Function paint_alignment_guide 

pub fn paint_alignment_guide(
    scene: &mut Scene,
    transform: Affine,
    from: Point,
    to: Point,
    theme: &Theme,
)

An alignment guide: the line a dragged object lines up with while it is near enough to snap (a display on the arrangement canvas, a shape on a slide), from from to to. The accent as a mark on a surface, one chrome rule wide; drawn only while the drag is snapped to that line.