[vtkusers] vtkImageSlice using UserTransform

[David Gobbi]

Hi Miro,

The PokeMatrix() method is used internally by VTK during pick
operations and render operations, so I advise against using it in your
own code.  By doing so, you might interfere with VTK's own internal
state machinery.  Also, all the PokeMatrix(matrix) does is cache the
current actor state (i.e. position, orientation, UserMatrix, etc) and
then replace the UserMatrix with the supplied matrix.   So for your
purposes, you can just call SetUserMatrix() directly to achieve the
same effect.  And, by calling SetUserMatrix() directly, you won't be
disturbing the aforementioned actor state cache.

Also, I recommend calling SetUserMatrix(NULL) instead of
SetUserMatrix(identity).  Having the user matrix set to NULL allows
the rendering machinery to enable certain optimizations.
Incidentally, calling PokeMatrix(NULL) causes the actor to restore its
state from its internal cache (i.e. this is what VTK's internally
machinery does to restore the actor state, and this is why calling
PokeMatrix() yourself can cause problems for VTK).

With respect to vtkImageSlice moving unexpectedly, I suspect one of
the following:
1) your interaction is actually moving the camera in addition to
moving the mesh (or instead of moving the mesh)
2) your callbacks are setting the UserMatrix on the vtkImageSlice
(i.e. what do you do to guarantee that  this->InteractionProp is never
the vtkImageSlice?).

So in general, if you haven't already done so, verify that your own
callbacks are being called, and also verify that the mouse callbacks
of VTK's own interactor style are _not_ being called.

  - David



On Tue, Nov 26, 2013 at 3:23 PM, Miro Drahos <mdrahos at robodoc.com> wrote:
> Hi David,
> thanks for the response.
> I do not call SetUserMatrix(m) on vtkImageSlice, that's why I am quite
> surprised to see it changing.
> I am only manipulating the UserMatrix of vtkActor (of the surface model).
> I was using actor->PokeMatrix(m) on each mouse move, let me illustrate with
> some code:
> //---------------------------------------------------
> // triggered by means of vtkCommand::MouseMoveEvent
> void PickImplantCallback::Pan()
> {
>     VTK_CREATE(vtkTransform, t);
>     // ... build a transform based on interaction event positions
>
> this->InteractionProp->PokeMatrix(t->GetMatrix());
>
>     this->Render();
> }
>
> //---------------------------------------------------
> // triggered by means of vtkCommand::MouseButtonReleaseEvent
> void PickImplantCallback::OnButtonUp()
> {
>     // transform the actual polydata
>     VTK_CREATE(vtkTransform, t);
> t->SetMatrix(this->InteractionProp->GetMatrix());
>
>     //... use vtkTransformPolyDataFilter to transform the vtkPolyData object
>
>     // reset the actor's matrix:
>     VTK_CREATE(vtkMatrix4x4, identity);
>     this->InteractionProp->PokeMatrix(identity);
>
>     // update the state vars, other cleanup
>
>     this->Render();
> }
>
> This callback class doesn't even know about the vtkImageSlice, yet the
> vtkImageSlice objects update their textures as the InteractionProp's matrix
> is being updated, and then on button up reset the view that was before
> interaction (as the InteractionProp's matrix is reset to identity).
>
> I have been using actor->PokeMatrix(m), which internally sets the
> UserMatrix; I tried to change all actor->PokeMatrix(m) calls to
> actor->SetUserMatrix(m) but that doesn't change anything.
>
> Best,
> Miro
>
>
>
> On 11/26/2013 01:25 PM, David Gobbi wrote:
>>
>> Hi Miro,
>>
>> Let me see if I understand... you have a vtkImageSlice, and you have a
>> vtkActor, and you have a matrix.  You call SetUserMatrix(matrix) on
>> the vtkImageSlice, and you call SetUserMatrix(matrix) on the vtkActor.
>>   Finally, you use the vtkRenderWindowInteractor to interact with the
>> vtkActor.
>>
>> Why not call a DeepCopy on the original matrix, so that the
>> vtkImageSlice and the vtkActor each has its own matrix?
>>
>> matrix2 = vtkMatrix4x4::New();
>> matrix2->DeepCopy(matrix);
>> imageSlice->SetUserMatrix(matrix2);
>> actor->SetUserMatrix(matrix);
>>
>>    David
>>
>>
>>
>> On Mon, Nov 25, 2013 at 6:31 PM, Miro Drahos <mdrahos at robodoc.com> wrote:
>>>
>>> Hi David,
>>> I was hoping you could advise on an issue I am experiencing with
>>> vtkImageSlice.
>>> Together with the sliced image I am rendering a surface model in the
>>> scene,
>>> that the user needs to be able to pick and interact with. When the
>>> surface
>>> (~ 20000 vertices) is picked, I call SetUserMatrix() on its actor to
>>> render
>>> the translation or rotation that user is performing in real-time.
>>> This, however has a side-effect that vtkImageSlice uses the matrix and so
>>> the displayed slice is modified during the interaction.
>>> Is there a way to tell vtkImageSlice not to use the UserMatrix? Or
>>> perhaps
>>> is there a better way to set the transformation matrix on the surface/its
>>> actor to render the interaction?
>>> I turned SliceAtFocalPointOff() and SliceFacesCameraOff() but that
>>> doesn't
>>> change this behavior.
>>> Thank you!
>>> Miro
>>>
>