DRC: Poor fill with skew step vectors

[klayoutmatthias]

See attached file.

The script is this:

left = input(1000, 0)

pattern = fill_pattern("FILL")
pattern.shape(1, 0, box(0.0, 0.0, 2.0, 2.0))

left.fill(pattern, hstep(2.5, 0), vstep(0.65, 2.5), origin(0, 0))

Result: the left side of the bar is poorly filled:

Expected result: the bar should be fully filled.

fill_test2.zip

[klayoutmatthias]

The PR contains some more goodies and bug fixes.

[stefanottili]

Just to make sure this doesn't get lost, testdata/drc/drcFullTest_au1.oas is not drc clean.
There are overlapping fill rectangles in three spots and some offgrid fill errors (maybe caused by offgrid M1 metal).

klayout \
        -b -zz \
        -r sg13g2_maximal.lydrc \
        -rd in_gds=klayout/testdata/drc/drcFullTest_au1.oas \
        -rd threads=8 \
        -rd report_file=drc_violations.drcFullTest_au1.xml \
        -rd density=0