Unable to get `vtkCamera*` from `vtkMRMLCameraNode*` (from C++ only)

Development
1

Hi,

From module widget (qSlicerMyModuleWidget.cxx) I was trying to get active camera of a 3D view and apply transform to it.

The only two working ways to do that were:

  qMRMLThreeDWidget* threeDWidget = app->layoutManager()->threeDWidget('View1');
  vtkCamera* camera =
      threeDWidget->threeDView()->renderer()->GetActiveCamera();

and

  qMRMLThreeDWidget* threeDWidget = app->layoutManager()->threeDWidget('View1');
  vtkCamera* camera =
     threeDWidget->threeDView()->activeCamera();

But there are other high level ways to get camera from vtkMRMLCameraNode.
For example:

  vtkMRMLCameraNode* cameraNode =
      threeDWidget->threeDView()->cameraNode();

  if (!cameraNode)
    qCritical() << Q_FUNC_INFO << ": No active camera node found";

  vtkCamera* camera = cameraNode->GetCamera();  // there I get an exception "read access violation" even the exception abovev was not triggered

I get an exception on line where I’m trying to get vtkCamera*. Is it normal behaviour?

Also I’ve tried to get comeras’s logic and then retrieve from that camera and apply transform to camera (preliminary I linked to the vtkSlicerCamerasModuleLogic):

  vtkSlicerCamerasModuleLogic* camerasLogic =
    vtkSlicerCamerasModuleLogic::SafeDownCast(this->moduleLogic("Cameras"));
  if (!camerasLogic)
    qCritical() << Q_FUNC_INFO << ": Cameras module is not found";

  vtkMRMLCameraNode* cameraNode =
      camerasLogic->GetViewActiveCameraNode(viewNode);

  if (!cameraNode)
    qCritical() << Q_FUNC_INFO << ": No active camera node found";

  vtkCamera* camera = cameraNode->GetCamera();

  if (!camera)
    qCritical() << Q_FUNC_INFO << ": No active camera found";

  vtkNew<vtkTransform> transform;
  transform->Scale(2, 1, 1);
  camera->SetModelTransformMatrix(transform->GetMatrix());    // here I gen an exception read access violation: `vtkObject::GetDebug()`

I get an exception now only when I try to apply transform.

All of this seemed to me strange so I decided to ask here… perhaps I don’t understand how vtkMRMLCameraNode is initialized?

By the way python example script works fine

2

All the code snorts above shows work. Probably your try to access the wrong objects, or access them to early, or from the wrong thread. Can you send a Github link to your module so that we can see the complete context of the method calls?

3

Yes, here is the link to an extension I just uploaded to github.
I work with SlicerCAT but the module Zoom depends on the native Slicer (you don’t need other modules).

The module is in progress.
You can find three GainWidgets (slider+spinbox). Try to use this widget for 3D view (only 3D view widgets are connected for now). I think you will understand what this widget is aimed for and if the community found it useful I could later add this widget to CTK library

4

The Zoom module works well for me. Probably you have memory corruption because of using outdated DLLs - most likely due to either an incomplete build or because you have copied DLLs around.

There is already a slider+spin widget in CTK: ctkSliderWidget. Instead of creating a new widget maybe you could improve this existing one.

1 Like
5

You are right, I have rebuilt the solution and now there is no problem to get the camera.
I didn’t have an idea that the reason is outdated libs…
Thank you!