[vtkusers] Re: deriving from vtkActor to add an ID (was: A question)

[Wiebke Timm]

Hi again!

Replying to my own post because just now I found out my answer was kind 
of wrong although in the first place the solution might have worked. I 
hope Luke Hua is still reading...

The question was how to extend a vtkActor to have an int more to hold 
an ID. Maybe some more experienced users could have a look because I'm 
still not sure how to extend a vtkSomething in an orderly manner.

My answer to that question was the following:

On 09.03.2004, at 10:31, Wiebke Timm wrote:

> You can extend vtkActor to have an ID. Did that and it works 
> flawlessly. Just use the extended vtkActor instead of the original. 
> When your picker/renderer returns an actor you can get the ID easily. 
> If you don't want to set that ID yourself you can add a static 
> variable that "counts" actors, i.e. it has to be incremented inside 
> the New() method, then set the ID accordingly.

This is still true. But the way _how_ this has to be done was wrong - I 
wonder why nobody spoke up... :

> vtkMyActor.h looks like this:
>
> #ifndef MYACT_H
> #define MYACT_H
>
> #include <vtkActor.h>
>
> class vtkMyActor : public vtkActor {
>    public:
>       int GetID();
>       void SetID(int id);
>       static vtkMyActor* New();
>       void Delete();
>
>    private:
>       int id;         // id of this glyph's actor
>
> };
> #endif
>
>
>
> vtkMyActor.cc looks like this:
>
> #include "vtkMyActor.h"
>
> vtkMyActor* vtkMyActor::New() {
>    vtkActor::New();
> }
>
> void vtkMyActor::Delete() {
>    vtkActor::Delete();
> }
>
> int vtkMyActor::GetID() {
>    return this->id;
> }
>
> void vtkMyActor::SetID(int id) {
>    this->id = id;
> }

Got a few seg faults at the end of my vtkqt program, valgrind reported 
memory leaks of 4 byte size (that's an int...) when I used the GetID() 
and SetID(int id) methods. That's because above

vtkActor::New();

inside the overwritten New() method doesn't allocate memory for that 
int!

Luke, did your version you posted have that leaks (should have if I 
read it correctly)?


Also I read in the vtk Users Guide that I have to derive a new factory 
from vtkObjectFactory, register the override of vtkActor with 
vtkMyActor and use some macros to get a create method to work. Isn't 
there an easier and shorter way to just add an int to a class... ??? I 
don't need any dynmically loaded classes during runtime.
I also thought about writing a wrapper class that holds the int ID 
_and_ the vtkActor without extending vtkActor. That would be shorter 
but kind of dirty in my understanding.

The book also says you have to implement the copy constructor, the 
operator=, and some other methods when deriving from a vtk class, but 
in the "own factory" example these methods aren't implemented. So now 
I'm confused _which_ methods really _have to_ be implemented and which 
are optional. (In general the book is a little cursory IMO.)

There have to be people who already derived from vtk classes, I'm sure. 
So does any of you have any recommendations...?

Ciao!
    Wiebke