Use supported codepoints instead of scripts in Monospace fallback

 This should/could improve fallback order.

 This could also probably be utilized for non-Monospace fallback too.
 But I didn't want to touch that code to avoid accidentally breaking
 anything.

Signed-off-by: Mohammad AlSaleh <[email protected]>

src/font/fallback/mod.rs

@@ -38,7 +38,7 @@ use log::warn as missing_warn;
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
 struct MonospaceFallbackInfo {
     weight_offset: Option<u16>,
-    script_non_matches: Option<usize>,
+    codepoint_non_matches: Option<usize>,
     id: fontdb::ID,
 }
 
@@ -49,6 +49,7 @@ pub struct FontFallbackIter<'a> {
     monospace_fallbacks: BTreeSet<MonospaceFallbackInfo>,
     default_i: usize,
     scripts: &'a [Script],
+    word: &'a str,
     script_i: (usize, usize),
     common_i: usize,
     other_i: usize,
@@ -61,6 +62,7 @@ impl<'a> FontFallbackIter<'a> {
         font_match_keys: &'a [FontMatchKey],
         default_families: &'a [&'a Family<'a>],
         scripts: &'a [Script],
+        word: &'a str,
     ) -> Self {
         Self {
             font_system,
@@ -69,6 +71,7 @@ impl<'a> FontFallbackIter<'a> {
             monospace_fallbacks: BTreeSet::new(),
             default_i: 0,
             scripts,
+            word,
             script_i: (0, 0),
             common_i: 0,
             other_i: 0,
@@ -161,44 +164,34 @@ impl<'a> Iterator for FontFallbackIter<'a> {
                             // Default font
                             let fallback_info = MonospaceFallbackInfo {
                                 weight_offset: None,
-                                script_non_matches: None,
+                                codepoint_non_matches: None,
                                 id: m_key.id,
                             };
-                            assert_eq!(self.monospace_fallbacks.insert(fallback_info), true);
+                            assert!(self.monospace_fallbacks.insert(fallback_info));
                         }
                     }
                 }
                 // Set a monospace fallback if Monospace family is not found
                 if is_mono {
-                    let script_tags = self
-                        .scripts
-                        .iter()
-                        .filter_map(|script| {
-                            let script_as_lower = script.short_name().to_lowercase();
-                            <[u8; 4]>::try_from(script_as_lower.as_bytes()).ok()
-                        })
-                        .collect::<Vec<_>>();
-
                     if let Some(face_info) = self.font_system.db().face(m_key.id) {
                         // Don't use emoji fonts as Monospace
                         if face_info.monospaced && !face_info.post_script_name.contains("Emoji") {
                             if let Some(font) = self.font_system.get_font(m_key.id) {
-                                let script_non_matches = self.scripts.len()
-                                    - script_tags
-                                        .iter()
-                                        .filter(|&&script_tag| {
-                                            font.scripts()
-                                                .iter()
-                                                .any(|&tag_bytes| tag_bytes == script_tag)
+                                let codepoint_non_matches = self.word.chars().count()
+                                    - self
+                                        .word
+                                        .chars()
+                                        .filter(|ch| {
+                                            font.unicode_codepoints().contains(&u32::from(*ch))
                                         })
                                         .count();
 
                                 let fallback_info = MonospaceFallbackInfo {
                                     weight_offset: m_key.weight_offset,
-                                    script_non_matches: Some(script_non_matches),
+                                    codepoint_non_matches: Some(codepoint_non_matches),
                                     id: m_key.id,
                                 };
-                                assert_eq!(self.monospace_fallbacks.insert(fallback_info), true);
+                                assert!(self.monospace_fallbacks.insert(fallback_info));
                             }
                         }
                     }

src/font/mod.rs

@@ -30,7 +30,7 @@ pub struct Font {
     data: Arc<dyn AsRef<[u8]> + Send + Sync>,
     id: fontdb::ID,
     monospace_em_width: Option<f32>,
-    scripts: Vec<[u8; 4]>,
+    unicode_codepoints: Vec<u32>,
 }
 
 impl fmt::Debug for Font {
@@ -50,8 +50,8 @@ impl Font {
         self.monospace_em_width
     }
 
-    pub fn scripts(&self) -> &[[u8; 4]] {
-        &self.scripts
+    pub fn unicode_codepoints(&self) -> &[u32] {
+        &self.unicode_codepoints
     }
 
     pub fn data(&self) -> &[u8] {
@@ -77,7 +77,7 @@ impl Font {
     pub fn new(db: &fontdb::Database, id: fontdb::ID) -> Option<Self> {
         let info = db.face(id)?;
 
-        let (monospace_em_width, scripts) = {
+        let (monospace_em_width, unicode_codepoints) = {
             db.with_face_data(id, |font_data, face_index| {
                 let face = ttf_parser::Face::parse(font_data, face_index).ok()?;
                 let monospace_em_width = info
@@ -93,16 +93,25 @@ impl Font {
                     None?;
                 }
 
-                let scripts = face
-                    .tables()
-                    .gpos
+                let mut unicode_codepoints = Vec::new();
+
+                face.tables()
+                    .cmap?
+                    .subtables
                     .into_iter()
-                    .chain(face.tables().gsub)
-                    .map(|table| table.scripts)
-                    .flatten()
-                    .map(|script| script.tag.to_bytes())
-                    .collect();
-                Some((monospace_em_width, scripts))
+                    .filter(|subtable| subtable.is_unicode())
+                    .for_each(|subtable| {
+                        unicode_codepoints.reserve(1024);
+                        subtable.codepoints(|code_point| {
+                            if subtable.glyph_index(code_point).is_some() {
+                                unicode_codepoints.push(code_point);
+                            }
+                        });
+                    });
+
+                unicode_codepoints.shrink_to_fit();
+
+                Some((monospace_em_width, unicode_codepoints))
             })?
         }?;
 
@@ -120,7 +129,7 @@ impl Font {
         Some(Self {
             id: info.id,
             monospace_em_width,
-            scripts,
+            unicode_codepoints,
             #[cfg(feature = "swash")]
             swash: {
                 let swash = swash::FontRef::from_index((*data).as_ref(), info.index as usize)?;

src/shape.rs

@@ -219,7 +219,13 @@ fn shape_run(
     let fonts = font_system.get_font_matches(attrs);
 
     let default_families = [&attrs.family];
-    let mut font_iter = FontFallbackIter::new(font_system, &fonts, &default_families, &scripts);
+    let mut font_iter = FontFallbackIter::new(
+        font_system,
+        &fonts,
+        &default_families,
+        &scripts,
+        &line[start_run..end_run],
+    );
 
     let font = font_iter.next().expect("no default font found");
 
@@ -341,7 +347,7 @@ fn shape_skip(
     let fonts = font_system.get_font_matches(attrs);
 
     let default_families = [&attrs.family];
-    let mut font_iter = FontFallbackIter::new(font_system, &fonts, &default_families, &[]);
+    let mut font_iter = FontFallbackIter::new(font_system, &fonts, &default_families, &[], "");
 
     let font = font_iter.next().expect("no default font found");
     let font_id = font.id();