# Multiple viewports and LIC surfaces
**URL:** https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398
**Category:** Support
**Tags:** python
**Created:** [April 25, 2026, 5:32pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398 "2026-04-25T17:32:32Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Carlos\_Montilla](https://discourse.vtk.org/u/Carlos_Montilla)
#### Post date: [April 25, 2026, 5:32pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398/1 "2026-04-25T17:32:32Z")
Hello,
I am trying to build a split view configuration using a single vtkRenderWindow and multiple viewports. Each viewport should render a different dataset using a SurfaceLICMapper, however only the bottom left pane shows anything. The other panes are empty. I checked with Claude Code and it seems the root issue is that the vtkSurfaceLICMapper renders incorrectly if the viewport’s y\_min \> 0. With its help, I made a few modifications to the VTK source code and they fixed my issue. I’m not an expert, by any means on VTK, so I’m submitting this to see if you can review it and tell me if I am doing something wrong or if the diagnosis is correct and this helps you fix it. I attached a python script to reproduce the issue and the patch of the modifications to the VTK source code that fixed the issue.
Thanks for your help,
Best regards,
Carlos Montilla
[test\_lic\_viewport\_bug.py](https://discourse.vtk.org/uploads/short-url/as9Kl0ZGslTL4tGkSVeBSIlIog9.py) (7.3 KB)
[fix\_lic\_viewport\_offset.patch](https://discourse.vtk.org/uploads/short-url/z7GhjcxrNZz6SlmJVffWoZ8uzQY.patch) (3.6 KB)
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [April 27, 2026, 2:24pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398/2 "2026-04-27T14:24:42Z")
Hello @Carlos_Montilla
I briefly looked at it and the patch makes sense. I will work on adding a unit test and integrating your patch upstream.
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### Author:  [@Carlos\_Montilla](https://discourse.vtk.org/u/Carlos_Montilla)
#### Post date: [April 27, 2026, 2:28pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398/3 "2026-04-27T14:28:14Z")
Hello @jaswantp
Thank you so much for the quick response and the help!
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [April 28, 2026, 7:23pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398/4 "2026-04-28T19:23:27Z")
the fix is merged in [https://gitlab.kitware.com/vtk/vtk/-/merge\_requests/13178](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/13178)
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### Author:  [@Carlos\_Montilla](https://discourse.vtk.org/u/Carlos_Montilla)
#### Post date: [April 28, 2026, 8:02pm UTC](https://discourse.vtk.org/t/multiple-viewports-and-lic-surfaces/16398/5 "2026-04-28T20:02:07Z")
Hello @jaswantp
Thank you very much for the quick fix!