From b7f4e9b83e1794b99c8fa8faf59a04ca1d8007f8 Mon Sep 17 00:00:00 2001
From: Cosimo Lupo <clupo@google.com>
Date: Thu, 25 May 2023 13:42:29 +0100
Subject: [PATCH] move dropImpliedOnCurvePoints function to glyf table module

so it can be used by client code on multiple glyf Glyph objects regardles of TTGlyphPen
---
 Lib/fontTools/pens/ttGlyphPen.py       | 56 +------------------------
 Lib/fontTools/ttLib/tables/_g_l_y_f.py | 57 ++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 54 deletions(-)

diff --git a/Lib/fontTools/pens/ttGlyphPen.py b/Lib/fontTools/pens/ttGlyphPen.py
index c1590e651..9db320dc3 100644
--- a/Lib/fontTools/pens/ttGlyphPen.py
+++ b/Lib/fontTools/pens/ttGlyphPen.py
@@ -11,65 +11,13 @@ from fontTools.ttLib.tables._g_l_y_f import flagOnCurve, flagCubic
 from fontTools.ttLib.tables._g_l_y_f import Glyph
 from fontTools.ttLib.tables._g_l_y_f import GlyphComponent
 from fontTools.ttLib.tables._g_l_y_f import GlyphCoordinates
+from fontTools.ttLib.tables._g_l_y_f import dropImpliedOnCurvePoints
 import math
 
 
 __all__ = ["TTGlyphPen", "TTGlyphPointPen"]
 
 
-def drop_implied_oncurves(*interpolatable_glyphs):
-    drop = None
-    for glyph in interpolatable_glyphs:
-        may_drop = set()
-        start = 0
-        flags = glyph.flags
-        coords = glyph.coordinates
-        for last in glyph.endPtsOfContours:
-            for i in range(start, last + 1):
-                if not (flags[i] & flagOnCurve):
-                    continue
-                prv = i - 1 if i > start else last
-                nxt = i + 1 if i < last else start
-                if (flags[prv] & flagOnCurve) or flags[prv] != flags[nxt]:
-                    continue
-                p0 = coords[prv]
-                p1 = coords[i]
-                p2 = coords[nxt]
-                if not math.isclose(p1[0] - p0[0], p2[0] - p1[0]) or not math.isclose(
-                    p1[1] - p0[1], p2[1] - p1[1]
-                ):
-                    continue
-
-                may_drop.add(i)
-        # we only want to drop if ALL interpolatable glyphs have the same implied oncurves
-        if drop is None:
-            drop = may_drop
-        else:
-            drop.intersection_update(may_drop)
-
-    if drop:
-        # Do the actual dropping
-        for glyph in interpolatable_glyphs:
-            glyph.coordinates = GlyphCoordinates(
-                coords[i] for i in range(len(coords)) if i not in drop
-            )
-            glyph.flags = array("B", (flags[i] for i in range(len(flags)) if i not in drop))
-
-            endPts = glyph.endPtsOfContours
-            newEndPts = []
-            i = 0
-            delta = 0
-            for d in sorted(drop):
-                while d > endPts[i]:
-                    newEndPts.append(endPts[i] - delta)
-                    i += 1
-                delta += 1
-            while i < len(endPts):
-                newEndPts.append(endPts[i] - delta)
-                i += 1
-            glyph.endPtsOfContours = newEndPts
-
-
 class _TTGlyphBasePen:
     def __init__(
         self,
@@ -199,7 +147,7 @@ class _TTGlyphBasePen:
 
         glyph.coordinates.toInt()
         if dropImpliedOnCurves:
-            drop_implied_oncurves(glyph)
+            dropImpliedOnCurvePoints(glyph)
 
         self.init()
 
diff --git a/Lib/fontTools/ttLib/tables/_g_l_y_f.py b/Lib/fontTools/ttLib/tables/_g_l_y_f.py
index f71fd3e2d..48c08df3a 100644
--- a/Lib/fontTools/ttLib/tables/_g_l_y_f.py
+++ b/Lib/fontTools/ttLib/tables/_g_l_y_f.py
@@ -22,6 +22,7 @@ import sys
 import struct
 import array
 import logging
+import math
 import os
 from fontTools.misc import xmlWriter
 from fontTools.misc.filenames import userNameToFileName
@@ -1530,6 +1531,62 @@ class Glyph(object):
         return result if result is NotImplemented else not result
 
 
+def dropImpliedOnCurvePoints(*interpolatable_glyphs):
+    drop = None
+    for glyph in interpolatable_glyphs:
+        may_drop = set()
+        start = 0
+        flags = glyph.flags
+        coords = glyph.coordinates
+        for last in glyph.endPtsOfContours:
+            for i in range(start, last + 1):
+                if not (flags[i] & flagOnCurve):
+                    continue
+                prv = i - 1 if i > start else last
+                nxt = i + 1 if i < last else start
+                if (flags[prv] & flagOnCurve) or flags[prv] != flags[nxt]:
+                    continue
+                p0 = coords[prv]
+                p1 = coords[i]
+                p2 = coords[nxt]
+                if not math.isclose(p1[0] - p0[0], p2[0] - p1[0]) or not math.isclose(
+                    p1[1] - p0[1], p2[1] - p1[1]
+                ):
+                    continue
+
+                may_drop.add(i)
+        # we only want to drop if ALL interpolatable glyphs have the same implied oncurves
+        if drop is None:
+            drop = may_drop
+        else:
+            drop.intersection_update(may_drop)
+
+    if drop:
+        # Do the actual dropping
+        for glyph in interpolatable_glyphs:
+            coords = glyph.coordinates
+            glyph.coordinates = GlyphCoordinates(
+                coords[i] for i in range(len(coords)) if i not in drop
+            )
+            glyph.flags = array.array(
+                "B", (flags[i] for i in range(len(flags)) if i not in drop)
+            )
+
+            endPts = glyph.endPtsOfContours
+            newEndPts = []
+            i = 0
+            delta = 0
+            for d in sorted(drop):
+                while d > endPts[i]:
+                    newEndPts.append(endPts[i] - delta)
+                    i += 1
+                delta += 1
+            while i < len(endPts):
+                newEndPts.append(endPts[i] - delta)
+                i += 1
+            glyph.endPtsOfContours = newEndPts
+
+
 class GlyphComponent(object):
     """Represents a component within a composite glyph.