[vtk-developers] Bug in vtkCamera::Elevation

[Xabi Riobe]

Hi,

There is an issue in vtkCamera::Elevation if the angle is 90.

It is 100% reproductible with VS2013 if compiled in 64bits, otherwise the
rounding epsilon makes it work by chance.

I'm willing to fix it in GitLab but first i would like your opinion about
the best way to do it.

with a simple example of a plane in a renderer, and a call to
renderer->GetActiveCamera()->Elevation(90)

What happens in the call stack of vtkCamera::Elevation :
   vtkCamera::SetPosition()
   vtkCamera::ComputeViewTransform
   vtkPerspectiveTransform::SetupCamera

   vtkMath::Cross(viewUp,viewPlaneNormal,viewSideways);

where viewUp and viewPlaneNormal are both (0,1,0)  so viewSideways is
(0,0,0) leading to bad camera parameters.
Here comes the VS13+64bits configuration case, when with others,
viewSideways is luckily different than 0

What do you think of applying the rotation to the viewUp vector in
vtkCamera::Elevation before the call to SetPosition?
Should we put a warning in vtkPerspectiveTransform::SetupCamera
when vtkMath::Normalize returns 0?
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