[vtkusers] Re: Scalar color / LookupTable / Interpolation problem...

[David.Pont at ForestResearch.co.nz]

Hi Mark,
I presume you know this is in the bug tracker as feature request:
http://www.vtk.org/Bug/bug.php?op=show&bugid=818&pos=1  I see you can vote,
dont know if that helps? it is assigned and rated high priority.

I have implemented 1D textures as a set of 2 vtk classes that can be used
as a workaround. The classes must be inserted in the pipeline, but I too
would like to see this supported transparently (behind the scenes). The
concept is straightfoward but it will impact on lots of lines of code. Also
it would probably be implemented as a non-default option to avoid breaking
tons of vtk tests and exisiting applications. I would probably switch this
feature on 'always'.
I note in the posting you referred to there was a performance hit from
using textures, do you know if the suggestion of changing to 2D texture
helped? Anyway it looks like there may be an OpenGL solution using
'ColorTables', analagous to textures but not actually textures, but they
'might' cause problems with textures and other nice features...

  regards
    Dave P



|---------+--------------------------------->
|         |           Mark Asbach           |
|         |           <mark.asbach at post.rwth|
|         |           -aachen.de>           |
|         |           Sent by:              |
|         |           vtkusers-admin at vtk.org|
|         |                                 |
|         |                                 |
|         |           11/05/2004 20:54      |
|         |                                 |
|---------+--------------------------------->
  >------------------------------------------------------------------------------------------------------------|
  |                                                                                                            |
  |       To:       vtkusers at vtk.org                                                                           |
  |       cc:       I.deBoer at polytec.de, Steve Joyce <Steve.Joyce at sercoassurance.com>                          |
  |       Subject:  Re: [vtkusers] Re: Scalar color / LookupTable / Interpolation problem...                   |
  >------------------------------------------------------------------------------------------------------------|




Hi folks,

> We would like a solution for this as well for colouring finite element
> models.

Okay, so we are indeed a couple of people now using vtk for FE
visualization? That's a fine thing.

>> calculations. So OpenGL will shade red to green producing=20
>> yellow along the way which is not in your lookup table!
> Yes, right.. That is the problem!
>
> BUT.. there must be a solution on that one! Are we the only
> one needing this ? ;)

As Rainer already pointed out, using a texture map is the only solution
that works for true colour and complex shader models. Our own FE
visualizer works that way but we're also moving to VTK and need to keep
the functionality. In addition to Rainers comment I would like to ask
the VTK team if they could enable 1D textures soon and probably
integrate the functionality into the usual rendering process as an
(automatic?) feature of vtkLookupTable and the vtkActors /
vtkRenderers.

You can have a look at our code at

             http://imoose.sourceforge.net

or look into a posting that explains 1D textures for vertex colouring
in a compact form and with source code

             http://www.geocrawler.com/archives/3/1291/2000/7/50/3977584

That was our information source, too. Unfortunately I don't have the
time to implement this in VTK at the moment (new job) ... :-/

Good luck,

Mark


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