Merge pull request #1058 from cmyr/erase-corners-two-segments

Fix edge case in open corner erasure logic
googlefonts · Jan 21, 2025 · ed39aa3 · ed39aa3
2 parents 74c6324 + e03ad3d
commit ed39aa3
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diff --git a/Lib/glyphsLib/filters/eraseOpenCorners.py b/Lib/glyphsLib/filters/eraseOpenCorners.py
@@ -52,7 +52,8 @@ def endPath(self):
             )
             logger.debug("Segments: %s", segs)
 
-        while ix < len(segs):
+        # we need at least two segments to find a corner
+        while len(segs) > 2 and ix < len(segs):
             next_ix = (ix + 1) % len(segs)
 
             # Am I a line segment?

diff --git a/tests/eraseOpenCorners_test.py b/tests/eraseOpenCorners_test.py
@@ -158,6 +158,19 @@
                         ("closePath", ()),
                     ],
                 },
+                # a pathological case, where a curve has two segments.
+                # the naive logic treats this as an open corner, treating the
+                # same curve segment as the 'prev' and 'next'.
+                {
+                    "name": "justTwoSegments",
+                    "width": 600,
+                    "outline": [
+                        ("moveTo", ((10, 10),)),
+                        ("lineTo", ((13, 10),)),
+                        ("curveTo", ((11, 8), (11, 8), (10, 10))),
+                        ("closePath", ()),
+                    ],
+                },
             ]
         }
     ]
@@ -321,6 +334,11 @@ def test_large_crossing(font):
     assert len(newcontour) == 3
 
 
+def test_only_two_segments(font):
+    philter = EraseOpenCornersFilter(include={"justTwoSegments"})
+    assert not philter(font)
+
+
 def structure(contour):
     return [x.segmentType for x in contour]