[vtk-developers] Gradient backgrounds in vtkRenderer.

[Francois Bertel]

You'd better not use query functions like glIsEnable() because it
requires the driver to send information back to the client (which may
involve a flush of OpenGL commands). glPushAttrib/glPopAttrib should
be  faster:

glPushAttrib(GL_ENABLE_BIT); // save depth test value and lighting value
glDisable(GL_DEPTH_TEST);
glDisable(GL_LIGHTING);
[...]
glPopAttrib();

glColor() change the current color. You don't need to call it before
each call to glVertex() if it does not change. Just write:

 //first Vertex (-1, -1)
         glColor3dv(this->Background);
         glVertex2f(-1.0, -1.0);

         //second vertex
         glVertex2f(1.0, -1.0);

         //third vertex
         glColor3dv(this->Background2);
         glVertex2f(1.0, 1.0);

         //fourth vertex
         glVertex2f(-1.0, 1.0);


On Mon, Apr 7, 2008 at 4:24 PM, Jeff Baumes <jeff.baumes at kitware.com> wrote:
> In certain applications, gradient backgrounds can add to the quality
>  of a visualization (in particular in information visualization). Does
>  anyone object to the addition of a top-to-bottom gradient in
>  vtkRenderer (by default it is disabled, of course)?
>
>  This involves adding the following functions to vtkViewport:
>
>   vtkSetVector3Macro(Background2,double);
>   vtkGetVector3Macro(Background2,double);
>
>   vtkSetMacro(GradientBackground,bool);
>   vtkGetMacro(GradientBackground,bool);
>   vtkBooleanMacro(GradientBackground,bool);
>
>  And the following to vtkOpenGLRenderer:
>
>   if (!this->Transparent() && this->GradientBackground)
>     {
>     GLboolean is_depth_en = glIsEnabled(GL_DEPTH_TEST);
>     GLboolean is_light_en = glIsEnabled(GL_LIGHTING);
>
>     if (is_depth_en)
>       {
>       glDisable(GL_DEPTH_TEST);
>       }
>
>     if (is_light_en)
>       {
>       glDisable(GL_LIGHTING);
>       }
>
>     glMatrixMode(GL_MODELVIEW);
>     glPushMatrix();
>     {
>       glLoadIdentity ();
>       glMatrixMode (GL_PROJECTION);
>       glPushMatrix ();
>       {
>         glLoadIdentity ();
>         glBegin(GL_QUADS);
>
>         //first Vertex (-1, -1)
>         glColor3dv(this->Background);
>         glVertex2f(-1.0, -1.0);
>
>         //second vertex
>         glColor3dv(this->Background);
>         glVertex2f(1.0, -1.0);
>
>         //third vertex
>         glColor3dv(this->Background2);
>         glVertex2f(1.0, 1.0);
>
>         //fourth vertex
>         glColor3dv(this->Background2);
>         glVertex2f(-1.0, 1.0);
>         glEnd();
>       }
>       glPopMatrix();
>       glMatrixMode(GL_MODELVIEW);
>     }
>     glPopMatrix();
>
>     if (is_depth_en)
>       {
>       glEnable(GL_DEPTH_TEST);
>       }
>
>     if (is_light_en)
>       {
>       glEnable(GL_LIGHTING);
>       }
>     }
>
>  --
>  Jeff Baumes, Ph.D.
>  R&D Engineer, Kitware Inc.
>  (518) 371-3971 x132
>  jeff.baumes at kitware.com
>  _______________________________________________
>  vtk-developers mailing list
>  vtk-developers at vtk.org
>  http://www.vtk.org/mailman/listinfo/vtk-developers
>



-- 
François Bertel, PhD | Kitware Inc. Suite 204
1 (518) 371 3971 x113 | 28 Corporate Drive
 | Clifton Park NY 12065, USA