performance of clipping methods

[David Gobbi]

Hi John,

vtkClipPolyData does all its work in software written by the VTK folks,
while vtkPolyDataMapper->AddClippingPlane uses OpenGL to do the clipping.

On a graphics board which supports it, method 2 will do the clipping in
hardware.  Depending on the implementation, though, the clipping will be
done every time the scene is rendered.

Conversely, using method one, the clipping is usually only done once,
and then the clipped geometry is rendered over and over again without
being re-clipped.

So even though vtkPolyDataMapper->AddClipping plane actually does the
clipping many times faster than vtkClipPolyData in general, for static
geometry (i.e. the clipping plane doesn't move around) vtkClipPolyData
might give better performance.

 - David

--David Gobbi, MSc                    dgobbi at irus.rri.on.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario

On Tue, 5 Oct 1999, John Washbourne wrote:

> I seem to experience a disparity in performance between two different
> clipping methods.
> 
> Method 1: vtkClipPolyData
> 
> Method 2: vtkPolyDataMapper->AddClippingPlane
> 
> 
> The first method is by far faster on this platform (vtk nightly 2.4; SUN
> ultra 60 creator 3D; OpenGL 1.2). Can this be due to different
> internal/hardware implementations? My speed tests consist of simply
> changing the pipeline from method 1 to method 2 and leaving all else the
> same.
> 
> Can anyone else verify similar behavior?
> 
> Regards,
> 
> john
> 



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