bezel

Components / Layout & organisation

Floating panel

Markdown crates/ui/src/floating.rs

use ui::floating::{self, Floating};

// The host holds the state, like a scrollbar's.
meter_at: Floating,   // Floating::new(Painter::of(cx))

div().relative().size_full()
    .child(page)
    .child(floating::panel("meter", &self.meter_at, home, child))

The panel lays a full-size layer over its container and places the box inside it, because the drag has to be heard somewhere larger than the thing being dragged. A pointer that outruns a frame is outside the box for most of the gesture, and a listener mounted on the box would go quiet and leave it stranded behind the cursor. scroll hangs its thumb drag off the track for the same reason.

It does not go through gpui's on_drag. That refreshes the entire window on every mouse-move event, and a pointer reports far faster than a window can paint — dragging a panel that way cost a full core. This claims frames from the shared clock instead, at a 60fps ceiling, so the rate belongs to the library rather than to the mouse. A claim is not a redraw: the pointer sample records where the panel now is and schedules, and the clock paints whatever the latest sample said.

Movement is carried as a delta from the last sample rather than as an offset from the box's corner. A delta reads the same from the window's origin or the container's, so the panel needs no element bounds to place itself — and a plain mouse listener is not offered any.

home is where it opens, and it is passed every render rather than stored, so a host can read it off the viewport and a window that grows never strands the panel out of reach. Once dragged, the panel holds a position of its own.

Two states, because they answer different questions. held is the pointer pressed on it, travelling or not — that is the closed hand, which closes on the press the way every other grabbable surface does. dragging is the panel actually moving, past the two pixels that separate a drag from a click — that is the lift, the shadow, whatever a host shows for a thing in flight.

It clamps nothing, snaps to nothing and remembers nothing across launches. A panel dragged half off the window stays there, and the point it was grabbed by is under the pointer, so it can always be dragged back. at() and move_to() are there for a host that wants to persist a position across sessions.

Floating panel