Fix underline position for bitmap fonts

Fixes #3235.

CHANGELOG.md

@@ -35,6 +35,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Incorrect selection status of the first cell when selection is off screen
 - Backwards bracket selection
 - Stack overflow when printing shader creation error
+- Underline position for bitmap fonts
 
 ### Removed
 

alacritty/src/renderer/rects.rs

@@ -86,7 +86,7 @@ impl RenderLine {
         let line_bottom = (start.line.0 as f32 + 1.) * size.cell_height;
         let baseline = line_bottom + metrics.descent;
 
-        let mut y = baseline - position - height / 2.;
+        let mut y = (baseline - position - height / 2.).ceil();
         let max_y = line_bottom - height;
         if y > max_y {
             y = max_y;

font/src/ft/mod.rs

@@ -108,7 +108,7 @@ impl Rasterize for FreeTypeRasterizer {
 
         // Fallback for bitmap fonts which do not provide underline metrics
         if underline_position == 0. {
-            underline_thickness = (descent / 5.).round();
+            underline_thickness = (descent.abs() / 5.).round();
             underline_position = descent / 2.;
         }