[vtkusers] Updating color transfer function for GPU volume

[Jim Peterson]

Eric and Shashwath,

I believe you will find the vtk pipeline is optimized to only process 
"new" data in the pipeline. Unfortunately there is no mechanism that 
automatically sets the last change time with a call that changes the 
content. What is required is a call to ->Modified() for any object with 
changed content. this includes changes to points, cells, scalars, 
transformations and maps.

I suggest you add a ->Modified() call to the affected pipeline objects 
to cause the ->Update() to recognize the need to re-evaluate the pipeline.

Hope that helps,
Jim

Shashwath T.R. wrote:
> Hi Eric,
>
> Try removing all points and modifying the same color transfer 
> function, instead of creating a new one... It seems to work for us.
>
> Shash
>
> On Tue, Dec 21, 2010 at 6:33 AM, Eric Foo <foo at iastate.edu 
> <mailto:foo at iastate.edu>> wrote:
>
>     Hi all,
>
>     Does anyone know how I can update the color transfer function for
>     a vtkOpenGLGPUVolumeRayCastMapper type volume?
>
>     The volume is constructed like so:
>
>     _volumeProperty = vtkVolumeProperty::New();
>     _volumeProperty->SetColor(_color);
>     _volumeProperty->SetScalarOpacity(_opacity);
>     _volumeProperty->SetInterpolationTypeToLinear();
>     _volumeProperty->ShadeOff();
>
>     _gpuVolumeMapper = vtkOpenGLGPUVolumeRayCastMapper::New();
>     _gpuVolumeMapper->SetImageSampleDistance(_imageSampleDistance);
>     _gpuVolumeMapper->SetSampleDistance(_sampleDistance);
>     _gpuVolumeMapper->AutoAdjustSampleDistancesOff();
>     _gpuVolumeMapper->SetInput(_voxels);
>
>     _volume = vtkVolume::New();
>     _volume->SetProperty(_volumeProperty);
>     _volume->SetMapper(_gpuVolumeMapper);
>
>     To swap between different predefined color transfer functions, I call:
>
>     _volumeProperty->SetColor(someNewColor);
>
>     This is where the problem starts. The only way the volume will
>     update to the new color is if I delete the current volume mapper
>     and then recreate it with the new color transfer function, which
>     is bad for performance. I've tried calling _volume->Update() and
>     _gpuVolumeMapper->Update(), which doesn't seem to work.
>
>     Any help or ideas would be appreciated. Thanks in advance!
>
>     eric
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