effect.cryptomatteAt rendered the effect's input on every call to learn its pixel grid (up
to ~1 s per hover on a 3D precomp). The aux channels and that grid are now kept in a
CryptoProbe on the Session, keyed by the project revision, layer, effect, frame, scale and
render prefs (nested switches, draft shadows). On footage with nothing animated before the
Cryptomatte effect the frame is the source frame, so a still or a held frame keeps one
probe for every comp time. The effect's own Selection doesn't count: the probe never reads
it, so an animated Selection keeps the probe too.
Session::crypto_probe_ready says whether a query answers from the kept probe and changes
nothing. Session::crypto_probe_job builds it on another thread for the viewer; asking for a
job is starting it. Each started job has a generation: it stores its result only while it
is the newest, a newer job or an edit cancels it, and a panic in the build becomes the
probe's error. A cancelled build checks its generation between its stages (reading the IDs,
rendering the effect's input), so it stops early and lets go of what it read. `probeOnly`
makes cryptomatteAt / pickCryptomatte answer {pending} instead of building on the caller.
A pick re-keys the probe (it only edits the Selection), and undo, redo and history jumps
over picks keep it too (each pick is labelled "Pick Cryptomatte"). Any other edit, footage
changes, Open / New and Session::drop_crypto_probe (the eyedropper disarmed) let it go. The
slot's type is crate-private (the Session field stays public, doc(hidden), so other crates
can still build a Session); crypto_probe_stats and crypto_probe_jobs (jobs run, cancelled
ones included) are doc(hidden), for tests.
Matej Kozlovský