N-gons have earned a bad name in the 3D industry. But are they really all that bad? It’s always been recommended you re-route your geometry to a quad when it comes to 3D modeling, and we’re going to discuss why and if the suggestion has any merit.
The truth is, most of the time, you shouldn’t be using n-gons. They cause a range of issues when you rig, animate, smooth, subdivide, sell, or render your model. But other times, when you’re modeling hidden areas, the cap of a cylinder or hard surface modeling – using n-gons can help save your polycount.
When and when not to use n-gons can be tricky to decipher, so we’re going to give an illustrated guide on specific instances you may come across when modeling. Whether you’re modeling for archviz, products, or games – keeping these basic instances in mind will ensure that your mesh is at the best quality it can be for its purpose.
What is an N-gon?
An n-gon is a face or polygon in a mesh that is made up of 5 or more sides. Any face with more than four sides is considered an n-gon. N-gons shouldn’t be confused with polygons, which are faces with three or more sides.
When Shouldn’t I Use N-gons?
- If you are going to add any deformers to your mesh. N-gons will generally cause issues when adding deformers to the model, so a general rule of thumb is if you would like to keep a non-destructive workflow with one or multiple deformers applied to your mesh, model it using quads. For example;
- Adding a subdivision surface modifier. N-gons can cause trouble with a subdivision surface modifier; they result in mega poles which all share one common vertex and will cause the geometry to overlap. Overlapping geometry causes your model to animate weirdly and also to not shade correctly. Also, you will be limited by the amount you are able to subdivide the entire mesh because there will be an exponential effect on your polycount when there are n=gons involved.
- If you are going to rig your model. It’s necessary to have clean topology for modeling and rigging a model so that your mesh can be associated with the correct quads and tris. Rigging with an unclean topology will result in your final animation being unclean and deformed as well
- If you are going to render your model. Ever rendered a surface and notices that the normals or shading of an n-gon looking super weird? N-gons cause issues at render time and should be avoided. I’ ver personally never understood why the mesh does this but it’s certainly a very irritating outcome because your mesh will look perfect before you render it.
- If you are going to smooth your model. N-gons cause issues when smoothing because of the extra vertices and edges.
- If you are going to export to other software. Well – this one isn’t as serious as the others because typically exporters will convert the models automatically. But this could also be a problem because your mesh just won’t look the same as it did before, and if you are unfamiliar with the typology of your mesh it opens you up to making mistakes. Rather be acquainted with your topology from the very beginning so that you can make the best out of it. I’ve experienced this when exporting hard surface models that I quickly made with SketchUp and then when I imported that mesh into Blender. I was very confused and it’s just better to stick with quads from the beginning.
- If you are going to sell your model. Not modeling using proper typology means that you’re going to have models sent back to you. Your clients will not be willing to re-typologise the model – especially if they’ve paid for it. Having bought a model that just animates, deforms, and behaves as it should keep your clients coming back for more.
- If you are going to render your model in real-time. N-gons will slow down your real-time rendering speeds and will slow down your game. N-gons should never be used on a real-time model because it will mess with the render output and render time.
When Should I Use N-gons?
- If you are modeling hard, flat surfaces. N-gons can be used for a perfectly flat and static surface like for architectural modeling. These will have to be models that you do not plan on animating, deforming, or models that have any of the characteristics above. But, in general, I have not ever had a problem with using n-gons in quick block / mass modeling architectural models that I have sent people as drafts.
- On hidden areas of the model. If you’re composing a scene and there is a part of your model that the viewer will never see – well, don’t spend any time and don’t charge your polycount for those areas. If you are not going to simply delete them, then keep them as is. If the n-gons cause shading problems, well – you’ll never see them.
- If you are mass modeling. I often made mass models when composing a scene and I’m really not going to stress about the typology of something I’m inevitably going to delete at a later stage. N-gons are perfect as temporary holding areas that will be replaced by future modeling.
- On the cap of a cylinder. Making quads out of the cap of a cylinder is silly and a huge waste of a polycount if made into tri’s or quads. Typically the cap of a cylinder does not need to deform as much and therefore will also not pose such a threat as an n-gon. If you subdivide the cap of a cylinder into an n-gon, it will result in a mega pole in which all faces share one common vertex and can cause the geometry to overlap.
- When you’re reducing your polycount. For emergencies only, but if you really are in need of a smaller model, you can reduce your polycount by using n-gons. When you are cleaning up your model and are desperate to save a flat surface, you can use an n-gon.
- When you are beveling planar edges. You’ll be stuck between a rock and a hard place on this one, but typically using an n-gon edge to bevel is better than not. If you do not use n-gons here, you will end up triangulating the edges and increasing your polycount by quite a bit.
- When you’re trying to simplify your UV mapping. Mesh can get messy and then can give you more problems when you are UV mapping for accurate texturing. I’ve sometimes gotten away with cleaning up my mesh in order to allow me to have a neater, less complicated UV map that I can play on.
- When you want a non-destructive workflow. If you keep on coming back to a model and keep making changes to your deformers, you won’t mind having n-gons in your mesh. After all, it’s better than clicking ‘apply’ and destroying all your checkpoints. If you are going to work with a non-destructive workflow, just be sure to clean up your mesh afterward.
What Can I Do if I Have N-gons?
If you are n-gons and want to get rid of them, you can select them and convert them. At the bottom of the 3D view, click Select > Select All By Trait > Select Faces By Sides. Now, in the tools menu of the left of the 3D View, click on the dropdown menu and select Greater Than and make sure it’s set to 4. Now all the polygons with more than 4 sides will be selected.
Once all the n-gons are selected, you will want to first convert them to tri’s before you convert them to quads. You can click on Mesh > Faces > Triangulate Faces. Then you will want to click on Mesh > Faces > Tri’s to Quads.