Hi Martin,

> I'm fine with your "border against background" method that gives me a rendering like this:

A couple of questions about the "border against background" option. I'm thinking of calling it something like "Generate outlines", and when enabled it would make an extra set of curves on separate kind of grouping (grouped either as an actual group or layer or separate color or lineweight or maybe any of these) that would be coincident with the regular edges. So that would mean that the outline curves would stack up on the "regular edges". The reason for this is that otherwise to not have separate stacked up curves would mean having the regular edges broken up into smaller pieces which seems kind of weird. Like on your example this area here:



And also another reason to make the outline a separate set of curves is that I think you'll want the outline to go underneath all the other regular edges and I guess underneath the shaded image as well so that when it's thickened it only adds thickness to only one side of the shape rather than having thickness on both sides. I don't believe that there is any way in PostScript to add thickness to just one side of a path rather than having the thickness be symmetrical around the path center line, I think it has to have some kind of masking for an effect like that.

Then the other thing is that if you have separate multiple objects, I would think that the outline would treat spots where it borders on either the background or the other object as an outline area, so for example with 3 objects like this (that don't touch each other, they just block one another in visibility):



Then I'd think that the outlines would go like this:




Does that seem right? The other possibility would be for outlines to only go against strictly the background and not other objects at all which would be like this:



- Michael