How it works
A model is a rig:
- Parameters are the numbers you drive: head angle, eye open, mouth open.
- Deformers bend and rotate regions of the model as parameters change.
- Meshes are the textured triangles that get drawn.
- Parts group meshes and can fade as a whole.
- Physics swings some parameters by itself (hair, earrings) from others.
You never touch deformers or keyforms. You set parameters, call update, and read where every mesh's vertices ended up.
Coordinates. Vertex positions are in model units. To get pixels on the
authored canvas: pixel = unit × pixels_per_unit + origin, with y running
down. UVs are 0 to 1 over the texture page, with v = 0 at the top row of
the image. Drawing shows how to frame it on screen.