[gtk/wip/Jehan/gimp-issue-1082-transparent-window] Add patch from GIMP project

[Jehan <jehanp src gnome org>]

commit a2c967abfead6b36f2d64b362d9c663f19872be7
Author: Patrick Storz <eduard braun2 gmx de>
Date:   Thu Jul 9 18:13:02 2020 +0200

    Add patch from GIMP project
    
    This prevents transparent top-level windows from intercepting mouse
    events as often the case with screen capturing software, see
    https://bugzilla.gnome.org/show_bug.cgi?id=780979

 gdk/win32/gdkdevice-win32.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/gdk/win32/gdkdevice-win32.c b/gdk/win32/gdkdevice-win32.c
index 190372de2d..3d89290b25 100644
--- a/gdk/win32/gdkdevice-win32.c
+++ b/gdk/win32/gdkdevice-win32.c
@@ -214,6 +214,10 @@ _gdk_device_win32_window_at_position (GdkDevice       *device,
        * WindowFromPoint() can find our windows, we follow similar logic
        * here, and ignore invisible and disabled windows.
        */
+       UINT cwp_flags = CWP_SKIPDISABLED  |
+                        CWP_SKIPINVISIBLE |
+                        CWP_SKIPTRANSPARENT;
+
       hwnd = GetDesktopWindow ();
       do {
         window = gdk_win32_handle_table_lookup (hwnd);
@@ -224,8 +228,7 @@ _gdk_device_win32_window_at_position (GdkDevice       *device,
           break;
 
         screen_to_client (hwnd, screen_pt, &client_pt);
-        hwndc = ChildWindowFromPointEx (hwnd, client_pt, CWP_SKIPDISABLED  |
-                                                         CWP_SKIPINVISIBLE);
+        hwndc = ChildWindowFromPointEx (hwnd, client_pt, cwp_flags);
 
        /* Verify that we're really inside the client area of the window */
        if (hwndc != hwnd)
@@ -236,6 +239,8 @@ _gdk_device_win32_window_at_position (GdkDevice       *device,
              hwndc = hwnd;
          }
 
+        /* Only ignore top-level transparent windows */
+        cwp_flags &= ~CWP_SKIPTRANSPARENT;
       } while (hwndc != hwnd && (hwnd = hwndc, 1));
 
     }