What does the term "support loop" specifically mean?

I want to enter a 3d modelling contest of a game for the skin of a character and one of the guideline was to "Remember to keep support loops for joints in the same place."

What does that mean exactly? I've been searching & searching and I can't find the answer, it just seems like some sort of unexplained jargon.

Any explanation for the "support loop" term would be greatly appreciated. (Is it just a special type of loop cut?)

An explanation in the context of my contest's guidelines would be even better.

The other answers explain well what a support loop does on a static mesh, but there is another thing that support loops do on an animated mesh: they help define how the joint deforms as it moves.

Since this is a skinning competition, you are creating a new mesh which needs to work with an existing armature which has existing animations. If the location of the joints and the supporting geometry is different on your mesh, then it will deform differently and unpredictably when animated.

Keeping the key areas of deformation in the same place helps to maintain the best compatibility with the existing armature and animations.

This video has a very good explanation of how the topology surrounding a joint affects the deformation of the joint.

• Thank you Wossname, that was the answer I was looking for! I recently consulted a more professional person who also participated in the competition just 2 days ago, and he said near exactly what you said. Wherever there was a joint, there were "support loops" above & below it which helped the joint stretch smoother when the limbs move. That's what it meant by support loops. And keeping it in the same place, as you said, helps keep the rigging consistent. Also thanks for the video! Oct 23, 2020 at 3:58

Basically, support loops mainly apply when using a Subdivision Surface modifier. Loosely put, the modifier acts to take an "average" of the angle between two faces, and then creates a curve to smoothly transition between the normal vectors of the two faces. See the images below:

By adding loop cuts or "support loops", you can control the size (area) of the faces that are being averaged (in one direction only if necessary) which in turn affects the degree of the averaging.

By adding more loops, or changing their position, you can change the "roundness" of your object. This is often used as a method to sharpen the corners of objects with a Subdivision Surface modifier applied. If you look at the effect of the two loops near the "corner", you can see that this is similar to how the Bevel Modifier works (by default) to sharpen edges.

• The same principle can be applied to armature deformation as well, joints can appear to collapse if there is not enough geometry around them to define the shape different poses/ allow for an appropriate transition between weights. Oct 20, 2020 at 23:24

I guess "support loop" means adding an edge loop close to an existing one, when for example you want to sharp an angle.

You can add an edge loop with CtrlR then slide it close to the existing one with GG.

You can also create an additional edge loop if you select the exising one, put your mouse cursor on the side you want and press AltV then G to slide.

If you select the existing edge and press CtrlShiftR it will create 2 additional edge loops, one on each side.