Check area of arabic letter high hamza (U+0621)

to be roughly the same as arabic letter hamza (U+0675).

com.google.fonts/check/arabic_high_hamza
On the Universal Profile.
(issue #4315)

CHANGELOG.md

@@ -4,6 +4,9 @@ A more detailed list of changes is available in the corresponding milestones for
 
 ## Upcoming release: 0.10.4 (2023-Nov-??)
 ### Changes to existing checks
+#### On the Universal Profile
+  - **[com.google.fonts/check/arabic_high_hamza]:** Check area of arabic letter high hamza (U+0621) to be roughly the same as arabic letter hamza (U+0675) (issue #4315)
+
 #### On the Google Fonts Profile
   - **[com.google.fonts/check/metadata/escaped_strings]:** Accept escaped quotes. They're fine. This check is really meant to detect things like "Juli\303\241n" instead of "Julián". (issue #4331)
   - **[com.google.fonts/check/glyphsets/shape_languages]:** Use tables to make the check results more readable. (issue #4326)

Lib/fontbakery/profiles/universal.py

@@ -841,9 +841,19 @@ def com_google_fonts_check_arabic_spacing_symbols(ttFont):
 def com_google_fonts_check_arabic_high_hamza(ttFont):
     """Check that glyph for U+0675 ARABIC LETTER HIGH HAMZA is not a mark."""
     import babelfont
+    from fontTools.pens.areaPen import AreaPen
 
+    ARABIC_LETTER_HAMZA = 0x0621
     ARABIC_LETTER_HIGH_HAMZA = 0x0675
 
+    glyph_set = ttFont.getGlyphSet()
+    if ARABIC_LETTER_HAMZA not in glyph_set or ARABIC_LETTER_HAMZA not in glyph_set:
+        yield SKIP, Message(
+            "glyphs-missing",
+            "This check will only run on fonts that have both glyphs U+0621 and U+0675",
+        )
+        return
+
     passed = True
     font = babelfont.load(ttFont.reader.file.name)
 
@@ -857,9 +867,27 @@ def com_google_fonts_check_arabic_high_hamza(ttFont):
                         "mark-in-gdef",
                         f'"{glyph.name}" is defined in GDEF as a mark (class 3).',
                     )
-    # TODO: Should we also validate the bounding box of the glyph and compare
-    #       it to U+0621 expecting them to have roughly the same size?
-    #       (within a certain tolerance margin)
+
+    # Also validate the bounding box of the glyph and compare
+    # it to U+0621 expecting them to have roughly the same size
+    # (within a certain tolerance margin)
+    area_pen = AreaPen(glyph_set)
+
+    glyph_set[ARABIC_LETTER_HAMZA].draw(area_pen)
+    hamza_area = area_pen.value
+
+    area_pen.value = 0
+    glyph_set[ARABIC_LETTER_HIGH_HAMZA].draw(area_pen)
+    high_hamza_area = area_pen.value
+
+    if abs((high_hamza_area - hamza_area) / hamza_area) > 0.1:
+        passed = False
+        yield FAIL, Message(
+            "glyph-area",
+            "The arabic letter high hamza (U+0675) should have roughly"
+            " the same size the arabic letter hamza (U+0621),"
+            " but a different glyph outline area was detected.",
+        )
 
     if passed:
         yield PASS, "Looks good!"