Font independent rendering for braille characters, which ensures they are properly aligned at all font sizes.

docs/changelog.rst

@@ -14,6 +14,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Options to control mouse pointer shape, :opt:`default_pointer_shape`, and
   :opt:`pointer_shape_when_dragging` (:pull:`3041`)
 
+- Font independent rendering for braille characters, which ensures they are properly
+  aligned at all font sizes.
+
 - Fix a regression in 0.19.0 that caused borders not to be drawn when setting
   :opt:`window_margin_width` and keeping :opt:`draw_minimal_borders` on
   (:iss:`3017`)

kitty/fonts.c

@@ -596,6 +596,7 @@ START_ALLOW_CASE_RANGE
         case 0x2500 ... 0x2573:
         case 0x2574 ... 0x259f:
         case 0xe0b0 ... 0xe0b4:
+        case 0x2800 ... 0x28ff:
         case 0xe0b6:
         case 0xe0b8: // 
         case 0xe0ba: //   
@@ -642,8 +643,10 @@ START_ALLOW_CASE_RANGE
             return 0xa0 + ch - 0xe0b0; // IDs from 0xa0 to 0xc4
         case 0x1fb00 ... 0x1fb8b:
             return 0xc5 + ch - 0x1fb00; // IDs from 0xc5 to 0x150
-        case 0x1fba0 ... 0x1fbae:
+        case 0x1fba0 ... 0x1fbae:  // IDs from 0x151 to 0x15f
             return 0x151 + ch - 0x1fba0;
+        case 0x2800 ... 0x28ff:
+            return 0x160 + ch - 0x2800;
         default:
             return 0xffff;
     }

kitty/fonts/box_drawing.py

@@ -685,6 +685,32 @@ def eight_block(buf: BufType, width: int, height: int, level: int = 1, which: Tu
         eight_bar(buf, width, height, level, x, horizontal)
 
 
+def braille_dot(buf: BufType, width: int, height: int, col: int, row: int) -> None:
+    dot_height = max(1, height // 8)
+    dot_width = max(1, width // 4)
+    top_margin = (height - 7 * dot_height) // 2
+    left_margin = (width - 3 * dot_width) // 2
+    x_start = left_margin + (col * 2 * dot_width)
+    y_start = top_margin + (row * 2 * dot_height)
+    if y_start < height:
+        for y in range(y_start, min(height, y_start + dot_height)):
+            if x_start < width:
+                offset = y * width
+                for x in range(x_start, min(width, x_start + dot_width)):
+                    buf[offset + x] = 255
+
+
+def braille(buf: BufType, width: int, height: int, which: int = 0) -> None:
+    if not which:
+        return
+    for i, x in enumerate(reversed(bin(which)[2:])):
+        if x == '1':
+            q = i + 1
+            col = 0 if q in (1, 2, 3, 7) else 1
+            row = 0 if q in (1, 4) else 1 if q in (2, 5) else 2 if q in (3, 6) else 3
+            braille_dot(buf, width, height, col, row)
+
+
 box_chars: Dict[str, List[Callable]] = {
     '─': [hline],
     '━': [p(hline, level=3)],
@@ -908,6 +934,9 @@ for chars, func_ in (('╒╕╘╛', dvcorner), ('╓╖╙╜', dhcorner), ('
     for ch in chars:
         box_chars[ch] = [p(cast(Callable, func_), which=ch)]
 
+for i in range(256):
+    box_chars[chr(0x2800 + i)] = [p(braille, which=i)]
+
 
 c = 0x1fb00
 for i in range(1, 63):