Add option to control built-in box drawing chars

This commit adds the config `font.builtin_box_drawing` option to
control built-in font, which is enabled by default.

CHANGELOG.md

@@ -11,6 +11,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 - Minimum Rust version has been bumped to 1.56.0
 
+### Added
+
+ - Option `font.builtin_box_drawing` to disable the built-in font for drawing box characters
+
 ### Changed
 
 - The `--help` output was reworked with a new colorful syntax

alacritty.yml

@@ -178,6 +178,13 @@
   # it is recommended to set `use_thin_strokes` to `false`.
   #use_thin_strokes: true
 
+  # Use built-in font for box drawing characters.
+  #
+  # If `true`, Alacritty will use a custom built-in font for box drawing
+  # characters (Unicode points 2500 - 259f).
+  #
+  #builtin_box_drawing: true
+
 # If `true`, bold text is drawn using the bright color variants.
 #draw_bold_text_with_bright_colors: false
 

alacritty/src/config/font.rs

@@ -14,7 +14,7 @@ use crate::config::ui_config::Delta;
 /// field in this struct. It might be nice in the future to have defaults for
 /// each value independently. Alternatively, maybe erroring when the user
 /// doesn't provide complete config is Ok.
-#[derive(ConfigDeserialize, Default, Debug, Clone, PartialEq, Eq)]
+#[derive(ConfigDeserialize, Debug, Clone, PartialEq, Eq)]
 pub struct Font {
     /// Extra spacing per character.
     pub offset: Delta<i8>,
@@ -38,6 +38,9 @@ pub struct Font {
 
     /// Font size in points.
     size: Size,
+
+    /// Whether to use the built-in font for box drawing characters.
+    pub builtin_box_drawing: bool,
 }
 
 impl Font {
@@ -72,6 +75,22 @@ impl Font {
     }
 }
 
+impl Default for Font {
+    fn default() -> Font {
+        Self {
+            builtin_box_drawing: true,
+            use_thin_strokes: Default::default(),
+            glyph_offset: Default::default(),
+            bold_italic: Default::default(),
+            italic: Default::default(),
+            offset: Default::default(),
+            normal: Default::default(),
+            bold: Default::default(),
+            size: Default::default(),
+        }
+    }
+}
+
 /// Description of the normal font.
 #[derive(ConfigDeserialize, Debug, Clone, PartialEq, Eq)]
 pub struct FontDescription {

alacritty/src/renderer/mod.rs

@@ -137,6 +137,9 @@ pub struct GlyphCache {
 
     /// Font metrics.
     metrics: crossfont::Metrics,
+
+    /// Whether to use the built-in font for box drawing characters.
+    builtin_box_drawing: bool,
 }
 
 impl GlyphCache {
@@ -167,6 +170,7 @@ impl GlyphCache {
             bold_italic_key: bold_italic,
             glyph_offset: font.glyph_offset,
             metrics,
+            builtin_box_drawing: font.builtin_box_drawing,
         };
 
         cache.load_common_glyphs(loader);
@@ -268,7 +272,10 @@ impl GlyphCache {
 
         // Rasterize the glyph using the built-in font for special characters or the user's font
         // for everything else.
-        let rasterized = builtin_font::builtin_glyph(glyph_key.character, &self.metrics)
+        let rasterized = self
+            .builtin_box_drawing
+            .then(|| builtin_font::builtin_glyph(glyph_key.character, &self.metrics))
+            .flatten()
             .map_or_else(|| self.rasterizer.get_glyph(glyph_key), Ok);
 
         let glyph = match rasterized {
@@ -355,6 +362,7 @@ impl GlyphCache {
         self.italic_key = italic;
         self.bold_italic_key = bold_italic;
         self.metrics = metrics;
+        self.builtin_box_drawing = font.builtin_box_drawing;
 
         self.clear_glyph_cache(loader);