Fix line metrics

Since bitmap fonts do not provide their own underline metrics, the
self-calculated metrics which have been used for rusttype are now also
used for bitmap fonts with freetype.

The rusttype and bitmap fallback metrics have incorrectly offset the
underline by the underline height. Since the position is already defined
as the center point, that is not necessary.

All rounding and clamping has also been removed from the font library,
so that the raw values are reported now. The clamping and rounding is
now done in the line renderer.

font/src/darwin/mod.rs

@@ -430,21 +430,17 @@ impl Font {
         let leading = self.ct_font.leading() as f64;
         let line_height = (ascent + descent + leading + 0.5).floor();
 
-        // Strikeout and underline metrics
-        // CoreText doesn't provide strikeout so we provide our own
-        let underline_position =
-            (self.ct_font.underline_position() - descent)
-            .round() as f32;
-        let underline_thickness = self.ct_font.underline_thickness()
-            .round()
-            .max(1.) as f32;
-        let strikeout_position = (line_height as f32 / 2. - descent as f32).round();
+        // Strikeout and underline metrics.
+        // CoreText doesn't provide strikeout so we provide our own.
+        let underline_position = (self.ct_font.underline_position() - descent) as f32;
+        let underline_thickness = self.ct_font.underline_thickness() as f32;
+        let strikeout_position = (line_height / 2. - descent) as f32;
         let strikeout_thickness = underline_thickness;
 
         Metrics {
             average_advance,
             line_height,
-            descent: -(self.ct_font.descent() as f32),
+            descent: -(descent as f32),
             underline_position,
             underline_thickness,
             strikeout_position,

font/src/ft/mod.rs

@@ -97,22 +97,22 @@ impl ::Rasterize for FreeTypeRasterizer {
 
         // Get underline position and thickness in device pixels
         let x_scale = full.size_metrics.x_scale as f32 / 65536.0;
-        let underline_position =
-            (f32::from(face.ft_face.underline_position()) * x_scale / 64.).round();
-        let underline_thickness =
-            (f32::from(face.ft_face.underline_thickness()) * x_scale / 64.)
-            .round()
-            .max(1.);
+        let mut underline_position = f32::from(face.ft_face.underline_position()) * x_scale / 64.;
+        let mut underline_thickness = f32::from(face.ft_face.underline_thickness()) * x_scale / 64.;
+
+        // Fallback for bitmap fonts which do not provide underline metrics
+        if underline_position == 0. {
+            underline_thickness = (descent / 5.).round();
+            underline_position = descent / 2.;
+        }
 
         // Get strikeout position and thickness in device pixels
         let (strikeout_position, strikeout_thickness) =
             match TrueTypeOS2Table::from_face(&mut face.ft_face.clone())
         {
             Some(os2) => {
-                let strikeout_position =
-                    (f32::from(os2.y_strikeout_position()) * x_scale / 64.).round();
-                let strikeout_thickness =
-                    (f32::from(os2.y_strikeout_size()) * x_scale / 64.).round();
+                let strikeout_position = f32::from(os2.y_strikeout_position()) * x_scale / 64.;
+                let strikeout_thickness = f32::from(os2.y_strikeout_size()) * x_scale / 64.;
                 (strikeout_position, strikeout_thickness)
             },
             _ => {

font/src/rusttype/mod.rs

@@ -38,11 +38,11 @@ impl crate::Rasterize for RustTypeRasterizer {
         let average_advance = f64::from(hmetrics.advance_width);
         let descent = vmetrics.descent;
 
-        // Strikeout and underline metrics
-        // RustType doesn't support these, so we make up our own
+        // Strikeout and underline metrics.
+        // RustType doesn't support these, so we make up our own.
         let thickness = (descent / 5.).round();
-        let underline_position = descent / 2. + thickness / 2.;
-        let strikeout_position = (line_height as f32 / 2. - descent).round();
+        let underline_position = descent / 2.;
+        let strikeout_position = line_height as f32 / 2. - descent;
 
         Ok(Metrics {
             descent,

src/renderer/lines.rs

@@ -122,12 +122,15 @@ fn create_rect(
     let end_x = (end.column.0 + 1) as f32 * size.cell_width;
     let width = end_x - start_x;
 
-    let (position, height) = match flag {
+    let (position, mut height) = match flag {
         Flags::UNDERLINE => (metrics.underline_position, metrics.underline_thickness),
         Flags::STRIKEOUT => (metrics.strikeout_position, metrics.strikeout_thickness),
         _ => unimplemented!("Invalid flag for cell line drawing specified"),
     };
 
+    // Make sure lines are always visible
+    height = height.max(1.);
+
     let cell_bottom = (start.line.0 as f32 + 1.) * size.cell_height;
     let baseline = cell_bottom + metrics.descent;
 
@@ -139,9 +142,9 @@ fn create_rect(
 
     let rect = Rect::new(
         start_x + size.padding_x,
-        y + size.padding_y,
+        y.round() + size.padding_y,
         width,
-        height,
+        height.round(),
     );
 
     (rect, start.fg)