From a1aee4602c1d872cc39b8f3814e8aa9e98d093f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A0=D1=83=D1=81=D0=BB=D0=B0=D0=BD=20=D0=98=D0=B6=D0=B1?=
 =?UTF-8?q?=D1=83=D0=BB=D0=B0=D1=82=D0=BE=D0=B2?= <lrn1986@gmail.com>
Date: Sun, 11 Dec 2016 16:26:34 +0000
Subject: [PATCH] GDK W32: Handle maximizing correctly for small primary
 monitors

When primary monitor is smaller than the actual monitor on which the
window is being maximized, the WM will do widnow size adjustments
that will completely screw the window size if we try to make it
smaller than 100% fullscreen (to account for taskbar size, for example).

Fix this by overriding maximized window size during WM_WINDOWPOSCHANGING.

https://bugzilla.gnome.org/show_bug.cgi?id=775808
---
 gdk/win32/gdkevents-win32.c | 44 ++++++++++++++++++++++++++++++++++++-
 gdk/win32/gdkwindow-win32.c |  4 ++++
 gdk/win32/gdkwindow-win32.h |  6 +++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/gdk/win32/gdkevents-win32.c b/gdk/win32/gdkevents-win32.c
index 7c77f0a472..1b160d8bcc 100644
--- a/gdk/win32/gdkevents-win32.c
+++ b/gdk/win32/gdkevents-win32.c
@@ -2040,6 +2040,25 @@ _gdk_win32_window_fill_min_max_info (GdkWindow  *window,
     }
   else
     {
+      /* According to "How does the window manager adjust ptMaxSize and
+       * ptMaxPosition for multiple monitors?" article
+       * https://blogs.msdn.microsoft.com/oldnewthing/20150501-00/?p=44964
+       * if ptMaxSize >= primary_monitor_size, then it will be adjusted by
+       * WM to account for the monitor size differences if the window gets
+       * maximized on a non-primary monitor, by simply adding the size
+       * difference (i.e. if non-primary monitor is larger by 100px, then
+       * window will be made larger exactly by 100px).
+       * If ptMaxSize < primary_monitor_size at least in one direction,
+       * nothing is adjusted.
+       * Therefore, if primary monitor is smaller than the actual monitor,
+       * then it is not possible to give window a size that is larger than
+       * the primary monitor and smaller than the non-primary monitor,
+       * because WM will always enlarge the window.
+       * Therefore, it is impossible to account for taskbar size.
+       * So we don't try at all. Instead we just remember that we're trying
+       * to maximize the window, catch WM_WINDOWPOSCHANGING and
+       * adjust the size then.
+       */
       HMONITOR nearest_monitor;
       MONITORINFO nearest_info;
 
@@ -3109,6 +3128,10 @@ gdk_event_translate (MSG  *msg,
 	case SC_RESTORE:
 	  do_show_window (window, msg->wParam == SC_MINIMIZE ? TRUE : FALSE);
 	  break;
+        case SC_MAXIMIZE:
+          impl = GDK_WINDOW_IMPL_WIN32 (window->impl);
+          impl->maximizing = TRUE;
+	  break;
 	}
 
       break;
@@ -3160,7 +3183,26 @@ gdk_event_translate (MSG  *msg,
 				  GetNextWindow (msg->hwnd, GW_HWNDPREV))));
 
       if (GDK_WINDOW_IS_MAPPED (window))
-	return_val = ensure_stacking_on_window_pos_changing (msg, window);
+        {
+	  return_val = ensure_stacking_on_window_pos_changing (msg, window);
+
+          impl = GDK_WINDOW_IMPL_WIN32 (window->impl);
+
+          if (impl->maximizing)
+            {
+              MINMAXINFO our_mmi;
+
+              if (_gdk_win32_window_fill_min_max_info (window, &our_mmi))
+                {
+                  windowpos = (WINDOWPOS *) msg->lParam;
+                  windowpos->cx = our_mmi.ptMaxSize.x;
+                  windowpos->cy = our_mmi.ptMaxSize.y;
+                }
+
+              impl->maximizing = FALSE;
+            }
+        }
+
       break;
 
     case WM_WINDOWPOSCHANGED:
diff --git a/gdk/win32/gdkwindow-win32.c b/gdk/win32/gdkwindow-win32.c
index dbb16fd1cb..f8823f20b1 100644
--- a/gdk/win32/gdkwindow-win32.c
+++ b/gdk/win32/gdkwindow-win32.c
@@ -5986,6 +5986,10 @@ GtkShowWindow (GdkWindow *window,
       break;
     }
 
+  /* Ensure that maximized window size is corrected later on */
+  if (cmd_show == SW_MAXIMIZE)
+    impl->maximizing = TRUE;
+
   return ShowWindow (hwnd, cmd_show);
 }
 
diff --git a/gdk/win32/gdkwindow-win32.h b/gdk/win32/gdkwindow-win32.h
index de18c45141..59b9a42c39 100644
--- a/gdk/win32/gdkwindow-win32.h
+++ b/gdk/win32/gdkwindow-win32.h
@@ -287,6 +287,12 @@ struct _GdkWindowImplWin32
    */
   guint have_temp_styles : 1;
 
+  /* If TRUE, the window is in the process of being maximized.
+   * This is set by WM_SYSCOMMAND and by gdk_win32_window_maximize (),
+   * and is unset when WM_WINDOWPOSCHANGING is handled.
+   */
+  guint maximizing : 1;
+
   /* GDK does not keep window contents around, it just draws new
    * stuff over the window where changes occurred.
    * cache_surface retains old window contents, because