Provided by: libsdl-perl_2.546-2build1_amd64 
NAME
SDL::Event - General event structure
CATEGORY
Core, Events, Structure
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 $event->type == SDL_QUIT;
}
# your screen drawing code will be here
}
DESCRIPTION
Event handling allows your application to receive input from the user. Event handling is
initalised (along with video) with a call to:
"SDL::init(SDL_INIT_VIDEO);"
Internally, SDL stores all the events waiting to be handled in an event queue. Using
functions like "SDL::Events::poll_event()", "SDL::Events::peep_events" and
"SDL::Events::wait_event()" you can observe and handle waiting input events.
The key to event handling in SDL is the "SDL::Event" union. The event queue itself is
composed of a series of "SDL::Event" unions, one for each waiting event. "SDL::Event"
unions are read from the queue with the "SDL::Events::poll_event()" function and it is
then up to the application to process the information stored with them.
METHODS
new
"new" creates an empty event-object, which can be used store information. Either by
calling "poll_event($event)" that transfers 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();
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 "type".
print 'heureka' if $event->type == SDL_MOUSEBUTTONDOWN;
Available type constants:
• SDL_ACTIVEEVENT - Application visibility event structure
• SDL_KEYDOWN - Keyboard event structure
• SDL_KEYUP - Keyboard event structure
• SDL_MOUSEMOTION - Mouse motion event structure
• SDL_MOUSEBUTTONDOWN - Mouse button event structure
• SDL_MOUSEBUTTONUP - Mouse button event structure
• SDL_JOYAXISMOTION - Joystick axis motion event structure
• SDL_JOYBALLMOTION - Joystick trackball motion event structure
• SDL_JOYHATMOTION - Joystick hat position change event structure
• SDL_JOYBUTTONDOWN - Joystick button event structure
• SDL_JOYBUTTONUP - Joystick button event structure
• SDL_VIDEORESIZE - Window resize event structure
• SDL_VIDEOEXPOSE - Window expose event
• SDL_QUIT - Quit requested event
• SDL_USEREVENT - A user-defined event type
• SDL_SYSWMEVENT - Platform-dependent window manager event.
Event types are grouped by masks. "SDL_EVENTMASK($type)" will return the proper mask for
the given "type".
Available event mask constants:
• SDL_ACTIVEEVENTMASK
• SDL_KEYDOWNMASK
• SDL_KEYUPMASK
• SDL_KEYEVENTMASK
• SDL_MOUSEMOTIONMASK
• SDL_MOUSEBUTTONDOWNMASK
• SDL_MOUSEBUTTONUPMASK
• SDL_MOUSEEVENTMASK
• SDL_JOYAXISMOTIONMASK
• SDL_JOYBALLMOTIONMASK
• SDL_JOYHATMOTIONMASK
• SDL_JOYBUTTONDOWNMASK
• SDL_JOYBUTTONUPMASK
• SDL_JOYEVENTMASK
• SDL_VIDEORESIZEMASK
• SDL_VIDEOEXPOSEMASK
• SDL_QUITMASK
• SDL_SYSWMEVENTMASK
This way you can check if a given "type" matches a mask:
(SDL_EVENTMASK(SDL_JOYBUTTONDOWN) & SDL_MOUSEEVENTMASK) # is false
(SDL_EVENTMASK(SDL_MOUSEBUTTONDOWN) & SDL_MOUSEEVENTMASK) # is true
(SDL_EVENTMASK(SDL_MOUSEBUTTONUP) & SDL_MOUSEEVENTMASK) # is true
(SDL_EVENTMASK(SDL_MOUSEMOTION) & SDL_MOUSEEVENTMASK) # is true
# and also true is:
(SDL_MOUSEEVENTMASK == SDL_EVENTMASK(SDL_MOUSEBUTTONDOWN)
| SDL_EVENTMASK(SDL_MOUSEBUTTONUP)
| SDL_EVENTMASK(SDL_MOUSEMOTION))
Application visibility events
"active" is used when an event of type "SDL_ACTIVEEVENT" is reported.
When the mouse leaves or enters the window area a "SDL_APPMOUSEFOCUS" type activation
event occurs, if the mouse entered the window then gain will be 1, otherwise gain will be
0.
A "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 "SDL_APPACTIVE" type event occurs when the application is either
minimised/iconified (gain=0) or restored.
A single event can have multiple values set in state.
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);
$event->active_state(SDL_APPMOUSEFOCUS);
# I think this is wrong, ->active_type() should get SDL_APPMOUSEFOCUS, but what state gets?
active_gain
See "active". 0 if the event is a loss or 1 if it is a gain.
active_state
A bitmask of the following values: SDL_APPMOUSEFOCUS if mouse focus was gained or lost,
SDL_APPINPUTFOCUS if input focus was gained or lost, and SDL_APPACTIVE if the application
was iconified (gain=0) or restored(gain=1).
Keyboard events
"key" is used when an event of type "SDL_KEYDOWN" or "SDL_KEYUP" is reported.
The type and state actually report the same information, they just use different values to
do it. A keyboard event generally occurs when a key is released ("type=SDL_KEYUP" or
"key_state=SDL_RELEASED") and when a key is pressed ("type=SDL_KEYDOWN" or
"key_state=SDL_PRESSED").
The "SDLK_CAPSLOCK" and "SDLK_NUMLOCK" keys are special cases and report an "SDL_KEYDOWN"
when first pressed, then an "SDL_RELEASED" when released and pressed again. For these keys
"KEYUP" and "KEYDOWN" events are therefore analogous to the state of the caps lock and num
lock LEDs rather than the keys themselves. These special cases are required for
compatibility with Sun workstations.
Note: Repeating "SDL_KEYDOWN" events will occur if key repeat is enabled (see
SDL::Events::enable_key_repeat).
key_state
"SDL_PRESSED" or "SDL_RELEASED"
key_scancode
The "scancode" field should generally be left alone, it is the hardware-dependent scancode
returned by the keyboard.
key_sym
The "sym" field is extremely useful. It is the SDL-defined value of the key (see the
keysym definitions in SDLKey). This field is very useful when you are checking for
certain key presses, like so:
while(poll_event($event))
{
switch($event->type)
{
case SDL_KEYDOWN:
move_left() if($event->key_sym == SDLK_LEFT);
break;
.
.
.
}
}
key_mod
"mod" stores the current state of the keyboard modifiers as explained in SDL_GetModState.
key_unicode
The "unicode" field is only used when UNICODE translation is enabled with
SDL::Events::enable_unicode. If "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
<http://lists.libsdl.org/pipermail/sdl-libsdl.org/2005-January/048355.html>
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 ("motion_x" and
"motion_y") and relative ("motion_xrel" and "motion_yrel") coordinates are reported along
with the current button states ("motion_state").
motion_state
The button state can be interpreted using the "SDL_BUTTON" macro (see
SDL::Events::get_mouse_state).
motion_x, motion_y
The X/Y coordinates of the mouse
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.
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
"button_button". The position of the mouse when this event occurred is stored in the
"button_x" and the "button_y" fields. Like a keyboard event, information on whether the
event was a press or a release event is stored in both the "button_type" and
"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 "SDL_MOUSEBUTTONDOWN" followed by a "SDL_MOUSEBUTTONUP" event.
button_which
The input device index
button_button
The mouse button index ("SDL_BUTTON_LEFT", "SDL_BUTTON_MIDDLE", "SDL_BUTTON_RIGHT",
"SDL_BUTTON_WHEELUP", "SDL_BUTTON_WHEELDOWN")
button_state
"SDL_PRESSED" or "SDL_RELEASED"
button_x, button_y
The X/Y coordinates of the mouse at press/release time
Joystick axis events
A "SDL_JOYAXISMOTION" event occurs whenever a user moves an axis on the joystick.
jaxis_which
The field "jaxis_which" is the index of the joystick that reported the event.
jaxis_axis
The "jaxis_axis" is the index of the axis (for a more detailed explanation see the
Joystick section).
jaxis_value
"jaxis_value" is the current position of the axis (range: -32768 to 32767).
Joystick button events
A "SDL_JOYBUTTONDOWN" or "SDL_JOYBUTTONUP" event occurs when ever a user presses or
releases a button on a joystick.
jbutton_which
The field "jbutton_which" is the index of the joystick that reported the event.
jbutton_button
The "jbutton_button" is the index of the button (for a more detailed explanation see the
Joystick section).
jbutton_state
"jbutton_state" is the current state of the button which is either "jbutton_SDL_PRESSED"
or "jbutton_SDL_RELEASED".
Joystick hat events
A "SDL_JOYHATMOTION" event occurs when ever a user moves a hat on the joystick.
jhat_which
The field "jhat_which" is the index of the joystick that reported the event.
jhat_hat
"jhat_hat" is the index of the hat (for a more detailed explanation see the Joystick
section).
jhat_value
"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):
• "SDL_HAT_CENTERED"
• "SDL_HAT_UP"
• "SDL_HAT_RIGHT"
• "SDL_HAT_DOWN"
• "SDL_HAT_LEFT"
The following defines are also provided:
• "SDL_HAT_RIGHTUP"
• "SDL_HAT_RIGHTDOWN"
• "SDL_HAT_LEFTUP"
• "SDL_HAT_LEFTDOWN"
Joystick trackball events
A "SDL_JOYBALLMOTION" event occurs when a user moves a trackball on the joystick.
jball_which
The field "jball_which" is the index of the joystick that reported the event.
jball_ball
"jball_ball" is the index of the trackball (for a more detailed explanation see the
Joystick section).
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 "jball_xrel" and
"jball_yrel".
Window resize events
resize_w, resize_h
When "SDL_RESIZABLE" is passed as a flag to "SDL_SetVideoMode" the user is allowed to
resize the applications window. When the window is resized an "SDL_VIDEORESIZE" is
reported, with the new window width and height values stored in the resize structure's
"resize_w" and "resize_h". When an "SDL_VIDEORESIZE" is received the window should be
resized to the new dimensions using SDL_SetVideoMode.
Window expose events
A "VIDEOEXPOSE" event is triggered when the screen has been modified outside of the
application, usually by the window manager and needs to be redrawn.
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 "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 <http://www.libsdl.org/cgi/docwiki.cgi/SDL_SysWMEvent>
syswm_msg
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 "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 "SDL_USEREVENT" to "SDL_NUMEVENTS-1" (inclusive)
my $event = SDL::Event->new();
$event->type ( SDL_USEREVENT + 3 );
$event->user_code(10);
$event->user_data1('hello event');
SDL::Events::push_event($event);
user_code
User defined event code (integer).
user_data1, user_data2
User defined data.
Quit event
As can be seen, the "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.
Note: The macro SDL_QuitRequested will return non-zero if a quit event is pending
AUTHORS
See "AUTHORS" in SDL.
SEE ALSO
perl