[vtk-developers] Bug in scalar color mapping?

[Utkarsh Ayachit]

David,

Try the attached patch and then set
SetScalarMaterialModeToAmbientAndDiffuse() on the mapper.
ScalarMaterialMode is the thing here. When set to
SetScalarMaterialModeToDefault(), which is the default, it determines
which material component should track the scalar color based on which
coefficient is greater (see vtkOpenGLScalarsToColorsPainter.cxx:175).
The patch fixes an issue where the painter was not respecting the
material mode set on the mapper.

Utkarsh

On Mon, Sep 8, 2014 at 8:15 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> Hi Utkarsh,
>
> Thanks for the reply.  If I use this:
>
>   mapper->InterpolateScalarsBeforeMappingOff();
>
> then the result is exactly the same as it was before I reverted that commit.
>
>
> If I use this:
>
>   mapper->InterpolateScalarsBeforeMappingOn();
>
> then the result looks like the attached image, i.e. like it did in my previous
> email with property->SetAmbient(0.49), property->SetDiffuse(0.51), but when
> I reverse these I don't get the greyscale ambient lighting like in the
> right side
> of the image from my previous email.
>
>
> Still, I don't get what I expect unless I set one of either the ambient or the
> diffuse coefficient to zero.  Whenever they are both nonzero, I get the wrong
> result.
>
>  - David
>
>
> On Mon, Sep 8, 2014 at 5:17 PM, Utkarsh Ayachit
> <utkarsh.ayachit at kitware.com> wrote:
>> This sounds familiar.
>>
>> Can you try reverting the following commit and see if that makes any difference:
>>
>> commit daf8c6e76ec7bb02f56dda17ce260141b7e960a5
>> Author: Utkarsh Ayachit <utkarsh.ayachit at kitware.com>
>> Date:   Fri Jul 18 15:30:37 2014 -0400
>>
>>     BUG #14828: Keep surface color from interacting with scalar color.
>>
>>     When using scalar coloring, if vtkScalarsToColorsPainter decided to use
>>     a texture for mapping the scalars to colors, we ended up with the
>>     surface color bleeding through the texture. This commit ensures that
>>     such bleeding is avoided.
>>
>>     We don't simply use glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,
>>     GL_REPLACE), since that results in the diffuse highlights being lost.
>>     By enabling GL_COLOR_MATERIAL and calling glColor3f(1,1,1), we follow
>>     the same lighting/coloring path as we would when not using the texture
>>     for scalar coloring.
>>
>>     Change-Id: I9c4db15dd0db699d5d045fa7ae27696d18828988
>>
>>
>> Utkarsh
>>
>> On Mon, Sep 8, 2014 at 4:55 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> Any comments on the "scalar color mapping" problem that I sent to the
>>> list last week?
>>>
>>>  - David
>>>
>>>
>>> On Thu, Sep 4, 2014 at 5:33 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>> I've run into very odd behavior when I use Ambient and Diffuse
>>>> coefficients in combination with vtkDataSetMapper.  This is with
>>>> VTK master.
>>> [ snip ]
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