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...