config: add curly-underline-height

config.c

@@ -1075,6 +1075,21 @@ parse_section_main(struct context *ctx)
     else if (streq(key, "underline-thickness"))
         return value_to_pt_or_px(ctx, &conf->underline_thickness);
 
+    else if (streq(key, "curly-underline-height")) {
+        float value;
+        if (!value_to_float(ctx, &value))
+            return false;
+
+        if (value < 0.5 || value > 5.0) {
+            LOG_CONTEXTUAL_WARN(
+                "curly-underline-height should be between 0.5 and 5.0, clamping");
+            value = value < 0.5 ? 0.5 : 5.0;
+        }
+
+        conf->curly_underline_height_multiplier = value;
+        return true;
+    }
+
     else if (streq(key, "strikeout-thickness"))
         return value_to_pt_or_px(ctx, &conf->strikeout_thickness);
 
@@ -3481,6 +3496,7 @@ config_load(struct config *conf, const char *conf_path,
         .use_custom_underline_offset = false,
         .box_drawings_uses_font_glyphs = false,
         .underline_thickness = {.pt = 0., .px = -1},
+        .curly_underline_height_multiplier = 3.0,
         .strikeout_thickness = {.pt = 0., .px = -1},
         .overline_thickness = {.pt = 0., .px = -1},
         .overline_offset = {.pt = 0., .px = -1},

config.h

@@ -270,6 +270,7 @@ struct config {
     bool use_custom_underline_offset;
     struct pt_or_px underline_offset;
     struct pt_or_px underline_thickness;
+    float curly_underline_height_multiplier;
 
     struct pt_or_px strikeout_thickness;
 

doc/foot.ini.5.scd

@@ -186,6 +186,19 @@ empty string to be set, but it must be quoted: *KEY=""*)
 
 	Default: _unset_
 
+*curly-underline-height*
+	Height multiplier for curly underlines (undercurl). This is a unitless
+	multiplier applied to the underline thickness to determine the vertical
+	amplitude of the curly wave.
+
+	For example, a value of *3.0* means the curly underline will extend
+	3 times the underline thickness vertically. Higher values make taller
+	waves, lower values make flatter waves.
+
+	Valid range: *0.5* to *5.0*. Values outside this range will be clamped.
+
+	Default: *3.0*
+
 *strikeout-thickness*
 	Use a custom thickness (height) for strikeouts. The thickness is, by
 	default, in _points_.

render.c

@@ -445,7 +445,7 @@ draw_styled_underline(const struct terminal *term, pixman_image_t *pix,
     case UNDERLINE_DOUBLE:
     case UNDERLINE_CURLY:
         y_ofs = min(underline_offset(term, font),
-                    term->cell_height - thickness * 3);
+                    term->cell_height - thickness * term->conf->curly_underline_height_multiplier);
         break;
 
     case UNDERLINE_DASHED:
@@ -525,7 +525,7 @@ draw_styled_underline(const struct terminal *term, pixman_image_t *pix,
 
     case UNDERLINE_CURLY: {
         const int top = y + y_ofs;
-        const int bot = top + thickness * 3;
+        const int bot = top + thickness * term->conf->curly_underline_height_multiplier;
         const int half_x = x + ceil_w / 2.0, full_x = x + ceil_w;
 
         const double bt_2 = (bot - top) * (bot - top);