[vtk-developers] bounds calculation in vtkActor

[Rusty Blue]

Folks,

 

We're setting the UserMatrix of an actor to... surprise, surprise...
transform the actor.  Nothing exciting, right?  

 

Wrong, because the last row of our matrix is not the trivial [0 0 0 1].
This is handled well enough in OpenGL, but the bounds calculation (in
vtkActor::GetBounds()) is seriously wrong because it is doing a linear
transformation of the bbox it gets from the mapper (Transform is a
vtkLinearTransform):

 

    fptr = bbox;

    for (n = 0; n < 8; n++) 

      {

      this->Transform->TransformPoint(fptr,fptr);

      fptr += 3;

      }

 

The easiest fix I found for the issue was the following (force call to
InternalTransformPoint of vtkHomogeneousTransform):

 

    fptr = bbox;

    this->Transform->Update();

    for (n = 0; n < 8; n++) 

      {

 
this->Transform->vtkHomogeneousTransform::InternalTransformPoint(fptr,fptr);

      fptr += 3;

      }

 

The change doesn't cause any tests to fail (for me)... and it seems like a
reasonable change (perhaps should be made in vtkImageActor and vtkVolume as
well?)... but I wanted to put it out there (before I committed and pushed
the change), because it is seriously likely that I'm not considering some
other special "situations", or perhaps the "right" way to fix this, or ????

 

Rusty

 

 

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