[vtkusers] vtkLookUpTable transparency bug?

[Jon Payne]

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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