Massive slowdown caused by ngons + subdivision (2.8)

Support Modeling
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1

This was bugging me for a while before I investigated. I’d found a model I was working on get to a stage where I was having massive performance issues. Undos became cripplingly slow. Trying to use the Last Operator controls also took glacial amounts of time.

I’m going to try and attach a blend file with the object in question. An example of the performance problem I’m seeing would be this:

  1. Shift+A.
  2. Add a circle.
  3. Change a value in the Last Operator panel, bottom left. I, for example changed the number of verts in the added circle from 32 to 64.

I’m seeing this take around 22 seconds of Blender straining before it completes the operation and hands me back control.

Undo operations take an almost identical amount of time. Which isn’t fun.

The object seemingly causing the slowdown is called ‘Base’. It has a number of ngons which, in conjunction with the Subdivision Surface modifier, appear to be causing the problem. If they are deleted, triangulated or the Subsurf modifier is turned off the problem greatly decreases.

The same object appended into 2.79 performs OK.

So, does anyone have any idea what is going on? It’s obviously a symptom of poor modeling on my part - and I’ve already worked out how to mitigate it, but I’d love to know why 2.8 is having an issue when 2.79 isn’t? Is it a bug and worth reporting?

goblin_mini.blend (2.2 MB)

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I was wondering about the exact same thing, only I couldn’t figure out that ngons are a possible cause.

When concept modeling I’ve gotten into the bad habbit of not really caring about ngons too much, just throwing a subsurf modifier on top, and was experiencing the same issues - adding a new object and changing the number of subdivisions takes ages, even more noticeable changing both spans on a uv sphere at the same time for example.

I’d say it’s definitely worth reporting. I have no intentions of giving up my messy modeling habits.

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3

It’s a known problem. I reported the same in January.
https://developer.blender.org/T60733

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4

Oops. I hurriedly reported it just before leaving for work. Thanks though… I’ll keep an eye on your report.

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Mine is at https://developer.blender.org/T64691 but I assume it might get merged.

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Yes mine got merged too.

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Oooh, so that´s the reason subsurf is so slow sometimes.
I often just add a bevel with 2 segments and a profile of 1 and then a subsurf, and don´t care about ngons etc at all :slight_smile: Have to quadify some model to see if the perf improvement is noticable

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