[vtk-developers] Picking problem with OpenGL2 and DepthPeeling

[Xabi Riobe]

Hi,

I try to pick in a scene that contains a translucent object and the pick
fails if I use the OpenGL2 backend (v6.3.0), tested on VS2013 32 bits with
nVidia Quadro 4000 (driver 353.30)

The same code works with OpenGL backend.

I can reproduce it with the sample code attached, based on the example at
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Interaction/Picking  with these
lines added:

   renderer->SetUseDepthPeeling(1);
   renderer->SetMaximumNumberOfPeels(8);
   renderWindow->SetAlphaBitPlanes(1);
   renderWindow->SetMultiSamples(0);

and the opacity set to 0.5 for the plane.

If i don't use depth peeling, or if the plane is opaque, the picker works
as expected.

It seems that the pick fails when in vtkOpenGLRenderer::DonePick the float
value returned by GetZbufferData is 1.0
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#include <vtkSmartPointer.h>
#include <vtkActor.h>
#include <vtkSphereSource.h>
#include <vtkRendererCollection.h>
#include <vtkCellArray.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkObjectFactory.h>
#include <vtkPlaneSource.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkPropPicker.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

// Handle mouse events
class MouseInteractorStyle2 : public vtkInteractorStyleTrackballCamera
{
public:
   static MouseInteractorStyle2* New();
   vtkTypeMacro(MouseInteractorStyle2, vtkInteractorStyleTrackballCamera);

   virtual void OnLeftButtonDown()
   {
      int* clickPos = this->GetInteractor()->GetEventPosition();

      // Pick from this location.
      vtkSmartPointer<vtkPropPicker>  picker =
         vtkSmartPointer<vtkPropPicker>::New();
      picker->Pick(clickPos[0], clickPos[1], 0, this->GetDefaultRenderer());

      double* pos = picker->GetPickPosition();
      std::cout << "Pick position (world coordinates) is: "
         << pos[0] << " " << pos[1]
         << " " << pos[2] << std::endl;

      std::cout << "Picked actor: " << picker->GetActor() << std::endl;
      //Create a sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
         vtkSmartPointer<vtkSphereSource>::New();
      sphereSource->SetCenter(pos[0], pos[1], pos[2]);
      sphereSource->SetRadius(0.1);

      //Create a mapper and actor
      vtkSmartPointer<vtkPolyDataMapper> mapper =
         vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(sphereSource->GetOutputPort());

      vtkSmartPointer<vtkActor> actor =
         vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);


      //this->GetInteractor()->GetRenderWindow()->GetRenderers()->GetDefaultRenderer()->AddActor(actor);
      this->GetDefaultRenderer()->AddActor(actor);
      // Forward events
      vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
   }

private:

};

vtkStandardNewMacro(MouseInteractorStyle2);

int main(int, char *[])
{
   vtkSmartPointer<vtkPlaneSource> planeSource =
      vtkSmartPointer<vtkPlaneSource>::New();
   planeSource->Update();

   // Create a polydata object
   vtkPolyData* polydata = planeSource->GetOutput();

   // Create a mapper
   vtkSmartPointer<vtkPolyDataMapper> mapper =
      vtkSmartPointer<vtkPolyDataMapper>::New();
#if VTK_MAJOR_VERSION <= 5
   mapper->SetInput(polydata);
#else
   mapper->SetInputData(polydata);
#endif

   // Create an actor
   vtkSmartPointer<vtkActor> actor =
      vtkSmartPointer<vtkActor>::New();
   actor->SetMapper(mapper);
   //actor->GetProperty()->SetOpacity(0.5);

   std::cout << "Actor address: " << actor << std::endl;

   // A renderer and render window
   vtkSmartPointer<vtkRenderer> renderer =
      vtkSmartPointer<vtkRenderer>::New();

   vtkSmartPointer<vtkRenderWindow> renderWindow =
      vtkSmartPointer<vtkRenderWindow>::New();
   renderWindow->AddRenderer(renderer);

   ////////////////////////////////////////
   // BUG : no picking !!!
   ////////////////////////////////////////
   renderer->SetUseDepthPeeling(1);
   renderer->SetMaximumNumberOfPeels(8);
   renderWindow->SetAlphaBitPlanes(1);
   renderWindow->SetMultiSamples(0);
   ////////////////////////////////////////

   // An interactor
   vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
      vtkSmartPointer<vtkRenderWindowInteractor>::New();
   renderWindowInteractor->SetRenderWindow(renderWindow);

   // Set the custom stype to use for interaction.
   vtkSmartPointer<MouseInteractorStyle2> style =
      vtkSmartPointer<MouseInteractorStyle2>::New();
   style->SetDefaultRenderer(renderer);

   renderWindowInteractor->SetInteractorStyle(style);

   // Add the actors to the scene
   renderer->AddActor(actor);
   renderer->SetBackground(0, 0, 1);

   // Render and interact
   renderWindow->Render();
   renderWindowInteractor->Initialize();
   renderWindowInteractor->Start();

   return EXIT_SUCCESS;
}