Function shape_drag_guides 

pub fn shape_drag_guides(
    data: &Drawing<'_>,
    dragged: &[ShapeId],
    offset: Vec2,
) -> Vec<[Pos2; 2]>

Guides for a shape (or group) drag: the dragged shapes — previewed at offset — contribute their features; every other shape (including areas) contributes the same at its resting position.