[vtkusers] Re: point picking question

[Obada Mahdi]

Hi Anja!

On Aug 31, 2006, at 7:08 PM, Anja Ende wrote:
> Ok, I figured out that the GetMapperPosition() was the answer to my  
> question. However, I have another problem now...
>
> I included the following code in my left mouse button handler and  
> it causes a segmentation fault!!!
>
> vtkRenderWindowInteractor *rwi = this->Interactor;
>  if (rwi)
>  {
>            vtkPointPicker *picker = (vtkPointPicker *)rwi->GetPicker 
> ();
>             picker->Pick(x, y, m_viewer->GetCurrentSlice(), this- 
> >CurrentRenderer);
>
>             std::cout << "PointId: " << picker->GetPointId() << "\n";
>             std::cout.flush();
>              if (picker->GetPointId() != -1)
>              {
>                         double * ptActual, *ptMapped;
>                         picker->GetSelectionPoint(ptActual); // OK
>                         picker->GetMapperPosition(ptMapped); //  
> CRASHES!!!!!
[...]

In case this is not pseudo-code with the "double *ptActual,  
*ptMapped;" added for clarification:

It seems that you mixed up the semantics of those "Get...(double*)"  
calls a bit -- you can either do

| double *ptActual, *ptMapped;
|
| ptActual = picker->GetSelectionPoint();
| std::cout << ptActual[0] ...

accessing some internal storage of the picker, or have it copy the  
return value to the location you specify as parameter, like

| double ptActual[3], ptMapped[3];
|
| picker->GetSelectionPoint(ptActual);
| std::cout << ptActual[0] ...

In the code above, results are written to the address pointed to by  
`ptActual' and `ptMapped', which are undefined and might hold about  
any value at run time.


HTH,

Obada