1 files changed, 115 insertions, 0 deletions
diff --git a/src/font.rs b/src/font.rs
new file mode 100644
index 00000000..78fc0d44
--- /dev/null
+++ b/src/font.rs
@@ -0,0 +1,115 @@
+//! Font handling.
+
+use std::fmt::{self, Display, Formatter};
+
+use fontdock::FaceFromVec;
+
+/// An owned font face.
+pub struct FaceBuf {
+    data: Box<[u8]>,
+    ttf: ttf_parser::Face<'static>,
+    buzz: rustybuzz::Face<'static>,
+}
+
+impl FaceBuf {
+    /// The raw face data.
+    pub fn data(&self) -> &[u8] {
+        &self.data
+    }
+
+    /// Get a reference to the underlying ttf-parser face.
+    pub fn ttf(&self) -> &ttf_parser::Face<'_> {
+        // We can't implement Deref because that would leak the internal 'static
+        // lifetime.
+        &self.ttf
+    }
+
+    /// Get a reference to the underlying rustybuzz face.
+    pub fn buzz(&self) -> &rustybuzz::Face<'_> {
+        // We can't implement Deref because that would leak the internal 'static
+        // lifetime.
+        &self.buzz
+    }
+}
+
+impl FaceFromVec for FaceBuf {
+    fn from_vec(vec: Vec<u8>, i: u32) -> Option<Self> {
+        let data = vec.into_boxed_slice();
+
+        // SAFETY: The slices's location is stable in memory since we don't
+        //         touch it and it can't be touched from outside this type.
+        let slice: &'static [u8] =
+            unsafe { std::slice::from_raw_parts(data.as_ptr(), data.len()) };
+
+        Some(Self {
+            data,
+            ttf: ttf_parser::Face::from_slice(slice, i).ok()?,
+            buzz: rustybuzz::Face::from_slice(slice, i)?,
+        })
+    }
+}
+
+/// Identifies a vertical metric of a font.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub enum VerticalFontMetric {
+    /// The distance from the baseline to the typographic ascender.
+    ///
+    /// Corresponds to the typographic ascender from the `OS/2` table if present
+    /// and falls back to the ascender from the `hhea` table otherwise.
+    Ascender,
+    /// The approximate height of uppercase letters.
+    CapHeight,
+    /// The approximate height of non-ascending lowercase letters.
+    XHeight,
+    /// The baseline on which the letters rest.
+    Baseline,
+    /// The distance from the baseline to the typographic descender.
+    ///
+    /// Corresponds to the typographic descender from the `OS/2` table if
+    /// present and falls back to the descender from the `hhea` table otherwise.
+    Descender,
+}
+
+impl VerticalFontMetric {
+    /// Look up the metric in the given font face.
+    pub fn lookup(self, face: &ttf_parser::Face) -> i16 {
+        match self {
+            VerticalFontMetric::Ascender => lookup_ascender(face),
+            VerticalFontMetric::CapHeight => face
+                .capital_height()
+                .filter(|&h| h > 0)
+                .unwrap_or_else(|| lookup_ascender(face)),
+            VerticalFontMetric::XHeight => face
+                .x_height()
+                .filter(|&h| h > 0)
+                .unwrap_or_else(|| lookup_ascender(face)),
+            VerticalFontMetric::Baseline => 0,
+            VerticalFontMetric::Descender => lookup_descender(face),
+        }
+    }
+}
+
+/// The ascender of the face.
+fn lookup_ascender(face: &ttf_parser::Face) -> i16 {
+    // We prefer the typographic ascender over the Windows ascender because
+    // it can be overly large if the font has large glyphs.
+    face.typographic_ascender().unwrap_or_else(|| face.ascender())
+}
+
+/// The descender of the face.
+fn lookup_descender(face: &ttf_parser::Face) -> i16 {
+    // See `lookup_ascender` for reason.
+    face.typographic_descender().unwrap_or_else(|| face.descender())
+}
+
+impl Display for VerticalFontMetric {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        f.pad(match self {
+            Self::Ascender => "ascender",
+            Self::CapHeight => "cap-height",
+            Self::XHeight => "x-height",
+            Self::Baseline => "baseline",
+            Self::Descender => "descender",
+        })
+    }
+}