Add methods to intercept low level system events.

This gives applications the means to handle some low level
integration with the system that might otherwise not be possible
without modifying FLTK itself.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@10310 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

1 files changed, 77 insertions, 0 deletions

diff --git a/src/Fl.cxx b/src/Fl.cxx
index 5386fc105..2b637aa37 100644
--- a/src/Fl.cxx
+++ b/src/Fl.cxx
@@ -888,6 +888,83 @@ static int send_handlers(int e) {
   return 0;
 }
 
+
+////////////////////////////////////////////////////////////////
+// System event handlers:
+
+
+struct system_handler_link {
+  Fl_System_Handler handle;
+  void *data;
+  system_handler_link *next;
+};
+
+
+static system_handler_link *sys_handlers = 0;
+
+
+/**
+ \brief Install a function to intercept system events.
+
+ FLTK calls each of these functions as soon as a new system event is
+ received. The processing will stop at the first function to return
+ non-zero. If all functions return zero then the event is passed on
+ for normal handling by FLTK.
+
+ Each function will be called with a pointer to the system event as
+ the first argument and \p data as the second argument. The system
+ event pointer will always be void *, but will point to different
+ objects depending on the platform:
+   - X11: XEvent
+   - Windows: MSG
+   - OS X: NSEvent
+
+ \param ha The event handler function to register
+ \param data User data to include on each call
+
+ \see Fl::remove_system_handler(Fl_System_Handler)
+*/
+void Fl::add_system_handler(Fl_System_Handler ha, void *data) {
+  system_handler_link *l = new system_handler_link;
+  l->handle = ha;
+  l->data = data;
+  l->next = sys_handlers;
+  sys_handlers = l;
+}
+
+
+/**
+ Removes a previously added system event handler.
+
+ \param ha The event handler function to remove
+
+ \see Fl::add_system_handler(Fl_System_Handler)
+*/
+void Fl::remove_system_handler(Fl_System_Handler ha) {
+  system_handler_link *l, *p;
+
+  // Search for the handler in the list...
+  for (l = sys_handlers, p = 0; l && l->handle != ha; p = l, l = l->next);
+
+  if (l) {
+    // Found it, so remove it from the list...
+    if (p) p->next = l->next;
+    else sys_handlers = l->next;
+
+    // And free the record...
+    delete l;
+  }
+}
+
+int fl_send_system_handlers(void *e) {
+  for (const system_handler_link *hl = sys_handlers; hl; hl = hl->next) {
+    if (hl->handle(e, hl->data))
+      return 1;
+  }
+  return 0;
+}
+
+
 ////////////////////////////////////////////////////////////////
 
 Fl_Widget* fl_oldfocus; // kludge for Fl_Group...