Extraneous points after remove overlap

[ryanbugden]

When I hit Remove Overlap in RoboFont, I get unexpected extraneous on-curve points.

I tested on multiple RF builds.
🟢 Last confirmed good build: 2601141441 (1/14/2026)
🔴 First confirmed bad build: 2602041514 (2/4/2026)

I think the bug is in flatten.py:

@typemytype @skef I am experiencing unexpected extraneous points after remove overlap. If I comment out these two lines, it fixes it. Bug report on RoboFont Discord.

It seems like this is a fix to avoid desync of logic of some sort, but it's causing another bug. Is there a better way we can do this?

cc @typesupply

_Originally posted by @ryanbugden in c83d3bc

Test glif

This is an example shape that results in two points on the inside corner.

<?xml version='1.0' encoding='UTF-8'?>
<glyph name="n" format="2">
  <advance width="1090"/>
  <outline>
    <contour>
      <point x="550" y="380" type="line"/>
      <point x="738" y="540"/>
      <point x="833" y="738"/>
      <point x="833" y="973" type="curve" smooth="yes"/>
      <point x="833" y="1148"/>
      <point x="781" y="1274"/>
      <point x="707" y="1274" type="curve" smooth="yes"/>
      <point x="676" y="1274"/>
      <point x="653" y="1251"/>
      <point x="643" y="1210" type="curve" smooth="yes"/>
      <point x="584" y="973"/>
      <point x="437" y="826"/>
      <point x="215" y="782" type="curve"/>
      <point x="253" y="629" type="line"/>
      <point x="484" y="688"/>
      <point x="656" y="850"/>
      <point x="731" y="1099" type="curve"/>
      <point x="689" y="1087" type="line"/>
      <point x="703" y="830"/>
      <point x="629" y="635"/>
      <point x="441" y="480" type="curve"/>
    </contour>
  </outline>
</glyph>

Here is another, to prove it's not related to extreme points.

<?xml version='1.0' encoding='UTF-8'?>
<glyph name="n" format="2">
  <advance width="1090"/>
  <outline>
    <contour>
      <point x="289" y="923" type="line"/>
      <point x="324" y="936"/>
      <point x="360" y="943"/>
      <point x="396" y="943" type="curve" smooth="yes"/>
      <point x="521" y="943"/>
      <point x="609" y="858"/>
      <point x="609" y="737" type="curve" smooth="yes"/>
      <point x="609" y="686"/>
      <point x="594" y="636"/>
      <point x="561" y="577" type="curve"/>
      <point x="632" y="547" type="line"/>
      <point x="695" y="664"/>
      <point x="725" y="768"/>
      <point x="725" y="868" type="curve" smooth="yes"/>
      <point x="725" y="1047"/>
      <point x="630" y="1159"/>
      <point x="478" y="1159" type="curve" smooth="yes"/>
      <point x="398" y="1159"/>
      <point x="317" y="1129"/>
      <point x="237" y="1070" type="curve"/>
      <point x="261" y="1003" type="line"/>
      <point x="332" y="1059"/>
      <point x="399" y="1086"/>
      <point x="468" y="1086" type="curve" smooth="yes"/>
      <point x="590" y="1086"/>
      <point x="659" y="1002"/>
      <point x="659" y="870" type="curve" smooth="yes"/>
      <point x="659" y="829"/>
      <point x="651" y="781"/>
      <point x="643" y="740" type="curve"/>
      <point x="653" y="712" type="line"/>
      <point x="683" y="884"/>
      <point x="568" y="1012"/>
      <point x="418" y="1012" type="curve" smooth="yes"/>
      <point x="368" y="1012"/>
      <point x="318" y="1001"/>
      <point x="269" y="978" type="curve"/>
    </contour>
  </outline>
</glyph>

[skef]

I can take a look but given that the underlying library uses line segments this is a sort of thing you sometimes get. The fixes that went in recently were to work around actual geometric errors, whereas this is more of a less-than-ideal representation problem.