I am trying to pick using scene picker but it doesn’t seem to find a cell or
vertex, while proppicker does.
How do I extract a pick position from scene picker? (Or even just a picked
cell)
Minimal example below, which gives -1 (not found) for scenepicker but proppicker works fine:
#include <vtkVersion.h>
#include <vtkSmartPointer.h>
#include <vtkActor.h>
#include <vtkSphereSource.h>
#include <vtkRendererCollection.h>
#include <vtkCellArray.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkObjectFactory.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPropPicker.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkPLYReader.h>
#include <vtkScenePicker.h>
#include <vtkSphereSource.h>
// Execute application.
int main(int, char *[])
{
vtkSmartPointer<vtkSphereSource> sphereSource =
vtkSmartPointer<vtkSphereSource>::New();
sphereSource->Update();
// Create a polydata object
vtkPolyData* polydata = sphereSource->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);
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->SetStencilCapable(1); // Needed for point picking on scene
picker
renderWindow->AddRenderer(renderer);
// An interactor
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow(renderWindow);
// Here comes the scene picker stuff. [ Just 2 lines ]
vtkScenePicker * scenepicker = vtkScenePicker::New();
scenepicker->SetRenderer(renderer);
scenepicker->EnableVertexPickingOn();
// Add the actors to the scene
renderer->AddActor(actor);
renderer->SetBackground(0, 0, 1);
// Render and interact
renderWindow->Render();
renderWindowInteractor->Initialize();
// Now the picking
stuff…
int e[2] = { 175, 215 };
// Pick from this location using standard prop picker (this works fine)
vtkSmartPointer<vtkPropPicker> picker =
vtkSmartPointer<vtkPropPicker>::New();
picker->Pick(e[0], e[1], 0, renderer);
double* pos = picker->GetPickPosition();
std::cout << "Pick position (world coordinates) is: "
<< pos[0] << " " << pos[1]
<< " " << pos[2] << std::endl;
// Pick using scene picker (this fails)
vtkIdType vertexId = scenepicker->GetVertexId(e);
vtkIdType cellId = scenepicker->GetCellId(e);
std::cout << "Scene pick vertex Id " << vertexId << std::endl;
std::cout << "Scene pick cell Id " << cellId << std::endl;
double world_point[3];
if (vertexId != -1)
{
polydata->GetPoint(vertexId, world_point);
std::cout << "Scene pick position is : " << world_point[0] << " " <<
world_point[1] << " " << world_point[2] << std::endl;;
}
renderWindowInteractor->Start();
return EXIT_SUCCESS;
}