Every slider, curve-point and crop-handle drag ran a full render
straight from its `moved` handler. A render ends in a blocking GPU
readback, so that stall sat directly on the input path: touch events
arrive far faster than a render completes, the queue backed up, and
positions reached the handlers several samples stale — the jumpy
dragging.
The worse consequence was gestures being lost outright. When events go
unconsumed for long enough Android reclaims the stream and hands it to
the view underneath, so a drag stopped mid-gesture never received `up`,
only `cancel` — which every handler here treats as "abort the drag".
`redraw` no longer renders. It marks the canvas dirty and posts one
render onto the event loop, coalescing any further requests that arrive
while it is pending, and re-checks the flag afterwards so a value that
moved during the render is not left on a stale frame. Handlers now
return immediately, which is what keeps the gesture consumed.
A zero-delay `Timer` rather than `invoke_from_event_loop`: the latter
requires `Send` and this state is deliberately `Rc` on the UI thread.
All existing `redraw` call sites are unchanged — the signature is the
same and coalescing is internal.
dtourolle
31dd86d8c0