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.
Create a new SDL::Event object.
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