A pinch is not one zoom step, it is a stream of them, and every step
changes both the column count and the capacity — two reports. Each report
re-queried the catalog, rebuilt all 360 rows of the model, re-read the
badges and ratings for every one of them and spawned a thumbnail batch,
synchronously, on the thread trying to draw the frame. Twice per step.
That is why zooming juddered while scrolling the same grid is smooth: a
scroll reloads a few times per screenful, a zoom reloaded twice a frame.
None of that work is urgent, because none of it is about which
photographs are on screen. The window holds the same images however they
are laid out — the model already has them, and the cells re-flow from
`columns` and `cell-size` with Rust not involved at all. What the reload
actually recomputes is which cells begin a row, so the month headings
land correctly, and which thumbnail size class to ask for now. Both can
wait for the gesture to finish, so both are now coalesced behind a single
settle timer: replacing the timer drops the previous one, and only the
last report of a run lives long enough to fire.
The anchor is captured on the first report of a run rather than read when
the timer fires. As the grid re-flows the viewport keeps its pixel offset
while the rows move underneath it, so the view drifts and reports the
drift; reading the anchor at the end would faithfully return to wherever
it had wandered. Taking it at the start returns to the photograph the
user was looking at when they started the gesture.
dtourolle
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