Reshaping with unsafe-to-break ⚡

Co-Authored-By: Martin <mhaug@live.de>

1 files changed, 40 insertions, 34 deletions

diff --git a/src/font.rs b/src/font.rs
index bcc64627..a816ed06 100644
--- a/src/font.rs
+++ b/src/font.rs
@@ -4,12 +4,19 @@ use std::fmt::{self, Display, Formatter};
 
 use fontdock::FaceFromVec;
 
+use crate::geom::Length;
+
 /// An owned font face.
 pub struct FaceBuf {
     data: Box<[u8]>,
     index: u32,
     ttf: ttf_parser::Face<'static>,
     buzz: rustybuzz::Face<'static>,
+    units_per_em: f64,
+    ascender: f64,
+    cap_height: f64,
+    x_height: f64,
+    descender: f64,
 }
 
 impl FaceBuf {
@@ -36,6 +43,22 @@ impl FaceBuf {
         // lifetime.
         &self.buzz
     }
+
+    /// Look up a vertical metric at a given font size.
+    pub fn vertical_metric(&self, size: Length, metric: VerticalFontMetric) -> Length {
+        self.convert(size, match metric {
+            VerticalFontMetric::Ascender => self.ascender,
+            VerticalFontMetric::CapHeight => self.cap_height,
+            VerticalFontMetric::XHeight => self.x_height,
+            VerticalFontMetric::Baseline => 0.0,
+            VerticalFontMetric::Descender => self.descender,
+        })
+    }
+
+    /// Convert from font units to a length at a given font size.
+    pub fn convert(&self, size: Length, units: impl Into<f64>) -> Length {
+        units.into() / self.units_per_em * size
+    }
 }
 
 impl FaceFromVec for FaceBuf {
@@ -47,11 +70,26 @@ impl FaceFromVec for FaceBuf {
         let slice: &'static [u8] =
             unsafe { std::slice::from_raw_parts(data.as_ptr(), data.len()) };
 
+        let ttf = ttf_parser::Face::from_slice(slice, index).ok()?;
+        let buzz = rustybuzz::Face::from_slice(slice, index)?;
+
+        // Look up some metrics we may need often.
+        let units_per_em = ttf.units_per_em().unwrap_or(1000);
+        let ascender = ttf.typographic_ascender().unwrap_or(ttf.ascender());
+        let cap_height = ttf.capital_height().filter(|&h| h > 0).unwrap_or(ascender);
+        let x_height = ttf.x_height().filter(|&h| h > 0).unwrap_or(ascender);
+        let descender = ttf.typographic_descender().unwrap_or(ttf.descender());
+
         Some(Self {
             data,
             index,
-            ttf: ttf_parser::Face::from_slice(slice, index).ok()?,
-            buzz: rustybuzz::Face::from_slice(slice, index)?,
+            ttf,
+            buzz,
+            units_per_em: f64::from(units_per_em),
+            ascender: f64::from(ascender),
+            cap_height: f64::from(cap_height),
+            x_height: f64::from(x_height),
+            descender: f64::from(descender),
         })
     }
 }
@@ -77,38 +115,6 @@ pub enum VerticalFontMetric {
     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 {