Rounding issue after etch

[klayoutmatthias]

This ticket is following https://www.klayout.de/forum/comments.php?DiscussionID=1041

See the attached xs file and layout.

This is the wrong output:

The expectation is to see the implant effective for both epi layers.

Technically the issue arises because of this code in xsection.lym, line 275++:

    # consume material and add to air
    if into
      into.each do |i|
        i.sub(res)
      end
    end

    @xs.air.add(res)

The "res" shape is subtracted from both "into" substrates, but due to grid snapping the effective "air" adder is different from the original shape.

epi.gds.gz
epi.xs.gz