Hardware clipping planes in VTK

[Lisa Sobierajski Avila]

Hi David,

Since you have named them "ClippingPlanes" it does not seem necessary to
have a more general representation (because even if in the future OpenGL
does allow more general clipping functions you would have to change the
name anyway, right?). If vtkImplicitFunctionCollection is the best way to
store this internally, that's fine (although I think there is probably a
simpler way) but you might want to add access methods (add/remove clipping
plane) that do the error checking when you set the clipping plane rather
than at render time. (So when a user adds a plane you can make sure it is
truly a plane and that you have not exceeded the limit) What do you think?

Lisa


At 04:05 PM 6/29/99 -0400, David Gobbi wrote:
>Hi Lisa,
>
>It would be easy to to add the SetClippingPlanes method to
>vtkDataSetMapper (it will just call the same method in its
>internal vtkPolyDataMapper), so I will do that.
>
>I used vtkImplicitFunctions because it already existed, there
>is no collection of vtkPlanes.  Instead, an error is reported 
>at render time if any of the functions is not a plane, or
>if too many planes are specified.  (Who knows, future versions
>of OpenGL might allow more complicated clipping functions -- I
>prefer to keep things general).
>
> - David
>
>On Tue, 29 Jun 1999, Lisa Sobierajski Avila wrote:
>
>> Hello David,
>> 
>> Now that XGL and Starbase are gone, this seems like a good addition - at
>> least until we add some new graphics language that doesn't support hardware
>> clipping! :-)
>> 
>> Why did you chose to add these changes to vtkPolyDataMapper instead of
>> vtkDataSetMapper? It would seem that they could be added to
>> vtkDataSetMapper which would allow for clipping of more than just polydata.
>> And why did you add vtkImplicitFunctions instead of some other
>> specification that allows for only planes? The implicit function seems too
>> general - doesn't OpenGL require simple planes for hardware clipping?
>> 
>> Lisa Avila
>> 
>> 
>> At 02:53 PM 6/29/99 -0400, David Gobbi wrote:
>> >
>> >I have added hardware clipping planes to VTK, and would
>> >like to get some feedback before contributing the change
>> >to Kitware.
>> >
>> >All of the changes are limited to vtkPolyDataMapper, which has
>> >the following new methods:
>> >
>> >void vtkPolyDataMapper::SetClippingPlanes(vtkImplicitFunctionCollection)
>> >vtkImplicitFunctionCollection vtkPolyDataMapper::GetClippingPlanes()
>> >
>> >These allow you to specify up to 6 clipping planes which are
>> >handled by OpenGL.  This is equivalent to piping vtkPolyData
>> >through a set of vtkClipPolyData filters.  When you are moving
>> >the clipping planes around, doing the clipping in hardware 
>> >makes the rendering go several times faster.
>> >
>> > - David
>> >
>> >--David Gobbi, MSc                    dgobbi at irus.rri.on.ca
>> >  Advanced Imaging Research Group
>> >  Robarts Research Institute, University of Western Ontario
>> >
>> >
>> >
>>
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