Changes between Initial Version and Version 1 of ~archive/EventHandler

Timestamp:

Nov 27, 2007, 10:20:09 PM (18 years ago)

Author:

landauf

Comment:

—

~archive/EventHandler

@@ +1 @@
+= Event-Handler =
+
+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