[vtkusers] vtkLookUpTable transparency bug?

[Artem Babayan]

Aha, it is actor->GetProperty()->SetOpacity(...)

Yes, thanks a lot -- it did solve the problem.

Best wishes
Artem

On 12 August 2011 12:58, Artem Babayan <artem.paraview at googlemail.com> wrote:
> Hi, Jon
>
> You lost me here -- I think vtkActor does not have SetOpacity or
> SetAlpha methods (at least this is what the compiler says).
> vtkDataSetMapper does not have these methods as well.
>
> Best wishes
> Artem
>
> On 12 August 2011 12:54, Jon Payne <jpayne at hgl-dynamics.com> wrote:
>> SetOpacity, I mean.
>>>
>>> Hi Artem,
>>>
>>> But did you try setting the whole surface to be very slightly transparent?
>>> Not via the lookup table but calling SetAlpha(0.95) on the actor? Otherwise
>>> it will still draw everything, even the transparent coloured bits, as though
>>> they were opaque (hiding the pixels behind).
>>>
>>> Cheers,
>>> Jon
>>>>
>>>> Hi, Jon,
>>>>
>>>> I did assign alpha 0.5 to the 'invisible' part -- it appears, that
>>>> transparency works only for some subsets of possible graphics
>>>> positions -- see attached pictures.
>>>>
>>>> Thank you for trying to help, by the way.
>>>>
>>>> Best wishes
>>>> Artem
>>>>
>>>>> Hi Artem,
>>>>>
>>>>> I can't remember exactly but have you tried setting the alpha of the
>>>>> whole
>>>>> surface to 0.95? The reason is that somehow VTK/OpenGL needs to know to
>>>>> ignore the z-buffer value (I think) so that pixels behind other pixels
>>>>> which
>>>>> are now transparent are still drawn.
>>>>>
>>>>> Cheers,
>>>>> Jon
>>>>> On 12/08/2011 09:08, Artem Babayan wrote:
>>>>>>
>>>>>> Hi, Thomas
>>>>>>
>>>>>> If you look at the second picture, you will see, that some of the
>>>>>> 'colorful' graphic is covered by the white (or background color) field
>>>>>> -- this white bit is the part of the graphics which correspond to
>>>>>> 'undefined' values and have alpha=0. So it is not transparent -- I
>>>>>> cannot see remaining graphics through it.
>>>>>>
>>>>>> To make it more clear (or more confusing) -- with alpha=1  the first
>>>>>> picture would look like a colorful 'mountain' in the flat black
>>>>>> 'field' extended to the vertical boundaries of the domain. With
>>>>>> alpha=0 the black 'field' is of background color, so it is invisible
>>>>>> on the first picture, but if I tilt the graphics slightly backwards
>>>>>> (as on the second picture) part of the 'field' comes in front of the
>>>>>> 'mountain' and you can see, that it is not actually transparent.
>>>>>>
>>>>>> Best wishes
>>>>>> Artem
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 12 August 2011 08:42, Kilgus, Thomas<t.kilgus at dkfz-heidelberg.de>
>>>>>>  wrote:
>>>>>>>
>>>>>>> Hi Artem,
>>>>>>>
>>>>>>> I don't if I get you right, but the pictures look correct. If you set
>>>>>>> the
>>>>>>> alpha value of something to 0, you will see the color of the stuff
>>>>>>> behind
>>>>>>> it. I guess in your case there is nothing behind it and that's why the
>>>>>>> background color can be seen?
>>>>>>>
>>>>>>> Best regards
>>>>>>> Thomas
>>>>>>>
>>>>>>> -----Ursprüngliche Nachricht-----
>>>>>>> Von: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] Im
>>>>>>> Auftrag von Artem Babayan
>>>>>>> Gesendet: Donnerstag, 11. August 2011 19:13
>>>>>>> An: vtkusers at vtk.org
>>>>>>> Betreff: [vtkusers] vtkLookUpTable transparency bug?
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I am trying to visualise a 2D scalar field as a 3D 'landscape'. Some
>>>>>>> of
>>>>>>> the numbers are just indicators of 'undefined' values, so I do not
>>>>>>> want to
>>>>>>> show them at all.
>>>>>>>
>>>>>>> I set these 'undefined' numbers to the values which correspond to the
>>>>>>> first row of vtkLookUpTable and then assign this row 'transparent'
>>>>>>> alpha=0:
>>>>>>>
>>>>>>>     lut->SetTableValue(0, 0, 0, 0, 0);
>>>>>>>
>>>>>>> However, there are 2 problems:
>>>>>>>
>>>>>>> 1) This results in 'background' color, not 'transparent' -- see second
>>>>>>> picture -- the transparent part actually closes some part of the
>>>>>>> graphics.
>>>>>>> 2) On one Unix system I haven't even got transparency -- the
>>>>>>> 'transparent' part was drawn in black color (as corresponds to the
>>>>>>> table
>>>>>>> value).
>>>>>>>
>>>>>>> So am I doing something wrong here or is it a bug in vtkLookUpTable?
>>>>>>>
>>>>>>> Also, may be there is a smarter way not to show 'undefined' values?
>>>>>>>
>>>>>>> Best wishes
>>>>>>> Artem
>>>
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