Basic Question about Loop Cut and Why it Cuts Through Multiple Edges

[Janitor]

I’m following along with making a low-poly dinosaur and I’m adding loop cuts to help make details. In the video, Grant’s vertical loop cut starts around the crown of the dinosaur but it stops at the mouth. When I loop cut at the same area, it cuts through the two edges running along the dino’s lips and right down to the chin.

I don’t mind, I can easily get rid of edges that I don’t need. I’m mostly curious on why it’s happening to me and not in Grant’s video.

[Janitor]

And now perplexed because I placed a loop cut at the snout but didn’t cut across from the top jaw to the bottom jaw.

[Gordon]

Add screenshots. Sounds like you have different edgeflow from Grant’s.

[Janitor]

I’m not sure what to screen shot (I’ve progressed to the point of maxing the T-Rex’s mouth hole). Going back to where Grant started the loop cutting (time stamp 5:03), he mentioned being in quads. I didn’t know the term so I did a little research. Afterwards I saw that his first loop cut was in a four-sided shape (quads) and below was a triangle. I can’t remember what shape was below when I made the first cut. Maybe but if there was a quad below the area I was loop cutting, would it extend right through? And if it was a triangle it wouldn’t cut though (based off of Grant’s video)?

[Gordon]

Yes, loop cuts only go through quads (faces that have four vertices). A triangle would have stopped the loop cut.

We have a plane on the left side and a plane on the right side.

1. The plane on the left side starts with a triangle and a quad. The plane on the right side starts with only quads.
2. I add a loop cut going through each plane. Marked in yellow. The loop cut in the plane on the left hand side stops when it meets the triangle, but goes all the way through the quad based plane on the right hand side.

However, note by adding this loop cut in the plane on the left, the triangle has now become a quad (a face with four vertices/edges), marked in blue.

3. I add loop cuts to both planes on either side of the previous loop cut, again marked in yellow. Because the loops cuts go from one edge to the opposite edge, the loop cuts on the left plane have a different “edge flow” than those on the right plane.

3D artist generally try to keep their mesh in quads for many reasons, adding more geometry (edge loops) in places where it’s needed being one of them. A lot of times, geometry needs to be manipulated so that the edge loops go a long with a certain shape of the model. That’s when techniques such as our example above is used to redirect the edge flow.

I hope that clarifies things!

[Janitor]

That really does, thank-you very much! I really appreciate the help!

[Gordon]

You’re welcome. Good luck!