Lasso selection

The gesture is defined by where it starts. A press on an item means move that item; a press on empty canvas means draw a boundary, and everything the boundary catches is selected when the pointer comes up. That one rule is what lets a canvas offer dragging and selecting with the same button and no mode switch, and it is why the empty space between items is load bearing rather than decoration. While the drag runs, the outline is drawn live and the items it currently holds are previewed as selected, so the reader can adjust the boundary before committing rather than releasing and finding out.

Strictly, the lasso is the freehand version inherited from image editors, where the pointer trail is the outline and the shape can wrap around anything, and the rectangle is the marquee. In interface work the two words long ago collapsed into each other, and what most canvases actually ship is the rectangle: it is easy to aim, easy to describe, and cheap to test items against. Be careful with the word marquee on the web, where it is also the name of the scrolling banner element, so say rubber band or selection rectangle if the context could go either way. The list world’s equivalent is range select, which spans an ordered sequence with Shift and a second click; a lasso is what you reach for when items have positions rather than an order.

Three decisions separate a lasso that feels right from one that fights you. The first is whether an item counts when the boundary merely touches it or only when the boundary fully contains it: design tools mostly intersect, illustration tools mostly contain, and the choice needs to be stated in the interface somewhere because guessing it is miserable. The second is the modifiers, where holding Shift adds the new catch to the existing selection and Alt removes it, which is what makes an irregular selection reachable in several passes. The third is that a press on empty canvas which never travels far enough to count as a drag should clear the selection instead of drawing a boundary of zero size, which is the drag threshold doing its usual job.

Everything else follows from those. A lasso that reaches the edge of its container has to autoscroll, or a canvas larger than its window can never be fully selected in one gesture. The pointer needs capturing so the boundary survives the pointer leaving the canvas, since people routinely overshoot. And because the whole thing is a drag, it cannot be the only route to a multiple selection: a keyboard reader needs select all, a click plus a modified click, or a filter that produces the same set, and the resulting count needs announcing rather than only being drawn.