Dear VTK users

i was trying to have a shaded Background using OpenGL in VTK 
rendered Window.
presently it(win32openglrenderwindow) supports a black background 
(by default) or can be changed to
some other color but uniform by calling SetBackground of 
vtkViewport Class.

To get a shaded background i have written some code in OpenGl and 
has added in vtkOpenGLRenderer::Clear(void) function
as follows

void vtkOpenGLRenderer::Clear(void)
{
   GLbitfield  clear_mask = 0;

   if (! this->Transparent())
     {
     glClearColor( ((GLclampf)(this->Background[0])),
                   ((GLclampf)(this->Background[1])),
                   ((GLclampf)(this->Background[2])),
                   ((GLclampf)(1.0)) );
     clear_mask |= GL_COLOR_BUFFER_BIT;
     }

   glClearDepth( (GLclampd)( 1.0 ) );
   clear_mask |= GL_DEPTH_BUFFER_BIT;

   vtkDebugMacro(<< "glClear\n");
   glClear(clear_mask);

/////////////////////////////////////////////////////////////////////////////////////////////
// Added Code
   	// Disable Depth
 	glDisable(GL_DEPTH_TEST);

 	glMatrixMode (GL_MODELVIEW);
 	glPushMatrix ();
 	//glLoadIdentity ();
 	glMatrixMode (GL_PROJECTION);
 	glPushMatrix ();
 	//glLoadIdentity ();


 	::glBegin(GL_QUADS);

 	//first Vertex (-1, -1)
 		glColor3f(0.0, 0.0, 1.0);
 		glVertex2f(-1.0, -1.0);

 	//second vertex
 		glColor3f(0.0, 0.0, 1.0);
 		glVertex2f(1.0, -1.0);

 	//third vertex
 		glColor3f(0.0, 0.0, .50);
 		glVertex2f(1.0, 1.0);

 	//fourth vertex
 		glColor3f(0.0, 0.0, .50);
 		glVertex2f(-1.0, 1.0);
 	glEnd();

 	glPopMatrix ();
 	glMatrixMode (GL_MODELVIEW);
 	glPopMatrix ();


 	glEnable(GL_DEPTH_TEST);
///////////////////////////////////End added Code 
////////////////////////////////////////
}


but shaded screen(blue) is coming for few seconds only & geting 
disappeared. it seems it is overwritten
by Black screen.

any help!!

thanks in advanced.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Amit Shrivastava
Scientist, ANURAG,
DRDO, Hyderabad,
Homepage:
s_amit4u.50megs.com
amitshonline.com