UV Straightening and its perks on LOD generation
Why Do we straighten UVs?
So people have been wondering why we are so anal about straight UVs, and it basically comes down to LODs. LODs could be used for various things, the obvious is that a mesh gets lower poly over the distance that it is drawn. The further away a model is, the lower the polycount. But they will also jump into action when you have a version of your game running on lower end specs, say Fortnite running on Mobile, or spyro running on Switch. While we usually do not create the LODs ourselves, they will be created after we delivered our work.
For the Level of Detail meshes we need to keep things straight to avoid texture breaks when loops get deleted. It doesnt really matter if this is done by algorithms like Simplygon or other automatic/semi automatic solutions, or if you do it by hand. ideally we want to keep everything between majore landmarks on a model straight. On a character that would be joints. On a prop this would be defining angles. But straight doesn't mean it has to be perfectly horizontally or vertically aligned. diagonally would work too! dependent on your final texture resolution horizontal or vertical is preferred, to avoid visual stepping.
How much of this makes sense in the age of nanine? i assume it still makes sense, because any automatic lodding solution ideally is able to kill mesh detail without hurting UV seams? But i have no data to prove that.
I know from one of our projects that Nanite still worked better with clean UVs than just some UVs
here is an example of hand UVs that will work better with Lodding.
Straightening UVs in 3dsmax
It might be that your version of max doesnt allow you to do it anymore. UNLESS you install one of our tools which you can find here
So my main tool of choice is welding verts that are not connected.
When asked why that feature was removed from 3dsmax, support told me, that it was never part of max and should by definition not work. If it did... it was a bug.
OH WELL...
unless you plug this script into your macroscripts folder and run it, that is
nevermind the old UI, it works in Max 2025 just as fine as in Max 2011 
this is the script you need to run to enable it in your version of max if it doesn't work what i am about to show you.
a normal relaxed UV layout like you would get from many apps nowadays. It's mathematical accurate. most faces are in line scale wise, there is little stretching. all cool. But this doesn't LOD well and it doesn't stack well inside the UVs puzzling phase.
My suggestion to what it should look like. Note: it doesnt have to be all rectangular. but lines should idealy be straight so when lodding you can remove loops without creating issues on the texture side.
So here is how i get there:
after running the script (its a toggle should only be needed once) set up the wel treshold to something high. be aware with the script on you can now weld the entire UV space into a single point.
I am sure with pinning and automatic live UV stuff you can get similar results nowadays
Weld all the verts on the centerline
Now relax the selection by Face Angles. The result is a pretty solid base to go on with. Note how the centerline is pretty well maintained not collapesed. not straight yet but easy to work with.
select the bottom edge and straighten it
invert the selection and relax all the other points but the just straightened line
do the same for the top line
and the sides
select a row of faces alongside one side of the centerline and scale it a bit away from the center
select and relax the center point
Tadaa! you got a nice and clean UV island to work with.
There is one downside to this method. you will get a decent amount of stretching in the crotch area. But this can be ignored or worked around well enough in many cases.
You obviously can do the same for hands:
or even the face:
Common Issues with straightening
One usual issue with edge straightening is, that people tend to do it blindly. and ignore obvious stretching caused by it
This is stuff we definitely should avoid, so dont just blindly straighten everything. check your UVs on the model for stretchmarks
luckily enough usually this is simple enough to fix
Straightening UVs with UnwrapPro (plugin)
We'll be using a third-party plugin for 3ds Max called UnwrapPro: https://mariussilaghi.com/products/unwrap-pro
This plugin adds a new modifier to 3ds Max, Unwrap Pro. It's almost the same as the default Unwrap UVW modifier with an added tab.
The second (and perhaps the most important) is the Unwrap button. Its basically a peel + relax with an improved relaxing system that provides less distortion than usual. (iterations = number of times relax is applied to the UV) The relax method in this plugin also works with Max's native vertice pins (unlike the default relax option) so we can take advantage of that to quickly straighten UVs while maintaining them overlap free. Example below:
1. Set up the seams for your UV island like you regularly would. We then set the peel mode to LSCM so that we can pin vertices (from 3ds Max 2020 onwards)
2. Select a loop that you want to straighten, straighten it using the align horizontal/vertical tools from Max and pin the selected vertices
3. Select the whole island, make sure to have "Prevent Border Overlap" checked on the modifier, and click Unwrap and see the magic happen!
4. Continue pinning and straightening loops, and hitting the unwrap button until you reach the desired result, knowing the UV will be relaxed while respecting pins and avoiding border overlaps at all times!
5. All done!
Sometimes you might need to click the Unwrap button a
few times until it relaxes the UV completely. Spacebar is the default
shortcut for this but you can set your own in the modifier's settings.
Troubleshoot:
In case the UV island starts acting up when you hit Unwrap, you might
need to check if you have any existing overlaps on your island, as the
plugin usually doesn't like that.
You're using a different software? Maya, Blender? You name it, feel free to add your method!
Replies
Default Blender can do decent "rubbergloving" of UVs by leveraging pinned UV verts. As follows :
- Bringing the desired UV verts between fingers together, either by scaling them down to 0 or by pseudo-welding them (the weld tool does *not* weld them like oldschool max would, but it does bring the verts to their center location in one single input so this can be a little faster than using Scale).
- Then, designing the desired outline of the glove shape by manipulating verts as desired.
- Running Unwrap on that, hence relaxing things within the pinned outline.
- Fixing anything that still needs straightening, then running Unwrap again.
Now of course this doesn't rely on performing an initial relax on the "stitched fingers" setup. Not sure if this is a good thing or a bad thing, but I believe that the overall time involved is similar.
I need to check if there is a way to select a bunch of verts along an edge, and have them be spaced similarly to their spacing on the mesh. This could probably shave off some time here and here, when setting up the outer borders of straightened islands.