[gtk+] wayland: scale down reported monitor geometry

[Matthias Clasen <matthiasc src gnome org>]

commit 999848e0c68dc7dbd319150208386b0a536d6780
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Tue Jun 27 11:12:57 2017 +0200

    wayland: scale down reported monitor geometry
    
    According to the documentation, gdk_monitor_get_geometry() reports the
    monitor geometry in ”application pixels”, not in ”device pixels”,
    meaning that the actual device resolution needs to be scaled down by the
    scale factor of the output.
    
    x11 backend does that downscaling, whereas Wayland backend did not,
    causing a discrepancy depending on the backend used.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=783995

 gdk/wayland/gdkscreen-wayland.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)
---
diff --git a/gdk/wayland/gdkscreen-wayland.c b/gdk/wayland/gdkscreen-wayland.c
index af2e2e2..b939fef 100644
--- a/gdk/wayland/gdkscreen-wayland.c
+++ b/gdk/wayland/gdkscreen-wayland.c
@@ -754,11 +754,22 @@ output_handle_scale (void             *data,
                      int32_t           scale)
 {
   GdkWaylandMonitor *monitor = (GdkWaylandMonitor *)data;
+  GdkRectangle previous_geometry;
+  int previous_scale;
+  int width;
+  int height;
 
   GDK_NOTE (MISC,
             g_message ("handle scale output %d, scale %d", monitor->id, scale));
 
+  gdk_monitor_get_geometry (GDK_MONITOR (monitor), &previous_geometry);
+  previous_scale = gdk_monitor_get_scale_factor (GDK_MONITOR (monitor));
+
+  width = previous_geometry.width * previous_scale;
+  height = previous_geometry.height * previous_scale;
+
   gdk_monitor_set_scale_factor (GDK_MONITOR (monitor), scale);
+  gdk_monitor_set_size (GDK_MONITOR (monitor), width / scale, height / scale);
 
   if (GDK_MONITOR (monitor)->geometry.width != 0 && monitor->version < OUTPUT_VERSION_WITH_DONE)
     {
@@ -776,6 +787,7 @@ output_handle_mode (void             *data,
                     int               refresh)
 {
   GdkWaylandMonitor *monitor = (GdkWaylandMonitor *)data;
+  int scale;
 
   GDK_NOTE (MISC,
             g_message ("handle mode output %d, size %d %d, rate %d",
@@ -784,7 +796,8 @@ output_handle_mode (void             *data,
   if ((flags & WL_OUTPUT_MODE_CURRENT) == 0)
     return;
 
-  gdk_monitor_set_size (GDK_MONITOR (monitor), width, height);
+  scale = gdk_monitor_get_scale_factor (GDK_MONITOR (monitor));
+  gdk_monitor_set_size (GDK_MONITOR (monitor), width / scale, height / scale);
   gdk_monitor_set_refresh_rate (GDK_MONITOR (monitor), refresh);
 
   if (width != 0 && monitor->version < OUTPUT_VERSION_WITH_DONE)