File slick-greeter-gtk-3.20.patch of Package slick-greeter

diff -ruN a/configure.ac b/configure.ac
--- a/configure.ac	2020-06-24 18:37:33.000000000 +0700
+++ b/configure.ac	2020-09-28 02:56:30.890501700 +0700
@@ -49,6 +49,16 @@
 fi
 
 dnl ###########################################################################
+dnl Check for GTK version - 3.24
+dnl ###########################################################################
+
++PKG_CHECK_MODULES(GTK_3_24_0, gtk+-3.0 >= 3.24.0 , gtk_check_pass=yes, gtk_check_pass=no)
+if test x$gtk_check_pass = xyes ; then
+  AM_VALAFLAGS="$AM_VALAFLAGS -D HAVE_GTK_3_24_0"
+  AC_SUBST([AM_VALAFLAGS])
+fi
+
+dnl ###########################################################################
 dnl Hack for vala >= 0.39
 dnl ###########################################################################
 
diff -ruN a/src/main-window.vala b/src/main-window.vala
--- a/src/main-window.vala	2020-06-24 18:37:33.000000000 +0700
+++ b/src/main-window.vala	2020-09-28 03:21:16.151097772 +0700
@@ -216,22 +216,37 @@
     private void monitors_changed_cb (Gdk.Screen screen)
     {
         Gdk.Display display = screen.get_display();
+#if HAVE_GTK_3_22_0
         Gdk.Monitor primary = display.get_primary_monitor();
+#else
+        int primary = screen.get_primary_monitor();
+#endif
         Gdk.Rectangle geometry;
 
         monitors = new List<Monitor> ();
         primary_monitor = null;
 
+#if HAVE_GTK_3_22_0        
         for (var i = 0; i < display.get_n_monitors (); i++)
         {
             Gdk.Monitor monitor = display.get_monitor(i);
             geometry = monitor.get_geometry ();
+#else
+        for (var i = 0; i < screen.get_n_monitors(); i++)
+        {
+            int monitor = i;
+            screen.get_monitor_geometry(monitor, out geometry);
+#endif
             debug ("Monitor %d is %dx%d pixels at %d,%d", i, geometry.width, geometry.height, geometry.x, geometry.y);
 
             if (monitor_is_unique_position (display, i))
             {
                 var greeter_monitor = new Monitor (geometry.x, geometry.y, geometry.width, geometry.height);
+#if HAVE_GTK_3_22_0
                 var plug_name = monitor.get_model();
+#else
+                var plug_name = screen.get_monitor_plug_name(monitor);
+#endif
                 monitors.append (greeter_monitor);
 
                 if (plug_name == only_on_monitor)
@@ -260,17 +275,28 @@
     private bool monitor_is_unique_position (Gdk.Display display, int n)
     {
         Gdk.Rectangle g0;
+#if HAVE_GTK_3_22_0
         Gdk.Monitor mon0;
         mon0 = display.get_monitor(n);
         g0 = mon0.get_geometry ();
 
         for (var i = n + 1; i < display.get_n_monitors (); i++)
+#else
+        Gdk.Screen screen = display.get_default_screen();
+        screen.get_monitor_geometry(n, out g0);
+
+        for (var i = n + 1; i < screen.get_n_monitors(); i++)
+#endif
         {
             Gdk.Rectangle g1;
+#if HAVE_GTK_3_22_0
             Gdk.Monitor mon1;
             mon1 = display.get_monitor(i);
             g1 = mon1.get_geometry();
-
+#else
+            screen.get_monitor_geometry(i, out g1);
+#endif
+            
             if (g0.x == g1.x && g0.y == g1.y)
                 return false;
         }
diff -ruN a/src/menubar.vala b/src/menubar.vala
--- a/src/menubar.vala	2020-06-24 18:37:33.000000000 +0700
+++ b/src/menubar.vala	2020-09-28 03:16:25.783849529 +0700
@@ -541,9 +541,15 @@
 
             /* Put keyboard at the bottom of the screen */
             var display = get_display ();
+#if HAVE_GTK_3_22_0
             var monitor = display.get_monitor_at_window (get_window ());
+            var geom = monitor.get_geometry();
+#else
+            var screen = display.get_default_screen();
+            var monitor = screen.get_monitor_at_window(get_window ());
             Gdk.Rectangle geom;
-            geom = monitor.get_geometry ();
+            screen.get_monitor_geometry(monitor, out geom);
+#endif
             keyboard_window.move (geom.x, geom.y + geom.height - 250);
             keyboard_window.resize (geom.width, 250);
         }
diff -ruN a/src/slick-greeter.vala b/src/slick-greeter.vala
--- a/src/slick-greeter.vala	2020-06-24 18:37:33.000000000 +0700
+++ b/src/slick-greeter.vala	2020-09-28 03:17:59.328894496 +0700
@@ -232,8 +232,14 @@
     {
         /* Explicitly set the right scale before closing window */
         var display = Gdk.Display.get_default();
+#if HAVE_GTK_3_22_0
         var monitor = display.get_primary_monitor();
         var scale = monitor.get_scale_factor ();
+#else
+        var screen = display.get_default_screen();
+        var monitor = screen.get_primary_monitor();
+        var scale = screen.get_monitor_scale_factor(monitor);
+#endif
         background_surface.set_device_scale (scale, scale);
 
         /* Paint our background onto the root window before we close our own window */