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Edges of concave geometry get clipped
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Description

System Information
Operating system: Linux-5.8.0-53-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: GeForce GTX 560/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 390.143

Blender Version
Broken: version: 2.93.0, branch: master, commit date: 2021-06-02 11:21, hash: rB84da05a8b806

Short description of error
It seems recent that viewport mesh drawing was visually greatly improved, however some time ago I started noticing problems.
Namely - edge wire overlay getting clipped on concave polygons, making viewport facing vertices unselectable and the topology unreadable (x-ray doesn't help surface shape readability either).
I might be doing something very obvious wrong, of course :)

Exact steps for others to reproduce the error

  • Open,
  • Some edges/vertices don't show up properly or at all.

Event Timeline

Konstantins Visnevskis (kivig) renamed this task from Wdges of concave geometry get clipped to Edges of concave geometry get clipped.Fri, Jun 4, 2:33 PM
Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Needs Information from Developers.Fri, Jun 4, 3:17 PM

Ortho view is kind of sensitive to a small range of View Clip Start > View Clip End.
This is not a problem in Perspective.

A Clip End of 200m gets rid of all this.

however some time ago I started noticing problems.

For me, this has been like this since 2.80, does this behave differently in 2.80 for you?

Anyways, why the range has to be so large in Ortho? Not sure to be honest, maybe @Clément Foucault (fclem) can share his wisdom.

For me, this has been like this since 2.80, does this behave differently in 2.80 for you?

Yes, it behaves the same, it's just that:

This is not a problem in Perspective.

this is why it seemed like happening semi "randomly" and probably wasn't noticed too often before.

A Clip End of 200m gets rid of all this.

Thanks! That did the trick. I always assumed narrowing clipping range reduces z-granularity, but apparently that's also what's used to offset wire Z clipping. For me it's 500m to draw it nicely in this case, which I wouldn't ever be thinking to enter for a 1m object modelling. In fact I've tried varying clipping, but not to such extent.

Thanks! That did the trick. I always assumed narrowing clipping range reduces z-granularity, but apparently that's also what's used to offset wire Z clipping. For me it's 500m to draw it nicely in this case, which I wouldn't ever be thinking to enter for a 1m object modelling. In fact I've tried varying clipping, but not to such extent.

This is why I also summon @Clément Foucault (fclem) here, I usually would also expect a tight range to be the better choice.

Relevant to the topic of Wireframe display quality on concave edges:
at oblique angles the concave edges are barely visible in perspective too, requiring Viewport rotation to see the topology or select with confidence. It's unlikely someone consciously notices this often but it does impact efficiency via additional actions.

I understand that it probably is not a trivial problem, but perhaps, if some day anything is to be done about this, a simpler solution could be an adjustable edge thickness, as also, googling on the topic, I've seen complaints on lack of thickness adjustment on it's own.