=head1 NAME

SDL::Event - General event structure

=head2 CATEGORY

Core, Events, Structure

=head1 SYNOPSIS

 use SDL::Event;  # for the event object itself
 use SDL::Events; # functions for event queue handling
 
 SDL::init(SDL_INIT_VIDEO);
 my $event = SDL::Event->new();
 
 while(1)
 {
     SDL::Events::pump_events();

     if(SDL::Events::poll_event($event))
     {
        if($event->type == SDL_MOUSEBUTTONDOWN)
        {
            # now you can handle the details
            $event->button_which;
            $event->button_button;
            $event->button_x;
            $event->button_y;
        }
        
        last if $event->type == SDL_QUIT;
     }

     # your screen drawing code will be here
 }
 
=head1 DESCRIPTION

Event handling allows your application to receive input from the user. 
Event handling is initalised (along with video) with a call to:

C<SDL::init(SDL_INIT_VIDEO);>

Internally, SDL stores all the events waiting to be handled in an event queue. 
Using functions like C<SDL::Events::poll_event()>, C<SDL::Events::peep_events> 
and C<SDL::Events::wait_event()> you can observe and handle waiting input events.

The key to event handling in SDL is the C<SDL::Event> union. 
The event queue itself is composed of a series of C<SDL::Event> unions, one for each waiting event. 
C<SDL::Event> unions are read from the queue with the C<SDL::Events::poll_event()> function 
and it is then up to the application to process the information stored with them. 

=head1	METHODS

=head2	new

C<new> creates an empty event-object, which can be used store information. 
Either by calling C<poll_event($event)> that transferes one event from the queue into our object 
or by setting all the needed data manually in order to push the event to the queue.

 use SDL::Event;

 my $event = SDL::Event->new();
 
=head2	type

SDL::Event is a union of all event structures used in SDL, using it is a simple matter of knowing 
which union member relates to which event C<type>.

 print 'heureka' if $event->type == SDL_MOUSEBUTTONDOWN;

Available type constants:

=over 4

=item *

L<SDL_ACTIVEEVENT|/active> - Application visibility event structure 

=item *

L<SDL_KEYDOWN|/active> - Keyboard event structure 

=item *

L<SDL_KEYUP|/active> - Keyboard event structure 

=item *

L<SDL_MOUSEMOTION|/active> - Mouse motion event structure 

=item *

L<SDL_MOUSEBUTTONDOWN|/active> - Mouse button event structure 

=item *

L<SDL_MOUSEBUTTONUP|/button> - Mouse button event structure 

=item *

L<SDL_JOYAXISMOTION|/active> - Joystick axis motion event structure 

=item *

L<SDL_JOYBALLMOTION|/active> - Joystick trackball motion event structure 

=item *

L<SDL_JOYHATMOTION|/active> - Joystick hat position change event structure 

=item *

L<SDL_JOYBUTTONDOWN|/active> - Joystick button event structure 

=item *

L<SDL_JOYBUTTONUP|/active> - Joystick button event structure 

=item *

L<SDL_VIDEORESIZE|/active> - Window resize event structure 

=item *

L<SDL_VIDEOEXPOSE|/active> - Window expose event 

=item *

L<SDL_QUIT|/active> - Quit requested event 

=item *

L<SDL_USEREVENT|/active> - A user-defined event type 

=item *

L<SDL_SYSWMEVENT|/active> - Platform-dependent window manager event. 

=back

Event types are grouped by masks. C<SDL_EVENTMASK($type)> will return the proper mask for the given C<type>.

Available event mask constants:

=over 4

=item *

SDL_ACTIVEEVENTMASK

=item *

SDL_KEYDOWNMASK

=item *

SDL_KEYUPMASK

=item *

SDL_KEYEVENTMASK

=item *

SDL_MOUSEMOTIONMASK

=item *

SDL_MOUSEBUTTONDOWNMASK

=item *

SDL_MOUSEBUTTONUPMASK

=item *

SDL_MOUSEEVENTMASK

=item *

SDL_JOYAXISMOTIONMASK

=item *

SDL_JOYBALLMOTIONMASK

=item *

SDL_JOYHATMOTIONMASK

=item *

SDL_JOYBUTTONDOWNMASK

=item *

SDL_JOYBUTTONUPMASK

=item *

SDL_JOYEVENTMASK

=item *

SDL_VIDEORESIZEMASK

=item *

SDL_VIDEOEXPOSEMASK

=item *

SDL_QUITMASK

=item *

SDL_SYSWMEVENTMASK

=back

This way you can check if a given C<type> matches a mask:

 (SDL_JOYBUTTONDOWN   & SDL_MOUSEEVENTMASK) # is false
 (SDL_MOUSEBUTTONDOWN & SDL_MOUSEEVENTMASK) # is true
 (SDL_MOUSEBUTTONUP   & SDL_MOUSEEVENTMASK) # is true
 (SDL_MOUSEMOTION     & SDL_MOUSEEVENTMASK) # is true
 
 # and also true is:
 
 (SDL_MOUSEEVENTMASK == SDL_EVENTMASK(SDL_MOUSEBUTTONDOWN) 
                      | SDL_EVENTMASK(SDL_MOUSEBUTTONUP) 
                      | SDL_EVENTMASK(SDL_MOUSEMOTION))

=head2 Application visibility events

C<active> is used when an event of type C<SDL_ACTIVEEVENT> is reported.

When the mouse leaves or enters the window area a C<SDL_APPMOUSEFOCUS> type activation event occurs, 
if the mouse entered the window then B<gain> will be 1, otherwise B<gain> will be 0. 

A C<SDL_APPINPUTFOCUS> type activation event occurs when the application loses or gains keyboard focus. 
This usually occurs when another application is made active. 

Finally, a C<SDL_APPACTIVE> type event occurs when the application is either minimised/iconified (B<gain>=0) or restored. 

A single event can have multiple values set in B<state>.

B<Note:> This event does not occur when an application window is first created. 

A new ActiveEvent (to fake focus loss) will be created like this:

 my $event = SDL::Event->new();
    $event->type(SDL_ACTIVEEVENT);
    $event->active_gain(0);
    $event->active_state(SDL_APPMOUSEFOCUS);

 # I think this is wrong, ->active_type() should get SDL_APPMOUSEFOCUS, but what state gets?

=head3 active_gain

See C<active>. 0 if the event is a loss or 1 if it is a gain.

=head3 active_state

A bitmask of the following values: SDL_APPMOUSEFOCUS if mouse focus was gained or lost, 
SDL_APPINPUTFOCUS if input focus was gained or lost, and SDL_APPACTIVE if the application was iconified (gain=0) or restored(gain=1).

=head2 Keyboard events

C<key> is used when an event of type C<SDL_KEYDOWN> or C<SDL_KEYUP> is reported.

The type and state actually report the same information, they just use different values to do it. 
A keyboard event generally occurs when a key is released (C<type=SDL_KEYUP> or C<key_state=SDL_RELEASED>) 
and when a key is pressed (C<type=SDL_KEYDOWN> or C<key_state=SDL_PRESSED>). 

The C<SDLK_CAPSLOCK> and C<SDLK_NUMLOCK> keys are special cases and report an C<SDL_KEYDOWN> when first pressed, 
then an C<SDL_RELEASED> when released and pressed again. For these keys C<KEYUP> and C<KEYDOWN> events are therefore 
analogous to the state of the caps lock and num lock LEDs rather than the keys themselves. 
These special cases are required for compatibility with Sun workstations.

B<Note:> Repeating C<SDL_KEYDOWN> events will occur if key repeat is enabled (see C<SDL_EnableKeyRepeat>). 

=head3 key_state

C<SDL_PRESSED> or C<SDL_RELEASED>

=head3 key_scancode

The C<scancode> field should generally be left alone, it is the hardware-dependent scancode returned by the keyboard.

=head3 key_sym

The C<sym> field is extremely useful. It is the SDL-defined value of the key (see the keysym definitions in SDLKey). 
This field is very useful when you are checking for certain key presses, like so: 

 while(poll_event($event))
 {
     switch($event->type)
     {
         case SDL_KEYDOWN:
             move_left() if($event->key_sym == SDLK_LEFT);
             break;
         .
         .
         .
     }
 }

=head3 key_mod

C<mod> stores the current state of the keyboard modifiers as explained in SDL_GetModState.

=head3 key_unicode

The C<unicode> field is only used when UNICODE translation is enabled with SDL_EnableUNICODE. 
If C<unicode> is non-zero then this is the UNICODE character corresponding to the keypress. 
If the high 9 bits of the character are 0, then this maps to the equivalent ASCII character:

 my $char;
 if(($event->key_unicode & 0xFF80) == 0)
 {
     $char = $event->key_unicode & 0x7F;
 }
 else
 {
     print("An International Character.\n");
 }

UNICODE translation does create a slight overhead so don't enable it unless its needed.

NOTE: Key release events (SDL_KEYUP) won't necessarily (ever?) contain unicode information. 
See L<http://lists.libsdl.org/pipermail/sdl-libsdl.org/2005-January/048355.html>

=head2 Mouse motion events

Simply put, a SDL_MOUSEMOTION type event occurs when a user moves the mouse within the 
application window or when SDL_WarpMouse is called. Both the absolute (C<motion_x> and C<motion_y>) 
and relative (C<motion_xrel> and C<motion_yrel>) coordinates are reported along with the current 
button states (C<motion_state>).

=head3 motion_state

The button state can be interpreted using the C<SDL_BUTTON> macro (see SDL_GetMouseState). 

=head3 motion_x, motion_y

The X/Y coordinates of the mouse

=head3 motion_xrel, motion_yrel

Relative motion in the X/Y direction.

If the cursor is hidden (SDL_ShowCursor(0)) and the input is grabbed (SDL_WM_GrabInput(SDL_GRAB_ON)), 
then the mouse will give relative motion events even when the cursor reaches the edge of the screen. 
This is currently only implemented on Windows and Linux/Unix-alikes.

=head2 Mouse button events

When a mouse button press or release is detected the number of the button pressed (from 1 to 255, 
with 1 usually being the left button and 2 the right) is placed into C<button_button>, the position of the mouse 
when this event occured is stored in the C<button_x> and the C<button_y> fields. Like SDL_KeyboardEvent, 
information on whether the event was a press or a release event is stored in both the C<button_type> 
and C<button_state> fields, but this should be obvious.

Mouse wheel events are reported as buttons 4 (up) and 5 (down). Two events are generated i.e. you get 
a C<SDL_MOUSEBUTTONDOWN> followed by a C<SDL_MOUSEBUTTONUP> event.

=head3 button_which

The input device index

=head3 button_button

The mouse button index (C<SDL_BUTTON_LEFT>, C<SDL_BUTTON_MIDDLE>, C<SDL_BUTTON_RIGHT>, C<SDL_BUTTON_WHEELUP>, 
C<SDL_BUTTON_WHEELDOWN>)

=head3 button_state

C<SDL_PRESSED> or C<SDL_RELEASED>

=head3 button_x, button_y

The X/Y coordinates of the mouse at press/release time

=head2 Joystick axis events

A C<SDL_JOYAXISMOTION> event occurs whenever a user moves an axis on the joystick.

=head3 jaxis_which

The field C<jaxis_which> is the index of the joystick that reported the event.

=head3 jaxis_axis

The C<jaxis_axis> is the index of the axis (for a more detailed explaination see the Joystick section).

=head3 jaxis_value

C<jaxis_value> is the current position of the axis (range: -32768 to 32767).

=head2 Joystick button events

A C<SDL_JOYBUTTONDOWN> or C<SDL_JOYBUTTONUP> event occurs when ever a user presses 
or releases a button on a joystick.

=head3 jbutton_which

The field C<jbutton_which> is the index of the joystick that reported the event.

=head3 jbutton_button

The C<jbutton_button> is the index of the button (for a more detailed explanation see the Joystick section).

=head3 jbutton_state

C<jbutton_state> is the current state of the button which is either C<jbutton_SDL_PRESSED> 
or C<jbutton_SDL_RELEASED>. 

=head2 Joystick hat events

A C<SDL_JOYHATMOTION> event occurs when ever a user moves a hat on the joystick. 

=head3 jhat_which

The field C<jhat_which> is the index of the joystick that reported the event.

=head3 jhat_hat

C<jhat_hat> is the index of the hat (for a more detailed explanation see the Joystick section).

=head3 jhat_value

C<jhat_value> is the current position of the hat. It is a bitwise OR'd combination of the following 
values (whose meanings should be pretty obvious):

=over 4

=item *

C<SDL_HAT_CENTERED>

=item *

C<SDL_HAT_UP>

=item *

C<SDL_HAT_RIGHT>

=item *

C<SDL_HAT_DOWN>

=item *

C<SDL_HAT_LEFT>

=back

The following defines are also provided:

=over 4

=item *

C<SDL_HAT_RIGHTUP>

=item *

C<SDL_HAT_RIGHTDOWN>

=item *

C<SDL_HAT_LEFTUP>

=item *

C<SDL_HAT_LEFTDOWN>

=back

=head2 Joystrick trackball events

A C<SDL_JOYBALLMOTION> event occurs when a user moves a trackball on the joystick.

=head3 jball_which

The field C<jball_which> is the index of the joystick that reported the event.

=head3 jball_ball

C<jball_ball> is the index of the trackball (for a more detailed explanation see the Joystick section).

=head3 jball_xrel, jball_yrel

Trackballs only return relative motion, this is the change in position on the ball since it was last 
polled (last cycle of the event loop) and it is stored in C<jball_xrel> and C<jball_yrel>.

=head2 Window resize events

=head3 resize_w, resize_h

When C<SDL_RESIZABLE> is passed as a flag to C<SDL_SetVideoMode> the user is allowed to resize the 
applications window. When the window is resized an C<SDL_VIDEORESIZE> is reported, with the new 
window width and height values stored in the resize structure's C<resize_w> and C<resize_h>. 
When an C<SDL_VIDEORESIZE> is received the window should be resized to the new dimensions using 
SDL_SetVideoMode. 

=head2 Window expose events

A C<VIDEOEXPOSE> event is triggered when the screen has been modified outside of the application, 
usually by the window manager and needs to be redrawn.

=head2 System window manager events

The system window manager event contains a system-specific information about unknown window manager 
events. If you enable this event using C<SDL_EventState>, it will be generated whenever unhandled 
events are received from the window manager. This can be used, for example, to implement cut-and-paste 
in your application.

If you want to obtain system-specific information about the window manager, you can fill in the 
version member of a SDL_SysWMinfo structure (details can be found in SDL_syswm.h, which must be included) 
using the SDL_VERSION() macro found in SDL_version.h, and pass it to the function:

 int SDL_GetWMInfo(SDL_SysWMinfo *info);
 
See L<http://www.libsdl.org/cgi/docwiki.cgi/SDL_SysWMEvent>

=head3 syswm_msg

=head2 User defined events

This event is unique, it is never created by SDL but only by the user. The event can be pushed onto
the event queue using C<SDL::Events::push_event>. The contents of the structure members are completely up to the 
programmer, the only requirement is that type is a value from C<SDL_USEREVENT> to C<SDL_NUMEVENTS-1> (inclusive)

 my $event = SDL::Event->new();
    $event->type ( SDL_USEREVENT + 3 );
    $event->event_code(10);
    $event->data1('hello event');

 SDL::Events::push_event($event);

=head3 user_code

User defined event code (integer).

=head3 user_data1, user_data2

User defined data.

=head2 Quit event

As can be seen, the C<SDL_QuitEvent> structure serves no useful purpose. The event itself, on the other hand, 
is very important. If you filter out or ignore a quit event then it is impossible for the user to close the 
window. On the other hand, if you do accept a quit event then the application window will be closed, and 
screen updates will still report success even though the application will no longer be visible.

B<Note>: The macro SDL_QuitRequested will return non-zero if a quit event is pending 

=head1 AUTHOR

=head1 SEE ALSO

L<perl>