Tutorial: Using screen_notify()

The following procedure describes how an application can request an asynchronous notification from Screen for keyboard events.

1. Define your pulse code:

   #define MY_PULSE_CODE _PULSE_CODE_MINAVAIL
                       

2. Create variables for your Screen and a keyboard device:

   screen_context_t screen_ctx = NULL;
   screen_device_t  keyboard   = NULL;
   screen_device_t* devices    = NULL;
                       

3. Create a native context:

   screen_create_context(&screen_ctx, SCREEN_APPLICATION_CONTEXT);
                       

4. Set up your device object as a keyboard type:

   int devcnt;
   screen_get_context_property_iv(screen_ctx, SCREEN_PROPERTY_DEVICE_COUNT, &devcnt);
   devices = malloc(devcnt*sizeof(void*));
   
   screen_get_context_property_pv(screen_ctx, SCREEN_PROPERTY_DEVICES, (void**)devices);
   
   int i=0;
   int type;
   for(; i<devcnt; i++)
   {
      screen_get_device_property_iv(devices[i], SCREEN_PROPERTY_TYPE, &type);
      if(type == SCREEN_EVENT_KEYBOARD)
      {
         keyboard = devices[i];
      }
   }
   
   if(keyboard == NULL)
   {
      printf("FATAL: Couldn't get keyboard device\n");
      exit(EXIT_FAILURE);
   }
                       

   Events specific to a keyboard can be detected by passing the appropriate screen_device_t handle in the obj argument of screen_notify().

5. Establish a connection:

      int chid = -1;
      chid = ChannelCreate(0);
   
      int coid = -1;
      coid = ConnectAttach(0, 0, chid, _NTO_SIDE_CHANNEL, 0);
                       

6. Request notification from Screen:

   struct sigevent event;
   SIGEV_PULSE_INIT(&event, coid, SIGEV_PULSE_PRIO_INHERIT, MY_PULSE_CODE, 0);
   screen_register_event(screen_ctx, &event);
   screen_notify(screen_ctx, SCREEN_NOTIFY_INPUT, keyboard, &event);
                       

7. Check for receipt of notification:

   while (1) {
      struct _pulse pulse;
      int rcvid = MsgReceivePulse(chid, &pulse, sizeof(pulse), NULL);
      if (rcvid == 0) {
         printf("keyboard input detected...\n");
      }
      ...
   }
                       

8. Disarm any further notifications of keyboard events from Screen in this context:

   SIGEV_NONE_INIT(&event);
   screen_notify(screen_ctx, SCREEN_NOTIFY_INPUT, keyboard, &event);
   screen_unregister_event(&event);
   free(devices);
   
                       

   Passing NULL or an event with the type of SIGEV_NONE disables notifications that were enabled with the same combination of arguments: ctx, flags, and obj.

9. Clean up your resources:

   ConnectDetach(coid);
   ChannelDestroy(chid);
   screen_destroy_context(screen_ctx);