Ho to check for left button single click event vs click and drag event

Support
1

I have a view with a vtkInteractorStyleTrackballCamera interactor. When you drag the mouse (left click and drag) it rotates the object. This is good. Now I want to return the mouse coordinates when the user does a single left button click and release.

At the moment, when I add a vtkCallbackCommand with the vtkCommand::KeyPressEvent the rotational ability of the object gets disabled. Any thoughts?

2

Hi, Daniel,

Do you extend vtkInteractorStyleTrackballCamera? If so, you need to forward the event to the superclass: vtkInteractorStyleTrackballCamera::OnLeftButtonDown(); in your class if you wish to maintain the original behavior in addition to the one of your code.

regards,

Paulo

3

Hi Paulo,

Thanks for your response. I have managed to find a solution to my problem. Not sure if it is the best one but it works.

I prefer to use observers then I do not have to do the whole inheritance thing. I added a callback method to my vtkInteractorStyleTrackballCamera object using the vtkCommand::LeftButtonPressEvent and the vtkCommand::LeftButtonReleaseEvent (on the same method).

I then record the mouse pointer location on the LeftButtonPressEvent and compare it to when the mouse button is released (LeftButtonReleaseEvent). If they match I then do my stuff. That is it.

Regards,
Daniel

1 Like
4

Hi, Paulo.I have a question. I Do not extend vtkInteractorStyleTrackballCamera,because I use C# program Kitware.VTK.When I drag the mouse (left click and drag) it rotates the object,but the event function: renWinInteractor.LeftButtonReleaseEvt+=LeftButtonReleaseEvt can not capture Button Release at once , As you say,in C++ program ,just need to forward the event to the superclass: vtkInteractorStyleTrackballCamera::OnLeftButtonDown(),I want to know how to realize this in Kitware.VTK using event function
regards

5

Hello,

You first need to derive vtkInteractorStyleTrackballCamera to “forward the event to the superclass”. C# certainly has an inheritance mechanism.

best,

PC

6

Not sure about what’s available from Kitware’s C# VTK. If you’re doing it without extending the interactor style, it is best to listen to the interactor for events and then forward the event to the interactor style.

Here’s an example in C++, it should apply to Python and C# assuming VTK C# exposes the enums from vtkCommand and functions from interactor style.

void OnLeftButtonDown(....)
{
   // ...
   // switch style could be a special case, so just to be safe, let's handle it.
   auto* style = vtkInteractorStyle::SafeDownCast(interactor->GetInteractorStyle());
   if (auto* switchableStyle = vtkInteractorStyleSwitch::SafeDownCast(style))
   {
      switchableStyle->GetCurrentStyle()->OnLeftButtonDown();
   }
   else
   {
      style->OnLeftButtonDown();
   }
}

void OnLeftButtonUp(....)
{
   // ...
   // switch style could be a special case, so just to be safe, let's handle it.
   auto* style = vtkInteractorStyle::SafeDownCast(interactor->GetInteractorStyle());
   if (auto* switchableStyle = vtkInteractorStyleSwitch::SafeDownCast(style))
   {
      switchableStyle->GetCurrentStyle()->OnLeftButtonUp();
   }
   else
   {
      style->OnLeftButtonUp();
   }
}
interactor->AddObserver(vtkCommand::LeftButtonPressEvent, OnLeftButtonDown);
interactor->AddObserver(vtkCommand::LeftButtonReleaseEvent, OnLeftButtonUp);
7

Hello,

In case it’s not clear, C++, I do this:

class MyInteractor : public vtkInteractorStyleTrackballCamera {
public:
   ...
   void OnLeftButtonDown() override {
      do_my_stuff();
      // Forward the event to the base class to keep current behavior.
      vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
   }
   ...
private:
   ...
protected:
   ...
};

I think translating this to C# is straightforward.

best,

PC