style: Add hdy_style_init()

This can be used to initialize the global style.

src/hdy-style-private.h

@@ -19,4 +19,6 @@ G_BEGIN_DECLS
  * can nonetheless apply custom styling on top of it. */
 #define HDY_STYLE_PROVIDER_PRIORITY (GTK_STYLE_PROVIDER_PRIORITY_SETTINGS + 1)
 
+void hdy_style_init (void);
+
 G_END_DECLS

src/hdy-style.c

+/*
+ * Copyright (C) 2020 Purism SPC
+ *
+ * SPDX-License-Identifier: LGPL-2.1+
+ */
+
+#include "config.h"
+#include <glib/gi18n-lib.h>
+
+#include "hdy-style-private.h"
+
+#include <gtk/gtk.h>
+
+/**
+ * PRIVATE:hdy-style
+ * @short_description: Style helpers
+ * @title: Style
+ * @stability: Private
+ *
+ * Helpers for styles.
+ *
+ * Since: 1.0
+ */
+
+/**
+ * hdy_style_init:
+ *
+ * Initializes the style classes. This must be called once GTK has been
+ * initialized.
+ *
+ * Since: 1.0
+ */
+void
+hdy_style_init (void)
+{
+  static volatile gsize guard = 0;
+  g_autoptr (GtkCssProvider) css_override_provider = NULL;
+  g_autoptr (GtkCssProvider) css_fallback_provider = NULL;
+
+  if (!g_once_init_enter (&guard))
+    return;
+
+  css_fallback_provider = gtk_css_provider_new ();
+
+  gtk_css_provider_load_from_resource (css_fallback_provider, "/sm/puri/handy/style/handy-fallback.css");
+  gtk_style_context_add_provider_for_screen (gdk_screen_get_default (),
+                                             GTK_STYLE_PROVIDER (css_fallback_provider),
+                                             GTK_STYLE_PROVIDER_PRIORITY_FALLBACK);
+
+  css_override_provider = gtk_css_provider_new ();
+
+  gtk_css_provider_load_from_resource (css_override_provider, "/sm/puri/handy/style/handy-override.css");
+  gtk_style_context_add_provider_for_screen (gdk_screen_get_default (),
+                                             GTK_STYLE_PROVIDER (css_override_provider),
+                                             HDY_STYLE_PROVIDER_PRIORITY);
+
+  g_once_init_leave (&guard, 1);
+}

src/meson.build

@@ -119,6 +119,7 @@ src_sources = [
   'hdy-shadow-helper.c',
   'hdy-squeezer.c',
   'hdy-string-utf8.c',
+  'hdy-style.c',
   'hdy-swipe-group.c',
   'hdy-swipe-tracker.c',
   'hdy-swipeable.c',