strm2oas: def path with first/last segment length < halfwidth are read wrong

[stefanottili]

strm2oas by default decomposes multi-point path with first or last segment length < halfwidth incorrectly.
They are read correctly as multi-point path by using the --lefdef-joined-paths option.

make bad; make xor shows the difference
make good; make xor doesn't

test_spnet.tgz

[klayoutmatthias]

Thanks! Perfect testcase preparation!

But hard to fix :(

[klayoutmatthias]

I mean, I don't know if the "good" version is even correct - that assumes a "GDS style" interpretation of path. Can you confirm the way these paths are build is compatible with other tools?

Like this "good" path:

while the "bad" version is correct if you imagine a square pen going round the corner left of the small segment:

[stefanottili]

It certainly looks like unintended, but I didn't just make it up. I would say the fix is to warn about it and not break it into two point path. The multipoint path is handled correctly after all. I have an option to turn this into a polygon, because somebody got burned somewhere years ago by some tool not doing the right thing.

[klayoutmatthias]

Okay ... my fix now is to join the first two segments if the initial segment is too short. Same for the last two segments.

Matthias

[stefanottili]

more elaborate then what I would have done, but I'll take it.
I would be nice to get a warning about this situation.