`craft_lottie::model` is the Lottie document as the file has it: one
struct per object of the lottie-spec 1.0 object model (animation, assets,
layers by type, transform, masks, effects, shape items, text, markers,
fonts, glyphs), one field per key. `Animation::read` reads within
`Limits` (bytes, nesting, layers, assets, shape items); `to_json` writes.
Keys the model does not name, values of another type than expected, and
layers and shape items of an unknown type stay in `extra` and are written
back, so a document survives a read and a write. Animatable properties
stay JSON (`Animated`) and are read with `read_prop`.
The encodings every Lottie layer, mask and shape reuses, on serde_json
values: the document header, animatable properties and their keyframes
(legacy end values, hold keys, spatial tangents), ease tangents to and
from speed and influence, bezier paths, gradient stop lists, the tolerant
number and colour readers, and embedded images as data URIs.
Taken from effectcraft crates/lottie at e18f48fb (anim.rs, shapes.rs,
import.rs, export.rs, base64.rs) with EffectCraft's project types replaced
by plain values. The layer, shape, effect and text mapping stays in
EffectCraft, and dotLottie is ZIP, which is not this crate's format.
Dylan M. Taylor