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<p class="MsoNormal"><span lang="EN-US">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I have an issue with color mapping using scalar-interpolation-before-mapping, while rendering off-screen. The attached python script demonstrates the issue. The script defines a bar with linear increasing point-scalars.
These are then rendered using a lookup table containing four colors. This work fine when rendering on-screen, but off-screen the number of colors is larger than the number of colors in the on-screen image. This problem occurs with VTK6.3.0 on both windows
and linux (using vncserver) platforms. With VTK6.2.0 we saw the same anomaly but only on our windows machines.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Debugging (on Linux + VNC server) I found that the root cause of this difference seems to be vtkOpenGLTexture, which will determine whether non-power-of-two textures are supported. If not it will resample the texture
map to increase the number of textures to a power of two. I suspect this resampling produces the additional colors.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I registered this in the bug tracker (<a href="http://www.vtk.org/Bug/view.php?id=15734">issue 15734</a>) and reported the OpenGL capabilities there.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">When I load the data into ParaView 4.3.1 (on windows) however, I can render the image, and also save a screen shot that shows the proper color mapping, so apparently it is possible after all.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">This issue is at the moment blocking our transition to VTK6.3.0 (which we need because it contains fixes to some other issues) because image tests use the off-screen rendering feature. Could someone please help to determine
a workaround or fix, and/or explain how ParaView manages to get the color mapping right?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks a lot for your help!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Andreas <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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