[vtkusers] Volume rendering Shading with dependent components

[Benoit Bleuze]

Hi list,

I have encountered this strange behaviour in VTK recently and wanted some knowledgeable vtk people to shade some light on it:

I am doing volume rendering of an rgba volume.
To do this I set the following 2 vtkVolume properties:

     vtkVolumeProperty::IndependentComponentsOff()
and  vtkVolumeProperty::ShadeOn()

I use the GPU Rendering: vtkSmartVolumeMapper::GPURenderMode

As a result, if I compile vtk in debug mode I stumble upon this failing assert call,
in vtkOpenGLGPUVolumeRayCastMapper.cxx, line 4159 in vtk 5.8.0 (in git at this time it's on line 4152),
in the following method:

void vtkOpenGLGPUVolumeRayCastMapper::PreRender(vtkRenderer *ren,
                                                vtkVolume *vol,
                                                double datasetBounds[6],
                                                double scalarRange[2],
                                                int numberOfScalarComponents,
                                                unsigned int numberOfLevels)
[...]
if ( vol->GetProperty()->GetShade() )
        {
        shadeMethod=vtkOpenGLGPUVolumeRayCastMapperShadeYes;
        assert("check: only_1_component_todo" && numberOfScalarComponents==1);
        }

[...]


If I run the same code in Release mode, nothing goes wrong and there is indeed shading performed on my rgba data.
Should this assert be removed, or is shading on dependent components not something to do?

Thank you for the insight.

Ben.