Thanks for the sticky :yes:
Loops are important when modeling in particular when you are doing organic modeling. An organic form should have smooth and sharp features alike and this all can be achieved with proper placement of loops.
From now on I will focus on face loops rather than edge loops. An edge loop exists because it is ‘drawn’ on a face loop. When explaining topology, it is far easier to comprehend the situation when you are looking at face loops.
When you create a loop, you are creating poles too. Poles will play a big role soon in organic modeling because they control the flow of the loops.
For now, there are 4 easy ways to create a loop:
- extrusion (EKey)
- spin quad/ spin edge (CTRL + EKey)
- rip (VKey)
- Knife tool (WKey) or related to it: Subdivide (WKey)
After you invoke the extrude command, you may pull a ‘limb’ out the mesh, or confirming the command right away, leaving a face loop on the mesh.
If you have a grid/ mesh and you perform a spin edge somewhere, 2 N poles and 2 E poles will be produced. It seems that in normal circumstances the number of E-poles is equal to the number of N-poles.
As you can see, after a spin, you are left with 2 loops like railroad tracks opposing each other. Notice that loops bend at N-poles. I’ll be explaining this effect extensively in the following posts.
The cool thing about the spin edge command is that you can bend the loops anyway you like. One major drawback is that each spin edge spawns a new loop.
As you can see that if you intent to use spin edge to create loops, you will get this rather nasty side effect.
But you can use spin edge in situations to eliminate poles (just reverse the procedure above by spinning the edge in the opposite direction) or to correct edge flow, which I will explain in a later stadium.
Remember the simple extrusion that leads to a closed loop? Well, you can make a closed loop too with spin edge and judge for yourself how much it differs from the extrusion method:
Here you have a closed edge loop, but with side loops bordering its corners.
RIP THE MESH:
What is mesh ripping? With this tool (VKey), you rip the mesh open by pulling at a vertex. Afterwards you should fill the hole it produces Select verts/ edges ==> FKey).
The mesh above was ripped open at the upper N-pole. So, like spin edge, rip mesh produces a pair of N-poles and E-poles. Like I said before, the direction of the face loop is determent by the N-pole.
The rip mesh tool is very flexible in conjuction with the knife tool. Depending on the method, you are left with a single C-loop, or with a mirror pair of C-loops.
Creating a single loop:
And after the cut:
This was a very minimalistic loop because I ripped at only one vertex.
If you want to make a much wider loop, you must rip all the vertices in a row. You need to use the knife tool to obtain the face loop. Depending of how you cut the mesh, the results will vary.
To obtain a single broader face loop:
Here I’ll cut before I fill the hole, else there will be triangles in the corners
And then after filling the holes and cutting (and smoothing) you are left with one C-loop (by the way: I assume that C-loop means C shaped loop and not closed loop).
There is a number of ways to make a number of wacky face loops/ edge loops with this method, but i suggest to keep it simple because simplicity and predictability is the name of the game here.
Lets try to make a a closed loop like in a extrusion:
After filling the quads, you are left with a standard extrusion topology.
The knife tool is the topology tool of choice. It has one drawback tough: if you want to cut around a model, you can’t rotate the model and then keep cutting. That’s why I use subdivide often. It works best in “edge” mode. Select the edges which you want to cut through. Using subdivide you can cut around a model. I think the knife tool is well known and it don’t need further explanation. There is a pitfall though in using the knife tool, but I want to discuss this further when I get more in depth with poles.
I’m sure that there are more wacky methods to produces loops, but the above method should cover most situations.