A history state was a Preset — a map of scalars — which was right while
every edit in the graph was a parameter. A spot is not one, and undo is the
first thing anyone does with a repair: place it, dislike it, take it back.
Left as it was, that press would have stepped some unrelated slider and
left the spot on the photograph, which reads as undo being broken rather
than as undo being absent.
So a state is now the pair, params and spot set. The same door is the one
the mask stack will come through: mask edits are outside undo today for
exactly this reason, and FR-DEV-5 is not finished until they are not.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Develop edits now save themselves to a sidecar the moment you leave the
image, so until this there was no way to undo one — the mistake was
persisted and the only recourse was to remember the old number.
The history is a stack of snapshots, because the edit graph is already
plain data: `Preset::capture` reduces it to what differs from default and
`Preset::apply` puts it back, so undo is those two calls and nothing else.
A command object per action, with an inverse beside it, would have been a
second thing every operation had to register — and operations are declared
in YAML precisely so that a new one needs no code written for it. A
snapshot cannot fall behind them.
The interesting part is coalescing. A slider drag emits an event per frame
and must be one step, not forty. Nothing in the interface reports a gesture
boundary — the same wall the render coalescing hit, and it is answered the
same way rather than by threading a "finger is down" out of every slider,
curve point and crop handle. What stands in for the boundary is the control
plus recency: changes to the same control within 700 ms amend one step.
Which control is "the same" is asked of the graph, not listed: an operation
whose declared presentation claims a parameter is one where a single
gesture moves several — a curve point carries an x and a y — so those
coalesce as one widget. Nothing in the history names the tone curve.
The compromise, and it is a real one: a control let go of and picked up
again within the window is one step rather than two. Buying the other
answer costs a gesture-boundary signal on every control, which is more
surface than the difference is worth.
The stack is bounded at 64 states for NFR-RES-1 — a develop session stays
open for hours. Sixty-four rather than a byte cap: what is being bounded is
steps a photographer would want back, and a byte cap would give the
elaborate edit the shallowest history, which is exactly backwards.
The session owns its history and every mutator records into it, so the
callbacks in `lib.rs` cannot change the edit and forget to — with a dozen
generic callbacks that would have been one press of undo away from wrong
every time a control was added. Opening a photograph makes its stored edit
the floor rather than a step: it is not work done in this sitting, and an
undo reaching behind it would discard a previous session's edit and then
save that on the way out.
Not yet done, from FR-DEV-5: history is per-session and in memory, and
there are no named snapshots. What mattered was that a saved mis-drag had
no way back at all.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
dtourolleandClaude Opus 5