[vtkusers] vtkColorTransferFunction and opacity

[Lisa Avila]

Hi Steve,

I think this Alpha value is not used because it is part of the superclass 
vtkScalarsToColors and vtkColorTransferFunction was not originally a 
subclass of this class. It can be used - but I suspect you will need to 
test that the alpha value is being set everywhere it needs to be set. This 
also only allows you to have a single opacity for the whole image - and I 
think what people want is an opacity per scalar value. What we real need is 
to associate a vtkPiecewiseFunction with a vtkColorTransferFunction for 
this - of course these are separately specified in the vtkVolumeProperty 
for volume rendering so this could be confusing...

Lisa


At 10:03 AM 1/28/2004, Steve Joyce wrote:
>Hi,
>
>Setting the opacity of actors does not work when using a
>vtkColorTransferFunction as the colour lookup table. This is because the
>alpha value for a colour is always returned as 255 by
>vtkColorTransferFunction.
>
>As a fix for this I replaced the places where this occurred in
>vtkColorTransferFunction  with
>(unsigned char)(this->GetAlpha() * 255.0)
>or
>(unsigned char)(self->GetAlpha() * 255.0)
>as appropriate.
>
>This seemed to work for me, so I was wondering why it was fixed at 255
>in the first place. Am I doing the wrong thing?
>
>Thanks,
>Steve
>
>
>
>
>
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