The age-old debate: quad or ngons? This question has created a divide in the Blender community, with some swearing by quad-only modeling while others defending the incorporation of ngons.
In today’s article, we will cover what are ngons, where they should be used, and how to adjust your topology to match Blender’s innate preferences.
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What are Ngons?
Ngons are any faces that are not tris (3 edges) or quads (4 edges). Ngons are not inherently bad; many of the preloaded assets in Blender, such as cylinders and cones, use ngons. However, the preference for using tris and particularly quads is evident in character models, game design, and Blender’s default modelling operations.
A little-known fact is that Blender interprets all ngons as tris! You can test this by creating a non-planar ngon (where the vertices do not lie on the same plane).
This will result in unusual shading effects (often referred to as artifacts) due to the hidden triangulation. In edit mode, press CRTL + T to use the triangulate function.
You will see edges forming across your model, revealing that Blender already treated the ngon as a collection of tris. This insight shows that while ngons appear as a single face, Blender processes them as multiple triangular faces – everything is tris!
The debate around using ngons stems from the belief that a truly skilled 3D modeler can avoid ngons through a better understanding of topology and edge flow.
However, is this true? We’ll first understand a bit more about how Blender perceives ngons, then we’ll delve into specific use cases of ngons vs quads
How Ngons Affect the Modelling Process
To understand why ngons are less desirable than quads, let’s demonstrate their effect on edge flow. Start by adding a plane to your scene by pressing shift + A and selecting plane.
Then, scale it on the Y-axis to create a long rectangle. Do this by pressing S followed by Y and drag using your mouse.
Press the tab key to enter edit mode, then press CTRL + R and scroll up on your mouse wheel to add several vertical cuts to the rectangle. Left click to confirm the number of loops to add to your mesh.
Now, if you press CTRL + R once more, and add a horizontal edge loop, you will see that it spans the entire subdivided rectangle. This is thanks to its continuous chain of quads.
But what happens if we introduce an ngon or a tri into this chain?
Let’s undo our previous step of adding in the horizontal edge loop by pressing CTRL + Z. Next, select four vertices of the central quad, then press CTRL + T to triangulate that face.
Now, we will attempt to add a horizontal edge loop again.
As you can see, the tri interrupts the edge loop – it has ruined our edge flow. As Blender prefers to work in quads, ngons, and tris may be incompatible with some features. This concept is crucial for character design and creating clean topology – a whole separate topic on its own.
Should I Use Ngons in My Models?
The answer depends on the purpose of your model and how much time you want to invest in the project. Let’s first discuss the scenarios in which you would not want to use ngons.
As mentioned previously, ngons will ruin your edge flow, which is particularly detrimental when creating models designed to deform, such as a character’s face that is rigged for different facial expressions.
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Without proper edge flow, Blender will struggle to deform your mesh as desired. This problem is further exacerbated when exporting these models to other render engines like Maya, which also prefer quad topology.
Additionally, when modeling high detail objects, working with quads is preferred as the subdivision surface modifier works best with quad-based models. This is best exemplified when you add a subsurface modifier to a cylinder.
As you can see, Blender struggles to interpret the correct way of adding higher detail to the ngon. Therefore, to achieve higher detail, it is recommended to model using quads.
So, I Should Never Be Using Ngons?
Ngon hate can be exaggerated, as often the only person who will appreciate good topology is the creator of the scene. Ngons are not inherently bad as they can help reduce modeling time, particularly if the model is not intended for animation or game design.
Many artists (myself included) opt for less-than-stellar topology because most viewers of the artwork will never see the wireframe of our scene.
Using ngons can be preferable as it can speed up the modeling process by reducing the time spent on cleaning up the topology. If the model’s purpose doesn’t require perfect edge flow, ngons can be a practical choice.
They are especially useful for flat surfaces or for creating circular shapes. While it is possible to use quads for these purposes, pressing F to fill and create an ngon can be more efficient and achieve the same visual result.
How do I get rid of Ngons?
There’s no one-fix solution as this will depend on your model and the number of vertices involved, however, there are several techniques that you can implement to create a more quad-friendly model.
One often overlooked function is the ‘grid fill’ function. This will fill any closed loop of vertices with a grid of quads. Let’s try it on a cylinder.
Add a cylinder to the scene by pressing shift + A and selecting the cylinder
Enter edit mode by pressing tab. To delete the top face, we can select the entire edge loop by ALT + right clicking one of the vertices on the top face. Then, to delete the face, we press X and select ‘Faces’.
Now to add in our grid-filled faces, we select the top edge loop once again by pressing ALT + right click and selecting ‘grid fill’.
A box will appear in the bottom left-hand corner of the screen with two fields: span and offset. The span parameter affects the number of divisions made in the grid, while the offset changes the rotation of the grid. The grid fill function is a powerful way to create many quads easily.
The knife tool has both the power to destroy and create ngons – the choice is yours. To use this incredibly versatile tool press the ‘K’ key on your keyboard. You can create new vertices anywhere on your mesh by left-clicking. Using the knife too, you have complete freedom to turn quads into ngons and vice versa.
The example below shows that by using the knife tool to divide the ngon, you can convert the entire mesh to quad topology.
To get rid of ngons, you can move and merge vertices to reduce the number of edges. To demonstrate this, let’s convert a pentagon into a quad.
Press shift + A, then add in a circle. Before clicking anything else, expand the menu in the bottom left corner.
In the circle menu, change the vertices to 5, and the fill type to N-Gon, this will give you your pentagon shape.
Next, select the vertices that you want to merge then press M and the merge options will appear. Typically you will use ‘At First’, ‘At Last’, or ‘At Center’. This will result in a mesh with four vertices.
The other method used to convert ngons to quads is through the edge slide and merging functions. Edge slide is a powerful tool that will preserve the edge flow.
As opposed to moving the vertex freely in space like what happens when we press the ‘G’ key, by pressing the ‘G’ key twice, we unlock the edge slide function, which means the vertices will be restricted to moving along its edge.
Create the mesh as you see in the image below by adding in a mesh, adding one horizontal edge loop and one vertical edge loop by pressing CRTL + R in edit mode.
Press K to use the knife tool and add four vertices across the mesh as you see in the image below. This will result in the top left faces becoming ngons
Select the second vertex from the top, then press G twice – this will enable the edge slide function. Using your mouse, drag it so that it overlaps with its neighboring vertex.
Then, still in edit mode, press the A key. This will highlight all vertices in your mesh, then go to the top of the menu and select Mesh > Clean Up > Merge by Distance to merge the overlapping vertices, now you will have complete quad topology once more. This method maintains a clean topology and is particularly useful for detailed adjustments.
Preserving edge flow while reducing vertex count
If we want to simplify our mesh while still preserving edge flow, we can use the method outlined before. As an example, add in a plane and add 4 horizontal edge loops and 1 vertical edge loop, resulting in 10 quads.
We can reduce the number of faces from 5 to 4 by doing the following:
Extrude the faces once again
Next, drag the central two vertices upwards like so:
Then, select the four central vertices and fill them by pressing the ‘F’ key
We have now reduced the vertices in the bottom row from 6 to 4 while preserving the quad topology and edge flow, which is evident when you try to add additional edge loops.
We can continue this once again to reduce the number of vertices in the row from 4 to 2.
Conclusion
In summary, the decision to use ngons in your modeling workflow depends largely on the intended use of your model. For animation and game design, it is recommended to stick to quad topology to ensure smooth deformations and compatibility with various game and render engines.
However, if you’re blocking out shapes, creating still models, or clean topology isn’t a primary goal of the project, ngons can be a perfectly acceptable and efficient choice.
Like any discipline, there is no set way to approach 3D modeling It often involves balancing well-known principles with customizing your workflow to suit your preferences. So whether you use tris, quads, or ngons, use whichever technique best aligns with your goals.
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