lstopo/windows: fix redrawing on autoresizing on Windows 10

When autoresizing the lstopo window, SetWindowPos() with
SWP_DEFERERASE causes a late background erase on Windows 10,
hence a white screen.

In theory this could cause some flickering since this flag
was preventing some redraw events in the meantime, but at
least things seem to work fine on both Windows 7 and 10 now.

Another solution would be to pass SWP_DEFERERASE|SWP_NOREDRAW
since we're going to redraw right after SetWindowPos() but
Windows 7 would not redraw the background unhidden when
downsizing the lstopo window.
There's also the possibility of preventing the erasing by
catching WM_ERASEBKGND and returning 1.

Too many possibilities without enough documentation to clearly
understand the best one. Maybe our event loop isn't properly
organized anyway.

Signed-off-by: Brice Goglin <[email protected]>

Author: bgoglin

NEWS

@@ -28,6 +28,7 @@ Version 2.3.0
     lists of flag names (substrings).
   + Tools that have a --restrict option may now receive a nodeset or
     some custom flags for restricting the topology.
+  + Fix lstopo drawing when autoresizing on Windows 10
 
 
 Version 2.2.0

tests/hwloc/ports/include/windows/windows.h

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2009-2019 Inria.  All rights reserved.
+ * Copyright © 2009-2020 Inria.  All rights reserved.
  * Copyright © 2009-2012 Université Bordeaux
  * See COPYING in top-level directory.
  */

utils/lstopo/lstopo-windows.c

@@ -205,7 +205,7 @@ WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
 
 	/* SetWindowPos() generates a WM_SIZE event, we don't want to scale the drawing there */
 	ignore_wm_size = 1;
-	SetWindowPos(the_output.toplevel, HWND_TOP, 0, 0, rect.right - rect.left, rect.bottom - rect.top, SWP_DEFERERASE|SWP_NOCOPYBITS|SWP_NOMOVE|SWP_NOOWNERZORDER|SWP_NOZORDER);
+	SetWindowPos(the_output.toplevel, HWND_TOP, 0, 0, rect.right - rect.left, rect.bottom - rect.top, SWP_NOCOPYBITS|SWP_NOMOVE|SWP_NOOWNERZORDER|SWP_NOZORDER);
 	ignore_wm_size = 0;
 
 	needs_resize = 0;