Generate UVs

A model with no UVs yet shows Generate UVs in the UV Layout. It's the quickest way to a working layout: one click finds the seams, flattens the pieces and packs them into the square.

What it does

1. Finds seams where the model turns sharply, between faces whose directions differ by more than a set angle, so smooth curves stay in one piece and hard edges come apart.
2. Opens closed shapes: a smooth closed surface, such as a sphere or a torus, can't lie flat whole, so it's cut along the planes through the model's middle, and a torus across its hole too.
3. Flattens each piece and packs them into the 0-1 square.

Afterwards

The seams it found are ordinary seams. Split and Weld more where you'd like, then Flatten again. To place every seam yourself instead, mark them before your first Flatten.