Marquee selection must start in empty space or it conflicts with object dragging

What it is

A marquee selection start region restricts rubber-band selection to blank canvas space; pressing on an object remains reserved for selecting or dragging that object. This division prevents one press-and-move sequence from ambiguously moving an object or drawing a selection rectangle.

Why it happens

The initial contact point supplies object semantics: starting on an object acts on it, starting in space acts on the workspace. The system then branches into object drag or marquee drawing after movement begins. If both behaviours could start from an object, a distance threshold alone cannot tell whether the intent was to move that object or to lasso its neighbours.

Going one layer deeper into how hit testing actually runs: at the instant of press-down the system performs a single top-down hit test, walking the render stack from the topmost object and stopping at the first one whose geometry or visible pixels contain the point — that decides "on an object." The branch is then locked in; even if the object later moves out from under the pointer mid-drag, the system does not re-evaluate. This has two consequences. First, an object's hit region is usually wider than its visual bounds (see cursor hotspots and hit testing), so a press that lands on a translucent edge or an anti-aliased pixel still counts as "on the object" — a deliberate margin, not an error. Second, because hit testing runs only once at press time, a press that registers as empty space stays on the marquee branch even if the finger later sweeps across many objects; it never switches to dragging mid-gesture.

Where it stops holding

Select-all modes, locked objects, and layer editors may use different rules but should show the active mode. A canvas packed with objects has no empty start region, making marquee unreachable; it then needs a menu, modifier, or temporary space. Touch often lacks a sufficiently precise blank point either — a fingertip's contact area spans several millimetres, and tightly packed icons leave no pixel band that reliably registers as "empty." Marquee selection is effectively unusable on touch in that layout, and needs a substitute route such as a long-press-to-select mode.

Applying it

• Interpret object starts consistently as object actions and empty-space starts as spatial selection, with hit testing evaluated once at press time.
• Offer an explicit marquee entry point (a toolbar "select" mode) when objects are dense or no blank area exists, instead of relying on people finding a sliver of empty space.
• How to check: record press points pixel by pixel at object edges, translucent regions, and narrow gaps, and compare against the resulting branch; on touch, additionally measure the offset between the finger-occluded contact point and the intended visual hit target.

Related

• Same group: C1.09.2 Intersection and containment selection yield different results · C1.09.3 Marquee selection and canvas pan need modes or modifiers when sharing empty space
• Nearby: C1.05 Cursor hotspots and hit testing · C1.08 Drag and drop
• Search terms: marquee selection · hit testing · gesture ambiguity