Apply documentation changes

crates/epaint/src/text/font.rs

@@ -516,10 +516,14 @@ impl Font<'_> {
     }
 }
 
+/// Metrics for a font at a specific screen-space scale.
 #[derive(Clone, Copy, Debug, PartialEq, Default)]
 pub struct ScaledMetrics {
+    /// The DPI part of the screen-space scale.
     pub pixels_per_point: f32,
+    /// Scale factor, relative to the font's units per em (so, probably much less than 1).
     pub px_scale_factor: f32,
+    /// Vertical offset, in UI points (not screen-space).
     pub y_offset_in_points: f32,
     /// This is the distance from the top to the baseline.
     ///

crates/epaint/src/text/fonts.rs

@@ -799,7 +799,7 @@ impl FontsImpl {
         }
     }
 
-    /// Get the right font implementation from  [`FontFamily`].
+    /// Get the right font implementation from [`FontFamily`].
     pub fn font(&mut self, family: &FontFamily) -> Font<'_> {
         let cached_family = self.family_cache.entry(family.clone()).or_insert_with(|| {
             let fonts = &self.definitions.families.get(family);

crates/epaint/src/text/text_layout.rs

@@ -173,7 +173,9 @@ fn layout_section(
 
     let mut last_glyph_id = None;
 
+    // Optimization: only recompute `ScaledMetrics` when `FontFaceKey` changes.
     let mut last_font: Option<(FontFaceKey, Option<ScaledMetrics>)> = None;
+
     for chr in job.text[byte_range.clone()].chars() {
         if job.break_on_newline && chr == '\n' {
             out_paragraphs.push(Paragraph::from_section_index(section_index));