UV Unwrap Becoming Skewed?

ne.____.il

Hey there! Not entirely sure how to best phrase my query, but I've noticed (what feels like) strange behavior with the UVW tools?

In previous versions (as best as I can recall), when I would select the seams for edges to be unwrapped (imagine a rectangular label, as an example), Cinema, most of the time, would do a pretty good job of keeping edges straight. However, over the last year or so, I've noticed that this doesn't seem to be the case anymore. For the most part, I've made my peace with it and have done a lot of manual 'fixing', to get edges to be straight.

Currently I'm doing some practice with texturing and modeling with various books from the Asset Library and as I'm resizing some of the books, I've now a need for the UVs to be re-unwrapped so that the square aspect ratio of the texels are maintained.

The issue I'm running into, and not really certain as how to best solve, is that when I re-unwrap one of these assets, the resulting map is skewed.

I've attached a screen recording demonstrating this. I feel like this is something that is very basic that I'm either A) ignorant of, or B) forgetting to do.

Here's a link to the screen recording: https://www.dropbox.com/scl/fi/ie7147j7fodndwrzyij5f/2024-07-25-15-58-58.mp4?rlkey=lmm0mb73a4v13q8d8nqnv3s9t&dl=0

Any/all insights are greatly appreciated!

Dr. Sassi

Hi ne.___.il,

If I follow correctly, you scaled the book in one direction more than another. Scaling will not affect the UV setup. The area of the image that should be the Cover, in this case, will fill the Cover even if you scale it much more in one direction and hence get stretched.

If the new cover image is based on the new format, you will see in the UV layout that it no longer covers the UV polygons, whether they are too large or small. If it covers it, it must be scaled to equalize the nonunified scale to appear proper; not advised, but adjusting the UVs according to it.

The bend or skew is a preview artifact (which, AFAIK, is highly dependent on the Graphic Card used and the version of Cinema 4D, I know that problem from the past, but I can't reproduce it anymore of the two large polygons. The space inside a single polygon (on the object itself is not defined for preview. With large polygons, you need to render it to get a precise result.

https://stcineversityprod02.blob.core.windows.net/$web/Cineversity_Forum_Support/2024_PROJECTS_DRS/20240725_CV4_2024_drs_24_TXbc_01.zip

Let me know if that works for you

Cheers

ne.____.il

Hey Dr. Sassi,

Thanks for passing that project file over. While it was helpful, sadly it's not the solution I was hoping for.

Let me try a different line of inquiry instead as I think this is actually more of a "How do I unwrap something 'correctly'?" sort of question and not that the UVs, due to scaling, or subsequent unwrapping, causes them to become skewed.

The UVs of the 'Book - Thick (Book)' produce no warping when a texture is applied to it.
When the seams which comprise that UV are selected and stored and then the original UV map deleted and the model unwrapped using the stored selection, the resulting UV is now warped.
For unwrapping objects, like books or anything that needs to be perfectly flat and cubic to allow textures to be applied to them without distortion, what is the most efficient way in which to create a UV that is not distorted or warped?

Here's a link to another screen recording: https://www.dropbox.com/scl/fi/5oaxq24r2vn9tpnzd12yq/2024-07-25-18-39-28.mp4?rlkey=0bzqn6go0zt1pkx26g0eh7wmh&dl=0
Additionally, here's the project file from that screen recording: https://www.dropbox.com/scl/fi/qhzxk3vqhk2v6x3ih3ydu/BookUV_Cineversity_Sassi.c4d?rlkey=ikcl2u1m1t6z11cgz2ycq40va&dl=0

In this recording I've done the following:

Scaled the 'Book - Thick (Book)' model in arbitrary amounts along two different axes.
Selected the edges used as the seams for the original UV map and stored them.
Deleted the original UV map.
Re-selected the stored edges and unwrapped the modele using those.
The resulting UV does not look like the previous UV map; this is the part that is confusing to me and the thing that I'm most curious to get your insights on.

Looking very forward to your thoughts!

Dr. Sassi

Hi ne.____.il,

How to unwrap some surfaces correctly is a general question that leads to a long series or two, and even then, it will not answer all questions.
https://cineversity.maxon.net/en/results?term=UV

Thanassis (AKA Noseman) will share many tricks in some series.

There are two main areas: organic and box-like. Sorry, there is no short answer to either of both, or there are some, but they are inefficient when expecting large islands and keeping them paintable.

Thanks for the file.

I would not have thought even to use the unwrap option here, with so many little parts in the border. You showed the path selected inside the book, meaning it is wrapped around, which is not solvable in a straight way. Unwrap would try to keep the surface relation of the 3D object in the same way in the 2D representation. That is impossible for obvious reasons; hence, it is a long story.
As mentioned from time to time, people have tried to fix that problem for over 2000 years, according to the book by John P. Snyder, "Flattening the Earth. It is that old example of wrapping an Orange in a piece of paper; it doesn't work without wrinkles. So, no worries, there is no click-and-go for all cases; in some cases, it will never be. I think I have repeated that now enough times to make you feel more comfortable.

The Original wrap is straight-lined for the larger areas of the book. If you would like to get the new dimensions done, select the UV islands (Select one polygon, then U~W) and perhaps use the UV-Edit> UV Transform to adjust the island's dimensions in this case.

The provided UV solution is usable; stretching the islands individually should do the trick. But first, load an image in, even if it is empty. As the UV space is normalized, always take the whole image dimension from 0-1 for both dimensions.

As a side note, the fastest way with a 90º based object, like a box or a flat book, might be the projection "Cubic 2" or Box, but again, it is inefficient in using the image space.

I hope that helps a little bit.

All the best

ne.____.il

Thank you for the link to Noseman's series on UV unwrapping. I'll definitely consult that series of instruction!

Dr. Sassi

You're very welcome, no.____.il,

He is also (typically) in the Ask The Trainer show twice a month:
https://www.youtube.com/c/MaxonTrainingTeam/search
Questions can be asked before the show or while it is live.
https://www.maxon.net/en/ask-your-question

We are both in the Learning/Training Team, but I know everyone has a different approach, and it is better to know more

Enjoy

Have a good one

CINEVERSITY

UV Unwrap Becoming Skewed?