csi: implement DECSET/DECRST/DECRQM 2027 - grapheme cluster processing

This implements private mode 2027 - grapheme cluster processing, as
defined in the "Terminal Unicode Core"[1] specification.

Internally, we just flip the already existing option "grapheme
shaping". Since it's now runtime changeable, we need a copy of it in
the terminal struct, rather than referencing the conf object.

[1]: 13fc5a8993/spec/terminal-unicode-core.tex (L50-L53)

CHANGELOG.md

@@ -58,6 +58,8 @@
 * New key binding: `select-quote`. This key binding selects text
   between quote characters, and falls back to selecting the entire
   row ([#1364][1364]).
+* Support for DECSET/DECRST/DECRQM 2027 (_Grapheme cluster
+  processing_).
 
 [1077]: https://codeberg.org/dnkl/foot/issues/1077
 [1364]: https://codeberg.org/dnkl/foot/issues/1364

csi.c

@@ -491,6 +491,10 @@ decset_decrst(struct terminal *term, unsigned param, bool enable)
             term_disable_app_sync_updates(term);
         break;
 
+    case 2027:
+        term->grapheme_shaping = enable;
+        break;
+
     case 8452:
         term->sixel.cursor_right_of_graphics = enable;
         break;
@@ -572,6 +576,7 @@ decrqm(const struct terminal *term, unsigned param)
     case 1070: return decrpm(term->sixel.use_private_palette);
     case 2004: return decrpm(term->bracketed_paste);
     case 2026: return decrpm(term->render.app_sync_updates.enabled);
+    case 2027: return decrpm(term->grapheme_shaping);
     case 8452: return decrpm(term->sixel.cursor_right_of_graphics);
     case 737769: return decrpm(term_ime_is_enabled(term));
     }
@@ -614,6 +619,7 @@ xtsave(struct terminal *term, unsigned param)
     case 1070: term->xtsave.sixel_private_palette = term->sixel.use_private_palette; break;
     case 2004: term->xtsave.bracketed_paste = term->bracketed_paste; break;
     case 2026: term->xtsave.app_sync_updates = term->render.app_sync_updates.enabled; break;
+    case 2027: term->xtsave.grapheme_shaping = term->grapheme_shaping; break;
     case 8452: term->xtsave.sixel_cursor_right_of_graphics = term->sixel.cursor_right_of_graphics; break;
     case 737769: term->xtsave.ime = term_ime_is_enabled(term); break;
     }
@@ -655,6 +661,7 @@ xtrestore(struct terminal *term, unsigned param)
     case 1070: enable = term->xtsave.sixel_private_palette; break;
     case 2004: enable = term->xtsave.bracketed_paste; break;
     case 2026: enable = term->xtsave.app_sync_updates; break;
+    case 2027: enable = term->xtsave.grapheme_shaping; break;
     case 8452: enable = term->xtsave.sixel_cursor_right_of_graphics; break;
     case 737769: enable = term->xtsave.ime; break;
 

doc/foot-ctlseqs.7.scd

@@ -328,6 +328,9 @@ that corresponds to one of the following modes:
 |  2026
 :  terminal-wg
 :  Application synchronized updates mode
+|  2027
+:  contour
+:  Grapheme cluster processing
 |  8452
 :  xterm
 :  Position cursor to the right of sixels, instead of on the next line

doc/foot.ini.5.scd

@@ -1307,6 +1307,8 @@ any of these options.
 		- foot must have been compiled with utf8proc support
 		- fcft must have been compiled with HarfBuzz support
 	
+	This option can also be set runtime with DECSET/DECRST 2027.
+	
 	See also: *grapheme-width-method*.
 	
 	Default: _yes_

terminal.c

@@ -1253,6 +1253,7 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
         },
         .foot_exe = xstrdup(foot_exe),
         .cwd = xstrdup(cwd),
+        .grapheme_shaping = conf->tweak.grapheme_shaping,
 #if defined(FOOT_IME_ENABLED) && FOOT_IME_ENABLED
         .ime_enabled = true,
 #endif
@@ -1903,6 +1904,8 @@ term_reset(struct terminal *term, bool hard)
         tll_remove(term->alt.sixel_images, it);
     }
 
+    term->grapheme_shaping = term->conf->tweak.grapheme_shaping;
+
 #if defined(FOOT_IME_ENABLED) && FOOT_IME_ENABLED
     term_ime_enable(term);
 #endif

terminal.h

@@ -469,6 +469,7 @@ struct terminal {
         bool alt_screen:1;
         bool ime:1;
         bool app_sync_updates:1;
+        bool grapheme_shaping:1;
 
         bool sixel_display_mode:1;
         bool sixel_private_palette:1;
@@ -718,6 +719,8 @@ struct terminal {
 
     char *foot_exe;
     char *cwd;
+
+    bool grapheme_shaping;
 };
 
 struct config;

vt.c

@@ -657,7 +657,7 @@ static void
 action_utf8_print(struct terminal *term, char32_t wc)
 {
     int width = c32width(wc);
-    const bool grapheme_clustering = term->conf->tweak.grapheme_shaping;
+    const bool grapheme_clustering = term->grapheme_shaping;
 
 #if !defined(FOOT_GRAPHEME_CLUSTERING)
     xassert(!grapheme_clustering);