pods::SDL::Event(3) User Contributed Perl Documentation pods::SDL::Event(3)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
perl v5.18.1 2013-09-28 pods::SDL::Event(3)
