= Event-Handler =
[[ArchivePage]]

Maintainer: Patrick Boenzli, boenzli at orxonox.ethz.ch

== Overview ==

All files used for event handling are located in the {{{./src/util/event}}} directory. Here a short overview:
 * {{{event_handler.{cc, h} }}} - this is where all the event handling is going on: signals from the SDL env are interpreted and transmitted to the registered event listener
 * {{{event_listener.{cc, h} }}} - this is an abstract class. A class that extends it will have to implement all abstract functions ({{{process(...)}}}) and will be able to register itself to the !EventHandler to receive events.
 * {{{event.{cc, h} }}} - a small class representing an event, that has occured
 * {{{key_mapper.{cc, h} }}} - a parser, that reads in the {{{orxonox.conf}}} file and translates the keynames to key-ids used in orxonox
 * {{{key_names.{cc, h} }}} - a file containig all key names with key-ids

== Usage ==
The usage of the !EventHandler System is realy stright forward: consider a case, where you have a !PNode, that wants to receive some key-events: [[br]]
The {{{pilot_me.h}}} could look like this:
{{{
#!cpp
#include "p_node.h"
#include "event_listener.h"

class Event;                                         // forward declaration of a Event class

class PilotMe : public PNode, public EventListener   // extending EventListener
{
   PilotMe();
   virtual ~PilotMe();

   void process(const Event &event);                // abstract process class

};
}}}
The {{{pilot_me.cc}}} class could look like this:
{{{
#!cpp
#include "pilot_me.h"
#include "event_listener.h"                        //the event listener interface
#include "event.h"                                 //the event structure

PilotMe::PilotMe()
{
  EventHandler::getInstance()->subscribe(this, ES_GAME, SDLK_LEFT);  //subscribe this class to the left-key  
  EventHandler::getInstance()->subscribe(this, ES_GAME, SDLK_RIGHT); //subscribe this class to the right-key
}

PilotMe::~PilotMe()
{
  EventHandler::getInstance()->unsubscribe(this);  //just unsubscribe all subscribtions of this class
}
.
void PilotMe::process(const Event &event)
{
  if( event.type == SDLK_LEFT)
  {
    if( event.bPressed == true)
      // whatever you want to do, when the left button is pressed 
    else 
      // whatever you want to do, when the left button is released 
  }
  else if( event.type == SDLK_RIGHT)
  {  
    if( event.bPressed == true)
      // whatever you want to do, when the right button is pressed 
    else
      // whatever you want to do, when the right button is released 

  }
}
}}}
As you have seen, the whole event-management system is very simple, let's review all the necessary steps:
 1. Extend {{{EventListener}}} with any class that want to receive events.

 2. Implement the {{{void process(const Event &event);}}} function.

 3. Subscribe for an event {{{EventHandler::subscribe(EventListener* el, elState state, int keyID)}}}.[[br]] You will find the complete list of all SDL Commands in the {{{usr/include/SDL/SDL_keysym.h}}} file. Orxonox has extended the list with some other events, that you will find in {{{./src/util/event/event_def.h}}}. The {{{elState}}} describes the state of the event handler: When the menu is displayed, there are is a diffrent key mapping than when you are playing the game. So this means that there are different states of the eventhandler: {{{ {ES_GAME, ES_MENU, ES_ALL} }}}. So if you subscribe to an event for the state {{{ES_GAME}}} this event will only shoot, if the eventhandler is in this state.

 4. Don't forget to unsubscribe the event again via {{{EventHandler::unsubscribe(EventListener* el)}}}[[br]]. If you forget to do this, there will be a reference to an object that is probably not existent anymore, this will most certanly cause a segfault :D


== Advanced ==
There is some more stuff to say :D. Its possible to define !KeyAliases in the {{{orxonox.conf}}} file. These aliases are wrapped in the {{{KeyMapper}}} class and are available from this class as static variables: Eg:
 * {{{KeyMapper::PEV_UP}}} - is the Up Key defined in the config file
 * {{{KeyMapper::PEV_FIRE1}}} - is the fire button defined in the config file
 * {{{KeyMapper::PEV_VIEW0}}} - is the view nr zero key
 * ...
To see the whole list (and to extend it) read the {{{./src/util/event/key_mapper.{cc, h}}}} files, they are very short. To subscribe to such an event, you can use the code from above and alter it just a little:
{{{
#!c
  //subscribe this class to the orxonox.conf left
  EventHandler::getInstance()->subscribe(this, ES_GAME, KeyMapper::PEV_LEFT); 
  //subscribe this class to the orxonox.conf right
  EventHandler::getInstance()->subscribe(this, ES_GAME, KeyMapper::PEV_RIGHT); 
}}}

== References ==
To see more references, look at some source code files, eg:
 * {{{./src/world_entities/camera.{cc, h} }}} - the camera can change the view by pressing some keys
 * {{{./src/world_entities/player.{cc, h} }}} - the player shoots and changes location