draw_svg_path: auto-close open sub-paths when drawing svg paths with …

…fonttools pen

The draw_svg_path function which we use to convert SVG paths to FontTools pen commands to create UFO glyphs from them, uses the presence/absence of 'z' to decide whether to call a pen's endPath (for open contours) and closePath (for closed ones). If a filled subpath does not explicily ends with 'z' (which is the case for some of our source files, e.g. 'one-o-clock.svg'), then upon converting it to UFO glyph using the FontTools pen protocol, the subpath is kept 'open' (i.e. the UFO GLIF contour's first point type is set to 'move').
Then, when the UFO glyph is converted to TrueType by ufo2ft with the TTGlyphPointPen, if the starting 'move' point and the last point of such 'open' contours are on top of each other (i.e. contour does a full loop despite being marked as 'open'), the result is a duplicate point at the end/start of the TrueType contour.
We fix this by adding an optional `close_subpath=False` parameter to draw_svg_path function, which when True signals that we want to interpret the SVG subpaths as if they were closed by an explicit 'z' command, which avoids the duplicate end/start points in the converted TrueType glyphs.
TrueType contours are always filled and automatically closed by an implicit line back to their staring point.

setup.py

@@ -43,7 +43,7 @@
         "pillow>=7.2.0",
         "regex>=2020.4.4",
         "toml>=0.10.1",
-        "ufo2ft[cffsubr]==2.21.0",  # TEMPORARY VERSION LOCK
+        "ufo2ft[cffsubr]>=2.23.0",
         "ufoLib2>=0.6.2",
     ],
     extras_require=extras_require,

src/nanoemoji/svg_path.py

@@ -31,7 +31,10 @@
 
 
 def draw_svg_path(
-    path: SVGPath, pen: AbstractPen, transform: Optional[Affine2D] = None
+    path: SVGPath,
+    pen: AbstractPen,
+    transform: Optional[Affine2D] = None,
+    close_subpaths: bool = False,
 ):
     """Draw SVGPath using a FontTools Segment Pen."""
     if transform is not None:
@@ -44,7 +47,10 @@ def draw_svg_path(
     for cmd, args in path.as_cmd_seq():
         if cmd == "M":
             if not closed:
-                pen.endPath()
+                if close_subpaths:
+                    pen.closePath()
+                else:
+                    pen.endPath()
             closed = False
 
         # pens expect args as 2-tuples; we use the 'grouper' itertools recipe
@@ -58,7 +64,10 @@ def draw_svg_path(
             closed = True
 
     if not closed:
-        pen.endPath()
+        if close_subpaths:
+            pen.closePath()
+        else:
+            pen.endPath()
 
 
 class SVGPathPen(DecomposingPen):

src/nanoemoji/write_font.py

@@ -246,7 +246,10 @@ def _create_glyph(color_glyph: ColorGlyph, painted_layer: PaintedLayer) -> Glyph
         glyph_names.append(base_glyph.name)
 
         draw_svg_path(
-            SVGPath(d=painted_layer.path), base_glyph.getPen(), svg_units_to_font_units
+            SVGPath(d=painted_layer.path),
+            base_glyph.getPen(),
+            svg_units_to_font_units,
+            close_subpaths=True,
         )
 
         glyph.components.append(
@@ -268,7 +271,10 @@ def _create_glyph(color_glyph: ColorGlyph, painted_layer: PaintedLayer) -> Glyph
     else:
         # Not a composite, just draw directly on the glyph
         draw_svg_path(
-            SVGPath(d=painted_layer.path), glyph.getPen(), svg_units_to_font_units
+            SVGPath(d=painted_layer.path),
+            glyph.getPen(),
+            svg_units_to_font_units,
+            close_subpaths=True,
         )
 
     ufo.glyphOrder += glyph_names

tests/svg_path_test.py

@@ -78,3 +78,10 @@ def test_roundtrip_path_with_pen(d):
     pen = SVGPathPen()
     draw_svg_path(path, pen)
     assert pen.path.d == d
+
+
+def test_draw_svg_close_subpaths():
+    path = SVGPath(d="M0,0 L0,10 L10,10 L10,0 M12,0 L12,10 L22,10 L22,0")
+    pen = SVGPathPen()
+    draw_svg_path(path, pen, close_subpaths=True)
+    assert pen.path.d == "M0,0 L0,10 L10,10 L10,0 Z M12,0 L12,10 L22,10 L22,0 Z"