[vtkusers] vtkPicker returned actor

[Lonni Besançon]

Hello everyone,

I'm facing a weird issue.
I've followed the vtkPicker example given  here
<http://www.itk.org/Wiki/VTK/Examples/Cxx/Interaction/Picking>   to suit my
needs.

I have a scene, with one renderer and two actors. 
One of them is removed from the scene at some point (it's a volume) so it
does not count when I'm using the picker.
The other one is a vtkActor containing a plane.

Now I'm using android and based on the VolumeRender code, I added a small
chunk of code to the onMotionEvent native function (called when fingers are
placed on the screen of the device).

In case you don't want to browse through the examples and the code, here is
what the native function does:

/JNIEXPORT void JNICALL
Java_com_kitware_VolumeRender_VolumeRenderLib_onMotionEvent(JNIEnv * env,
jobject obj, jlong udp,
      jint action,
      jint eventPointer,
      jint numPtrs,
      jfloatArray xPos, jfloatArray yPos,
      jintArray ids, jint metaState)
{
  struct userData *foo = (userData *)(udp);

  int xPtr[VTKI_MAX_POINTERS];
  int yPtr[VTKI_MAX_POINTERS];
  int idPtr[VTKI_MAX_POINTERS];

  /*vtkSmartPointer<vtkTransform> t = vtkSmartPointer<vtkTransform>::New();
  double * origin = foo->plane->GetOrigin();
  origin[2] += 0.3 ;
  foo->plane->SetOrigin(origin);*/

  // only allow VTKI_MAX_POINTERS touches right now
  if (numPtrs > VTKI_MAX_POINTERS)
    {
    numPtrs = VTKI_MAX_POINTERS;
    }

  // fill in the arrays
  jfloat *xJPtr = env->GetFloatArrayElements(xPos, 0);
  jfloat *yJPtr = env->GetFloatArrayElements(yPos, 0);
  jint *idJPtr = env->GetIntArrayElements(ids, 0);
  for (int i = 0; i < numPtrs; ++i)
  {
    xPtr[i] = (int)xJPtr[i];
    yPtr[i] = (int)yJPtr[i];
    idPtr[i] = idJPtr[i];
  }/

So I just added this small piece of code to try and detect when the user is
placing his/her finger on my planeActor:

/vtkSmartPointer<vtkPropPicker>  picker
=vtkSmartPointer<vtkPropPicker>::New();
      int* clickPos = foo->Interactor->GetEventPosition();
      picker->Pick(xPtr[0], yPtr[0], 0, foo->Renderer);
    
      if(picker->GetActor() == foo->planeActor){
        LOGW("Plane Picked ********************");
        // Case of the seeding point positionning
      }
else{
        LOGW("#################### Outside of plane");
}/

Now when I check my logcat while having my finger on the plane I get
something like:
/W/NativeVTK(29678): Plane Picked ********************
W/NativeVTK(29678): #################### Outside of plane
W/NativeVTK(29678): #################### Outside of plane
W/NativeVTK(29678): #################### Outside of plane
W/NativeVTK(29678): Plane Picked ********************/

When my finger is not located on my plane, this is correctly detected, but
it's on it would appear to trigger both events.

Would you mind giving me some explanations on that matter?

Thanks in advance



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