Function draw_remote_presence 

pub fn draw_remote_presence(
    scene: &mut Scene,
    transform: Affine,
    viewport: Rect,
    text_renderer: &mut TextRenderer,
    theme: &Theme,
    presence: &PresenceCtx,
) -> Vec<Rect>

The one call the app makes each frame to render all cross-process peer presence: on-screen peers get a dot + pill, off-screen peers get an edge mist. viewport is the visible rect in the same (logical) space as cursor positions.

Returns the bounds, in scene coordinates, of everything painted (see draw_peer_cursors), so the frame damages only those.