Missing polygon point after substraction of two rectangles leads to "flagging" artefact

ChristianP

When I substract or XOR two rectangles, Klayout transforms this into a polygon with a hole, as shown in the sketch below. I added the numbers to show the order of the polygon points for this example. When I now apply a rotation to the polygon, a small gap along the line between points 2 and 3 appears. I assume this is due to snapping of the points to the grid, which leads to slightly different angles for the lines 2-3 vs. 6-7.
This "flagging" artefact could be overcome if point 3 was included as an additional point between 6 and 7. Is there a way to tell KLayout to do so in the substraction algorithm?
Thanks for any assistance with this.

tomas2004

Hello,

This is indeed a snapping issue as explained above. Not sure if 3 or more points on one line are kept except for the outer two... Why not rotating the two rectangles first and do the subtraction at the end?

Cheers,

Tomas

Matthias

Hi @ChristianP,

A rotation by any angle will induce snapping as @tomas2004 explained. I think his approach is the right one.

Problem is that the rotation is "stupid" and does not remove the cut line before rotation.

Using a short DRC script you can merge all shapes on a layer - this will create polygons with holes which rotate without this artefact:

# merge polygons from layer 1/0
input(1, 0).merged.output(1, 0)

However, this function has side effects: it will merge all shapes, turn boxes and paths into polygons and combine overlapping shapes. If you do not want that, here is a Python script that merges selected polygons into ones without cut lines:

import klayout.lay as klay
import klayout.db as kdb

lv = klay.LayoutView.current()

lv.transaction("Merge selected polygons")

try:

  for sel in lv.each_object_selected():
    if not sel.is_cell_inst() and sel.shape.is_polygon():
      r = kdb.Region(sel.shape.polygon).merged()
      if r.size() == 1:
        # Note: "downcast" converts a PolygonWithProperties to a Polygon
        sel.shape.polygon = r[0].downcast()

finally:
  lv.commit()

Note that on saving to GDS or OASIS, the cut lines will re-appear as GDS does not have polygons with holes.

Matthias