[vtkusers] timer problems when subclassing vtkInteractorStyleTrackball

[Lawrence M. Lifshitz]

Hi,
  I wanted movement of the mouse while the left button was down
to change the zslice of a 3D dataset, instead of rotating the 3D
image. So I derived a new style class (InteractorStyleFlow)
from vtkInteractorStyleTrackball.
I then changed a the left button methods, and added my own state
to OnTimer.  But as far as I can tell, the timer is never activated
when I push the left button down; ie, OnTimer is never called when
the left button is down.  I saw  no documentation on how to use
the timer routines.  What am I leaving out?  thanks.
I get the error messages from OnMouseMove,OnLeftButtonDown, and
OnLeftButtonUp.  The other button functions still work fine (I didn't
override them).

code snippet (win32 platform, vtk 3.1):

void InteractorStyleFlow::OnMouseMove (int ctrl, int shift, int X, int
Y)
{

 this->vtkInteractorStyleTrackball::OnMouseMove(ctrl,shift,X,Y);
 //  this call just does:
 //this->LastPos[0] = X;
 //this->LastPos[1] = Y;


 cerr << "InteractorStyleFlow::OnMouseMove: " << ctrl << " "<<shift<<"
"<<X<<" "<<Y<<"\n";

} 

//take out the rotation from the left button, change it to zslice
update.
void InteractorStyleFlow::OnLeftButtonDown(int ctrl, int shift, int X,
int Y) 
{
  //
  this->OldX = X;
  this->OldY = Y;

  // leave these in. what do they do?
  this->UpdateInternalState(ctrl, shift, X, Y);
  this->Preprocess = 1;
  this->FindPokedCamera(X, Y);

  if (this->State == VTKIS_START) 
    this->State = LML_ZSLICE;

  cerr << "state set to "<< this->State << "\n";


}

void InteractorStyleFlow::OnLeftButtonUp(int ctrl, int shift, int X, int
Y) 
{
  //
 this->UpdateInternalState(ctrl, shift, X, Y);
  //
  if (this->LeftButtonReleaseMethod) 
    {
    (*this->LeftButtonReleaseMethod)(this->LeftButtonReleaseMethodArg);
    }

  this->OldX = 0.0;
  this->OldY = 0.0;

  this->State = VTKIS_START;
  cerr << "state set to "<< this->State << "\n";

}

// Add LML_ZSLICE to this version of OnTimer (from
vtkInteractorStyleTrackball::OnTimer)
//----------------------------------------------------------------------------
// By overriding the RotateCamera, RotateActor members we can
// use this timer routine for Joystick or Trackball - quite tidy
//----------------------------------------------------------------------------
void InteractorStyleFlow::OnTimer(void) 
{
  cerr << "InteractorStyleFlow::OnTimer:  state = " << this->State <<
"\n";

  vtkRenderWindowInteractor *rwi = this->Interactor;
  switch (this->State) 
    {
    case LML_ZSLICE:
	// OnTimer is never called when State == LML_ZSLICE. why not?
	rwi->CreateTimer(VTKI_TIMER_UPDATE);
	this->ZsliceChanger();
	break;
    ...
    }
}


-- 
Lawrence M. Lifshitz, Ph.D.	    
Biomedical Imaging Group - University of Massachusetts Medical School
Phone: (508) 856-3392  	   email:    Lawrence.Lifshitz at umassmed.edu
FAX: (508) 856-1840	   web:	     http://invitro.umassmed.edu/~lml