Pan and swipe share an onset and must split on speed
Aliases: pan versus swipe · velocity split · gesture onset
What it is
When a finger goes down and starts to move, the system does not yet know whether this is grab the surface and look slowly or throw a page command. The first millimetres of both gestures look the same. The split is speed (and speed with distance): slow sustained motion stays with pan tracking; a short ballistic stroke becomes a swipe at lift. This is disambiguation from the pan side, not a rewrite of swipe’s three gates.
Why it happens
The recognizer stays neutral in the early contact: content may track a little, but it does not turn a page or fire a command. If speed stays low, tracking deepens into a pan. If speed crosses a threshold inside a short displacement and then lifts, tracking is discarded and a swipe fires. Locking to pan too early turns a committed flip into a tiny canvas nudge. Locking to swipe too early yanks a slow inspection over by a page. Neutral tracking has to be small enough not to look like a flip, large enough to feel like a live surface. A medium-speed lift can still exit into inertial pan rather than a swipe detent—that is a fling, a third door, and it must not share the swipe’s velocity threshold.
Studying it
On a surface that both pans and pages (a pinchable paging magazine), run “inspect this corner of the image” and “go to the next article.” Vary the neutral window and the speed threshold. Dependent measures include inspections interrupted by a page flip, and flips that became small pans. Plot the decision boundary on a speed–distance plane and see whether the two tasks’ traces separate. The overlap is where the product “sometimes works.”
Where it stops holding
A pure map has no swipe command, so there is no split: every motion may track, and lift may coast. A pure pager has no pannable canvas, so the neutral window should be shorter or flips feel meaty. System edge gestures key off origin, not this speed boundary. Two-finger motion usually goes straight to scale/rotate; the one-finger speed split does not apply.
Applying it
- On UI that offers both canvas pan and paging swipe, write the exits: sustained motion below a speed = pan; short high-speed lift = swipe; medium-speed lift = inertial pan. Do not share one threshold across three doors.
- During the neutral window, track only a little; do not yank the whole page and then decide to put it back.
- Alternate ten inspections and ten article-flips, and plot each trace on a speed–distance chart. The classes should land on opposite sides of the boundary. If they mix, lengthen the neutral window or raise the swipe speed threshold; do not twist both knobs at once.