`:over` was specified in animation-model.md, refused in two places, and
produced by nothing: `check-unimplemented!` threw on read and `channel/problems`
reported it. It reads now. This is the part of the model the rotoscoping half
depends on — generate motion, correct it by hand, turn the knob, keep the
correction — and it was the last thing in the design that had never been tried.
The shape that made it small: A LAYER'S VALUES ARE A CHANNEL.
{:id :nudge :support [88 98] :op :offset
:values {:animated? true :interp :linear :keys {88 [2 0], 96 [0 0]}}}
So the three commands the lane model asks for over a selected range — a
constant adjustment, a ramp, a return motion — are one mechanism and not three:
framed values say the same thing on every frame they cover, keyed values move,
and neither needs a new way to say what a value is over time. A layer reads
through `value-at` and `cursor` like any channel, which is also what stopped
blending from becoming two implementations: `over-at` is shared, and the
specification and the playback path differ only in how they READ a layer —
recursively through `value-at`, or through a reading head of its own. One level
deep; a layer's values may not carry layers, which the stack already orders.
That was the risk worth spiking for. A cursor that drifts produces the wrong
pose rather than an error, and a stack means several reading heads per channel
where there was one. The agreement test that holds the cursor to the
specification in forward, backward and random frame order now covers stacked
channels too — including a layer whose head is asked for nothing across the long
stretches outside its support and then asked again, which is where drift would
hide.
`:support` is half-open and explicit. Outside it the base evaluates exactly as
it did before, which is the whole difference between a bounded correction and
inserting boundary keys: the latter alters the neighbouring segments, and the
lane model says so.
A LAYER HAS NO TIME SPACE OF ITS OWN, and this is the design question the doc
left open. Its support and its values' keys are in the frames the base channel's
keys are in — the node's. A correction on a lane is therefore in lane frames and
reaches across the drawings exposed beneath it; one on a single occurrence is in
that occurrence's frames and travels with it when the exposure moves. Ownership
had already answered it, so there is no field to disagree with, and both halves
are under test at lane level.
Two things cost nothing, which is worth recording. A channel is ONE LEAF, so a
correction persists inside it with no codec change at all. And `node/problems`
already reports every channel's problems, so a malformed layer surfaces at the
document level and in the sequence commands' post-check without plumbing.
What is still missing is a command that MAKES one, and with it the question of
how a view offers a constant, a ramp and a return over a selected range. The
evaluator no longer has an opinion about that, which was the point.
`offset` adds component-wise and never writes into a dense value, which is a
view onto the block itself; a shape mismatch throws rather than being dropped,
since a correction that silently does not take is the failure this design exists
to prevent. `replace` can supply a value over an absent base and `offset`
cannot, as animation-model.md required.
408 tests, 5,655 assertions.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Everything could only be added to the end, because `append` computed its own
position — the max end of the lane — and so had no opinion to state. Insert is
not a new command; it is the argument that function was missing. `:at` takes a
lane frame or `:end`, `:end` is the position where nothing has to move, and
appending stops being a separate operation from inserting. New, reused and
duplicated drawings all take it, because there was only ever one placement rule.
Placing ripples: occurrences at or after the position move later by the new
exposure's duration, and `:keep` against `:grow-symbol` still decides what
happens at the shot's end. OVERWRITE is deliberately not a policy argument yet.
Taking frames away from the occurrence already there is TRIMMING, and an
argument whose second value is unimplemented is worse than an argument that is
not there. A position strictly inside an existing exposure refuses and names
`split`, rather than splitting on the quiet: one command performing two is how
a command stops being predictable.
Then split, which turned out to cost almost nothing, and that is the
interesting part. The two pieces keep ONE `:time` and differ only in `:span`.
The right piece's own frames therefore carry on exactly where the left's
stopped, so its source clock, its keys and its corrections go on meaning what
they meant: a held drawing holds the same frame either side of the cut, and a
playing insert plays through it without a seam. There is no arithmetic on
in-points to get wrong, and no shot-length question, since the pieces occupy
the frames the one exposure occupied. The test samples every frame before and
after and asserts the picture is identical — for a hold, for an exposure with a
correction of its own, and for a playing insert.
That is not a clever split. It is `:span` being in the node's OWN coordinates,
which was decided long before there were lanes, paying for something it was not
designed for. The same property is why extending a hold leaves lane keys alone.
Both new commands act at the playhead, which needed `lane-frame` — the symbol's
frame as a frame of the lane's own time, nil through a stepped or looping lane
where one is not the other. Nil refuses; it does not snap to a nearby frame.
Two smaller things found while doing it. `placeable` promised "a whole lane
frame" in its refusal and then accepted 2.5, so both it and `split` now require
an integer, as `extend-hold` already did for its delta. And `lane-end` is
private: `:end` is the only way to ask for it.
401 tests, 5,612 assertions. The browser flow now splits an exposure at the
playhead and puts a drawing in the gap, and checks that six exposures are still
one row.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The model's whole claim is that content and its occurrences are different
things, and until now nothing in the editor could tell them apart: you could
make a drawing and time it, but not expose one drawing twice, and so never find
out whether an edit arrives in two places. That is the first proof obligation in
the lane model and it was the one the commands could not reach.
Three commands, and the distinctions between them are the point:
reuse another occurrence of the same drawing. A decision to share,
made on purpose, because sharing discovered later — when an edit
turns up somewhere you did not expect — is the bad version.
duplicate a copy of the drawing, appended, for when what is on screen is
the starting point for the next one.
make unique this occurrence gets a private copy; the others keep sharing.
The undo of reuse, and refused when nothing else uses the
drawing: a copy nobody asked for is a second identical symbol in
the library for no reason a person could see.
Duplicate copies the CONTENT and not the exposure. Its new occurrence is a plain
one-frame hold, not a copy of the source occurrence's transform or corrections,
because those belong to that use of the drawing — carrying them over would make
duplicating a drawing quietly duplicate the treatment of one exposure of it.
A copy is SHALLOW by default and keeps its references to other symbols, so a
head built out of reusable eyes still uses those eyes. `:deep? true` copies
everything it places with new ids throughout. The lane model asks for both and
says why: never promise decoupling while leaving the edited object shared, and
only the deep copy can keep that promise. `bring/symbols` already did the
reachability walk and the id remapping, so the deep copy is that function
pointed at its own clip.
`node/sources` was still being read as a SET at five call sites, each with a
comment about a lane that cuts between several drawings — the keyed source that
no longer exists. An occurrence names one symbol, so they now ask `node/source`,
and `placed-frame` answers with `:symbol` rather than `:of`, which was the last
echo of the retired field name.
To let the commands use `clip/free-id` and the copy machinery, the lane's own
validation moved from `domain/sequence` to `domain/symbol`, which is where it
belonged anyway: a sequence is the one composition rule a node map carries, and
it now sits beside the parent and stencil checks rather than in the namespace
that happens to build lanes. That also breaks the cycle — sequence can require
clip and bring, and nothing below it requires sequence. Preconditions still
check only the LANE's shape: refusing an exposure edit over an unrelated defect
elsewhere in the symbol would be this command answering for a part of the
document it never touches.
The cel strip gains reuse, duplicate and make unique, the last shown only where
the selected exposure actually shares its drawing. Drawing on twos is also now
under test: exposure length is the cadence, the lane's transform has its own
clock, and it still moves on every frame — stepping it would be the cel cadence
leaking into continuous motion.
397 tests, 5,561 assertions. `test/browser/sequence.mjs` drives the three new
commands through the real editor and checks that three exposures are still one
row.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A lane's drawings were going to be one instance whose source was a KEYED
channel: frame 0 says `:drawing-a`, frame 4 says `:drawing-b`, and the cels of
a row are that channel's keys. Two things followed from it, and both were
wrong.
The first is that playback meant whichever shape the channel happened to have.
A framed source played its symbol; a keyed source froze the selected frame.
So `node/placed-at` read animation out of storage, and adding an ordinary key
to a still turned it into an animation — the last-key bug, which was not a bug
in the code so much as the rule working as written. But WHICH drawing is used
and HOW time runs inside it are independent questions, and all four combinations
are ordinary: hold one drawing, play one animation, cut between held drawings,
cut between playing ones.
So an occurrence names one symbol in `:source {:symbol ...}` and says how its
source time advances in `:playback {:in :speed :end}` — `source = in + speed *
f`, a hold being speed 0, with `:stop`, `:hold` or `:loop` at the end named
rather than guessed. `node/placed-frame` samples it forwards, which works for
holds too, and `node/source-time` is the separate, invertible edit map, nil
where inversion is meaningless. The two were one function before, and a hold
had to lie about one of them.
The second is that a keyed source only looked necessary because an occurrence
was assumed to need a ROW. It does not. A lane is a group with `:layout
:sequence`, its occurrences are ordinary instances in the same flat node map,
and `timeline/rows` draws them as cel blocks on the lane's own row: twelve
exposures, one row, each cel still separately selectable and addressable. The
vertical growth that justified the keyed source is a presentation question, and
it is answered in the view.
`arthur.domain.sequence` holds the first commands over that shape — add lane,
append drawing, extend hold — each one history step, each refusing rather than
half-applying. Extending a hold leaves the lane's keys at their authored times,
because you are adjusting drawings underneath timed motion; a correction owned
by an occurrence travels with it. Ownership does that work, so no key needs a
flag saying what it follows. Ripple past the symbol's end is refused with the
frame count it would need, and `:extent :grow-symbol` is the caller saying yes.
`clip/blank` no longer carries `:subjects {} :features {} :groups {}`. Empty
maps write no leaf, so a blank document could not survive its own round trip —
`leaf/leaves` promises exactness and was the only honest side of that.
Documents are schema 3. A version 2 document is not read; nothing here converts
one. `docs/lane-model.md` is the design, and says which of its parts are built.
392 tests, 5,525 assertions, and `test/browser/sequence.mjs` drives the editor
through create, hold, explicit overflow and undo.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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