Twitsing cylinders to increase percived segment count

Format64 · May 21, 2022, 8:27pm

From time to time in some assets I see twisted cylinders like these:

And they kept puzzling me - is there a reason for this or it’s just artefact of some triangulation algorithm? Segment / polygon count is same so that discards simple optimization.

Googling “3d rotated cylinder” or “3d twisted cylinder” didn’t provide much answers so I decided to do some experiments and found something very interesting - this twisting of the top by half of segment has big effect on baked normal map:

If you look very closely you will see what twisted cylinder (2) looks more similar to cylinder with double segment count (3) than regular cylinder (1):

When using more complex shape for high poly difference is even more noticeable:

Looking at it in detail it seems what effect is mostly restricted to top half of cylinders:

File: cylinders_half_rotated_tops.blend (150.5 KB)

How to:

Manual triangulation interferes with a quad based selection methods and prevents ring selecting caps so I suggest leaving it until later or using triangulate modifier to not forget about it.

More complex example:

File: cylinders_half_rotated_tops_complex.blend (584.3 KB)

If you know official name for this trick please share it

RPaladin · May 21, 2022, 11:02pm

3D game engines triangulate all of their meshes. Blender and most other 3D modeling software hide those tringulations to display a cleaner topology (unless enabled by user) to avoid confusion, frustration and wasted time. Most assets on the web will have them because - as I mentioned earlier - that is how game engines render polygons. They’re rendered that way for optimal performance.

I’m not sure what the official term is named either, although I know what you mean. What I do know however, is that when you come across this issue, tools such as K → Knife can help create loop cuts when you seemingly can’t on a certain part of a face.