The drop target must stay visible during a drag

What it is

A drag closes the loop by carrying an object to a drop. Finger and floating object both cover the screen. If the drop, insertion line, or receiving slot sits under the contact, people drop blind. Keeping the target visible means that throughout the carry they can see which slot they are aiming at, rather than learning it at lift.

Why it happens

Direct touch collocates the drop with the effector—an advantage for tapping, occlusion for dragging. A pad covers about a square centimetre, and a floating thumbnail stacks another layer. Without an offset pointer or an insertion gap, hit-testing still runs under the contact while vision cannot. Usual compensations: float the object above or beside the contact, open a gap in the list at the predicted insertion, highlight a receiver’s border on roll-over. The gap and ghost slot are space for the drop, not decoration. Tracking delay puts the gap where the finger already left, so visibility has to keep up in time as well as in space.

Studying it

Run drop tasks with different offsets (none, above, a side magnifier) and different insertion previews (highlight, opened gap, numbered slots). Dependent measures include drops into the wrong neighbor, corrections before lift, and reports of “I could see the slot I was entering.” If the finger blocks eye tracking, compare the lift drop with the slot the participant points to as “the one I meant.” Effects are largest on small, dense targets; a large card grid hides the problem.

Where it stops holding

A stylus occludes far less than a finger, and zero offset may be enough. Turning drag into “select, then tap the destination” moves visibility onto two taps and out of in-carry occlusion. AR or mid-air drags have no pad on the plane, but they have depth alignment; touchscreen results do not move unchanged. When auto-scroll carries the drop out of the current viewport, visibility depends on edge scrolling (next) rather than offset itself.

Applying it

• Do not glue the floating object under the contact: shift it up, shrink it, or leave only an insertion line at the contact and park the thumbnail above the finger.
• Open a stable gap in the list at the would-be insertion; let receivers answer “you are aiming at me” with a border or a slot number.
• In the last ten frames before lift, check whether the insertion line is under the pad and whether the gap tracks the contact. Ask people to name the slot number before they lift; a mismatch means visibility was not sustained.

Related

• Same group: C3.04.1 Drag may start from a long-press or from an immediate down, with different meanings · C3.04.2 Competition between drag-start slop and scroll-direction discrimination · C3.04.4 Auto-scroll and speed when a drag hits the screen edge
• Adjacent: C2.05 Finger occlusion · C3.18 Long-press drag to reorder
• Search: drop target · finger occlusion · insertion caret