SDL::Event - General event structure
use SDL::Event; # for the event object itself use SDL::Events qw(pump_events poll_event); # functions for event queue handling SDL::init(SDL_INIT_VIDEO); my $event = SDL::Event->new(); while(1) { pump_events(); if(poll_event($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 $event->type == SDL_QUIT; } # your screen drawing code will be here }
Event handling allows your application to receive input from the user. Event handling is initalised (along with video) with a call to:
SDL::init(SDL_INIT_VIDEO);
Internally, SDL stores all the events waiting to be handled in an event queue.
Using functions like SDL::Events::poll_event()
, SDL::Events::peep_events
and SDL::Events::wait_event()
you can observe and handle waiting input events.
The key to event handling in SDL is the SDL::Event
union.
The event queue itself is composed of a series of SDL::Event
unions, one for each waiting event.
SDL::Event
unions are read from the queue with the SDL::Events::poll_event()
function
and it is then up to the application to process the information stored with them.
new
creates an empty event-object, which can be used store information.
Either by calling poll_event($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();
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 $event->type == SDL_MOUSEBUTTONDOWN;
Available type constants:
Event types are grouped by masks. SDL_EVENTMASK($type)
will return the proper mask for the given type
.
Available event mask constants:
This way you can check if a given 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))
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); $event->active_state(SDL_APPMOUSEFOCUS); # I think this is wrong, ->active_type() should get SDL_APPMOUSEFOCUS, but what state gets?
See active
. 0 if the event is a loss or 1 if it is a gain.
A bitmask of the following values: SDL_APPMOUSEFOCUS if mouse focus was gained or lost, SDL_APPINPUTFOCUS if input focus was gained or lost, and SDL_APPACTIVE if the application was iconified (gain=0) or restored(gain=1).
key
is used when an event of type SDL_KEYDOWN
or SDL_KEYUP
is reported.
The type and state actually report the same information, they just use different values to do it.
A keyboard event generally occurs when a key is released (type=SDL_KEYUP
or key_state=SDL_RELEASED
)
and when a key is pressed (type=SDL_KEYDOWN
or key_state=SDL_PRESSED
).
The SDLK_CAPSLOCK
and SDLK_NUMLOCK
keys are special cases and report an SDL_KEYDOWN
when first pressed,
then an SDL_RELEASED
when released and pressed again. For these keys KEYUP
and KEYDOWN
events are therefore
analogous to the state of the caps lock and num lock LEDs rather than the keys themselves.
These special cases are required for compatibility with Sun workstations.
Note: Repeating SDL_KEYDOWN
events will occur if key repeat is enabled (see SDL_EnableKeyRepeat
).
SDL_PRESSED
or SDL_RELEASED
The scancode
field should generally be left alone, it is the hardware-dependent scancode returned by the keyboard.
The sym
field is extremely useful. It is the SDL-defined value of the key (see the keysym definitions in SDLKey).
This field is very useful when you are checking for certain key presses, like so:
while(poll_event($event)) { switch($event->type) { case SDL_KEYDOWN: move_left() if($event->key_sym == SDLK_LEFT); break; . . . } }
mod
stores the current state of the keyboard modifiers as explained in SDL_GetModState.
The unicode
field is only used when UNICODE translation is enabled with SDL_EnableUNICODE.
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
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
).
The button state can be interpreted using the SDL_BUTTON
macro (see SDL_GetMouseState).
The X/Y coordinates of the mouse
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.
A SDL_JOYAXISMOTION
event occurs whenever a user moves an axis on the joystick.
The field jaxis_which
is the index of the joystick that reported the event.
The jaxis_axis
is the index of the axis (for a more detailed explaination see the Joystick section).
jaxis_value
is the current position of the axis (range: -32768 to 32767).
A SDL_JOYHATMOTION
event occurs when ever a user moves a hat on the joystick.
The field jhat_which
is the index of the joystick that reported the event.
jhat_hat
is the index of the hat (for a more detailed explanation see the Joystick section).
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
A SDL_JOYBALLMOTION
event occurs when a user moves a trackball on the joystick.
The field jball_which
is the index of the joystick that reported the event.
jball_ball
is the index of the trackball (for a more detailed explanation see the Joystick section).
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
.
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.
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.
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);
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->event_code(10); $event->data1('hello event'); SDL::Events::push_event($event);
User defined event code (integer).
User defined data.
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
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