[vtkusers] using glStencilFunc() and glStencilOp() function in vtk

[刘卓]

Hi all:

I have read some mails about using Stencil Buffer in vtk. I know the
function vtkWin32OpenGLRenderWindow:: SetupPixelFormat() must be
overwritten. I save the buffer data to a Text file. And When I draw an
object to Stencil buffer, the result is not my desire. The code is listed
below:

       pCone = vtkConeSource::New();

       pCone->SetCenter( -10.0 , 0.0 , 0.0 );

       pCone->SetRadius( 2.0 );

       pCone->SetHeight(10);

       vtkPolyDataMapper* mapMest = vtkPolyDataMapper::New();

       mapMest->SetInput(pSphere->GetOutput());

       meshActot = vtkOpenGLActor::New();

       meshActor->SetMapper(mapMest);

       meshActor->GetProperty()->SetColor(1,0,0);

 

       ren1 = new vtkOpenGLRenderer;

       ren1->AddActor( meshActor );

       renWin = new vtkWin32OpenGLRenderWindow;

       renWin->AddRenderer(ren1);

      iren = vtkRenderWindowInteractor::New();

       iren->Initialize();

 

       glClear (GL_DEPTH_BUFFER_BIT |
GL_STENCIL_BUFFER_BIT|GL_COLOR_BUFFER_BIT);

       glEnable(GL_STENCIL_TEST);

       glStencilFunc(GL_ALWAYS,1,1);

       glStencilOp(GL_KEEP,GL_REPLACE,GL_REPLACE);

 

       renWin->Render();

         iren->Start();

 

float pSphereZBuffer[WINDOW_SIZE*WINDOW_SIZE];

         glDisable( GL_TEXTURE_2D );

         glDisable( GL_SCISSOR_TEST );

         glPixelStorei( GL_PACK_ALIGNMENT, 1 );

  glReadPixels( 0, 0, 

                WINDOW_SIZE, WINDOW_SIZE,

                GL_STENCIL_INDEX, GL_FLOAT,

                pSphereZBuffer );

 

         ofstream file("zbuffer1.txt");

         for(i = 0 ; i < WINDOW_SIZE ; i++ )

         {

         for(j = 0 ; j < WINDOW_SIZE ; j++ )

 
file<<setprecision(0)<<setw(4)<<pSphereZBuffer[WINDOW_SIZE*i+j];

                   file<<endl;

}

         file.close();

 

 

The result is not right. But When these codes are moved in the front of the
function renWin->Render(), the result is right.

 

       glClear (GL_DEPTH_BUFFER_BIT |
GL_STENCIL_BUFFER_BIT|GL_COLOR_BUFFER_BIT);

       glEnable(GL_STENCIL_TEST);

       glStencilFunc(GL_ALWAYS,1,1);

       glStencilOp(GL_KEEP,GL_REPLACE,GL_REPLACE);

 

just like that, the function vtkOpenGLRenderWindow::Render is overwritten.

vtkMYOpenGLRenderWindow ::Render()

{

       glClear (GL_DEPTH_BUFFER_BIT |
GL_STENCIL_BUFFER_BIT|GL_COLOR_BUFFER_BIT);

       glEnable(GL_STENCIL_TEST);

       glStencilFunc(GL_ALWAYS,1,1);

       glStencilOp(GL_KEEP,GL_REPLACE,GL_REPLACE);

         …………..

         …………….

}

 

 

Who can tell me the reason? 

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