[gtk/hint-metrics-setting] Add a gtk-hint-metrics setting

[Matthias Clasen <matthiasc src gnome org>]

commit ae7079199cdba87c74135a72dafd63194ffabeaa
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Sep 1 15:17:53 2021 -0400

    Add a gtk-hint-metrics setting
    
    This lets people switch back to font rendering that is closer
    to what GTK 3 does. It is not perfect - subpixel antialiasing
    is not going to work. But it give us an Escape hatch while
    we shake out the bugs in our linear layout.
    
    Related: #3787

 gtk/gtksettings.c | 28 +++++++++++++++++++++++++++-
 gtk/gtkwidget.c   | 13 ++++++++++---
 2 files changed, 37 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtksettings.c b/gtk/gtksettings.c
index af4538e94f..a0d55bc11a 100644
--- a/gtk/gtksettings.c
+++ b/gtk/gtksettings.c
@@ -166,6 +166,7 @@ enum {
   PROP_XFT_HINTSTYLE,
   PROP_XFT_RGBA,
   PROP_XFT_DPI,
+  PROP_HINT_METRICS,
   PROP_CURSOR_THEME_NAME,
   PROP_CURSOR_THEME_SIZE,
   PROP_ALTERNATIVE_BUTTON_ORDER,
@@ -556,6 +557,7 @@ gtk_settings_class_init (GtkSettingsClass *class)
 
   g_assert (result == PROP_XFT_RGBA);
 
+  
   /**
    * GtkSettings:gtk-xft-dpi:
    *
@@ -572,6 +574,25 @@ gtk_settings_class_init (GtkSettingsClass *class)
 
   g_assert (result == PROP_XFT_DPI);
 
+  /**
+   * GtkSettings:gtk-hint-metrics:
+   *
+   * Whether hinting should be applied to font metrics.
+   *
+   * Note that this also turns off subpixel positioning of glyphs,
+   * since it conflicts with metrics hinting.
+   *
+   * Since: 4.6
+   */
+  result = settings_install_property_parser (class,
+                                             g_param_spec_boolean ("gtk-hint-metrics",
+                                                                   P_("Hint Metrics"),
+                                                                   P_("Whether hinting should be applied to 
font metrics"),
+                                                                   FALSE,
+                                                                   GTK_PARAM_READWRITE));
+
+  g_assert (result == PROP_HINT_METRICS);
+
   /**
    * GtkSettings:gtk-cursor-theme-name:
    *
@@ -1439,6 +1460,7 @@ gtk_settings_notify (GObject    *object,
     case PROP_XFT_HINTING:
     case PROP_XFT_HINTSTYLE:
     case PROP_XFT_RGBA:
+    case PROP_HINT_METRICS:
       settings_update_font_options (settings);
       gtk_system_setting_changed (settings->display, GTK_SYSTEM_SETTING_FONT_CONFIG);
       break;
@@ -1678,6 +1700,7 @@ settings_update_font_options (GtkSettings *settings)
   cairo_antialias_t antialias_mode;
   char *rgba_str;
   cairo_subpixel_order_t subpixel_order;
+  gboolean hint_metrics;
 
   if (settings->font_options)
     cairo_font_options_destroy (settings->font_options);
@@ -1687,11 +1710,14 @@ settings_update_font_options (GtkSettings *settings)
                 "gtk-xft-hinting", &hinting,
                 "gtk-xft-hintstyle", &hint_style_str,
                 "gtk-xft-rgba", &rgba_str,
+                "gtk-hint-metrics", &hint_metrics,
                 NULL);
 
   settings->font_options = cairo_font_options_create ();
 
-  cairo_font_options_set_hint_metrics (settings->font_options, CAIRO_HINT_METRICS_OFF);
+  cairo_font_options_set_hint_metrics (settings->font_options,
+                                       hint_metrics ? CAIRO_HINT_METRICS_ON
+                                                    : CAIRO_HINT_METRICS_OFF);
 
   hint_style = CAIRO_HINT_STYLE_DEFAULT;
   if (hinting == 0)
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 2a8e288232..db5ec6dc69 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -6441,8 +6441,16 @@ update_pango_context (GtkWidget    *widget,
   pango_context_set_font_description (context, font_desc);
   pango_font_description_free (font_desc);
 
-  if (cairo_version () >= CAIRO_VERSION_ENCODE (1, 17, 4))
-    pango_context_set_round_glyph_positions (context, FALSE);
+  settings = gtk_widget_get_settings (widget);
+
+  if (settings &&
+      cairo_version () >= CAIRO_VERSION_ENCODE (1, 17, 4))
+    {
+      gboolean hint_metrics;
+
+      g_object_get (settings, "gtk-hint-metrics", &hint_metrics, NULL);
+      pango_context_set_round_glyph_positions (context, hint_metrics);
+    }
 
   pango_context_set_base_dir (context,
                               _gtk_widget_get_direction (widget) == GTK_TEXT_DIR_LTR ?
@@ -6450,7 +6458,6 @@ update_pango_context (GtkWidget    *widget,
 
   pango_cairo_context_set_resolution (context, _gtk_css_number_value_get (style->core->dpi, 100));
 
-  settings = gtk_widget_get_settings (widget);
   font_options = (cairo_font_options_t*)g_object_get_qdata (G_OBJECT (widget), quark_font_options);
   if (settings && font_options)
     {