Offer the film stock in its own group, and let its list scroll itself

Two faults in one control, both reported from the tablet.

The stock picker appeared in every group. It is not a parameter, so it is not
a row, so the filter that hides every other control when a group is chosen
never saw it — "Kodachrome" sat at the top of Light, of Colour and of Detail
alike. Three places it does not belong, and the one it does no more prominent
than the rest. The descriptor has said `Effect` and only `Effect` since the
film moved there; nothing was asking it.

So the panel now asks. It cannot ask directly — a generated panel may not know
which operation a control belongs to — so the session answers, from what the
operation declares it is about, and a stock re-declared as something else would
move on its own. The flag is recomputed when the group changes as well as when
the film does, which is the half that would have made it stale exactly when it
mattered.

And the open list was unbounded, so it made the develop column taller and the
column scrolled as one: reaching Velvia dragged every slider below it off the
screen, an answer given once pushing aside the controls used constantly. It now
scrolls within a bounded height of its own.

That viewport is counted rather than measured, for the reason the tool rail
records a few files away: a viewport that asks a layout how tall it wants to be,
while the layout takes its height from the viewport, is a cycle Slint settles by
handing back the height it was given — and the content is then clipped in
silence rather than scrolling. Every row here is one fixed height, so
multiplying is exact.

The group rule has a test. The scrolling does not, and cannot: it is a layout,
and a layout fault is invisible to the compiler and to every assertion that can
be written about it.

docs/gestures.md

@@ -5,7 +5,7 @@
 
 Every entry here is extracted from the comment beside the code that implements it, so this file cannot describe a gesture the application does not have. Add one by writing a `GESTURE:` block next to the implementation; there is nowhere else to write it.
 
-30 gestures, in 3 places.
+36 gestures, in 4 places.
 
 ## Develop
 
@@ -25,7 +25,16 @@ Sampling a neutral is the first move of the tonal pass — every colour judgemen
 
 Anchored on the fingers' midpoint, and on the pointer, so the gesture reads as magnifying the picture rather than sliding it about. Double-tap is the way to an exact 1:1; this is the way to everything in between.
 
-<sub>`ui/dr-ui/ui/app.slint:1849`</sub>
+<sub>`ui/dr-ui/ui/app.slint:1941`</sub>
+
+### Paint a mask by hand
+
+- **Touch** — Choose Paint or Erase, then drag on the photograph
+- **Pointer** — Choose Paint or Erase, then drag
+
+A model's mask stops inside a shoulder and leaks into the hair, and no single edge control fixes two errors that go opposite ways. The whole stroke is one step in the history, so taking a mark back costs one press however long it took to make.
+
+<sub>`ui/dr-ui/ui/app.slint:2014`</sub>
 
 ### Move a magnified photograph about
 
@@ -34,7 +43,7 @@ Anchored on the fingers' midpoint, and on the pointer, so the gesture reads as m
 
 Only once there is something outside the viewport to reach, which is why the cursor becomes a hand exactly then. The view is clamped to the frame: panning past the edge would show undefined area beside the photograph, and that reads as a rendering fault rather than as the end of the picture.
 
-<sub>`ui/dr-ui/ui/app.slint:2002`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2147`</sub>
 
 ### Take back the last change
 
@@ -44,7 +53,7 @@ Only once there is something outside the viewport to reach, which is why the cur
 
 A whole drag is one step, so undo takes back a decision rather than a frame of a gesture. The list is there because arriving six steps back costs what arriving from one does.
 
-<sub>`ui/dr-ui/ui/app.slint:2169`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2314`</sub>
 
 ### Do it again after taking it back
 
@@ -52,7 +61,7 @@ A whole drag is one step, so undo takes back a decision rather than a frame of a
 - **Pointer** — Click it, or press Redo in the History header
 - **Keyboard** — Ctrl+Shift+Z
 
-<sub>`ui/dr-ui/ui/app.slint:2182`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2327`</sub>
 
 ### Copy the settings from this photograph
 
@@ -62,7 +71,7 @@ A whole drag is one step, so undo takes back a decision rather than a frame of a
 
 The panel is the copy that has to work: a tablet has no modifier key to hold and no menu bar to hang the action from. The shortcut is an accelerator for a control that is on screen either way.
 
-<sub>`ui/dr-ui/ui/app.slint:2215`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2360`</sub>
 
 ### Paste the settings onto this photograph
 
@@ -72,7 +81,7 @@ The panel is the copy that has to work: a tablet has no modifier key to hold and
 
 The button names what would be pasted — "3 adjustments", and whether the crop is coming with it — which the shortcut cannot say. Both paste the same scope.
 
-<sub>`ui/dr-ui/ui/app.slint:2227`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2372`</sub>
 
 ### Change which group of adjustments is on screen
 
@@ -82,7 +91,7 @@ The button names what would be pasted — "3 adjustments", and whether the crop
 
 The groups are whatever the operation set declares itself to be about, so there are as many as the pipeline has and no key can be assigned to one of them by name. Stepping is the binding that survives a node being added.
 
-<sub>`ui/dr-ui/ui/app.slint:2255`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2400`</sub>
 
 ### Look at the photograph at 1:1
 
@@ -92,7 +101,7 @@ The groups are whatever the operation set declares itself to be about, so there
 
 Noise reduction and capture sharpening are judgements about single pixels, and a fitted view averages several of the file's into each one on screen — so the frame looks softer than it is and the correction goes too far. The point and the magnification survive opening the next photograph, which is what makes checking the same eye across forty portraits forty keystrokes rather than forty pans.
 
-<sub>`ui/dr-ui/ui/app.slint:2290`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2435`</sub>
 
 ### Move to the next or previous photograph
 
@@ -102,7 +111,7 @@ Noise reduction and capture sharpening are judgements about single pixels, and a
 
 The edit on screen is saved on the way out, so stepping through a folder is as much a departure as going back to the grid and loses nothing.
 
-<sub>`ui/dr-ui/ui/app.slint:2320`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2465`</sub>
 
 ### See the photograph before you edited it
 
@@ -112,7 +121,7 @@ The edit on screen is saved on the way out, so stepping through a folder is as m
 
 Held rather than toggled, and no split screen: a split halves the working image on the tablet the column was sized for, and the comparison photographers describe making is a flick back and forth. It takes no history step, so checking whether a frame is overcooked costs nothing to undo afterwards.
 
-<sub>`ui/dr-ui/ui/app.slint:2444`</sub>
+<sub>`ui/dr-ui/ui/app.slint:2589`</sub>
 
 ### Put one control back to its default
 
@@ -130,7 +139,45 @@ The column is 280px wide and the colour mixer alone puts thirty-six of these in
 
 Disabling a layer is the before-and-after a local edit constantly wants, so it is one press away rather than inside the row. It is an edit and does take a history step, unlike holding "Before" — the layer really is off until it is switched back on.
 
-<sub>`ui/dr-ui/ui/masks.slint:164`</sub>
+<sub>`ui/dr-ui/ui/masks.slint:196`</sub>
+
+## Collections sidebar
+
+### Pick a collection up to rearrange the tree
+
+- **Touch** — Press and hold it until it lifts, then drag it
+- **Pointer** — Drag it, or hold it until it lifts and then drag
+
+The tree is inside a Flickable, which claims any drag beginning inside it — so with a finger a drag on a row is a scroll until something says otherwise. The hold is that something, and it is what every mobile list already uses to pick a row up. The row lifts the moment it fires, so the gesture says it has been understood before anything moves.
+
+<sub>`ui/dr-ui/ui/collections.slint:335`</sub>
+
+### Act on a collection — rename, nest, un-nest, delete
+
+- **Touch** — Press and hold the collection, then let go without moving
+- **Pointer** — Right-click it
+
+The hold arms a drag and opens this menu, and which one you get is decided by whether you moved — the same fork the grid uses. One menu for everything done to a row, because there is one hold per row: while the hold opened the offline question by itself, nothing else the tree can do had a touch route.
+
+<sub>`ui/dr-ui/ui/collections.slint:346`</sub>
+
+### Take a collection back out of the one it is nested in
+
+- **Touch** — Hold it, then drag it onto "All photographs" — or let go and choose "Move to top level"
+- **Pointer** — Drag it onto "All photographs", or right-click it and choose "Move to top level"
+
+Nesting is a drag of one row onto another, and its inverse had no gesture at all: "All photographs" refused every drop, which is right for a photograph — it is already in the library — and wrong for a collection, which has a top level to be returned to. Without it a collection dragged into another was in there permanently.
+
+<sub>`ui/dr-ui/ui/collections.slint:356`</sub>
+
+### Rename a collection
+
+- **Touch** — Hold the collection, then "Rename"
+- **Pointer** — Double-click its name, or right-click it and choose "Rename"
+
+Double-click is what a file manager and a Lightroom panel use for the same thing, so it needs no discovering — but nothing on screen says so, which is what the menu item is for.
+
+<sub>`ui/dr-ui/ui/collections.slint:369`</sub>
 
 ## People
 
@@ -223,7 +270,7 @@ This replaced a double tap, which had no visible state and could take forty phot
 
 "Any of them" is a union and "all of them" is an intersection. The tray is where both terms and the choice between them live, because a filter belongs on the filter bar.
 
-<sub>`ui/dr-ui/ui/library.slint:2096`</sub>
+<sub>`ui/dr-ui/ui/library.slint:2102`</sub>
 
 ### Resize the thumbnails
 
@@ -232,7 +279,7 @@ This replaced a double tap, which had no visible state and could take forty phot
 
 There is no wheel on a tablet, so without the pinch the cell size could only be changed by a control a finger cannot reach.
 
-<sub>`ui/dr-ui/ui/library.slint:2749`</sub>
+<sub>`ui/dr-ui/ui/library.slint:2755`</sub>
 
 ### File photographs in a collection
 
@@ -241,7 +288,7 @@ There is no wheel on a tablet, so without the pinch the cell size could only be
 
 The selection is what the drag carries, which is why selecting several is worth the mode: forty photographs file in one gesture.
 
-<sub>`ui/dr-ui/ui/library.slint:2946`</sub>
+<sub>`ui/dr-ui/ui/library.slint:2952`</sub>
 
 ### Open a photograph
 
@@ -250,7 +297,7 @@ The selection is what the drag carries, which is why selecting several is worth
 
 A tap opens; a tap that *moved* does not. Travel is what separates a deliberate tap from a hand brushing past, and it is the only thing that does: the two are the same length. An earlier version required the finger to dwell 120 ms instead, and that rejected ordinary taps — a real tap is often quicker than a brush.
 
-<sub>`ui/dr-ui/ui/library.slint:3214`</sub>
+<sub>`ui/dr-ui/ui/library.slint:3220`</sub>
 
 ### Rate a photograph without opening it
 
@@ -260,7 +307,7 @@ A tap opens; a tap that *moved* does not. Travel is what separates a deliberate
 
 A star has to take the press without it also reaching the cell, or every rating throws the user into develop.
 
-<sub>`ui/dr-ui/ui/library.slint:3334`</sub>
+<sub>`ui/dr-ui/ui/library.slint:3340`</sub>
 
 ### Choose the frame a folded burst shows
 
@@ -269,7 +316,7 @@ A star has to take the press without it also reaching the cell, or every rating
 
 A folded burst draws its earliest frame, which is a fact about the clock and not a judgement about the photograph — nothing in this application ranks a frame (FR-CULL-5). But the point of a burst is that one of the twelve is better than the other eleven, and the photographer is the only one who knows which. So the choice is offered on the frames themselves, while they are open and side by side, which is the one moment the alternatives are on screen to be compared.
 
-<sub>`ui/dr-ui/ui/library.slint:3465`</sub>
+<sub>`ui/dr-ui/ui/library.slint:3471`</sub>
 
 ### Drop the selection but keep selecting
 
@@ -278,7 +325,7 @@ A folded burst draws its earliest frame, which is a fact about the clock and not
 
 Distinct from Done, which leaves the mode entirely. Clearing keeps it, so the next selection can start straight away.
 
-<sub>`ui/dr-ui/ui/library.slint:4126`</sub>
+<sub>`ui/dr-ui/ui/library.slint:4132`</sub>
 
 ### Select everything the grid is showing
 
@@ -287,4 +334,13 @@ Distinct from Done, which leaves the mode entirely. Clearing keeps it, so the ne
 
 A scoped grid of two hundred frames is two hundred taps otherwise, and "all of them, except those three" is a far more common shape than the taps it took to say it.
 
-<sub>`ui/dr-ui/ui/library.slint:4143`</sub>
+<sub>`ui/dr-ui/ui/library.slint:4149`</sub>
+
+### Take photographs out of a collection
+
+- **Touch** — Select them, then "Collections…" in the selection bar
+- **Pointer** — Select them, then "Collections…" in the selection bar
+
+The badge on a cell says a photograph is filed in three collections and never which. This is the sheet that names them, and the only way out of one the grid is not currently scoped to.
+
+<sub>`ui/dr-ui/ui/library.slint:4264`</sub>