[vtkusers] Updating color transfer function for GPU volume

[Eric Foo]

Hi Jim,

Thanks for your response. Calling Modified() in the color transfer function object did the trick.

eric

On Dec 21, 2010, at 6:02 AM, Jim Peterson wrote:

> 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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