[vtkusers] Mappers and vtkLookupTable

[Cory Quammen]

Allen,

I don't know of a way to set the line width based on a variable in
stock VTK. Maybe you could do something with a custom geometry shader,
which you can set in the OpenGL2 backend version of
vtkOpenGLPolyDataMapper via SetGeometryShaderCode(const char*).

Another approach could be using vtkTubeFilter to automatically set the
radius of the cylinders. The input to this filter should be a set of
line segments with point data with your variable for each line defined
at each endpoint of the line.

HTH,
Cory

On Tue, Feb 16, 2016 at 5:32 PM, Allen Sanderson <allen at sci.utah.edu> wrote:
> Thanks David, we thought that was the case.
>
> Let me ask a somewhat parallel question. When rendering lines one typically
> sets a line width and sends the geometry downstream. The lines will be
> colored base on a variable but the line width is constant. At the same time
> when doing point glyphs we set the color and size based on a variable. If we
> wanted to vary the line width using a variable is our only choice to use a
> cylinder?
>
> Cheers,
>
>
> Allen
>
>
>
> Allen Sanderson
>
> SCI Institute
>
> University of Utah
>
> www.sci.utah.edu
>
>
>
>
> On Feb 16, 2016, at 12:20 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>
> Hi Allen,
>
> You are correct, vtkLookupTable does not provide a way of doing this.
>
> I'm not sure what work-arounds there are for geometry, but for images
> you can map the RGB and A separately, and then combine them into
> RGBA with vtkImageAppendComponents.
>
>  - David
>
>
> On Tue, Feb 16, 2016 at 11:48 AM, Allen Sanderson <allen at sci.utah.edu>
> wrote:
>>
>> Hello,
>>
>> We are trying to render geometry using a lookup table for the RGB value
>> using one scalar variable, but we want to use a secondary scalar variable
>> for determining the opacity.  Something like the following:
>>
>> RGB -> variable one
>> A -> variable two
>>
>> In looking through the VTK 6 documentation on mappers we have not found
>> anything that leads us to believe this functionality is possible. But we
>> have done an exhaustive search.
>>
>> If it is possible we would greatly appreciate pointers. Thanks.
>>
>>
>>
>> Cheers,
>>
>> Allen
>>
>>
>> Allen Sanderson
>> SCI Institute
>> University of Utah
>> www.sci.utah.edu
>
>
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-- 
Cory Quammen
R&D Engineer
Kitware, Inc.