Support of MacOS 10.13 to appear soon: fix handling of window moves i…

…n presence of subwindows.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12318 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_cocoa.mm

@@ -1317,7 +1317,13 @@ - (void)windowDidMove:(NSNotification *)notif
     if (parent && window->as_gl_window()) parent->redraw();
   }
   resize_from_system = NULL;
-  [nsw recursivelySendToSubwindows:@selector(setSubwindowFrame)];
+  // before 10.13: OS sends windowDidMove to parent window only,
+  // FLTK recursively sends setSubwindowFrame to children,
+  // setSubwindowFrame sends setFrame, this triggers windowDidMove to child which sets child position.
+  //
+  // with 10.13: OS sends windowDidMove to parent window and then to children
+  // FLTK sets position of parent and children. setSubwindowFrame is no longer necessary.
+  if (fl_mac_os_version < 101300) [nsw recursivelySendToSubwindows:@selector(setSubwindowFrame)];
   [nsw checkSubwindowFrame];
   fl_unlock_function();
 }