# \[Coincident Topology\] backside lines blink when "PolygonOffset" is set

**URL:** https://discourse.vtk.org/t/coincident-topology-backside-lines-blink-when-polygonoffset-is-set/16158
**Category:** Development
**Tags:** rendering, code
**Created:** [November 25, 2025, 10:50am UTC](https://discourse.vtk.org/t/coincident-topology-backside-lines-blink-when-polygonoffset-is-set/16158 "2025-11-25T10:50:57Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![a-ciue](https://discourse.vtk.org/user_avatar/discourse.vtk.org/a-ciue/32/9590_2.png) [@a-ciue](https://discourse.vtk.org/u/a-ciue)
#### Post date: [November 25, 2025, 10:50am UTC](https://discourse.vtk.org/t/coincident-topology-backside-lines-blink-when-polygonoffset-is-set/16158/1 "2025-11-25T10:50:57Z")

</div>

Hi,

I have a polydata with polys and lines. Some part of lines is behind the polys and they are covered by polys. I found and activated the “PolygonOffset” coincident topology. The “covered” issue is unsolved and I encounted a new problem:

After

```cpp
vtkMapper::SetResolveCoincidentTopologyToPolygonOffset();

```

is applied,

1. the “cover“ problem remains, before I zoom in:

 ![image](https://discourse.vtk.org/uploads/default/original/2X/4/473abb76f141f981620c19ab5645bf3a7f854276.jpeg)

1. when I zoom in and rotate a little bit, the “cover“ issue is solved but the backside lines also appears.

 ![image](https://discourse.vtk.org/uploads/default/original/2X/c/cdddeebdfd97e2fd54e463d912368d0994f8cdfb.jpeg)

BTW, when I import this model to paraview 5.13.1, the problem is also reproduced.

 ![image](https://discourse.vtk.org/uploads/default/original/2X/e/ea7bae29dc61dc95404ffb74a8b1eee24f42f4c0.png)

I wonder,

- is it a proper/normal behavior for VTK?
- if I set something wrong, could you please correct me?

[test.vtp](https://discourse.vtk.org/uploads/short-url/19gAGfhp3BNTYlP4ICCtVLTLUUV.vtp) (3.4 MB)

Best Regards,

aciue