Fix builtin font block elements going invisible

alacritty/src/renderer/builtin_font.rs

@@ -385,7 +385,7 @@ fn box_drawing(character: char, metrics: &Metrics, offset: &Delta<i8>) -> Raster
  '\u{2580}'..='\u{2587}' | '\u{2589}'..='\u{2590}' | '\u{2594}' | '\u{2595}' => {
  let width = width as f32;
  let height = height as f32;
- let rect_width = match character {
+ let mut rect_width = match character {
  '\u{2589}' => width * 7. / 8.,
  '\u{258a}' => width * 6. / 8.,
  '\u{258b}' => width * 5. / 8.,
@@ -397,7 +397,8 @@ fn box_drawing(character: char, metrics: &Metrics, offset: &Delta<i8>) -> Raster
  '\u{2595}' => width * 1. / 8.,
  _ => width,
  };
- let (rect_height, y) = match character {
+
+ let (mut rect_height, mut y) = match character {
  '\u{2580}' => (height * 4. / 8., height * 8. / 8.),
  '\u{2581}' => (height * 1. / 8., height * 1. / 8.),
  '\u{2582}' => (height * 2. / 8., height * 2. / 8.),
@@ -409,12 +410,18 @@ fn box_drawing(character: char, metrics: &Metrics, offset: &Delta<i8>) -> Raster
  '\u{2594}' => (height * 1. / 8., height * 8. / 8.),
  _ => (height, height),
  };
+
  // Fix `y` coordinates.
- let y = height - y;
+ y = height - y;
+
+ // Ensure that resulted glyph will be visible and also round sizes instead of straight
+ // flooring them.
+ rect_width = cmp::max(rect_width.round() as i32, 1) as f32;
+ rect_height = cmp::max(rect_height.round() as i32, 1) as f32;
 
  let x = match character {
  '\u{2590}' => canvas.x_center(),
- '\u{2595}' => width as f32 - width / 8.,
+ '\u{2595}' => width as f32 - rect_width,
  _ => 0.,
  };