[vtkusers] Mappers and vtkLookupTable

[Allen Sanderson]

Cheers,

Allen


Allen Sanderson
SCI Institute
University of Utah
www.sci.utah.edu



Hello,

A followup question with the vtkTubeFilter and vtkRibbonFilter. If the input vtkPolyData contains objects other than lines the filter strips those objects out only return the tubes or ribbons. Is there a way to prevent this from happening? Or does one need to handle that themselves? 


> 
> 
>> On Feb 16, 2016, at 3:44 PM, Cory Quammen <cory.quammen at kitware.com <mailto:cory.quammen at kitware.com>> wrote:
>> 
>> 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 <mailto: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 <http://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.
> 
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