Get halfway through a model and find it's an unworkable mess? Can't add edge loops where you need them? Can't subdivide a mesh properly? If any of this sounds familiar check this course out.
I'm new to 3d and don't entirely understand the concept. I know that most models are done using quads which are later split into triangles for use in game engines.
Quads are apparently easier to split (4:2=2), while triangles are not (3:2=1.5) - so they might create artifacts. Now, I don't understand why would a triangle need to be split in the first place since it's already a triangle.
So I've hear to avoid triangles whenever possible.
On the other end of spectrum are people who claim that it's not a big deal and paying too much attention to making sure that everything is quads will hurt the model, because it gives you more restrictions to the modelling as well as takes you out of the so called 'zone' (it's hard to be creative when you focus on counting edges).
I personally like to keep my polygons a simple as possible with minimal amount of faces. If I have to add a vertex - I prefer to split a face and make a triangle, instead of splitting the whole polygon, but I'm not sure if that's a good approach.
What is your opinion and why? And how important is it in low poly modelling?
Tri's and ngons in models that will not deform for the most part will not matter at render time but as a general rule they are frowned upon. So, to me, the important questions are why they can cause issues and are there any exceptions?
Even in models that will not deform tri's and ngons can present problems. Here are some of reasons why tri's and ngon are discouraged and a few cases where they really do not matter.
Take your elf foot above. Suppose you wanted to add an edge loop in example B. Lets start at the vertical edge at the heel and go left. It hits the edge of the triangle and stops (see paint over).
Now even if it did go through the triangle and hit the other edge, then which way does it go? Down and around the bottom or across where it hits the other triangle (see paint over)? You probably should go both directions and as you see we generate 2 new tri's!
So the issue here is that triangles create problems when trying to add edge loops.
The next issue is with smoothing. When you smooth example B those triangles get converted to quads. So what is the problem you say? Well here is how CC or (Catmull Clark named after the two Stanford guys that created the algorithm one of which founded the late SGI) works.
For every polygon put a vert in the center and then draw an edge from that vert to the center of each surrounding edge. For a quad you can easily see you get 4 smaller quads (see paint over). For a triangle though you get 3 quads but they are diamond shaped. This can quickly create some very ugly geometry that is routing edges at right angles as they pass through the triangles.
Every ngon can be broken evenly into some number of quads or some number of quads + 1 triangle, but you cannot be sure how they will be tessellated and so they present the same problem as a triangles for smoothing, adding edge loops, and deformation.
So the first two reasons triangles and ngons are frowned on is they create problems when trying to add edge loops (1) and also create kites (diamond shapes) when subdividing (2). Which in turn creates messy geometry when smoothing and turns edges at some angle as they pass through the triangles.
The other issue with triangles and especially ngons has to do with artifacts on surfaces when they are deformed (3). You can see in the last image with a 50 sided ngon the problem when the surface becomes non-planar.
And there is one more issue some applications like zbrush just will not play nicely with triangles (4).
In general organics are far more sensitive to tri's and ngons as they are more likely to be deformed. Hard surface models are more tolerant of tri's and ngons as they are less likely to be deformed.
Now having said this I would point out that if you know what causes problems with trianlges and ngons then you'll know when they are not going to be an issue. For instance, for planar surfaces that will not deform then ngons do not matter (PERIOD!)(see the attached image). For triangles that are in hidden areas of the mesh - then the smoothing, edge loop, and deformation issues will be minimum.
In other words if you understand the rules, just like in the MATRIX, then you know when you can safely bend them!
Now if you are selling your work on say turbo squid and you don't know how it is intended to be used then you would want to definately avoid ngons and minimize tris.
If you are working for a production house and your TD forbids tri's and ngons well then you have to follow these rules.
If you are doing your own work, You know how the model is going to be used and you understand when tri's and ngons can be used safely then it's up to you whether it is important enough to add the necessary geometry and take the additional time to remove them. For me, when working on hard surface objects and on planar surfaces that I know will not deform I often do not worry about ngons and I just ignore people that feel it makes them sound smart when they rag on me about it.
What irks me is when people just blindly say all ngons and all trianlges are bad period, usually because some "expert" told it to them, and so they just parrot it without thought or any understanding why or if there are situations where it just does not matter!
I hope you found this helpful. It can be a very sensitive topic and I believe I have covered it quite evenhandedly.
For organics Steven Stahlberg has written some very good white papers on how he uses ngons and tri's in his female models topology as in certain situations they actually deform better then quads. Here is a practical example of where ngons are used intentionally to model a bottle cap in the art department at coca-cola. The point here is that in some situations tri's and ngons are beneficial.
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