generated .notdef glyph should be left unmapped

https://learn.microsoft.com/en-us/typography/opentype/spec/cmap#overview 'Regardless of the encoding scheme, character codes that do not correspond to any glyph in the font should be mapped to glyph index 0. The glyph at this location must be a special glyph representing a missing character, commonly known as .notdef.'
googlefonts · Sep 5, 2023 · 2dba808 · 2dba808
1 parent da4fd2a
commit 2dba808
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Showing 2 changed files with 8 additions and 8 deletions.
diff --git a/fontc/src/lib.rs b/fontc/src/lib.rs
@@ -1021,7 +1021,6 @@ mod tests {
                 .collect();
             assert_eq!(
                 vec![
-                    (0x0000, 0),
                     (0x002C, 2),
                     (0x002E, 1),
                     (0x0030, 3),
@@ -1288,10 +1287,12 @@ mod tests {
         let buf = fs::read(font_file).unwrap();
         let font = FontRef::new(&buf).unwrap();
 
-        assert_eq!(
-            GlyphId::new(0),
-            font.cmap().unwrap().map_codepoint(0u32).unwrap()
-        );
+        // Character 0x0000 (NULL) != '.notdef' glyph, and neither are any other
+        // characters actually, because '.notdef' (glyph index 0) means the absence
+        // of a character-to-glyph mapping:
+        // https://github.com/googlefonts/fontc/pull/423/files#r1309257127
+        // https://learn.microsoft.com/en-us/typography/opentype/spec/cmap#overview
+        assert_eq!(None, font.cmap().unwrap().map_codepoint(0u32));
     }
 
     #[test]
@@ -1312,13 +1313,12 @@ mod tests {
 
         assert_eq!(
             vec![
-                GlyphId::new(0),
                 GlyphId::new(1),
                 GlyphId::new(2),
                 GlyphId::new(3),
                 GlyphId::new(6),
             ],
-            [0x00, 0x20, 0x21, 0x2d, 0x3d]
+            [0x20, 0x21, 0x2d, 0x3d]
                 .iter()
                 .map(|cp| font.cmap().unwrap().map_codepoint(*cp as u32).unwrap())
                 .collect::<Vec<_>>()

diff --git a/fontir/src/ir.rs b/fontir/src/ir.rs
@@ -1028,7 +1028,7 @@ impl GlyphBuilder {
 
         Self {
             name: GlyphName::NOTDEF.clone(),
-            codepoints: HashSet::from([0]),
+            codepoints: HashSet::new(),
             sources: HashMap::from([(
                 default_location,
                 GlyphInstance {