Write down the develop gestures, since only their author knew them

FR-UI-4 says a gesture with no visible counterpart is a feature only its
author knows about, and the vocabulary the application actually publishes had
two sections in it — the library grid and people. Develop had none. Every one
of its gestures was documented in the comment beside the `TouchArea` that
implements it, which is where the previous sixteen were before this scanner
existed, and unreachable to anybody not reading the source.

Thirteen now carry tags: magnify by pinch or wheel, pan a magnified frame,
fit and 1:1, hold to see the original, sample a neutral, undo and redo, step
through the folder, reset one control, show or hide a mask layer, choose a
group of adjustments, and copy and paste the settings. Each has a pointer and
a touch route, so none of them is keyboard-only.

Three bindings were genuinely missing and are added here rather than merely
described. Ctrl+C and Ctrl+V for the settings clipboard, which the Settings
panel's own comment has claimed existed for as long as the panel has and
nothing bound; and [ and ] to step through the adjustment groups. 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 name one of them — stepping is the
binding that survives a node being added, and "everything" is part of the
cycle rather than a way out of it.

Two are described and not bound. Resetting a control from the keyboard and
toggling a mask layer from the keyboard both need a notion of which control
or layer has focus, and the generated panel has none — the rows are a model
the repeater rebuilds, and inventing a focus ring for them is a larger change
than a keyboard shortcut. Both are reachable by pointer and by finger, and
the tags say so rather than promising a key that is not there.

docs/gestures.md

@@ -6,6 +6,81 @@
 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.
 
 17 gestures, in 2 places.
+29 gestures, in 3 places.
+
+## Develop
+### Set the white balance from the photograph
+- **Touch** — Press "pick" in the group's heading, then tap something neutral in the picture
+- **Pointer** — Press "pick", then click something neutral
+Sampling a neutral is the first move of the tonal pass — every colour judgement afterwards is measured against where the grey was put — and guessing at two sliders until a wall stops looking green is the wrong way round. One click is one sample and one step to undo; the sliders stay, because a sampled neutral is where the decision starts rather than where it ends.
+<sub>`ui/dr-ui/ui/adjust.slint:157`</sub>
+### Magnify the photograph by any amount
+- **Touch** — Pinch it with two fingers
+- **Pointer** — The scroll wheel over it
+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:1981`</sub>
+### Move a magnified photograph about
+- **Touch** — Drag it
+- **Pointer** — Drag it
+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:2134`</sub>
+### Take back the last change
+- **Touch** — Tap the step above the current one in the History list
+- **Pointer** — Click it, or press Undo in the History header
+- **Keyboard** — Ctrl+Z
+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:2301`</sub>
+### Do it again after taking it back
+- **Touch** — Tap the step below the current one in the History list
+- **Pointer** — Click it, or press Redo in the History header
+- **Keyboard** — Ctrl+Shift+Z
+<sub>`ui/dr-ui/ui/app.slint:2314`</sub>
+### Copy the settings from this photograph
+- **Touch** — Press Copy in the Settings panel
+- **Pointer** — Press Copy in the Settings panel
+- **Keyboard** — Ctrl+C
+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:2347`</sub>
+### Paste the settings onto this photograph
+- **Touch** — Press Paste in the Settings panel
+- **Pointer** — Press Paste in the Settings panel
+- **Keyboard** — Ctrl+V
+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:2359`</sub>
+### Change which group of adjustments is on screen
+- **Touch** — Tap a group in the rail down the left
+- **Pointer** — Click a group in the strip above the develop column
+- **Keyboard** — [ and ] step through them, wrapping round through "everything"
+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:2387`</sub>
+### Look at the photograph at 1:1
+- **Touch** — Double-tap the photograph
+- **Pointer** — Double-click it, or press the zoom readout floating over the canvas
+- **Keyboard** — Z
+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:2422`</sub>
+### Move to the next or previous photograph
+- **Touch** — Tap a frame in the roll along the foot of the canvas
+- **Pointer** — Click a frame in the roll
+- **Keyboard** — Right arrow or space for the next, left arrow for the one before
+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:2452`</sub>
+### See the photograph before you edited it
+- **Touch** — Press and hold "Before"
+- **Pointer** — Press and hold "Before"
+- **Keyboard** — Hold \
+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:2576`</sub>
+### Put one control back to its default
+- **Touch** — Double-tap its track
+- **Pointer** — Double-click its track, or right-click it
+The column is 280px wide and the colour mixer alone puts thirty-six of these in it, so a reset button per row would be most of the width. Two ways in with a pointer because right-click is the one a hand already reaches for and double-click is the one that needs no second button. A group's own reset is in its heading; this is the single control.
+<sub>`ui/dr-ui/ui/controls.slint:294`</sub>
+### Show or hide one mask layer
+- **Touch** — Tap the ring at the head of its row
+- **Pointer** — Click the ring at the head of its row
+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:137`</sub>
 
 ## People