term: increase/decrease custom line-height with font size changes

When the user has set a custom line-height, we now adjust it when
increasing/decreasing (“zooming”) the font size at run-time.

Previously, the line-height was fixed at the size specified in
foot.ini.

CHANGELOG.md

@@ -33,6 +33,8 @@
 
 * Logic that repairs invalid key bindings ended up breaking valid key
   bindings instead (https://codeberg.org/dnkl/foot/issues/407).
+* Custom `line-height` settings now scale when increasing or
+  decreasing the font size at run-time.
 
 
 ### Security

config.h

@@ -53,12 +53,6 @@ struct config_mouse_binding {
     struct config_binding_pipe pipe;
 };
 
-/* If px != 0 then px is valid, otherwise pt is valid */
-struct pt_or_px {
-    int16_t px;
-    float pt;
-};
-
 struct config_spawn_template {
     char *raw_cmd;
     char **argv;

terminal.c

@@ -649,8 +649,8 @@ term_set_fonts(struct terminal *term, struct fcft_font *fonts[static 4])
          : term->fonts[0]->max_advance.x)
         + pt_or_px_as_pixels(term, &conf->letter_spacing);
 
-    term->cell_height = conf->line_height.px >= 0
-        ? pt_or_px_as_pixels(term, &conf->line_height)
+    term->cell_height = term->font_line_height.px >= 0
+        ? pt_or_px_as_pixels(term, &term->font_line_height)
         : max(term->fonts[0]->height,
               term->fonts[0]->ascent + term->fonts[0]->descent);
 
@@ -979,6 +979,7 @@ load_fonts_from_conf(struct terminal *term)
         }
     }
 
+    term->font_line_height = term->conf->line_height;
     return reload_fonts(term);
 }
 
@@ -1196,6 +1197,7 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
                 .pt_size = it->item.pt_size, .px_size = it->item.px_size};
         }
     }
+    term->font_line_height = conf->line_height;
 
     /* Start the slave/client */
     if ((term->slave = slave_spawn(
@@ -1780,6 +1782,15 @@ term_font_size_adjust(struct terminal *term, double amount)
         }
     }
 
+    if (term->font_line_height.px >= 0) {
+        double old_pt_size = term->font_line_height.px > 0
+            ? term->font_line_height.px * 72. / term->font_dpi
+            : term->font_line_height.pt;
+
+        term->font_line_height.px = 0;
+        term->font_line_height.pt = fmax(old_pt_size + amount, 0);
+    }
+
     return reload_fonts(term);
 }
 

terminal.h

@@ -261,6 +261,12 @@ struct url {
 };
 typedef tll(struct url) url_list_t;
 
+/* If px != 0 then px is valid, otherwise pt is valid */
+struct pt_or_px {
+    int16_t px;
+    float pt;
+};
+
 struct terminal {
     struct fdm *fdm;
     struct reaper *reaper;
@@ -312,6 +318,7 @@ struct terminal {
 
     struct fcft_font *fonts[4];
     struct config_font *font_sizes[4];
+    struct pt_or_px font_line_height;
     float font_dpi;
     int font_scale;
     int16_t font_x_ofs;