plib-users

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

[Stanford N. <st...@th...>]

Hi everyone!  I just got started with Plib and I like it a lot!  Great
work, guys!

I'm stuck with a rather embarrassing problem: I can't seem to mix SSG &
my OpenGL code together.  My SSG code loads a model and displays it.  My
OpenGL code draws some colored polys to the screen.  They both work
individually, but I can't mix and match...

It seems that the ssgInit() call will setup some GL state that causes
the GL calls in my custom code to not render... This is rather
perplexing as I have managed to work the 2-d font rendering via an 2-d
orthogonal projection into the code.  Is this something obvious I'm
missing?  

If someone could point me to an example that has both SSG & OpenGL code
working together, I'm sure I can figure out what I'm doing wrong.

Thanks in advance!

-- stan  c",)

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

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

Stanford Ng wrote:
> 
> Hi everyone!  I just got started with Plib and I like it a lot!  Great
> work, guys!
> 
> I'm stuck with a rather embarrassing problem: I can't seem to mix SSG &
> my OpenGL code together.  My SSG code loads a model and displays it.  My
> OpenGL code draws some colored polys to the screen.  They both work
> individually, but I can't mix and match...
> 
> It seems that the ssgInit() call will setup some GL state that causes
> the GL calls in my custom code to not render... This is rather
> perplexing as I have managed to work the 2-d font rendering via an 2-d
> orthogonal projection into the code.  Is this something obvious I'm
> missing?
> 
> If someone could point me to an example that has both SSG & OpenGL code
> working together, I'm sure I can figure out what I'm doing wrong.

Well, all of my games do - so check out TuxKart for example.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

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

[Stanford N. <st...@th...>]

Thanks for the pointers!

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.  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!

-- stan

<< CODE SNIPPETS FOR REFERENCE >>

void redraw()
{
	update_game() ;

	glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
	ssgCullAndDraw( scene );
	draw_water();
	draw_text();
	glutPostRedisplay();
	glutSwapBuffers();
}


void draw_water()
{
	glMatrixMode( GL_PROJECTION );
	glPushMatrix();
	glLoadIdentity();

	glMatrixMode( GL_MODELVIEW );
	glPushMatrix();
	glLoadIdentity();
	GLfloat lmodel_ambient[] = { 0.8, 0.8, 0.8, 1.0 };
	glLightModelfv( GL_LIGHT_MODEL_AMBIENT, lmodel_ambient );

	glColor3f( 0.0f, 0.0f, 1.0f );
	
	glBegin( GL_QUADS );
	glVertex3f( 0.3f, 0.3f, 0.0f );
	glVertex3f( -0.3f, 0.3f, 0.0f );
	glVertex3f( -0.3f, -0.3f, 0.0f );
	glVertex3f( 0.3f, -0.3f, 0.0f );
	glEnd();


	glPopMatrix();
	glMatrixMode( GL_PROJECTION );
	glPopMatrix();
}


-----Original Message-----
From: steve [mailto:steve] On Behalf Of Steve Baker
Sent: Friday, May 10, 2002 2:07 PM
To: Stanford Ng
Cc: pli...@li...
Subject: Re: [Plib-users] Newbie Question: Mixing SSG & OpenGL


Stanford Ng wrote:
> 
> Hi everyone!  I just got started with Plib and I like it a lot!  Great

> work, guys!
> 
> I'm stuck with a rather embarrassing problem: I can't seem to mix SSG 
> & my OpenGL code together.  My SSG code loads a model and displays it.

> My OpenGL code draws some colored polys to the screen.  They both work

> individually, but I can't mix and match...
> 
> It seems that the ssgInit() call will setup some GL state that causes 
> the GL calls in my custom code to not render... This is rather 
> perplexing as I have managed to work the 2-d font rendering via an 2-d

> orthogonal projection into the code.  Is this something obvious I'm 
> missing?
> 
> If someone could point me to an example that has both SSG & OpenGL 
> code working together, I'm sure I can figure out what I'm doing wrong.

Well, all of my games do - so check out TuxKart for example.

----------------------------- Steve Baker
-------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net

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 -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
       http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
       http://prettypoly.sf.net http://freeglut.sf.net
       http://toobular.sf.net   http://lodestone.sf.net