eglnative: Use gnome-settings-daemon font settings

While the X11 backend gets its font settings from XSettings, the native
backend did not use any user font preferences till now. So all shell fonts
were rendered with grayscale un-hinted, which some people describe as
"blurry text in Wayland sessions".

Although it's somewhat confusing using the "xsettings" schema on eglnative,
this is consistent with what GTK does already for its Wayland backend. It
is also documented here:

https://wiki.gnome.org/Initiatives/Wayland/GTK%2B#XSettings
https://wiki.gnome.org/Initiatives/Wayland/gnome-settings-daemon#xsettings

No more blurry shell text in Wayland sessions.

https://bugzilla.gnome.org/show_bug.cgi?id=645433

2 files changed, 178 insertions, 0 deletions

diff --git a/clutter/clutter/egl/clutter-backend-eglnative.c b/clutter/clutter/egl/clutter-backend-eglnative.c
index 6f64379..f222469 100644
--- a/clutter/clutter/egl/clutter-backend-eglnative.c
+++ b/clutter/clutter/egl/clutter-backend-eglnative.c
@@ -48,6 +48,7 @@
 #include "clutter-private.h"
 #include "clutter-main.h"
 #include "clutter-stage-private.h"
+#include "clutter-settings-private.h"
 
 #ifdef COGL_HAS_EGL_SUPPORT
 #include "clutter-egl.h"
@@ -60,6 +61,8 @@ clutter_backend_egl_native_dispose (GObject *gobject)
 {
   ClutterBackendEglNative *backend_egl_native = CLUTTER_BACKEND_EGL_NATIVE (gobject);
 
+  g_clear_object (&backend_egl_native->xsettings);
+
   if (backend_egl_native->event_timer != NULL)
     {
       g_timer_destroy (backend_egl_native->event_timer);
@@ -77,9 +80,181 @@ clutter_backend_egl_native_class_init (ClutterBackendEglNativeClass *klass)
   gobject_class->dispose = clutter_backend_egl_native_dispose;
 }
 
+typedef struct
+{
+  cairo_antialias_t cairo_antialias;
+  gint clutter_font_antialias;
+
+  cairo_hint_style_t cairo_hint_style;
+  const char *clutter_font_hint_style;
+
+  cairo_subpixel_order_t cairo_subpixel_order;
+  const char *clutter_font_subpixel_order;
+} FontSettings;
+
+static void
+get_font_gsettings (GSettings    *xsettings,
+                    FontSettings *output)
+{
+  /* org.gnome.settings-daemon.GsdFontAntialiasingMode */
+  static const struct
+  {
+    cairo_antialias_t cairo_antialias;
+    gint clutter_font_antialias;
+  }
+  antialiasings[] =
+  {
+    /* none=0      */ {CAIRO_ANTIALIAS_NONE,     0},
+    /* grayscale=1 */ {CAIRO_ANTIALIAS_GRAY,     1},
+    /* rgba=2      */ {CAIRO_ANTIALIAS_SUBPIXEL, 1},
+  };
+
+  /* org.gnome.settings-daemon.GsdFontHinting */
+  static const struct
+  {
+    cairo_hint_style_t cairo_hint_style;
+    const char *clutter_font_hint_style;
+  }
+  hintings[] =
+  {
+    /* none=0   */ {CAIRO_HINT_STYLE_NONE,   "hintnone"},
+    /* slight=1 */ {CAIRO_HINT_STYLE_SLIGHT, "hintslight"},
+    /* medium=2 */ {CAIRO_HINT_STYLE_MEDIUM, "hintmedium"},
+    /* full=3   */ {CAIRO_HINT_STYLE_FULL,   "hintfull"},
+  };
+
+  /* org.gnome.settings-daemon.GsdFontRgbaOrder */
+  static const struct
+  {
+    cairo_subpixel_order_t cairo_subpixel_order;
+    const char *clutter_font_subpixel_order;
+  }
+  rgba_orders[] =
+  {
+    /* rgba=0 */ {CAIRO_SUBPIXEL_ORDER_RGB,  "rgb"}, /* XXX what is 'rgba'? */
+    /* rgb=1  */ {CAIRO_SUBPIXEL_ORDER_RGB,  "rgb"},
+    /* bgr=2  */ {CAIRO_SUBPIXEL_ORDER_BGR,  "bgr"},
+    /* vrgb=3 */ {CAIRO_SUBPIXEL_ORDER_VRGB, "vrgb"},
+    /* vbgr=4 */ {CAIRO_SUBPIXEL_ORDER_VBGR, "vbgr"},
+  };
+  guint i;
+
+  i = g_settings_get_enum (xsettings, "hinting");
+  if (i < G_N_ELEMENTS (hintings))
+    {
+      output->cairo_hint_style = hintings[i].cairo_hint_style;
+      output->clutter_font_hint_style = hintings[i].clutter_font_hint_style;
+    }
+  else
+    {
+      output->cairo_hint_style = CAIRO_HINT_STYLE_DEFAULT;
+      output->clutter_font_hint_style = NULL;
+    }
+
+  i = g_settings_get_enum (xsettings, "antialiasing");
+  if (i < G_N_ELEMENTS (antialiasings))
+    {
+      output->cairo_antialias = antialiasings[i].cairo_antialias;
+      output->clutter_font_antialias = antialiasings[i].clutter_font_antialias;
+    }
+  else
+    {
+      output->cairo_antialias = CAIRO_ANTIALIAS_DEFAULT;
+      output->clutter_font_antialias = -1;
+    }
+
+  i = g_settings_get_enum (xsettings, "rgba-order");
+  if (i < G_N_ELEMENTS (rgba_orders))
+    {
+      output->cairo_subpixel_order = rgba_orders[i].cairo_subpixel_order;
+      output->clutter_font_subpixel_order = rgba_orders[i].clutter_font_subpixel_order;
+    }
+  else
+    {
+      output->cairo_subpixel_order = CAIRO_SUBPIXEL_ORDER_DEFAULT;
+      output->clutter_font_subpixel_order = NULL;
+    }
+
+  if (output->cairo_antialias == CAIRO_ANTIALIAS_GRAY)
+    output->clutter_font_subpixel_order = "none";
+}
+
+static void
+init_font_options (ClutterBackendEglNative *backend_egl_native)
+{
+  GSettings *xsettings = backend_egl_native->xsettings;
+  cairo_font_options_t *options = cairo_font_options_create ();
+  FontSettings fs;
+
+  get_font_gsettings (xsettings, &fs);
+
+  cairo_font_options_set_hint_style (options, fs.cairo_hint_style);
+  cairo_font_options_set_antialias (options, fs.cairo_antialias);
+  cairo_font_options_set_subpixel_order (options, fs.cairo_subpixel_order);
+
+  clutter_backend_set_font_options (CLUTTER_BACKEND (backend_egl_native),
+                                    options);
+
+  cairo_font_options_destroy (options);
+}
+
+static gboolean
+on_xsettings_change_event (GSettings *xsettings,
+                           gpointer   keys,
+                           gint       n_keys,
+                           gpointer   user_data)
+{
+  /*
+   * A simpler alternative to this function that does not update the screen
+   * immediately (like macOS :P):
+   *
+   *   init_font_options (CLUTTER_BACKEND_EGL_NATIVE (user_data));
+   *
+   * which has the added benefit of eliminating the need for all the
+   * FontSettings.clutter_ fields. However the below approach is better for
+   * testing settings and more consistent with the existing x11 backend...
+   */
+  ClutterSettings *csettings = clutter_settings_get_default ();
+  FontSettings fs;
+  gint hinting;
+
+  get_font_gsettings (xsettings, &fs);
+  hinting = fs.cairo_hint_style == CAIRO_HINT_STYLE_NONE ? 0 : 1;
+  g_object_set (csettings,
+                "font-hinting",        hinting,
+                "font-hint-style",     fs.clutter_font_hint_style,
+                "font-antialias",      fs.clutter_font_antialias,
+                "font-subpixel-order", fs.clutter_font_subpixel_order,
+                NULL);
+
+  return FALSE;
+}
+
 static void
 clutter_backend_egl_native_init (ClutterBackendEglNative *backend_egl_native)
 {
+  static const gchar xsettings_path[] = "org.gnome.settings-daemon.plugins.xsettings";
+  GSettingsSchemaSource *source = g_settings_schema_source_get_default ();
+  GSettingsSchema *schema = g_settings_schema_source_lookup (source,
+                                                             xsettings_path,
+                                                             FALSE);
+
+  if (!schema)
+    {
+      g_warning ("Failed to find schema: %s", xsettings_path);
+    }
+  else
+    {
+      backend_egl_native->xsettings = g_settings_new_full (schema, NULL, NULL);
+      if (backend_egl_native->xsettings)
+        {
+          init_font_options (backend_egl_native);
+          g_signal_connect (backend_egl_native->xsettings, "change-event",
+                            G_CALLBACK (on_xsettings_change_event),
+                            backend_egl_native);
+        }
+    }
+
   backend_egl_native->event_timer = g_timer_new ();
 }
 
diff --git a/clutter/clutter/egl/clutter-backend-eglnative.h b/clutter/clutter/egl/clutter-backend-eglnative.h
index d98013d..e871c99 100644
--- a/clutter/clutter/egl/clutter-backend-eglnative.h
+++ b/clutter/clutter/egl/clutter-backend-eglnative.h
@@ -61,6 +61,9 @@ struct _ClutterBackendEglNative
 
   /* event timer */
   GTimer *event_timer;
+
+  /* "xsettings" is still the defacto place for Xft settings, even in Wayland */
+  GSettings *xsettings;
 };
 
 struct _ClutterBackendEglNativeClass