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I've always wanted to ask this. The objective is to keep an all-quad topology.

Basically, if the cylinder has an even vertex number, it's fairly easy : enter image description here

You just extrude half of the vertices,

enter image description here

And merge them at the center :

enter image description here

enter image description here

But what to do in case of an odd number of vertices?

I think a remember that Blender Guru made a tutorial about this and he explained what to do if the number of vertices in the cylinder happen to be odd but I don't remember the name of the tutorial.

Of course I am aware of the trivial method that consists of creating a loop cut to even the number of vertices but I would like to know if there is another method.

Thanks in advance.

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  • $\begingroup$ I don't know what tutorial are you talking about but this depends on what you want to do with your mest next, If you want quads you will always end up with at least 1 triangle, maybe there is a way to fill it with only quads but I don't know it... There is an option called Grid fill, but that only works with even numbers (odd will give you error) , you can also try to fill 2 quads with 1 triangle or select whole loop and press Alt+F (this will give you triangles... if you don't want triangles and want to keep working with it, I would suggest to simply press F with loop selected $\endgroup$
    – MikoCG
    Commented Dec 16, 2021 at 9:07
  • $\begingroup$ one more way is to extrude all vertices in loop into center and merge (this will give you only triangles as well) $\endgroup$
    – MikoCG
    Commented Dec 16, 2021 at 9:09
  • $\begingroup$ @MikoCG YOu will not always end up with at least one triangle... see my answer below. The question is, if this topology is really better than others just because it's all quads. $\endgroup$
    – Gordon Brinkmann
    Commented Dec 16, 2021 at 9:22

2 Answers 2

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As @Gordon has noted, all-quads are probably not necessary on a flat, rigid surface.

After a level of Subdiv. the faces will be quads anyway.

But that means..

enter image description here

.. subdividing once can often offer a solution this sort of puzzle. If the blocked-out model is coarse enough, (leaving enough room for more density) I often subdivide once, apply, and carry on modelling from there.

A snapshot 'Editable Mesh' modifier, like 3DS's, would be nice for this approach. But you can't have everything, I guess :).

Edit

The downside to that method is that if you apply a subdiv to the mesh, it will give some sort of smooth pentagon instead of a circle like the original :

enter image description here enter image description here

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  • $\begingroup$ This would be a good workaround if the mesh was not supposed to receive a subdivision surface or a smooth shading, otherwise, the shape of the mesh would differ from the original. $\endgroup$
    – mqbaka mqbaka
    Commented Dec 17, 2021 at 5:52
  • $\begingroup$ @mqbakamqbaka Actually, my answer was just to show there are possibilities but they are not always preferable, as MikoCG said it depends on what you want to do afterwards. Adding a Subdivision Surface of course creates a mesh differing from the original, if it wouldn't why should we add it to the object anyway (if we don't use "Simple" method)? And regarding a 5-sided cylinder, Robin's method preserves the original shape definitely more than mine after adding subdiv, and it's a way of symmetrically splitting the topology whereas my result is asymmetrical. $\endgroup$
    – Gordon Brinkmann
    Commented Dec 17, 2021 at 7:07
  • $\begingroup$ @mqbakamqbaka Your edit: True! .. (It wasn't clear to me from your Q. that you wanted a circle after subdiv.) A BTW: If you do want Catmull-Clark to give you a reasonable approximation to a circle, IMO, 6 is the minimum number of sides . $\endgroup$
    – Robin Betts ♦
    Commented Dec 17, 2021 at 7:36
  • $\begingroup$ @RobinBetts Yes, you are right. 5 here is just a arbitrary number chosen to simplify the example as the problem concerns odd numbers in general. $\endgroup$
    – mqbaka mqbaka
    Commented Dec 17, 2021 at 11:06
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It depends a lot on what you are going to do with your mesh. Although some people are almost preaching that you always try to keep all quads, that's not necessary in all cases. You can watched videos on Youtube where differences, advantages and disadvantages of quads and n-gons are discussed.

And I guess there are also different ways how to get all quads with an odd number, so this question comes close to asking for opinion-based answers. One possibility you can see in the following image with a five-sided cylinder. If this is a favourable topology I'll let you decide:

quad topology

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    $\begingroup$ I mean that's even number because you had to add once vert at the loop edge to accomplish this, without making extra 5-gon at the side, there is no way you could do this, you can always do this in many ways with even number of vertices $\endgroup$
    – MikoCG
    Commented Dec 16, 2021 at 9:24
  • $\begingroup$ Retopology sometimes involves creating new edges or vertices where there were none before. It still keeps the shape of a five-sided cylinder. Look at sites with topology guides, there are sometimes edges split to get a quad. $\endgroup$
    – Gordon Brinkmann
    Commented Dec 16, 2021 at 9:29
  • $\begingroup$ yes but now I cannot decide if it is better to get 1 5gon or 1 triangle as result $\endgroup$
    – MikoCG
    Commented Dec 16, 2021 at 9:31
  • $\begingroup$ As you said yourself in the comments below the question, it depends on what you want to do with your mesh. And if you take the method I pictured above there is neither a 5-gon nor a triangle. (Okay, that one cylinder side is a 5-gon, but just because I didn't care for the side, only for the top. If I cut the side down to the bottom I'll get two quads as well. Maybe I'll change the pic.) $\endgroup$
    – Gordon Brinkmann
    Commented Dec 16, 2021 at 9:34
  • $\begingroup$ yea but if you cut it all the way down, then you will have even cylinder with 6 verts :D only with one side split in two, well, nevermind $\endgroup$
    – MikoCG
    Commented Dec 16, 2021 at 9:41

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