app: small ordering cleanup.

No functional change, just some include cleanup, as well as reordering
with a private function made public.

Also adding a comment saying why we have somewhat unrelated code (about
color-scheme) in gui-unique.c. Maybe eventually we should generalize
this message-handling invible window code into a separate file, if it
becomes further used for more message handling.

app/gui/gui-unique.c

@@ -30,6 +30,8 @@
 
 #include "gui/gui-types.h"
 
+#include "config/gimpguiconfig.h"
+
 #include "core/gimp.h"
 #include "core/gimpcontainer.h"
 
@@ -41,7 +43,6 @@
 
 #include "gimpdbusservice.h"
 #include "gui-unique.h"
-#include "config/gimpguiconfig.h"
 #include "themes.h"
 
 
@@ -205,6 +206,11 @@ gui_unique_win32_message_handler (HWND   hWnd,
       return TRUE;
 
     case WM_SETTINGCHANGE:
+      /* This message is not about the unique GUI code, but we reuse the
+       * existing top-level (hidden) window used for receiving messages
+       * for other purposes too, such as color scheme in this case.
+       * See !2308.
+       */
       if (lParam != 0 && lstrcmpW((LPCWSTR)lParam, L"ImmersiveColorSet") == 0)
         {
           themes_theme_change_notify (GIMP_GUI_CONFIG (unique_gimp->config), NULL, unique_gimp);

app/gui/themes.c

@@ -276,6 +276,44 @@ themes_get_theme_file (Gimp        *gimp,
   return file;
 }
 
+void
+themes_theme_change_notify (GimpGuiConfig *config,
+                            GParamSpec    *pspec,
+                            Gimp          *gimp)
+{
+  GFile  *theme_css;
+  GError *error = NULL;
+
+  g_object_set (gtk_settings_get_for_screen (gdk_screen_get_default ()),
+                "gtk-application-prefer-dark-theme",
+                config->theme_scheme != GIMP_THEME_LIGHT,
+                NULL);
+
+  themes_apply_theme (gimp, config);
+
+  theme_css = gimp_directory_file ("theme.css", NULL);
+
+  if (gimp->be_verbose)
+    g_print ("Parsing '%s'\n",
+             gimp_file_get_utf8_name (theme_css));
+
+  if (! gtk_css_provider_load_from_file (GTK_CSS_PROVIDER (themes_style_provider),
+                                         theme_css, &error))
+    {
+      g_printerr ("%s: error parsing %s: %s\n", G_STRFUNC,
+                  gimp_file_get_utf8_name (theme_css), error->message);
+      g_clear_error (&error);
+    }
+
+  g_object_unref (theme_css);
+
+  gtk_style_context_reset_widgets (gdk_screen_get_default ());
+
+#ifdef G_OS_WIN32
+  themes_set_title_bar (gimp);
+#endif
+}
+
 
 /*  private functions  */
 
@@ -713,44 +751,6 @@ themes_name_compare (const void *p1,
   return strcmp (* (char **) p1, * (char **) p2);
 }
 
-void
-themes_theme_change_notify (GimpGuiConfig *config,
-                            GParamSpec    *pspec,
-                            Gimp          *gimp)
-{
-  GFile  *theme_css;
-  GError *error = NULL;
-
-  g_object_set (gtk_settings_get_for_screen (gdk_screen_get_default ()),
-                "gtk-application-prefer-dark-theme",
-                config->theme_scheme != GIMP_THEME_LIGHT,
-                NULL);
-
-  themes_apply_theme (gimp, config);
-
-  theme_css = gimp_directory_file ("theme.css", NULL);
-
-  if (gimp->be_verbose)
-    g_print ("Parsing '%s'\n",
-             gimp_file_get_utf8_name (theme_css));
-
-  if (! gtk_css_provider_load_from_file (GTK_CSS_PROVIDER (themes_style_provider),
-                                         theme_css, &error))
-    {
-      g_printerr ("%s: error parsing %s: %s\n", G_STRFUNC,
-                  gimp_file_get_utf8_name (theme_css), error->message);
-      g_clear_error (&error);
-    }
-
-  g_object_unref (theme_css);
-
-  gtk_style_context_reset_widgets (gdk_screen_get_default ());
-
-#ifdef G_OS_WIN32
-  themes_set_title_bar (gimp);
-#endif
-}
-
 static void
 themes_theme_paths_notify (GimpExtensionManager *manager,
                            GParamSpec           *pspec,
@@ -892,5 +892,4 @@ themes_win32_is_darkmode_active (void)
 
   return status == ERROR_SUCCESS && val == 0;
 }
-
 #endif

app/gui/themes.h

@@ -28,9 +28,11 @@ GFile  * themes_get_theme_dir  (Gimp        *gimp,
 GFile  * themes_get_theme_file       (Gimp          *gimp,
                                       const gchar   *first_component,
                                       ...) G_GNUC_NULL_TERMINATED;
+
 void     themes_theme_change_notify  (GimpGuiConfig *config,
                                       GParamSpec    *pspec,
                                       Gimp          *gimp);
+
 #ifdef G_OS_WIN32
 void     themes_set_title_bar        (Gimp          *gimp);
 #endif