Let’s say I’ve got a UV-unwrapped base mesh from which I’m creating a dyntopo sculpt. I’m aware that dyntopo strips the UV mapping from the mesh when it subdivides, basically creating “holes” in the UV where the new geometry is. Once the sculpt is done I need to restore those “holes” to something close to the original UV map so the two models can share textures.
Thing is, I know I’ve done this before but it was one of those late-night/early-morning experiments and I can’t remember exactly how I did it, and I don’t have the blend anymore. Googling gets me lots of hits on how to do this with identical-topology meshes, or how to start from a nicely-unwrapped high-poly model and go to a lower-poly version, both of which are useful but not what I’m doing here.