[vtkusers] vtkLookUpTable transparency bug?

[Artem Babayan]

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
>