Use line_gap as top padding

Fixes #143

layout/CHANGELOG.md

@@ -1,3 +1,6 @@
+# Unreleased
+* Use font line_gap as top-padding for layouts to address issues with glyphs taller than the font ascent.
+
 # 0.2.3
 * Default layouts: Keep word trailing space width if ending in a hard break or end of all glyphs _e.g. `"Foo  \n"`_ _(This particularly changes the layout of right & centre aligned text ending in spaces)_. 
 

layout/src/builtin.rs

@@ -723,11 +723,12 @@ mod layout_test {
             ],
         );
 
+        let sfont = A_FONT.as_scaled(40.0);
         for g in glyphs {
             println!("{:?}", (g.glyph.scale, g.glyph.position));
             // all glyphs should have the same ascent drawing position
             let y_pos = g.glyph.position.y;
-            assert_relative_eq!(y_pos, A_FONT.as_scaled(40.0).ascent());
+            assert_relative_eq!(y_pos, sfont.ascent() + sfont.line_gap());
         }
     }
 

layout/src/lines.rs

@@ -20,17 +20,21 @@ impl Line {
     /// Returns line glyphs positioned on the screen and aligned.
     pub fn aligned_on_screen(
         mut self,
-        screen_position: (f32, f32),
+        (screen_x, screen_y): (f32, f32),
         h_align: HorizontalAlign,
         v_align: VerticalAlign,
     ) -> Vec<SectionGlyph> {
         if self.glyphs.is_empty() {
             return Vec::new();
         }
 
+        // use line_gap as top-padding for all lines
+        // fixes issues with glyphs taller than the ascent
+        let screen_y = screen_y + self.max_v_metrics.line_gap;
+
         // implement v-aligns when they're are supported
         let screen_left = match h_align {
-            HorizontalAlign::Left => point(screen_position.0, screen_position.1),
+            HorizontalAlign::Left => point(screen_x, screen_y),
             // - Right alignment attained from left by shifting the line
             //   leftwards by the rightmost x distance from render position
             // - Central alignment is attained from left by shifting the line
@@ -40,7 +44,7 @@ impl Line {
                 if h_align == HorizontalAlign::Center {
                     shift_left /= 2.0;
                 }
-                point(screen_position.0 - shift_left, screen_position.1)
+                point(screen_x - shift_left, screen_y)
             }
         };
 

layout/src/words.rs

@@ -17,7 +17,7 @@ pub(crate) struct VMetrics {
 impl VMetrics {
     #[inline]
     pub fn height(&self) -> f32 {
-        self.ascent - self.descent
+        self.ascent - self.descent + self.line_gap
     }
 
     #[inline]