[vtkusers] vtkCamera::SetPosition causes delayed rendering?

[David Doria]

On Tue, Jul 26, 2011 at 5:54 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi David,
>
> You should never, ever call renderer->Render().  That method is only
> meant to be called by the vtkRenderWindow.  The documentation says
> so quite clearly.  By calling it you are probably causing some timestamps
> to be set (indicating that all actors in the renderer have rendered), but
> you
> aren't actually doing any rendering.  Then, when you call
> renderWindow->Render() it sees that those timestamps have been updated
> and thinks that there is nothing to be done.
>
> Also it is a good idea to always set the ViewUp when setting the
> Position and FocalPoint.  All three are needed in order to uniquely
> define the view transform.
>
>  - David


Thanks for pointing that out. After removing those calls, it works properly:

  vtkCamera* camera = renderer->GetActiveCamera();
  camera->SetPosition(450, 100, 100);
  camera->SetFocalPoint(200, 0, 0);
  camera->SetViewUp(0, 0, 1);

  renderWindow->Render();
  renderWindowInteractor->Start();

However, if I have called renderWindow->Render(); before positioning the
camera, even if I call Modified() on the renderer and renderWindow before
the next Render() call, the output is still incorrect before an interaction
occurs:

  renderWindow->Render();

  vtkCamera* camera = renderer->GetActiveCamera();
  camera->SetPosition(450, 100, 100);
  camera->SetFocalPoint(200, 0, 0);
  camera->SetViewUp(0, 0, 1);

  renderer->Modified();
  renderWindow->Modified();
  renderWindow->Render();
  renderWindowInteractor->Start();

Does this make sense?

Thanks,

David
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