Hi Marc,

> Maybe edges could be highlighted "over" the external surface, a bit like the yellow curves.

The tricky thing with this is that it can also change the display of just simple objects that are not obscured.

For example selecting just a box might look something like this:



The problem is having stuff that is normally hidden get accented too much tends to interfere with depth perception of the object.

Maybe drawing the "hidden edges" (the faint dashed lines) in a slightly different style for selected objects would work. But it is kind of difficult to find a way that is distinctive from regular hidden-line but also not too heavily accented to avoid the depth perception problem. I just experimented with a couple of different variations on this, but so far I haven't found a very satisfying method, things seem to be too faint if drawn in a faint version of the selected color, or stand out too much if drawn at full opacity with the regular selected color...

The second one (draw hidden lines at full opacity with selected color) does a good job of identifying hidden selected objects:



But still doesn't look good to me for the regular single selected object case:



Maybe doing a more significant change to the dash pattern itself beyond just the whole color would be good, like possibly alternating between black and a faint yellow... It is harder to mess around with that though.

- Michael