dix: add CreateScreenResources callback mechanism

Right now, extensions that need to be called after the CreateScreenResources
proc had been run, must wrap the screen proc vector directly (all of them
forming kind of daisy chain), and so - when called - temporarily restore the
previous one, call it, wrap again, and if the call was successful finally
doing it's own stuff. (same is done for many other procs)

While that approach is looking nice and elegant on the drawing board, it's
complicated, dangerous like a chainsaw and makes debugging hard, leading to
pretty blurred API borders.

Instead introducing a simple approach for letting extension hook into a
post-CreateScreenResources callback list safely, w/o having to care much
about side effects with the call chain. Extensions now can simply register
their business logic and get called back - w/o ever having to mess with the
ScreenRec's internal structures.

Note that these hooks are executed *AFTER* the original CreateScreenResources()
proc had been called SUCCESSFULLY (returned TRUE), so callees can rely on
the DDX/driver had already done it's job.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

dix/screen_hooks_priv.h

@@ -20,6 +20,7 @@
 #ifndef XORG_DIX_SCREEN_HOOKS_H
 #define XORG_DIX_SCREEN_HOOKS_H
 
+#include <X11/Xdefs.h>
 #include <X11/Xfuncproto.h>
 
 #include "include/callback.h" /* CallbackListPtr */
@@ -185,4 +186,36 @@ _X_EXPORT
 void dixScreenUnhookPixmapDestroy(ScreenPtr pScreen,
                                   XorgScreenPixmapDestroyProcPtr func);
 
+/* prototype of screen close notification handler */
+typedef void (*XorgScreenPostCreateResourcesProcPtr)(CallbackListPtr *pcbl,
+                                                     ScreenPtr pScreen,
+                                                     Bool *ret);
+
+/**
+ * @brief register post-CreateScreenResources hook on the given screen
+ *
+ * @param pScreen pointer to the screen to register the notify hook into
+ * @param func pointer to the hook function
+ * @param arg opaque pointer passed to the hook
+ *
+ * This hook is called when CreateScreenResources() had been called
+ * and returned TRUE.
+ **/
+_X_EXPORT
+void dixScreenHookPostCreateResources(ScreenPtr pScreen,
+                                      XorgScreenPostCreateResourcesProcPtr func);
+
+/**
+ * @brief unregister a post-CreateScreenResources hook on the given screen
+ *
+ * @param pScreen pointer to the screen to unregister the hook from
+ * @param func pointer to the hook function
+ * @param arg opaque pointer passed to the destructor
+ *
+ * @see dixScreenHookPostCreateResources
+ **/
+_X_EXPORT
+void dixScreenUnhookPostCreateResources(ScreenPtr pScreen,
+                                        XorgScreenPostCreateResourcesProcPtr func);
+
 #endif /* DIX_SCREEN_HOOKS_H */