config: add tweak.grapheme-width-method=wcswidth|at-most-2

CHANGELOG.md

@@ -36,6 +36,9 @@
   terminfo entries. This should make 24-bit RGB colors work in tmux and
   neovim, without the need for config hacks or detection heuristics
   (https://codeberg.org/dnkl/foot/issues/615).
+* `[tweak].grapheme-width-method=wcswidth|at-most-2` option to
+  `foot.ini`.
+
 
 ### Changed
 ### Deprecated

config.c

@@ -2255,6 +2255,15 @@ parse_section_tweak(
             LOG_WARN("tweak: grapheme shaping");
     }
 
+    else if (strcmp(key, "grapheme-width-method") == 0) {
+        if (strcmp(value, "at-most-2") == 0)
+            conf->tweak.grapheme_width_method = GRAPHEME_WIDTH_MAX_2;
+        else if (strcmp(value, "wcswidth") == 0)
+            conf->tweak.grapheme_width_method = GRAPHEME_WIDTH_WCSWIDTH;
+
+        LOG_WARN("%s:%d [tweak]: grapheme-width-method=%s", path, lineno, value);
+    }
+
     else if (strcmp(key, "render-timer") == 0) {
         if (strcmp(value, "none") == 0) {
             conf->tweak.render_timer_osd = false;
@@ -2823,6 +2832,7 @@ config_load(struct config *conf, const char *conf_path,
             .fcft_filter = FCFT_SCALING_FILTER_LANCZOS3,
             .allow_overflowing_double_width_glyphs = true,
             .grapheme_shaping = false,
+            .grapheme_width_method = GRAPHEME_WIDTH_MAX_2,
             .delayed_render_lower_ns = 500000,         /* 0.5ms */
             .delayed_render_upper_ns = 16666666 / 2,   /* half a frame period (60Hz) */
             .max_shm_pool_size = 512 * 1024 * 1024,

config.h

@@ -246,6 +246,7 @@ struct config {
         enum fcft_scaling_filter fcft_filter;
         bool allow_overflowing_double_width_glyphs;
         bool grapheme_shaping;
+        enum {GRAPHEME_WIDTH_WCSWIDTH, GRAPHEME_WIDTH_MAX_2} grapheme_width_method;
         bool render_timer_osd;
         bool render_timer_log;
         bool damage_whole_window;

doc/foot.ini.5.scd

@@ -997,8 +997,26 @@ any of these options.
 	  but is necessary to not break cursor synchronization with the
 	  application running in foot.
 	
+	See also: *grapheme-width-method*.
+	
 	Default: _no_
 
+*grapheme-width-method*
+	Selects which method to use when calculating the width
+	(i.e. number of columns) of a grapheme cluster. One of *at-most-2*
+	and *wcswidth*.
+	
+	*wcswidth* simply adds together the individual width of all
+	codepoints making up the cluster.
+	
+	*at-most-2* does the same, but limits the maximum number of
+	columns to 2. This is more correct, but is likely to break
+	applications since applications typically use *wcswidth*(3)
+	internally to calculate the width. This results in cursor
+	de-synchronization issues.
+	
+	Default: _at-most-2_
+
 *max-shm-pool-size-mb*
 	This option controls the amount of virtual address space used by
 	the pixmap memory to which the terminal screen content is

vt.c

@@ -764,17 +764,26 @@ action_utf8_print(struct terminal *term, wchar_t wc)
                        (wanted_count - 2) * sizeof(new_cc->chars[0]));
             }
 
-            int grapheme_width = composed != NULL ? composed->width : base_width;
+            const int grapheme_width =
+                composed != NULL ? composed->width : base_width;
 
-            if (wc == 0xfe0f)
-                width = 2;
-            new_cc->width = min(max(grapheme_width, width), 2);
+            switch (term->conf->tweak.grapheme_width_method) {
+            case GRAPHEME_WIDTH_MAX_2:
+                if (unlikely(wc == 0xfe0f))
+                    width = 2;
+                new_cc->width = min(grapheme_width + width, 2);
+                break;
+
+            case GRAPHEME_WIDTH_WCSWIDTH:
+                new_cc->width = grapheme_width + width;
+                break;
+            }
 
             term->composed_count++;
             composed_insert(&term->composed, new_cc);
 
             wc = CELL_COMB_CHARS_LO + key;
-            width = grapheme_width;
+            width = new_cc->width;
 
             xassert(wc >= CELL_COMB_CHARS_LO);
             xassert(wc <= CELL_COMB_CHARS_HI);