I have an 3D openGL app that renders a vanilla scene, spheres, cylinders,
etc, and can be rotated using the mouse.

I would like to put a 2D graphic on the "window" and not have it be a part
of the 3D world.  For example, I would like to draw a square or a circle
inset from the window edges.  When the scene is rotated, the 2D elements are
not affected.

I want the 2D elements to always be "in front" of anything in the 3D scene.

I've sort-of accomplished this using gluUnProject to unproject window-based
coords back to world space, turning off the depth test, and drawing the
circle.  However, this seems like too much work to make the 2D object part
of the 3D scene.

Here's what I currently do....
glDisable(GL_DEPTH_TEST);
gluUnProject(windowCentX, windowCentY, 0, mvmatrix, projmatrix, viewport,
&worldCentX, &worldCentY, &worldCentZ);
draw some stuff using worldCentX, worldCentY, worldCentZ......
glEnable(GL_DEPTH_TEST);


Is there any snappier way to just do a 2D rendering to a window without all
the back-transforms, etc.?

Any ideas or suggestions would be welcome.

Thanks in advance,
Mark

Mark,

I'm new to OpenGL as well, but what I think you are looking for is an
orthographic projection.  Take a look at a tutorial for projections, and
look at the man pages for gluOrtho2d.  I think this will help you do what
you are looking for.

http://www.cprogramming.com/tutorial/gl7.html

Justin

"Mark" <markt158_REMOVE_@comcast.net> wrote in message
news:mXbWb.142268$U%5.646527@attbi_s03...
>
> I have an 3D openGL app that renders a vanilla scene, spheres, cylinders,
> etc, and can be rotated using the mouse.
>
> I would like to put a 2D graphic on the "window" and not have it be a part
> of the 3D world.  For example, I would like to draw a square or a circle
> inset from the window edges.  When the scene is rotated, the 2D elements
are
> not affected.
>
> I want the 2D elements to always be "in front" of anything in the 3D
scene.
>
> I've sort-of accomplished this using gluUnProject to unproject
window-based
> coords back to world space, turning off the depth test, and drawing the
> circle.  However, this seems like too much work to make the 2D object part
> of the 3D scene.
>
> Here's what I currently do....
> glDisable(GL_DEPTH_TEST);
> gluUnProject(windowCentX, windowCentY, 0, mvmatrix, projmatrix, viewport,
> &worldCentX, &worldCentY, &worldCentZ);
> draw some stuff using worldCentX, worldCentY, worldCentZ......
> glEnable(GL_DEPTH_TEST);
>
>
> Is there any snappier way to just do a 2D rendering to a window without
all
> the back-transforms, etc.?
>
> Any ideas or suggestions would be welcome.
>
> Thanks in advance,
> Mark
>
>

Mark wrote:
> I have an 3D openGL app that renders a vanilla scene, spheres, cylinders,
> etc, and can be rotated using the mouse.
> 
> I would like to put a 2D graphic on the "window" and not have it be a part
> of the 3D world.  For example, I would like to draw a square or a circle
> inset from the window edges.  When the scene is rotated, the 2D elements are
> not affected.
> 
> I want the 2D elements to always be "in front" of anything in the 3D scene.
> 
> I've sort-of accomplished this using gluUnProject to unproject window-based
> coords back to world space, turning off the depth test, and drawing the
> circle.  However, this seems like too much work to make the 2D object part
> of the 3D scene.
> 
> Here's what I currently do....
> glDisable(GL_DEPTH_TEST);
> gluUnProject(windowCentX, windowCentY, 0, mvmatrix, projmatrix, viewport,
> &worldCentX, &worldCentY, &worldCentZ);
> draw some stuff using worldCentX, worldCentY, worldCentZ......
> glEnable(GL_DEPTH_TEST);
> 
> 
> Is there any snappier way to just do a 2D rendering to a window without all
> the back-transforms, etc.?
> 
> Any ideas or suggestions would be welcome.
> 
> Thanks in advance,
> Mark
> 
> 
  You don't need to perform back-transforms.

  A very simple way to perform this is to define a 2d projection over 
your 3d projection

  After the code for drawing your 3d scene and before sending all to 
your window :
	
   add for example :


   glMatrixMode(GL_PROJECTION); /* enter projection mode */
   glPushMatrix();
   glLoadIdentity();
   gluOrtho2D(0,100, 0, 100); /* defines a 2d projection */

   glDisable(GL_DEPTH_TEST); /* disable depth test to enable overlay */
   glDisable(GL_LIGHTING);

   glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); /* add blending */
   glEnable(GL_BLEND);

   glColor4f(0.8, 0.8, 0.8, 0.5); /* color for blending */

   glRecti(20, 20, 80, 80);  /* draw a rectangle */


   glDisable(GL_BLEND);
   glEnable(GL_LIGHTING);
   glEnable(GL_DEPTH_TEST);

   glPopMatrix();
   glMatrixMode(GL_MODELVIEW);

   As a result this draw a fixed blended grey rectangle over your 3d scene

	Hope this helps.


-- 
Alexis GOURDON			| mailto:Alexis.Gourdon@sophia.inria.fr
INRIA Projet PLANETE            | Phone: +33 (0)4 92 38 50 21
2004 route des Lucioles BP 93	| Fax  : +33 (0)4 92 38 79 78
06902 Sophia-Antipolis FRANCE	| http://www.inria.fr/planete/agourdon

Do everything on your own.
Draw 3d objects first then disable depth test and change the matrices

// draw 3d stuff
// SWITCH to 2D MODE

  glMatrixMode(GL_PROJECTION);
  glPushMatrix();
  glLoadIdentity();

   glMatrixMode(GL_MODELVIEW);
   glPushMatrix();
   glLoadIdentity();

  // this will allow you to use pixel coordinates
   glOrtho(0, m_nSizeX, m_nSizeY, 0, 1, -1);
   glDisable(GL_DEPTH_TEST);

// draw objects in 2D

// go back to 3D mode
  glMatrixMode(GL_MODELVIEW);
   glPopMatrix();
  glMatrixMode(GL_PROJECTION);
   glPopMatrix();

  glEnable(GL_DEPTH_TEST);


Dmitri


"Mark" <markt158_REMOVE_@comcast.net> �������/�������� � �������� ���������:
news:mXbWb.142268$U%5.646527@attbi_s03...
>
> I have an 3D openGL app that renders a vanilla scene, spheres, cylinders,
> etc, and can be rotated using the mouse.
>
> I would like to put a 2D graphic on the "window" and not have it be a part
> of the 3D world.  For example, I would like to draw a square or a circle
> inset from the window edges.  When the scene is rotated, the 2D elements
are
> not affected.
>
> I want the 2D elements to always be "in front" of anything in the 3D
scene.
>
> I've sort-of accomplished this using gluUnProject to unproject
window-based
> coords back to world space, turning off the depth test, and drawing the
> circle.  However, this seems like too much work to make the 2D object part
> of the 3D scene.
>
> Here's what I currently do....
> glDisable(GL_DEPTH_TEST);
> gluUnProject(windowCentX, windowCentY, 0, mvmatrix, projmatrix, viewport,
> &worldCentX, &worldCentY, &worldCentZ);
> draw some stuff using worldCentX, worldCentY, worldCentZ......
> glEnable(GL_DEPTH_TEST);
>
>
> Is there any snappier way to just do a 2D rendering to a window without
all
> the back-transforms, etc.?
>
> Any ideas or suggestions would be welcome.
>
> Thanks in advance,
> Mark
>
>