[gtk+] GDK W32: Different maximized window position for non-CSD windows

[Руслан Ижбулатов <ruslanizhb src gnome org>]

commit 27ed9fb11d0597dc489d1af4ccb834b4371db440
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Thu Jan 26 17:44:01 2017 +0000

    GDK W32: Different maximized window position for non-CSD windows
    
    It seems that WM interprets the same MINMAXINFO contents differently
    depending on which styles the window has. Play along.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765161

 gdk/win32/gdkevents-win32.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)
---
diff --git a/gdk/win32/gdkevents-win32.c b/gdk/win32/gdkevents-win32.c
index 614fa68..1cba4c4 100644
--- a/gdk/win32/gdkevents-win32.c
+++ b/gdk/win32/gdkevents-win32.c
@@ -2242,8 +2242,25 @@ _gdk_win32_window_fill_min_max_info (GdkWindow  *window,
            * window will actually end up.
            * "0" here is the top-left corner of the primary monitor.
            */
-          mmi->ptMaxPosition.x = 0 + (nearest_info.rcWork.left - nearest_info.rcMonitor.left);
-          mmi->ptMaxPosition.y = 0 + (nearest_info.rcWork.top - nearest_info.rcMonitor.top);
+          /* An investigation into bug 765161 turned up a weird Windows WM behaviour
+           * where it would interpret "0:0" as "top-left of the workea" (accounting for a taskbar
+           * possibly being along the left/top edge of the screen) when window has styles
+           * (i.e. not CSD), and interpret the same "0:0" as "top-left of the screen" (not
+           * accounting for a taskbar) when window has no styles (i.e. a CSD window).
+           * This doesn't seem to be documented anywhere.
+           * The following code uses a simple CSD/non-CSD test, but it could be that
+           * this behaviour hinges on just one particular window style.
+           * Finding exactly which style that could be is not very useful for GTK, however.
+           */
+          mmi->ptMaxPosition.x = 0;
+          mmi->ptMaxPosition.y = 0;
+
+          if (_gdk_win32_window_lacks_wm_decorations (window))
+            {
+              mmi->ptMaxPosition.x += (nearest_info.rcWork.left - nearest_info.rcMonitor.left);
+              mmi->ptMaxPosition.y += (nearest_info.rcWork.top - nearest_info.rcMonitor.top);
+            }
+
           mmi->ptMaxSize.x = nearest_info.rcWork.right - nearest_info.rcWork.left;
           mmi->ptMaxSize.y = nearest_info.rcWork.bottom - nearest_info.rcWork.top;
         }