[gtk+] GDK W32: Add a comment for clarity

[Руслан Ижбулатов <ruslanizhb src gnome org>]

commit 3701a604015f3d877734edb7faba213a8a60c626
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Sat Nov 21 04:00:33 2015 +0000

    GDK W32: Add a comment for clarity
    
    This is a copy of a similar comment in another place, which explains
    why WS_EX_TRANSPARENT windows get a special treatment.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=758484

 gdk/win32/gdkwindow-win32.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gdk/win32/gdkwindow-win32.c b/gdk/win32/gdkwindow-win32.c
index 272b740..b3ee422 100644
--- a/gdk/win32/gdkwindow-win32.c
+++ b/gdk/win32/gdkwindow-win32.c
@@ -1229,6 +1229,9 @@ gdk_win32_window_hide (GdkWindow *window)
   if (GDK_WINDOW_TYPE (window) == GDK_WINDOW_TOPLEVEL)
     ShowOwnedPopups (GDK_WINDOW_HWND (window), FALSE);
 
+  /* Use SetWindowPos to hide transparent windows so automatic redraws
+   * in other windows can be suppressed.
+   */
   if (GetWindowLong (GDK_WINDOW_HWND (window), GWL_EXSTYLE) & WS_EX_TRANSPARENT)
     {
       SetWindowPos (GDK_WINDOW_HWND (window), SWP_NOZORDER_SPECIFIED,