This is kind of a very specific issue and I'm not sure I'll find a (simple) solution for it. I'm trying to apply an image of a seamless pattern to a car livery (paint job) for a racing simulator. Obviously the car is a very complex shape and just using stencils has resulted in a lot of distortion, overlapping and ugliness. I've read about unwrapping the object and creating a UV map. The game already provides UV maps for all the cars and the standard way to create liveries is to simply paint over them in Photoshop. This is how the game understands the coordinates of the paint on the car so you have to use the UV maps from the game. The problem with this is that these existing UV maps have all kinds of irregular gaps and the different body panels and small parts of the car are seemingly randomly placed, so you can't just drag and drop an image on them. The way people normally deal with this is by manually matching the pattern across the different body panels. However, this is a massively tedious and time consuming process that I'm trying to avoid. I've found it damn near impossible with the pattern I'm trying to apply to the car. All I've managed to do with Blender thus far is to paint on the 3D obj of the car (by hand and with stencils) and it applying it to the game UV map so I can export it as a png and drop it in the game files.
Any help would be appreciated.
I'll include a picture of the problem I'm trying to solve, an Example of a finished livery and the UV map for the finished livery in Photoshop.
Edit: Damn. Thanks guys for taking the time to answer my question but I don't think I'll be able to pull this off. I just don't know what I'm doing. Maybe it'll help someone else in the future.