[vtkusers] Win32 OffScreen Rendering and Visibility cell selector

[Lim, Theodore]

Hi,
 
Not sure how to put this but here goes...
 
I'm trying to get get visible cell data for a series of camera positions and would like to do this using the Win32 offscreen rendering capabilities.
 
However, i discovered that the offscreen render window color buffer size returns all 0 values. This seems to be the reason why the visible cell selector fails. Is there a way to set (or force) values into it?
 
Or rather, can the new class vtkVisibilityCellSelector be used in Offscreen rendering mode? And if so, how can this be achieved. I've attached the code which i'm testing below.
 
One note: i compiled with cmake option VTK_USE_OFFSCREEN set to 'Off' as this caused the vtkMFC examples (i.e. vtkDLG, vtkSDI, vtkMDI) to crash. It also caused the same response to my own VTK-MFC app. Not sure if this has anything to do with it not being able to use Offscreen. In the test code below, i use the vtkWindowToImageFilter to grab a snapshot of the offscreen render window and the results was as expected.
 
Any help would be greatly appreciated.
 
Many thanks, Theo.
 
/**************************************************************************************************/
int main()
{
 //Load model
 vtkSmartPointer<vtkSTLReader> reader = vtkSmartPointer<vtkSTLReader>::New();
 reader->SetFileName("C:/Model/Data/MillCut.stl");
 vtkSmartPointer<vtkPolyDataMapper> map1 = vtkSmartPointer<vtkPolyDataMapper>::New(); 
 map1->SetInput(reader->GetOutput());

 // set up offscreen renderer
 vtkSmartPointer<vtkRenderer> ofsrenderer = vtkSmartPointer<vtkRenderer>::New();
 ofsrenderer->SetBackground(0.0,0.0,0.0); 
 vtkSmartPointer<vtkRenderWindow> ofsrenWin = vtkSmartPointer<vtkRenderWindow>::New();
 ofsrenWin->AddRenderer(ofsrenderer);
 ofsrenWin->SetSize(800,800);
 ofsrenWin->SetOffScreenRendering(1);
 // set interactor
 vtkSmartPointer<vtkRenderWindowInteractor> iren = vtkSmartPointer<vtkRenderWindowInteractor>::New();
 iren->SetRenderWindow(ofsrenWin);  

 //set up the view
 renderer->GetActiveCamera()->SetViewUp(0, 1, 0);
 renderer->SetBackground(0.0,0.0,0.0); 
  
 
 // set actor
 vtkSmartPointer<vtkActor> act1 = vtkSmartPointer<vtkActor>::New();
 act1->SetMapper(map1);
 // add actor to renderer
 double diagonal = act1->GetLength();
 double *center = act1->GetCenter(); 
 ofsrenderer->AddActor(act1);
 ofsrenderer->GetActiveCamera()->SetFocalPoint(center);
 ofsrenderer->GetActiveCamera()->SetPosition(20, -20, -27);
 ofsrenderer->ResetCamera();

 ofsrenWin->Render();
 //-----------------------------------------------
 // check offscreen render window...
 int rgba[4];
 ofsrenWin->GetColorBufferSizes(rgba);
 vtkSmartPointer<vtkWindowToImageFilter> wif = vtkSmartPointer<vtkWindowToImageFilter>::New();//
 wif->SetInput(ofsrenWin);
 wif->Update(); 
 vtkSmartPointer<vtkJPEGWriter> jpgw = vtkSmartPointer<vtkJPEGWriter>::New();
 jpgw->SetInput(wif->GetOutput());
 jpgw->SetQuality(100);
 jpgw->SetFileName("D:/Projects/VTK/testoffscreen.jpg");
 jpgw->Write();
 //-----------------------------------------------

 // get visible cells
 vtkSmartPointer<vtkVisibleCellSelector> sel1 = vtkSmartPointer<vtkVisibleCellSelector>::New();
 sel1->SetRenderer(ofsrenderer);
        // grab everything in the render window viewport
 int *size = ofsrenderer->GetRenderWindow()->GetSize();
 sel1->SetRenderPasses(0,1,0,1,1);
 sel1->SetArea(size[0],size[1],size[2],size[3]);
 sel1->Select();
 vtkSmartPointer<vtkSelection> res1 = vtkSmartPointer<vtkSelection>::New();
 sel1->GetSelectedIds(res1);
 vtkSmartPointer<vtkSelection> cellids = res1->GetChild(0);
 vtkSmartPointer<vtkExtractSelectedPolyDataIds> extr = vtkSmartPointer<vtkExtractSelectedPolyDataIds>::New();
        if (cellids)
         {
          extr->SetInput(1, act1->GetMapper()->GetInput());
          extr->SetInput(0, cellids);
          extr->Update();
          sMap->SetInput(extr->GetOutput());
         }
        else
         {
          cerr << "Empty color buffer selection -" << endl;
          cerr << "Check display color depth. Must be at least 24 bit." << endl;
          sMap->SetInput(emptyPD);
         }
 ////////////////////////////////////////////////////////////
 ofsrenWin->Render();

 // Set the user method (bound to key 'u')
 iren->Initialize();
 iren->Start();

 return 0;
}
 
 
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