Window manager

In Windows and Mac OS X the window manager is tied into the OS. That's not the case for Linux or BSD. Window Maker is the recommended window manager for GNUstep, but a standard feature-set is needed. GNUstep-based applications have additional needs beyond traditional window managers, like handling the dock icon or the menus. Collecting the requirements here will lead to a specification, so any window manager can clearly state whether or not it is GNUstep-compliant.

Backend WM Attributes

Headers/x11/XGServerWindow.h defines

 unsigned long flags
 unsigned long window_style
 unsigned long window_level
 unsigned long reserved
 Pixmap miniaturize_pixmap;    // pixmap for miniaturize button
 Pixmap close_pixmap;          // pixmap for close button.
 Pixmap miniaturize_mask;      // miniaturize pixmap mask
 Pixmap close_mask;            // close pixmap mask
 unsigned long extra_flags;

 #define GSWindowStyleAttr                   (1<<0)
 #define GSWindowLevelAttr                   (1<<1)
 #define GSMiniaturizePixmapAttr             (1<<3)
 #define GSClosePixmapAttr                   (1<<4)
 #define GSMiniaturizeMaskAttr               (1<<5)
 #define GSCloseMaskAttr                     (1<<6)
 #define GSExtraFlagsAttr                    (1<<7)
 #define GSDocumentEditedFlag                (1<<0)
 #define GSWindowWillResizeNotificationsFlag (1<<1)
 #define GSWindowWillMoveNotificationsFlag   (1<<2)
 #define GSNoApplicationIconFlag             (1<<5)
 #define WMFHideOtherApplications            10
 #define WMFHideApplication                  12

Window Level

GNUstep needs arbitrary window levels. EWMH defines these two:

 _NET_WM_STATE_ABOVE, ATOM
 _NET_WM_STATE_BELOW, ATOM

The rest depends on the function of a window. To obtain good interoperability between different Desktop Environments, the following layered stacking order is recommended, from the bottom to the top:

1. windows of type _NET_WM_TYPE_DESKTOP
2. windows having state _NET_WM_STATE_BELOW
3. windows not belonging in any other layer
4. windows of type _NET_WM_TYPE_DOCK (unless they have state _NET_WM_TYPE_BELOW) and windows having state _NET_WM_STATE_ABOVE
5. focused windows having state _NET_WM_STATE_FULLSCREEN