Start work on rendering box drawing characters directly

kitty/fonts/box_drawing.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2017, Kovid Goyal <kovid at kovidgoyal.net>
+
+import math
+from functools import partial as p
+
+from kitty.utils import get_logical_dpi
+
+
+def thickness(level=1, horizontal=True):
+    dpi = get_logical_dpi()[0 if horizontal else 1]
+    pts = (1, 1, 2, 4)[level]
+    return int(math.ceil(pts * dpi / 72.0))
+
+
+def half_hline(buf, width, height, level=1, which='left'):
+    sz = thickness(level=level, horizontal=True)
+    start = height // 2 - sz // 2
+    for y in range(start, start + sz):
+        for x in (range(0, width // 2) if which == 'left' else range(width // 2, width)):
+            buf[y * width + x] = 255
+
+
+box_chars = {
+    '─': [half_hline, p(half_hline, which='right')],
+    '━': [p(half_hline, level=3), p(half_hline, level=3, which='right')],
+}
+
+
+is_renderable_box_char = box_chars.__contains__
+
+
+def render_box_char(ch, buf, width, height):
+    for func in box_chars[ch]:
+        func(buf, width, height)
+    return buf

kitty/fonts/freetype.py

@@ -11,6 +11,7 @@ from threading import Lock
 
 from kitty.fast_data_types import Face, FT_PIXEL_MODE_GRAY
 from .fontconfig import find_font_for_character, get_font_files
+from .box_drawing import is_renderable_box_char, render_box_char
 
 from kitty.utils import get_logical_dpi, wcwidth
 
@@ -193,6 +194,8 @@ def render_cell(text=' ', bold=False, italic=False, underline=0, strikethrough=F
     # TODO: Handle non-normalizable combining chars. Probably need to use
     # harfbuzz for that
     text = unicodedata.normalize('NFC', text)[0]
+    if is_renderable_box_char(text):
+        return render_box_char(text, CharTexture(), cell_width, cell_height), None
     width = wcwidth(text)
     bitmap_char = render_char(text, bold, italic, width)
     second = None