[vtkusers] vertex colors

[dean.inglis at camris.ca]

thanks Amy!  

I tried assigning random numbers 
(vtkMath::Random(0,1)) to a vtkDoubleArray 
and it did work: I got a mix of r,g,b etc. all
over the mesh. I figured out what was unexpected
and I am getting what I expect now.  Also, it
seems that opacity values are ignored (fourth 
element of tuple 4 in my case) so that one
has to set opacity (globally and not per vertex)
through an actor's property.  If I'm wrong on this
please correct...

Dean

> Hi Dean,
> 
> The problem is that vtkMappers can do what you're trying to do only if 
> the type of the scalars is unsigned char. If the scalars are of any 
> other type, they are passed through a lookup table to determine the 
> color associated with a particular scalar value.
> 
> If you create your colors array as a vtkUnsignedChar array (and thus 
> using the range 0 - 255 instead of 0 - 1), then if ScalarVisibility in 
> the mapper is set to 1 and ColorMode is set to VTK_COLOR_MODE_DEFAULT, 
> you should get what you're looking for.
> 
> If you don't have control over the creation of the colors array, then 
> you'd need to do something like vtkImageShiftScale, but for vtkPolyData 
> to convert your colors array to the appropriate type. I don't think such 
> a class exists in VTK, but it wouldn't be hard to write.
> 
> - Amy
> 
> Dean Inglis wrote:
> > I have a triangluar surface mesh with 
> > rgba color data associated with each
> > vertex (point) of the polydata mesh:
> >
> > vtkDoubleArray* colors = vtkDoubleArray::New();
> > colors->SetNumberOfComponents(4);
> > for( int i = 0 i< nverts; i++)
> >   {
> >   colors->SetTuple4(i, r[i], g[i], b[i], o[i] );
> >   }
> >
> > // where r,g,b,o are double precision red green blue and opacity values
> > // ranging from 0 - 1
> >
> > vtkPolyData* surf =  vtkPolyData::New();
> > surf->SetPoints(surfPoints);
> > surf->SetPolys(surfCells);
> > surf->GetPointData()->SetScalars(colors);
> >
> > How do I get the polydata mapper to use these
> > scalars to color the mesh?  Is it...
> >
> > mapper->SetInput(surf);
> > mapper->SetScalarVisibilityOn();
> >
> > ? I'm not getting what I expect.
> >
> > thanks,
> > Dean