Limbs in Roblox have very simple UV maps: They have square tops and bottoms, and four rectangular sides, even if the actual geometry of the limbs is very different.
How is this done?
I need to somehow make a UV island fit a rectangle of specific scale and position.
I use Blender like most people, but if someone knows a dedicated tool for making sensible UVs I’ll happily use it.
The specific thing I’m trying to do is get three different meshes to all conform to a texture of this format:
I know a guy named Krystal Flynn that does this for a living, feel free to PM me so I can get you guys in touch to fix this problem!
Here’s the long answer:
UVs don’t have to stay on their separate islands (or even faces) as a normal unwrapped mesh like this
What I do if I know that my mesh’s islands are going to be a solid colour or have similar faces, I move all similar islands on top of each other:
So the answer to “how do they give complex geometry such a simple UV” is that the islands are stretched/vertexes are moved so fit that simple UV fits the mesh. This also keeps the textures simple and repeatable instead of having to give every mesh a unique UV.
Obviously this isn’t a perfect solution - you can see that some Roblox shirts don’t fit as snug on a Robloxian 2.0 as it does on a classic Robloxian, but they’re Close Enough 
which is fine for most people.
Don’t flood the thread with an overly-long pointless answer.
I clearly asked how to make a UV island fit a rectangle, what your answer says is where to move the UV islands to achieve an entirely different goal.
Not the nicest of replies to someone who explained the answer to your problem but alright. The shorter answer is to simply just hook up the meshes with a node map (Image Texture > Diffuse BSDF > Material Output, make sure to be in the Cycles render engine) then free placing the islands where you want them on the image texture.
Make sure that you apply the texture image first before starting to unwrap otherwise the islands will be stretched to fit the default 1x1 ratio UV map. If you do this right you’ll get a similar result as this, where each individual object (arms, legs, torso, helmet and all of that jazz are separated) use the exact same texture.
If this doesn’t answer your question then you’ll have to rephrase yourself and preferably appear less snappy when replying to people who take time out of their lives to try and help you.
You just gave the same answer as the last guy.
Free placing the islands isn’t enough: The islands have to be rectangles of specific dimensions.
Given how many likes your post has received though, I can already see where this is going; I’ve seen this situation happen before to someone else, where a bunch of people misinterpret an OP’s question, praise each other for giving such good answers, and the OP spends the whole time trying to explain what the question is.
It gets even messier when people who don’t understand the question assume that everyone else understood the question, so they interpret the question based on misinterpretations and the entire conversation derails at mach 3.
So I’ll just ask some more knowledgable modellers or figure it out myself.
Alright, I figured it out. It’s just a matter of pinning and unwrapping.
The likes are because he’s reacting to your condescending attitude towards people who are trying to help you. Cut it out.
If you don’t get your question answered the first two times somebody takes a stab at it, consider the possibility that you might need to rephrase it.
Being that you figured it out, I’m going to lock the topic now.
