrib ( GL_ALL_ATTRIB_BITS ) ;
  ssgCullAndDraw () ;
  glPopAttrib () ;

...that will almost certainly fix your problem - but at some performance
cost.  If you find that cost is acceptable - then you're done. If not
then you'll have to ascertain which things that SSG changed are not
acceptable to your draw_water() function.

----------------------------- Steve Baker -------------------------------
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