[vtkusers] Reverse clipping box

[Christopher Mullins]

Hi Julien,

Thanks for the suggestion, it's clear that this is one place where clipping
planes are being computed.  However these volume mappers are not supported
on my architecture (Mac OS X). So the SmartVolumeMapper is using
the vtkFixedPointVolumeRayCastMapper.  So would it be correct to look at a
corresponding function in this mapper [1] ?

vtkClipVolume appears to have my functionality in mind, but its Update()
function returns a vtkUnstructuredGrid [2], which makes it seem like this
is not what I should use (I'm operating on vtkImageData).

[1]
https://github.com/Kitware/VTK/blob/master/Rendering/Volume/vtkFixedPointVolumeRayCastMapper.h#L709
[2] http://www.vtk.org/doc/release/4.0/html/classvtkClipVolume.html#a19


On Mon, Apr 22, 2013 at 10:19 AM, Julien Finet <julien.finet at kitware.com>wrote:

> Hi Chris,
>
> You would need to look at the 2 classes: vtkGPUVolumeRayCastMapper and
> vtkOpenGLGPUVolumeRayCastMapper.
> Some option would need to be added to the classes to handle inside
> cropping (vs outside clipping).
> j.
>
>
> On Sun, Apr 21, 2013 at 10:54 PM, Christopher Mullins <
> christopher.mullins at kitware.com> wrote:
>
>> Hi all,
>>
>> My question is probably fairly simple.  I'd like to implement something
>> like a reverse clipping box.  Instead of rendering everything inside the
>> box and clipping outside the box, I'd like to render what is outside the
>> box and clip what is inside the box.
>>
>> My code is almost exactly the SmartVolumeMapper example [1].  I've been
>> able to create a regular clipping box with the vtkBoxWidget, and placing
>> within a callback:
>>
>> vtkPlanes *planes = vtkPlanes::New();
>>  boxWidget->GetPlanes(planes);
>> volumeMapper->SetClippingPlanes(planes);
>>
>> There exists a function called boxWidget->InsideOutOn();, but it appears
>> this was not made with my use case in mind.  I've also tried (in the
>> callback function) manually getting each plane from the boxWidget and
>> reversing each normal - but this also does nothing.
>>
>> Does anyone have an idea of where I should look?  I've looked into
>> vtkClipVolume, but I'm not sure what the point is of using this, if the
>> volume mapper will accept clipping planes.
>>
>> Thanks for all your help,
>>
>> [1]
>> http://www.vtk.org/Wiki/VTK/Examples/Cxx/VolumeRendering/SmartVolumeMapper
>>  --
>> Christopher Mullins
>> R&D Engineer
>> Kitware Inc.,
>> 919.869.8871
>>
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-- 
Christopher Mullins
R&D Engineer
Kitware Inc.,
919.869.8871
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