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8

UV unwrapping is a difficult topic. They can be both combinatorial algorithms or variational methods but in general they're optimization based, i.e. you setup an optimization problem and you solve it using some numerical optimization solver. I'm just going to give you some names and some libraries you can use eventually. I'll give you few names (both classic ...

2

Are the two sets well correlated? This would boil down to having a good set of vertex attributes for each set of uv's. If each set of uv's in mapping 1 has a know set of mappings in set 2 then it should be relatively straight forward to read from the first set of uv's and write to the second set. If this is as simple as vertex 1 has a mapping in uv set 1 and ...

2

I think it's easiest to get the tangent frame by writing the forward mapping from $(u,v)$ to $\mathbf{p}$: $$\mathbf{p}(u,v) = \begin{bmatrix} R \, \cos (2\pi u) \\ R \, \sin (2\pi u) \\ vL \end{bmatrix}$$ Then you can see that the derivatives are:  \frac{\partial\mathbf{p}}{\partial u} = \begin{bmatrix} -2\pi R \, \sin(2\pi u) \\ 2\pi R \, \cos(...

1

I can't give you a "better" approach here, but I think that the approach to project each individual brush image onto the surface of the object is not really a performance issue if you implement that using the GPU. Especially in an editor environment, where not much is going on in comparison to a computer game. All you basically want to do is to ...

1

As long as no pixel on the texture is used twice, you can render the geometry and display the uv-coordinates (texture coordinates). Usually they are a combination of red and green (2d). When using a brush, you only need to read out the uv-coordinates you've hit and color the texture at position (uv) in the desired color. Hint: paint onto a second texture, so ...

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