Function cursor_motion_rects 

fn cursor_motion_rects(
    drawn: Option<(i32, i32, i32, i32)>,
    from: Option<(i16, i16)>,
    to: (i16, i16),
) -> Vec<Rectangle>

Where on the root a cursor moving from from to to changed the frame: the rectangle it was drawn in (drawn, root coordinates) and the same rectangle moved with the pointer, or boxes around both positions where it was not drawn or the pointer’s earlier place is unknown. The exact rectangle the grab then draws is added to the frame’s change beside these.