Are Ngons Really That Evil in 3D Modeling?

    Some people say that ngons should be avoided at all costs, while others say that this hatred and phobia of N-sided polygons needs to stop.

    In this tutorial we’ll take an in-depth look at the problems with ngons to raise our 3d modeling game.

    Blender 2.8 beta has been used for all demos.

    What is an Ngon?

    An ngon is simply a face with more than 4 edges.

    ngon

    Your typical n-sided polygon, or ngon.

    There are modeling methods like boolean operations or software like computer-aided design (or CAD) that tend to output ngons in large numbers.

    Ngons seem to have a bad reputation among 3d modelers. Well, that is a divisive topic and people feel strongly about the issue, some for it and some against it:

    “Quad only is a stupid myth that serves no one.”

    “NGons should never be present in a final model.”

    “It is better to avoid Ngons altogether since quads and tris will always subdivide properly.”

    “…This hatred and phobia of Ngons needs to stop.”

    “Ngons as intelligent modeling strategy? No.”

    In my opinion there is a certain bias towards the no-ngons modeling strategy. Let’s take a look at what is considered to be the disadvantages of using ngons in 3d modeling, then try to defend the opposite point of view.

    ngons issues

    Some of the problems with ngons.

    Ngons Problems

    1. Rendering (shading) issues

    Ngons are associated with degraded surfaces that are supposed to be flat, but the shading or the curvature suggests that they aren’t. If all vertices of an ngon don’t lie in the same plane it can look really weird because it isn’t clear how to display such shape before it gets passed to render engine.

    ngons in 3d modeling

    A non-planar ngon.

    Ngons can be the cause of shading issues that ruin otherwise great boolean operations for aspiring 3d modelers.

    It’s not easy to get over the initial frustration of seeing an after-boolean mesh. Why does it look so strange? What’s wrong with it? It must be ngons.

    ngons boolean

    Incorrect shading example.

    In addition to that, shading issues associated with ngons tarnish the boolean ops based workflow and we become suspicious of the entire workflow for that matter.

    2. Limited use of subdivision surfaces

    Ngons are claimed to not only look glitchy, but also result in all sorts of mesh editing problems. They disrupt the edge flow of your model and make standard modeling operations like extrusion less effective because we can’t use subdivision surfaces.

    Unlike quads or triangles, ngons subdivide poorly in many cases, so it’s a potential showstopper for workflows that need subdivision surfaces for whatever purposes, car creation for example.

    ngons subdivision surfaces

    A mesh without a proper edge flow that has been subdivided.

    3. Awful looking wireframe

    Chaotic-looking topology is another reason why ngons are frowned upon.

    ngons wireframe

    An edge flow not following the contours of the mesh.

    4. Deformation

    Ngons often lead to animation (or more precisely, deformation) problems. Topology for animation relies on proper edge flow, and thus ngons are a big no-no if the mesh is supposed to be bent or deformed in any other way.

    ngon blender deformation

    A grid-like topology (left) and a mesh with ngons (right).

    5. Interoperability

    Ultimately, ngons behave in an unpredictable way when the mesh is imported/exported to game engines or to other modeling and sculpting applications (because some applications do not handle ngons well and there are always no guarantees about how exactly ngons will be interpreted, because there are no standards).

    ngons 3d modeling tutorial

    A mesh with ngons exported from Blender then imported into SculptGL and automatically triangulated.

    But all things considered, are ngons really that evil as we might have thought about it?

    Before moving on let’s get down to basics and talk about triangulation.

    3D Modeling Basics: Triangulation

    On rendering, every ngon is subdivided into triangles or triangulated.

    And so are quads. Quads are also split into triangles.

    triangulation quads

    Technically every quad is made of two triangles.

    That’s how most render engines work, because triangles form the simplest closed area and thus are easy to rasterize and raytrace.

    Under the hood, all shading and rendering calculations use triangles as basic units, even though it may seem that we, 3d modelers, work with quads or ngons.

    triangulation computer graphics

    Depending on how the quads are triangulated causes quite different profiles (the quads are identical).

    So, every ngon gets split into triangles, but how exactly? For example there are five possibilities to split a pentagon into triangles and it gets even more complicated in case of higher ordered ngons. So ngon is always an implicit surface and different types of triangulation produce different looking results, some better than others.

    That’s a crucial thing to understand, because what we perceive as the inherent problem of ngons (bad shading) can partly be attributed to non optimal triangulation among other things.

    Now let’s go ahead and take a closer look at the disadvantages of using ngons.

    Disadantages of Using Ngons – Closer Look

    1. Rendering (shading) issues: Triangulation

    So what do we actually mean when we say “a non optimal triangulation” and what is an optimal triangulation then?

    There are different methods of triangulation. In Blender, we have the clip and beauty methods. Beauty arranges the new triangles evenly, while clip splits the polygons with so called ear clipping algorithm, that generally performs a bit faster but produces a noticeably worse set of triangles.

    blender ngon triangulation clip

    Triangulation method: Clip (Ear Clipping algorithm).

    blender triangulation beauty

    Triangulation method: Beauty.

    So just by changing the triangulation method we can get a more optimal triangulation and as a result, much better shading.

    2. Rendering (shading) issues: non-planar surfaces

    If a surface should be perfectly flat by design, let’s just make sure it is flat (for example, by using the flatten command in the Loop Tools Addon amongst other methods). By the way, perfectly flat surfaces with sharp hard-surface connections are an ideal case for using ngons, as they always shade in a proper way. Curved surfaces are a different story, we will talk about it shortly.

    ngon problems

    Non-planar surfaces cause incorrect shading.

    3. Rendering (shading) issues: smoothing

    As for smooth shading errors in relation to ngons, controlling smooth shading by marking edges sharp often does the trick. Marking edges sharp means telling 3d modeling application to stop trying to smooth out the connection between two surfaces based on their normals.

    blender mark edges sharp

    Marking edges sharp in Blender.

    blender auto smooth

    Auto Smooth in Blender.

    Taking control of smoothing, e.g. marking edges sharp manually or paying attention to auto smooth angle turns out to be liberating in terms of what modeling styles can be used. Together with the bevel modifier it opens up boolean operations because now we can sharpen some edges and still get a gradual transition from one surface to the other (with the help of the bevel modifier). This workaround unleashes enormous creative potential.

    ngons boolean modeling

    Ngons are not that big of a deal if all the right boxes can be ticked: beveled edges, no smoothing artifacts and so on.

    4. Shading issues: bad topology

    The source of rendering glitches can be sloppy topology in general (like, not having enough polygons to support some mesh editing operations or having an uneven distribution of polygons).

    ngon problems 3d modeling

    The reason for incorrect shading is not having enough geometry to work with in first place.

    ngon tutorial 3d modeling

    With a few more knife cuts or subdivisions the resulting shading would be much more acceptable as there will be less triangles that are super long and thin (after triangulation).

    Another defining characteristic of all kinds of bad topology issues is poles. To explain that, let’s revisit topology basics once again.

    3D Modeling Basics: N-Poles

    A pole is when 3 or more edges converge at a single vertex.

    3d modeling basics poles

    Circled in red are the 3 poles, and circled in blue we have the 5 pole.

    Sometimes 3 and 5 poles are called N or E poles respectively, though we prefer using the number in the name as it’s easier to remember since the number of edges coming to a point defines the pole. 3 edges come to a point for the 3 pole, 5 edges for the 5 pole, 6 edges for a 6 pole etc.

    So why do we have those poles in a quad filled mesh? Because without those poles we can’t effectively have the topology flow to match the 3d shape of whatever it is that we’re trying to create. So we just try our best to place those poles in sensible places.

    3d modeling poles

    Poles are used to change a faceloop direction.

    So why are poles noteworthy?

    • This is where our edge loop selection or creation gets terminated
    • No matter how much we subdivide the mesh our poles won’t change
    • These areas can shade not as smoothly and predictably as a uniformly grid like mesh with no poles
    poles 3d modeling tutorial

    Geometry pinching.

    poles 3d modeling tutorial

    Poles never change their properties, even after subdivision.

    If like in Scooby Doo we were to unmask the real villain we would finally locate and unmask the ngon and find a 3 pole or 5 pole or more underneath complaining they would have ruined the shading on our mesh and would have gotten away with it too (if it wasn’t for those meddling kids).

    3d modeling poles

    Ngons!

    3d modeling poles

    …Oh actually there are poles here that cause pinching.

    5. Displacement

    The other case in which we may want to work with quadrilaterals and avoid poles is displacement.

    displacement ngons

    N-poles (or vertices with more than 3 edges coming out of it) lead to pinching and other problems with geometry, especially after subdivision.

    So why do ngons and triangles get so much criticism? It’s because that’s where we are guaranteeing the creation of a pole and therefore issues of shading under certain deformation and where the selection of an edge loop or creation of an edge loop will terminate.

    6. Limited use of subdivision surfaces.

    Because subdivision algorithms like Catmull-Clark used in Blender, 3ds max, Zbrush and other 3d modeling apps requires strict rules for mesh topology (that means having good edge flow and using mostly quads and having no poles), ngons don’t work well with subdivision. I would say, mainly because of long thin triangles and also poles which lead to pinching and other modeling issues from hell.

    3d modeling tutorial theory

    A mesh with lots of long thin triangles and poles.

    3d modeling subdivision

    The same mesh after subdivision.

    That’s a shame, because subdivision surfaces are great for approximating curved meshes, so not being able to use from start to end it makes it a lot harder to model smooth flowing surfaces.

    In practice, that means that after we start carving boolean shapes and all that stuff, the only way to reestablish good edge flow would be retopology. I think it’s a decent tradeoff for using boolean ops which are amazing for mechanical design though.

    blender boolean operations ngons

    Ngons are important elements of the non-destructive (or boolean) workflow.

    retopology ngons blender

    Retopology is always a possibility.

    On the other hand, some shapes are easier modeled without subdivision and without all-quads for that matter.

    topology 3d

    Sometimes, meshes with ngons make better friends with the bevel modifier than the quadrilateral meshes.

    7. Beveled edges

    The curved or beveled edges that we lose by waiving the subsurf modifier can be created with the bevel modifier instead. It works perfectly fine with ngons and helps us to achieve these sexy bevels with proper smooth shading.

    In that sense ngons are much more appropriate for hard-surface modeling rather than automotive, organic or, god forbid, character modeling. Conversely, quadrilateral geometry could be better suited for organic, automotive and character modeling.

    8. Awful looking wireframe

    That’s… arguable. In fact, in many cases ngons make for much more elegant wireframe (especially if we don’t show a triangulated version). By collapsing the edges that don’t follow the contours of the surface we make it more, not less, readable in my opinion.

    In addition to that, one notable advantage of using ngons is having less polygons overall. As a rule of thumb, boolean meshes and other kinds of meshes with ngons require less polygons to describe the surface area than the meshes, originated from subdivision surfaces.

    ngons wireframe

    Ngons and elegant topology are not mutually exclusive.

    ngons

    Models with ngons often need less polygons to describe the surface.

    9. Deformation

    Deformation is a pretty serious problem of ngons.

    ngons deformation problem

    If you know that the model is going to be deformed, clean topology is a must-have.

    Although, with enough geometry and more or less uniform polygonal density meshes with ngons can bend reasonably well, but not perfect by any means. So if you know that the mesh isn’t going to be deformed, then it’s ok. If it is going to be deformed, proceed with caution.

    Additional loopcuts help to contain the ngons and lead to more even triangulation.

    Again, following good modeling practices like having enough polygons is always helpful, no matter whether it’s 4-sided polygons or n-sided polygons.

    ngons deformation 3d

    Meshes with ngons can deform reasonably well.

    10. Interoperability

    Unfortunately there are no guarantees that ngons will import/export as expected because often times 3d applications make arbitrary decisions on how ngons should be triangulated. Once ready to export, it’s worth double-checking what triangulation algorithm you’d like to use.

    zbrush triangulation ngons

    The triangulated mesh in ZBrush.

    The triangulated mesh in Sketchfab.

    Conclusion

    The key takeaway is that ngons are neither universally good or bad, it depends on what modeling goal you want to achieve.

    ngons tutorial 3d modeling

    Pros and cons of n-sided polygons.

    In conclusion, there are numerous disadvantages of using ngons, but some of their disadvantages are continuation of their merits and can be ignored in favor of 3d modeling possibilities you get in exchange. And they do have pros such as:

    • Less polygons overall
    • Elegant wireframe (arguably)
    • Boolean operations unlocked
    • Bevel modifier
    • Quick concepting

    I would say, the real arguments against ngons are bad deformation and interoperability, these are just bad things.

    Also I’ve heard that ngons make it really tough to get good uv maps. And probably, physics engine operations on ngons could be problematic.

    In my opinion, the other issues discussed in this video can be mitigated or even framed positively.

    A Few Practical Takeaways:

    Curved and going to be deformed = quads. Flat and not going to be deformed = ngons.

    quads vs ngons

    Quads vs ngons.

    3d modeling

    Quadrilateral polygons followed by ngons.

    Pay attention to smooth shading settings, what surfaces should be marked as sharp, what’s the auto smooth angle and so on.

    smooth shading normals

    Incorrect shading

    If it’s going to be exported to game engine or to application that doesn’t handle ngons well, triangulate it first to reduce the chances of incorrect triangulation.

    mesh triangulation

    There are two ways of triangulating a quad.

    Watch out for poles!

    poles 3d

    Watch out for N-poles!

    Ngons or quads, having enough polygons to allow deformation (and an even distribution of polygons for that matter) is always a good practice.

    topology tutorial blender

    Even distribution of polygons is a good modeling practice.

    Lastly, when working with ngons, retopology may be required. 

    retopology in blender

    Retopology saves the day.

    On a side note, there are numerous ways of masking the shading artifacts with the help of the data transfer modifier, shrinkwrap modifier and so on.

    Links:

    Blender

    Hard-surface Modeling in Blender (Blender Market)

    Hard-surface Modeling in Blender (Gumroad)

    Master Car Creation in Blender

    masterxeon1001 on Youtube

    Vitaly Bulgarov – Artstation

    Khan Academy Pixar SubD Explained

    Aidy Burrows on Twitter

    Gleb Alexandrov on Twitter

    Over to You

    Embracing polygons with more than four edges will open up a wonderful world of boolean operations for you, especially if you’re interested in hard-surface modeling. If not for production, then at least for concepting. Let us know in the comments below, do you use ngons in your modeling?