Render known country flags designated by a pair of unicode codepoints in two cells instead of four.

docs/changelog.rst

@@ -16,6 +16,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 
 - Update to Unicode 13.0 (:iss:`2513`)
 
+- Render known country flags designated by a pair of unicode codepoints
+  in two cells instead of four.
+
 
 0.17.2 [2020-03-29]
 --------------------

gen-wcwidth.py

@@ -51,7 +51,8 @@ all_symbols: Set[int] = set()
 name_map: Dict[int, str] = {}
 word_search_map: DefaultDict[str, Set[int]] = defaultdict(set)
 zwj = 0x200d
-marks = set(emoji_skin_tone_modifiers) | {zwj}
+flag_codepoints = frozenset(range(0x1F1E6, 0x1F1E6 + 26))
+marks = set(emoji_skin_tone_modifiers) | {zwj} | flag_codepoints
 not_assigned = set(range(0, sys.maxunicode))
 
 
@@ -278,7 +279,7 @@ def gen_emoji() -> None:
             p(comma, '{', ', '.join(map(str, arr)), '}')
         p('};')
         p('if (a < 0x1F1E6 || b < 0x1F1E6 || a >= 0x1F1E6 + 26 || b >= 0x1F1E6 + 26) return false;')
-        p('return flag_combinations[a][b];')
+        p('return flag_combinations[a - 0x1F1E6][b - 0x1F1E6];')
         p('};')
 
 
@@ -486,7 +487,7 @@ def gen_names() -> None:
 def gen_wcwidth() -> None:
     seen: Set[int] = set()
 
-    def add(p: Callable, comment: str, chars_: Set[int], ret: int) -> None:
+    def add(p: Callable, comment: str, chars_: Union[Set[int], FrozenSet[int]], ret: int) -> None:
         chars = chars_ - seen
         seen.update(chars)
         p(f'\t\t// {comment} ({len(chars)} codepoints)' + ' {{' '{')
@@ -500,6 +501,7 @@ def gen_wcwidth() -> None:
         p('\tswitch(code) {')
 
         non_printing = class_maps['Cc'] | class_maps['Cf'] | class_maps['Cs']
+        add(p, 'Flags', flag_codepoints, 2)
         add(p, 'Marks', marks | {0}, 0)
         add(p, 'Non-printing characters', non_printing, -1)
         add(p, 'Private use', class_maps['Co'], -3)

kitty/emoji.h

@@ -811,7 +811,7 @@ static const unsigned char flag_combinations[26][26] = {
 , { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0 }
 };
 if (a < 0x1F1E6 || b < 0x1F1E6 || a >= 0x1F1E6 + 26 || b >= 0x1F1E6 + 26) return false;
-return flag_combinations[a][b];
+return flag_combinations[a - 0x1F1E6][b - 0x1F1E6];
 };
 
 END_ALLOW_CASE_RANGE

kitty/screen.c

@@ -14,6 +14,7 @@
 #include "fonts.h"
 #include "lineops.h"
 #include "screen.h"
+#include "emoji.h"
 #include <structmember.h>
 #include <limits.h>
 #include <sys/types.h>
@@ -357,6 +358,27 @@ selection_has_screen_line(Selection *s, int y) {
     return top <= y && y <= bottom;
 }
 
+static inline bool
+draw_second_flag_codepoint(Screen *self, char_type ch) {
+    index_type xpos = 0, ypos = 0;
+    if (self->cursor->x > 1) {
+        ypos = self->cursor->y;
+        xpos = self->cursor->x - 2;
+    } else if (self->cursor->y > 0 && self->columns > 1) {
+        ypos = self->cursor->y - 1;
+        xpos = self->columns - 2;
+    } else return false;
+
+    linebuf_init_line(self->linebuf, ypos);
+    CPUCell *cell = self->linebuf->line->cpu_cells + xpos;
+    if (!is_flag_pair(cell->ch, ch) || cell->cc_idx[0]) return false;
+    line_add_combining_char(self->linebuf->line, ch, xpos);
+    self->is_dirty = true;
+    if (selection_has_screen_line(&self->selection, ypos)) self->selection = EMPTY_SELECTION;
+    linebuf_mark_line_dirty(self->linebuf, ypos);
+    return true;
+}
+
 static inline void
 draw_combining_char(Screen *self, char_type ch) {
     bool has_prev_char = false;
@@ -372,6 +394,17 @@ draw_combining_char(Screen *self, char_type ch) {
         xpos = self->columns - 1;
         has_prev_char = true;
     }
+    if (self->cursor->x > 0) {
+        ypos = self->cursor->y;
+        linebuf_init_line(self->linebuf, ypos);
+        xpos = self->cursor->x - 1;
+        has_prev_char = true;
+    } else if (self->cursor->y > 0) {
+        ypos = self->cursor->y - 1;
+        linebuf_init_line(self->linebuf, ypos);
+        xpos = self->columns - 1;
+        has_prev_char = true;
+    }
     if (has_prev_char) {
         line_add_combining_char(self->linebuf->line, ch, xpos);
         self->is_dirty = true;
@@ -412,6 +445,10 @@ screen_draw(Screen *self, uint32_t och) {
         draw_combining_char(self, ch);
         return;
     }
+    bool is_flag = is_flag_codepoint(ch);
+    if (UNLIKELY(is_flag)) {
+        if (draw_second_flag_codepoint(self, ch)) return;
+    }
     int char_width = wcwidth_std(ch);
     if (UNLIKELY(char_width < 1)) {
         if (char_width == 0) return;

kitty/wcwidth-std.h

@@ -8,6 +8,11 @@ START_ALLOW_CASE_RANGE
 static int
 wcwidth_std(int32_t code) {
 	switch(code) {
+		// Flags (26 codepoints) {{{
+		case 0x1f1e6 ... 0x1f1ff:
+			return 2;
+		// }}}
+
 		// Marks (2302 codepoints) {{{
 		case 0x0:
 			return 0;
@@ -1494,9 +1499,7 @@ wcwidth_std(int32_t code) {
 			return 2;
 		// }}}
 
-		// Emoji Presentation (26 codepoints) {{{
-		case 0x1f1e6 ... 0x1f1ff:
-			return 2;
+		// Emoji Presentation (0 codepoints) {{{
 		// }}}
 
 		// Not assigned in the unicode character database (765365 codepoints) {{{