[glyf] keep single-component glyphs if component is reused

Fixes #114

src/nanoemoji/write_font.py

@@ -275,14 +275,15 @@ def _draw_glyph_extents(ufo: ufoLib2.Font, glyph: Glyph):
 def _glyf_ufo(ufo, color_glyphs):
     # glyphs by reuse_key
     glyphs = {}
+    reused = set()
     for color_glyph in color_glyphs:
         logging.debug(
             "%s %s %s",
             ufo.info.familyName,
             color_glyph.glyph_name,
             color_glyph.transform_for_font_space(),
         )
-        parent_glyph = ufo.get(color_glyph.glyph_name)
+        parent_glyph = ufo[color_glyph.glyph_name]
         for painted_layer in color_glyph.as_painted_layers():
             # if we've seen this shape before reuse it
             reuse_key = _inter_glyph_reuse_key(painted_layer)
@@ -291,10 +292,16 @@ def _glyf_ufo(ufo, color_glyphs):
                 glyphs[reuse_key] = glyph
             else:
                 glyph = glyphs[reuse_key]
+                reused.add(glyph.name)
             parent_glyph.components.append(Component(baseGlyph=glyph.name))
 
-        # No great reason to keep single-component glyphs around
-        if len(parent_glyph.components) == 1:
+    for color_glyph in color_glyphs:
+        parent_glyph = ufo[color_glyph.glyph_name]
+        # No great reason to keep single-component glyphs around (unless reused)
+        if (
+            len(parent_glyph.components) == 1
+            and parent_glyph.components[0].baseGlyph not in reused
+        ):
             component = ufo[parent_glyph.components[0].baseGlyph]
             del ufo[component.name]
             component.unicode = parent_glyph.unicode

tests/reused_rect_glyf.ttx

@@ -0,0 +1,68 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont sfntVersion="\x00\x01\x00\x00">
+
+  <GlyphOrder>
+    <!-- The 'id' attribute is only for humans; it is ignored when parsed. -->
+    <GlyphID id="0" name=".notdef"/>
+    <GlyphID id="1" name=".space"/>
+    <GlyphID id="2" name="e000"/>
+    <GlyphID id="3" name="e001"/>
+    <GlyphID id="4" name="e000.0"/>
+  </GlyphOrder>
+
+  <hmtx>
+    <mtx name=".notdef" width="0" lsb="0"/>
+    <mtx name=".space" width="100" lsb="0"/>
+    <mtx name="e000" width="100" lsb="20"/>
+    <mtx name="e000.0" width="100" lsb="20"/>
+    <mtx name="e001" width="100" lsb="20"/>
+  </hmtx>
+
+  <cmap>
+    <tableVersion version="0"/>
+    <cmap_format_4 platformID="0" platEncID="3" language="0">
+      <map code="0x20" name=".space"/><!-- SPACE -->
+      <map code="0xe000" name="e000"/><!-- ???? -->
+      <map code="0xe001" name="e001"/><!-- ???? -->
+    </cmap_format_4>
+    <cmap_format_4 platformID="3" platEncID="1" language="0">
+      <map code="0x20" name=".space"/><!-- SPACE -->
+      <map code="0xe000" name="e000"/><!-- ???? -->
+      <map code="0xe001" name="e001"/><!-- ???? -->
+    </cmap_format_4>
+  </cmap>
+
+  <loca>
+    <!-- The 'loca' table will be calculated by the compiler -->
+  </loca>
+
+  <glyf>
+
+    <!-- The xMin, yMin, xMax and yMax values
+         will be recalculated by the compiler. -->
+
+    <TTGlyph name=".notdef"/><!-- contains no outline data -->
+
+    <TTGlyph name=".space"/><!-- contains no outline data -->
+
+    <TTGlyph name="e000" xMin="20" yMin="60" xMax="80" yMax="80">
+      <component glyphName="e000.0" x="0" y="0" flags="0x204"/>
+    </TTGlyph>
+
+    <TTGlyph name="e000.0" xMin="20" yMin="60" xMax="80" yMax="80">
+      <contour>
+        <pt x="20" y="80" on="1"/>
+        <pt x="20" y="60" on="1"/>
+        <pt x="80" y="60" on="1"/>
+        <pt x="80" y="80" on="1"/>
+      </contour>
+      <instructions/>
+    </TTGlyph>
+
+    <TTGlyph name="e001" xMin="20" yMin="60" xMax="80" yMax="80">
+      <component glyphName="e000.0" x="0" y="0" flags="0x204"/>
+    </TTGlyph>
+
+  </glyf>
+
+</ttFont>

tests/write_font_test.py

@@ -100,6 +100,8 @@ def test_keep_glyph_names(svgs, color_format, keep_glyph_names):
             "untouchedsvg",
             ".ttf",
         ),
+        # keep single-component composites if component reused by more than one glyph
+        (("one_rect.svg", "one_rect.svg"), "reused_rect_glyf.ttx", "glyf", ".ttf"),
     ],
 )
 def test_write_font_binary(svgs, expected_ttx, color_format, output_format):