Add check for outline glitches

[davelab6]

Observed behaviour

notofonts/noto-source#245 has an outline glitch

Expected behaviour

I wonder if there is some way to detect it.

[simoncozens]

It’s going to be very difficult to distinguish a cut like that from an ink trap.

[simoncozens]

Here’s an idea: take every pair of successive segments and treat them as a sub path. Close the sub path with a line segment and calculate the area. If the area is less than epsilon, there is a glitch.

[kalapi]

FontBakery v0.12.9

I'm getting a lot of false positives on the com.google.fonts/check/outline_jaggy_segments check. In very large families double checking all the warnings to ensure if any are actually affecting output can become very cumbersome and time consuming. Is there a way we can make this algorithm more efficient?

The algorithm in its current state might flag mild to extreme condensed designs.

Some examples:

⚠️ WARN The following glyphs have jaggy segments:

• M (U+004D): L<<276.0,86.0>--<163.0,592.0>>/L<<163.0,592.0>--<163.0,143.0>> = 12.588740511051117
• M (U+004D): L<<584.0,143.0>--<584.0,592.0>>/L<<584.0,592.0>--<443.0,0.0>> = 13.396859158897033
• trademark (U+2122): L<<586.0,400.0>--<519.0,664.0>>/L<<519.0,664.0>--<519.0,434.0>> = 14.2403237429406

Warning 1 'M': is related to the selected segments in the image below:

Warning 2 'M': is related to the selected segments in the image below:

Warning 3 'trademark': is related to the selected segments in the image below: