Support for N-Gons (polygons consisting of more than 4 vertices) has been in Blender for a while now, but many of us still may not know when to use them, and how to do so effectively.

In what situations do N-Gons really come in handy? When should they be just plain left out? Do they have any place in finished models?

up vote 45 down vote accepted

Honestly in my opinion, NGons should never be present in a final model. Every artist will have slightly different opinions on this but here is my take.

When NGons are okay

  • On completely flat surfaces.
  • Hidden areas of models that will never be seen or used for any reason (but this still sloppy and not desirable)
  • As a temporary holding surface that will later be replaced with clean quads.

When NGons are not okay

  • On any model that will be exported to another artist or engine
  • On a model that will deform through animation
  • On a model with SubD (unless that area is completely flat, and surrounded by a quad-loop)

There's many different reasons for each of the above, but here's a few:

  1. NGons should not be used on deforming models as you want to have absolute control over how the surface is generated and how it appears at render time.
  2. NGons should never be used on a model that is being exported as you don't necessarily know if the importer on the other side will support NGons or if the next artist will treat them as you intended.
  3. NGons should never be used on real-time models as you won't know how they'll be triagulated.

In general, I like to use NGons as a temporary topology block. But I never keep them in my final models.

  • 5
    Great answer - but minor knit pick. For architectural modeling: flat surfaces. - OK, bordered by a quad loop. - is this really needed? This part of the answer seems like you assume smooth shading or subsurf, which isn't typically the case for buildings. – ideasman42 Oct 7 '13 at 22:25
  • Ah no, that's not really needed. You're right. I address the quad loop in the second half of the question. I'll edit. – Jonathan Williamson Oct 8 '13 at 1:42

N-gons are useful and detrimental for various things.

If you're using Blender, they are usually fine.

So long as you always save as a .blend, n-gons are fine, and I've never had issues within Blender from them without having other serious issues with my models.

That said, n-gons have their advantages and disadvantages; you have to consider all the things that go on with vertices and faces, so if your vertices are weird relative to your ngons you'll see bad stuff happen (for reference, n-gons in the cap on a cylinder are usually fine, but when you start having whole sides of something be a single n-gon you'll start seeing issues that could easily be solved by slicing the n-gon down into smaller polygons).

For export, n-gons can be bad.

Not everything supports n-gons, and some formats don't like them. Typically, the exporter will automatically convert them, but this isn't always the case. In addition, exporters may not always be aware of manifold issues when they're exporting n-gons, which can lead to issues for 3d printing but even for digital use.

  • 4
    which exporters don't tessellate ngons? I'd be interested to know since all should. – ideasman42 May 23 '13 at 3:58
  • I don't know which don't try, but I had some ngons that only liked .obj export. – Kyle Willey May 23 '13 at 4:08
  • Not sure how manifold issues are relevant here, you can have non-manifold meshes which are made of quads/tris too, think this part of the answer is irreverent unless I misunderstood somehow. – ideasman42 Oct 7 '13 at 22:28
  • I've only ever had serious manifold issues with n-gons, for some reason. They can certainly happen with both, but n-gons tend to be a little less flexible and if something goes wrong they're often harder to fix. Maybe it's just how I model (which is not terribly prolifically). – Kyle Willey Oct 8 '13 at 5:56
  • I've found that for finished static meshes for game export, doing a limited dissolve and letting blender figure out how to retriangulate things can result in e.g. 50-100 less triangles in a 300-500 triangle mesh. Whether this is good in the long term, i have no idea. – StarWeaver Nov 27 '14 at 2:46

Ngons can cause trouble with the subsurf modifier. Let's look at two examples:

Ngons with a subsurf result in what I would call megapoles (poles are verts with 3, 5 or more edges connected to them in a surface). They have one vertex in the center and the border is usually star shaped like the object to the left. That results in an uneven transition. The triangle fan has no such problems.

enter image description here

It's even worse with this U-shaped form (left mesh). Again the Ngon is transformed into a quad fan. Here the subsurf causes the geometry to overlap. The right mesh (consisting of 5 quads as the main surface) is fine. Notice that the faceloops around the border have a much more even and controlled appearance.

enter image description here

As a product designer and object rendering professional NGONs are an essencial tool for my workflow:

  • they reduce the polygon count
  • clean up the model
  • make beveling of planar edges much easier
  • greatly simplify UV texturing because of less dense mesh

Also:

  • enable local subdivisions inside the mesh of the polygon mesh when modeling organic objects and the subdivision surface modifier generates a perfect quad based mesh for you

  • this simulates T-Splines for NURBS modeling and is thus a totally valid modeling tool for organic product design

  • When exporting, applying the subdivision surface modifier will generate a perfect quad mesh mode for you.

For character animators or game asset design NGONS as mentioned should not be in the finale model at all.

protected by stacker Feb 22 '15 at 10:13

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