Let the crop be held to a ratio while it is dragged

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A photographer cropping for a print, a phone wallpaper or a 16:9 frame is
not choosing four edges — they are choosing one edge and a known shape.
Free-dragging every corner made them do that arithmetic by eye on every
drag, and get it slightly wrong.

The panel now offers Free, Original, 1:1, 3:2, 4:3 and 16:9, with a
Portrait switch for the ones that have two orientations. Original follows
the frame rather than naming a number, so it stays right on the next
photograph from another body and after a quarter turn.

**The ratio is of output pixels, and the rect is not.** `CropRect` is
stored in fractions of a frame that is not itself square, so holding a
shape needs the frame's size — `ratio * height / width` of the frame.
Skipping that gives a "1:1" crop that is square only on a square
photograph, which is the one case nobody would test on, so the conversion
lives in `CropRect::with_aspect` where it is explained and pinned by a
test that asserts the fractions are *not* equal.

Two decisions worth recording:

The reshaped rect **grows** onto the ratio rather than shrinking onto it,
then scales down only as far as the frame's edge demands. Fitting inside
instead makes a one-axis drag do nothing at all — the other axis clamps
the first straight back, and the handle simply refuses to move.

The overlay now reports **which corner the drag is holding**, because
reshaping onto a ratio has to know which corner is nailed down and only
the handle that took the press knows that. A move reports no corner and
keeps its shape: reshaping about a centre would pull an over-moved rect
smaller instead of sliding it along the edge.

The lock lives with the window rather than the session. A `DevelopSession`
is per image, and cropping a set of frames to one shape is exactly when
the lock earns its place. It is not an edit and reaches no sidecar — what
is saved is the rectangle it produced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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dtourolle

2026-08-29 13:48:51 +02:00

co-authored by Claude Opus 5

parent dbaf5358d1

commit e6ad906bc1

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