[gtkmm-documentation/gtkmm-3-22] Don't use the deprecated Gdk::screen_width() and screen_height()

[Kjell Ahlstedt <kjellahl src gnome org>]

commit c51c85d007971553e8371ad96a2741538ed32e93
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Dec 28 11:48:40 2017 +0100

    Don't use the deprecated Gdk::screen_width() and screen_height()

 .../others/cellrenderercustom/cellrendererpopup.cc |   16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)
---
diff --git a/examples/others/cellrenderercustom/cellrendererpopup.cc 
b/examples/others/cellrenderercustom/cellrendererpopup.cc
index 2f59e59..303f35a 100644
--- a/examples/others/cellrenderercustom/cellrendererpopup.cc
+++ b/examples/others/cellrenderercustom/cellrendererpopup.cc
@@ -157,17 +157,21 @@ void CellRendererPopup::on_show_popup(const Glib::ustring&, int, int y1, int x2,
 
   const int button_height = y2 - y1;
 
-  int       screen_height = Gdk::screen_height() - y;
-  const int screen_width  = Gdk::screen_width();
+  auto display = Gdk::Display::get_default();
+  auto monitor = display->get_monitor_at_point(x2, y2);
+  Gdk::Rectangle workarea;
+  monitor->get_workarea(workarea);
+  int monitor_height = workarea.get_height() - y;
+  const int monitor_width = workarea.get_width();
 
   // Check if it fits in the available height.
-  if(alloc.get_height() > screen_height)
+  if(alloc.get_height() > monitor_height)
   {
     // It doesn't fit, so we see if we have the minimum space needed.
-    if((alloc.get_height() > screen_height) && (y - button_height > screen_height))
+    if((alloc.get_height() > monitor_height) && (y - button_height > monitor_height))
     {
       // We don't, so we show the popup above the cell instead of below it.
-      screen_height = y - button_height;
+      monitor_height = y - button_height;
       y -= (alloc.get_height() + button_height);
       y = std::max(0, y);
     }
@@ -175,7 +179,7 @@ void CellRendererPopup::on_show_popup(const Glib::ustring&, int, int y1, int x2,
 
   // We try to line it up with the right edge of the column, but we don't
   // want it to go off the edges of the screen.
-  x = std::min(x, screen_width);
+  x = std::min(x, monitor_width);
 
   x -= alloc.get_width();
   x = std::max(0, x);