Yes, I’ve just tried and found that you can plot lines directly onto the scene:
lines!(fig.scene, [0.08, 0.93], [0.13, 0.13],
space = :relative,
color=:grey65, linewidth=1, linestyle=:dot)
The remaining problem I wan to solve is to find the relationship between the user coordinates within the “axes” to the “scene” coordinates.
Currently I need a lot of trial and error to place the lines at the desirable positions on the “scene”, which is because I don’t know how to relate the user-coordinate positions within the axes to the “scene” coordinates.