Linux: Don't crash when fontconfig is unable to find a font for a character.

Instead render it as a missing glyph

kitty/fonts/box_drawing.py

@@ -26,7 +26,7 @@ def draw_hline(buf, width, x1, x2, y, level):
 
 
 def draw_vline(buf, width, y1, y2, x, level):
-    ' Draw a horizontal line between [y1, y2) centered at x with the thickness given by level '
+    ' Draw a vertical line between [y1, y2) centered at x with the thickness given by level '
     sz = thickness(level=level, horizontal=True)
     start = x - sz // 2
     for x in range(start, start + sz):
@@ -345,6 +345,15 @@ def render_box_char(ch, buf, width, height):
     return buf
 
 
+def render_missing_glyph(buf, width, height):
+    hgap = thickness(level=0, horizontal=True) + 1
+    vgap = thickness(level=0, horizontal=False) + 1
+    draw_hline(buf, width, hgap, width - hgap + 1, vgap, 0)
+    draw_hline(buf, width, hgap, width - hgap + 1, height - vgap, 0)
+    draw_vline(buf, width, vgap, height - vgap + 1, hgap, 0)
+    draw_vline(buf, width, vgap, height - vgap + 1, width - hgap, 0)
+
+
 def join_rows(width, height, rows):
     import ctypes
     ans = (ctypes.c_ubyte * (width * height * len(rows)))()

kitty/fonts/fontconfig.py

@@ -2,10 +2,12 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
+import os
 import re
 import subprocess
 from collections import namedtuple
 from functools import lru_cache
+
 from kitty.fast_data_types import Face
 
 
@@ -16,9 +18,15 @@ def escape_family_name(name):
 Font = namedtuple('Font', 'face hinting hintstyle bold italic')
 
 
+class FontNotFound(ValueError):
+    pass
+
+
 def get_font(query, bold, italic):
     query += ':scalable=true:outline=true'
-    raw = subprocess.check_output(['fc-match', query, '-f', '%{file}\x1e%{hinting}\x1e%{hintstyle}']).decode('utf-8')
+    raw = subprocess.check_output(
+        ['fc-match', query, '-f', '%{file}\x1e%{hinting}\x1e%{hintstyle}'
+         ]).decode('utf-8')
     parts = raw.split('\x1e')
     hintstyle, hinting = 1, 'True'
     if len(parts) == 3:
@@ -32,12 +40,21 @@ def get_font(query, bold, italic):
 
 @lru_cache(maxsize=4096)
 def find_font_for_character(family, char, bold=False, italic=False):
-    q = escape_family_name(family) + ':charset={}'.format(hex(ord(char[0]))[2:])
+    q = escape_family_name(family) + ':charset={}'.format(
+        hex(ord(char[0]))[2:])
     if bold:
         q += ':weight=200'
     if italic:
         q += ':slant=100'
-    return get_font(q, bold, italic)
+    try:
+        ans = get_font(q, bold, italic)
+    except subprocess.CalledProcessError as err:
+        raise FontNotFound(
+            'Failed to find font for character U+{:X}, error from fontconfig: {}'.
+            format(ord(char[0]), err))
+    if not ans.face or not os.path.exists(ans.face):
+        raise FontNotFound('Failed to find font for character U+{:X}'.format(ord(char[0])))
+    return ans
 
 
 @lru_cache(maxsize=64)
@@ -52,7 +69,11 @@ def get_font_information(q, bold=False, italic=False):
 
 def get_font_files(opts):
     ans = {}
-    attr_map = {'bold': 'bold_font', 'italic': 'italic_font', 'bi': 'bold_italic_font'}
+    attr_map = {
+        'bold': 'bold_font',
+        'italic': 'italic_font',
+        'bi': 'bold_italic_font'
+    }
 
     def get_family(key=None):
         ans = getattr(opts, attr_map.get(key, 'font_family'))
@@ -61,11 +82,17 @@ def get_font_files(opts):
         return ans
 
     n = get_font_information(get_family())
-    ans['regular'] = Font(Face(n.face), n.hinting, n.hintstyle, n.bold, n.italic)
+    ans['regular'] = Font(
+        Face(n.face), n.hinting, n.hintstyle, n.bold, n.italic)
 
     def do(key):
-        b = get_font_information(get_family(key), bold=key in ('bold', 'bi'), italic=key in ('italic', 'bi'))
+        b = get_font_information(
+            get_family(key),
+            bold=key in ('bold', 'bi'),
+            italic=key in ('italic', 'bi'))
         if b.face != n.face:
-            ans[key] = Font(Face(b.face), b.hinting, b.hintstyle, b.bold, b.italic)
+            ans[key] = Font(
+                Face(b.face), b.hinting, b.hintstyle, b.bold, b.italic)
+
     do('bold'), do('italic'), do('bi')
     return ans

kitty/fonts/freetype.py

@@ -2,18 +2,18 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
-import unicodedata
 import ctypes
+import sys
+import unicodedata
 from collections import namedtuple
 from functools import lru_cache
 from threading import Lock
 
-from kitty.fast_data_types import Face, FT_PIXEL_MODE_GRAY
+from kitty.fast_data_types import FT_PIXEL_MODE_GRAY, Face
-from kitty.utils import ceil_int
+from kitty.fonts.box_drawing import render_missing_glyph
-from .fontconfig import find_font_for_character, get_font_files
+from kitty.utils import ceil_int, get_logical_dpi, safe_print, wcwidth
-
-from kitty.utils import get_logical_dpi, wcwidth
 
+from .fontconfig import find_font_for_character, get_font_files, FontNotFound
 
 current_font_family = current_font_family_name = cff_size = cell_width = cell_height = baseline = None
 CharTexture = underline_position = underline_thickness = None
@@ -168,12 +168,29 @@ def current_cell():
     return CharTexture, cell_width, cell_height, baseline, underline_thickness, underline_position
 
 
+@lru_cache(maxsize=8)
+def missing_glyph(width):
+    w = cell_width * width
+    ans = bytearray(w * cell_height)
+    render_missing_glyph(ans, w, cell_height)
+    first, second = CharBitmap(ans, 0, 0, 0, cell_height, w), None
+    if width == 2:
+        first, second = split_char_bitmap(first)
+        second = create_cell_buffer(second, 0, 0, second.rows, 0, 0, second.columns)
+    first = create_cell_buffer(first, 0, 0, first.rows, 0, 0, first.columns)
+    return first, second
+
+
 def render_cell(text=' ', bold=False, italic=False):
     # TODO: Handle non-normalizable combining chars. Probably need to use
     # harfbuzz for that
     text = unicodedata.normalize('NFC', text)[0]
     width = wcwidth(text)
+    try:
         bitmap_char = render_char(text, bold, italic, width)
+    except FontNotFound as err:
+        safe_print('ERROR:', err, file=sys.stderr)
+        return missing_glyph(width)
     second = None
     if width == 2:
         if bitmap_char.columns > cell_width: