I've read many times that triangles should be avoided in meshes, too give one reference: "Introducing Character Animation with Blender by Tony Mullen" says that equilateral triangles work fine as long you don't deform them. It seems to be common in game development that the models are triangulated.

  • What issues are introduced by using triangles?
  • Does the same apply for n-gons?
up vote 26 down vote accepted

Rather than thinking of limitations with using triangles (I think this is an over simplification of the topic), you need to understand common workflows that take advantage of quad-dominant meshes.

  • adding and removing edge loops (to increase or remove detail)
  • using loops to better define features of the mesh (such as facial features, around eyes etc).
  • operations on faceloops and edge-loops that speed up selection loop selecting, loop sliding for example.
  • operations on grids. ripping & grid-fill for example.
  • better deformation with shape keys (a lot could be written on this, read up on mesh topology, facial shapes, deformation).
  • better subsurface results (edge loops along important features of the form allow your to use creases too).

However in a specific situation you may find it's not a problem to have a 100% triangle mesh so don't be single minded about this.

Instead of defining triangle meshes as bad, try to learn to use these tools and you'll better understand why in most cases, triangle heavy meshes are not ideal for character animation.

  When people refer to character animation, they often don't include robots with rigid surfaces where, apart from the modelling process, tris for flat surfaces aren't that bad. They refer to human faces or otherwise flexible surfaces.

  To simplify controlling the mesh for facial expressions or lipsync, faces of characters are modeled more or less low poly to control their features and then a Subsurf Modifier is used to create a high degree of smoothness. That's the point where tris cause all the mentioned problems.

Look at this simple example. The tris to the left give some nasty bumps when subsurfed, the quads to the right are wonderfully smooth. Imagine the difference in a character's face.

enter image description here

Since Ideasman has a point, here's another example of topology. To the right you have a very clean structure and the desired smooth result. The left shape is not so lucky. Achieving the same amount of smoothness would require a high amount of tris if it's possible at all.

tris, quads and subsurf

  Regarding modelling: Add a UV Sphere and put an edge ring somewhere at the equator with the Loop Cut. That's fast and easy. Then try to put an edge ring around the single vertex at the top. It's harder to add detail if your topology doesn't follow the form.

  • 3
    This example is a bit misleading, if you have a mesh with evenly spaced quads, then triangulating will give noticeably uneven shading (as with your example). But if the mesh was created with evenly distributed triangles the shading can be fine. – ideasman42 Sep 17 '13 at 7:18
  • You're right. An example for this is the Icosphere. The question is, can one conveniently maintain the even distribution when doing less regular shapes and is it worth the hassle? Actually I agree with your answer. – Haunt_House Sep 17 '13 at 9:42

N-Gons with more than 4 sides and Tris are bad because they do not subdivide smoothly and so break up the flow of edges through a model. Tris are only bad when you need to smooth a mesh ie add subdivisions. This diagram shows the effect of using quads and the subdividing as you see you still have quads after subdivision, so you could do it again for example. enter image description here

There is nothing wrong with Tris except were you are wanting to smooth and sometimes they can't be avoided, in which case hide them in a unseen part of the mesh, under a arm etc.

Tris are not bad and in fact when the mesh is rendered all polygons are reduced to Tris.

  • 1
    its not always true that all geometry is triangulated before rendering. It depends on the rendering engine. blender-internal for example doesn't do this unless the faces are non-planar. – ideasman42 Sep 16 '13 at 9:55

Triangles work fine in lowpoly models (such as for games).

However, when you subdivide them, they dont respond well. You will often see stretching and artifacts. Since subdivision is such a common workflow, it has become a general rule of thumb to avoid triangles.

I will at a later time (if nobody beats me to it) show an example.

It can be ok to use triangles if the surrounding area is completely flat. Or if the triangle is hidden away in inside of something (like an ear).

Pentagons are a little better than triangles (I think, please correct me if I am wrong), but generally avoid them too, if you can. More vertices than 5 are really bad.

I'm relativly new to modeling characters, but what I've found is:

  • Triangles don't deform well when rigging.
  • It's easier to read edge loops when looking at quads in a low poly model.

I am not sure about ngons and issues using them in character animation.

protected by iKlsR Sep 18 '14 at 16:55

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