Dragging the crop rectangle tracked the pointer at half speed: the rect
slid out from under the cursor, and the handle being held stopped being
the one under the finger. On a photograph where the whole point is to
place an edge by eye, that made the tool close to unusable.
The cause is that a `TouchArea` reports `mouse-x` relative to itself, and
every area in the overlay is positioned *by the very rect the drag is
editing*. Rust echoes the applied rect back on each step, so the area
moves under the pointer and the reported position falls by exactly the
amount it had just risen. `mouse-x - pressed-x` therefore subtracts the
drag from itself, and the fixed point of that feedback is a rect that
moves half as far as the pointer does — which is why it looked like
sluggish tracking rather than like a coordinate bug.
Both terms are now taken in the frame's own coordinates: `parent.x +
mouse-x`, where `parent.x` tracks precisely the movement `mouse-x` lost,
with the press captured in those same coordinates on the way down. The
two movements cancel and the rect follows the pointer exactly.
`GradientHandles` in masks.slint was already written this way, and for
the same reason — its handles are placed by the mask they drag. The
header note here now says why the shape matters, since the wrong version
compiles, looks plausible, and is only wrong once the rect starts moving.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5
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