Event system and events
These functions are declared in the main Allegro header file:
#include <allegro5/allegro.h>Events are generated by event sources. Most notably, each of the input subsystems provides an event source, but also timers, displays, and audio streams will generate events.
Event sources are registered to event queues which aggregate events from multiple sources. A single event source can also be registered to multiple event queues.
Event queues can then be queried for events. In particular, it is possible to wait until events become available in order to save CPU time. You can combine this with timers to make your main-loop run at a specific speed without wasting CPU time or missing events.
In addition to the predefined event types, Allegro also allows for user-defined events that can be generated by user-defined event sources.
The appropriate reaction to an event is determined by examining the fields of the ALLEGRO_EVENT union according to the event type.
In addition to the events sent by Allegro core, there’s also events send by the addons, see ALLEGRO_AUDIO_EVENT_TYPE and ALLEGRO_VIDEO_EVENT_TYPE.
ALLEGRO_EVENT
typedef union ALLEGRO_EVENT ALLEGRO_EVENT;An ALLEGRO_EVENT is a union of all builtin event structures, i.e. it is an object large enough to hold the data of any event type. All events have the following fields in common:
- type (ALLEGRO_EVENT_TYPE)
- Indicates the type of event.
- any.source (ALLEGRO_EVENT_SOURCE *)
- The event source which generated the event.
- any.timestamp (double)
- When the event was generated.
By examining the type field you can then access type-specific fields. The any.source field tells you which event source generated that particular event. The any.timestamp field tells you when the event was generated. The time is referenced to the same starting point as al_get_time.
Each event is of one of the following types, with the usable fields given.
Examples:
ALLEGRO_EVENT_JOYSTICK_AXIS
A joystick axis value changed.
- joystick.id (ALLEGRO_JOYSTICK *)
- The joystick which generated the event. This is not the same as the event source
joystick.source. - joystick.stick (int)
- The stick number, counting from zero. Axes on a joystick are grouped into “sticks”.
- joystick.axis (int)
- The axis number on the stick, counting from zero.
- joystick.pos (float)
- The axis position, from -1.0 to +1.0.
ALLEGRO_EVENT_JOYSTICK_BUTTON_DOWN
A joystick button was pressed.
- joystick.id (ALLEGRO_JOYSTICK *)
- The joystick which generated the event.
- joystick.button (int)
- The button which was pressed, counting from zero.
ALLEGRO_EVENT_JOYSTICK_BUTTON_UP
A joystick button was released.
- joystick.id (ALLEGRO_JOYSTICK *)
- The joystick which generated the event.
- joystick.button (int)
- The button which was released, counting from zero.
ALLEGRO_EVENT_JOYSTICK_CONFIGURATION
A joystick was plugged in or unplugged. See al_reconfigure_joysticks for details.
ALLEGRO_EVENT_KEY_DOWN
A keyboard key was pressed.
- keyboard.keycode (int)
- The code corresponding to the physical key which was pressed. See the Key codes section for the list of ALLEGRO_KEY_* constants.
- keyboard.display (ALLEGRO_DISPLAY *)
- The display which had keyboard focus when the event occurred.
Note: this event is about the physical keys being pressed on the keyboard. Look for ALLEGRO_EVENT_KEY_CHAR events for character input.
ALLEGRO_EVENT_KEY_UP
A keyboard key was released.
- keyboard.keycode (int)
- The code corresponding to the physical key which was released. See the Key codes section for the list of ALLEGRO_KEY_* constants.
- keyboard.display (ALLEGRO_DISPLAY *)
- The display which had keyboard focus when the event occurred.
ALLEGRO_EVENT_KEY_CHAR
A character was typed on the keyboard, or a character was auto-repeated.
- keyboard.keycode (int)
- The code corresponding to the physical key which was last pressed. See the Key codes section for the list of ALLEGRO_KEY_* constants.
- keyboard.unichar (int)
A Unicode code point (character). This may be zero or negative if the event was generated for a non-visible “character”, such as an arrow or Function key. In that case you can act upon the
keycodefield.Some special keys will set the
unicharfield to their standard ASCII values: Tab=9, Return=13, Escape=27. In addition if you press the Control key together with A to Z theunicharfield will have the values 1 to 26. For example Ctrl-A will setunicharto 1 and Ctrl-H will set it to 8.As of Allegro 5.0.2 there are some inconsistencies in the treatment of Backspace (8 or 127) and Delete (127 or 0) keys on different platforms. These can be worked around by checking the
keycodefield.- keyboard.modifiers (unsigned)
- This is a bitfield of the modifier keys which were pressed when the event occurred. See “Keyboard modifier flags” for the constants.
- keyboard.repeat (bool)
- Indicates if this is a repeated character.
- keyboard.display (ALLEGRO_DISPLAY *)
- The display which had keyboard focus when the event occurred.
Note: in many input methods, characters are not entered one-for-one with physical key presses. Multiple key presses can combine to generate a single character, e.g. apostrophe + e may produce ‘é’. Fewer key presses can also generate more characters, e.g. macro sequences expanding to common phrases.
ALLEGRO_EVENT_MOUSE_AXES
One or more mouse axis values changed.
- mouse.x (int)
- x-coordinate
- mouse.y (int)
- y-coordinate
- mouse.z (int)
- z-coordinate. This usually means the vertical axis of a mouse wheel, where up is positive and down is negative.
- mouse.w (int)
- w-coordinate. This usually means the horizontal axis of a mouse wheel.
- mouse.dx (int)
- Change in the x-coordinate value since the previous ALLEGRO_EVENT_MOUSE_AXES event.
- mouse.dy (int)
- Change in the y-coordinate value since the previous ALLEGRO_EVENT_MOUSE_AXES event.
- mouse.dz (int)
- Change in the z-coordinate value since the previous ALLEGRO_EVENT_MOUSE_AXES event.
- mouse.dw (int)
- Change in the w-coordinate value since the previous ALLEGRO_EVENT_MOUSE_AXES event.
- mouse.pressure (float)
- Pressure, ranging from
0.0to1.0. - mouse.display (ALLEGRO_DISPLAY *)
- The display which had mouse focus.
Note: Calling al_set_mouse_xy also will result in a change of axis values, but such a change is reported with ALLEGRO_EVENT_MOUSE_WARPED events instead which are identical except for their type.
Note: currently mouse.display may be NULL if an event is generated in response to al_set_mouse_axis.
ALLEGRO_EVENT_MOUSE_BUTTON_DOWN
A mouse button was pressed.
- mouse.x (int)
- x-coordinate
- mouse.y (int)
- y-coordinate
- mouse.z (int)
- z-coordinate
- mouse.w (int)
- w-coordinate
- mouse.button (unsigned)
- The mouse button which was pressed, numbering from 1. As a convenience, the constants ALLEGRO_MOUSE_BUTTON_LEFT, ALLEGRO_MOUSE_BUTTON_RIGHT, ALLEGRO_MOUSE_BUTTON_MIDDLE are provided. However, depending on the hardware there may be more or fewer mouse buttons. You can check al_get_mouse_num_buttons if you want to be sure.
- mouse.pressure (float)
- Pressure, ranging from
0.0to1.0. - mouse.display (ALLEGRO_DISPLAY *)
- The display which had mouse focus.
ALLEGRO_EVENT_MOUSE_BUTTON_UP
A mouse button was released.
- mouse.x (int)
- x-coordinate
- mouse.y (int)
- y-coordinate
- mouse.z (int)
- z-coordinate
- mouse.w (int)
- w-coordinate
- mouse.button (unsigned)
- The mouse button which was released, numbering from 1. As a convenience, the constants ALLEGRO_MOUSE_BUTTON_LEFT, ALLEGRO_MOUSE_BUTTON_RIGHT, ALLEGRO_MOUSE_BUTTON_MIDDLE are provided. However, depending on the hardware there may be more or fewer mouse buttons. You can check al_get_mouse_num_buttons if you want to be sure.
- mouse.pressure (float)
- Pressure, ranging from
0.0to1.0. - mouse.display (ALLEGRO_DISPLAY *)
- The display which had mouse focus.
ALLEGRO_EVENT_MOUSE_WARPED
al_set_mouse_xy was called to move the mouse. This event is identical to ALLEGRO_EVENT_MOUSE_AXES otherwise.
ALLEGRO_EVENT_MOUSE_ENTER_DISPLAY
The mouse cursor entered a window opened by the program.
- mouse.x (int)
- x-coordinate
- mouse.y (int)
- y-coordinate
- mouse.z (int)
- z-coordinate
- mouse.w (int)
- w-coordinate
- mouse.display (ALLEGRO_DISPLAY *)
- The display which had mouse focus.
ALLEGRO_EVENT_MOUSE_LEAVE_DISPLAY
The mouse cursor left the boundaries of a window opened by the program.
- mouse.x (int)
- x-coordinate
- mouse.y (int)
- y-coordinate
- mouse.z (int)
- z-coordinate
- mouse.w (int)
- w-coordinate
- mouse.display (ALLEGRO_DISPLAY *)
- The display which had mouse focus.
ALLEGRO_EVENT_TOUCH_BEGIN
The touch input device registered a new touch.
- touch.display (ALLEGRO_DISPLAY)
- The display which was touched.
- touch.id (int)
- An identifier for this touch. If supported by the device it will stay the same for events from the same finger until the touch ends.
- touch.x (float)
- The x coordinate of the touch in pixels.
- touch.y (float)
- The y coordinate of the touch in pixels.
- touch.dx (float)
- Movement speed in pixels in x direction.
- touch.dy (float)
- Movement speed in pixels in y direction.
- touch.primary (bool)
- Whether this is the only/first touch or an additional touch.
Since: 5.1.0
ALLEGRO_EVENT_TOUCH_END
A touch ended.
Has the same fields as ALLEGRO_EVENT_TOUCH_BEGIN.
Since: 5.1.0
ALLEGRO_EVENT_TOUCH_MOVE
The position of a touch changed.
Has the same fields as ALLEGRO_EVENT_TOUCH_BEGIN.
Since: 5.1.0
ALLEGRO_EVENT_TOUCH_CANCEL
A touch was cancelled. This is device specific but could for example mean that a finger moved off the border of the device or moved so fast that it could not be tracked any longer.
Has the same fields as ALLEGRO_EVENT_TOUCH_BEGIN.
Since: 5.1.0
ALLEGRO_EVENT_TIMER
A timer counter incremented.
- timer.source (ALLEGRO_TIMER *)
- The timer which generated the event.
- timer.count (int64_t)
- The timer count value.
ALLEGRO_EVENT_DISPLAY_EXPOSE
The display (or a portion thereof) has become visible.
- display.source (ALLEGRO_DISPLAY *)
- The display which was exposed.
- display.x (int)
- The X position of the top-left corner of the rectangle which was exposed.
- display.y (int)
- The Y position of the top-left corner of the rectangle which was exposed.
- display.width (int)
- The width of the rectangle which was exposed.
- display.height (int)
- The height of the rectangle which was exposed.
Note: The display needs to be created with ALLEGRO_GENERATE_EXPOSE_EVENTS flag for these events to be generated.
ALLEGRO_EVENT_DISPLAY_RESIZE
The window has been resized.
- display.source (ALLEGRO_DISPLAY *)
- The display which was resized.
- display.x (int)
- The X position of the top-left corner of the display.
- display.y (int)
- The Y position of the top-left corner of the display.
- display.width (int)
- The new width of the display.
- display.height (int)
- The new height of the display.
You should normally respond to these events by calling al_acknowledge_resize. Note that further resize events may be generated by the time you process the event, so these fields may hold outdated information.
ALLEGRO_EVENT_DISPLAY_CLOSE
The close button of the window has been pressed.
- display.source (ALLEGRO_DISPLAY *)
- The display which was closed.
ALLEGRO_EVENT_DISPLAY_LOST
When using Direct3D, displays can enter a “lost” state. In that state, drawing calls are ignored, and upon entering the state, bitmap’s pixel data can become undefined. Allegro does its best to preserve the correct contents of bitmaps (see the ALLEGRO_NO_PRESERVE_TEXTURE flag) and restore them when the device is “found” (see ALLEGRO_EVENT_DISPLAY_FOUND). However, this is not 100% fool proof (see discussion in al_create_bitmap’s documentation).
Note: This event merely means that the display was lost, that is, DirectX suddenly lost the contents of all video bitmaps. In particular, you can keep calling drawing functions – they just most likely won’t do anything. If Allegro’s restoration of the bitmaps works well for you then no further action is required when you receive this event.
- display.source (ALLEGRO_DISPLAY *)
- The display which was lost.
ALLEGRO_EVENT_DISPLAY_FOUND
Generated when a lost device is restored to operating state. See ALLEGRO_EVENT_DISPLAY_LOST.
- display.source (ALLEGRO_DISPLAY *)
- The display which was found.
ALLEGRO_EVENT_DISPLAY_SWITCH_OUT
The window is no longer active, that is the user might have clicked into another window or “tabbed” away. In response to this event you might want to call al_clear_keyboard_state (possibly passing display.source as its argument) in order to prevent Allegro’s keyboard state from getting out of sync.
- display.source (ALLEGRO_DISPLAY *)
- The display which was switched out of.
ALLEGRO_EVENT_DISPLAY_SWITCH_IN
The window is the active one again.
- display.source (ALLEGRO_DISPLAY *)
- The display which was switched into.
ALLEGRO_EVENT_DISPLAY_ORIENTATION
Generated when the rotation or orientation of a display changes.
- display.source (ALLEGRO_DISPLAY *)
- The display which generated the event.
- event.display.orientation
Contains one of the following values:
- ALLEGRO_DISPLAY_ORIENTATION_0_DEGREES
- ALLEGRO_DISPLAY_ORIENTATION_90_DEGREES
- ALLEGRO_DISPLAY_ORIENTATION_180_DEGREES
- ALLEGRO_DISPLAY_ORIENTATION_270_DEGREES
- ALLEGRO_DISPLAY_ORIENTATION_FACE_UP
- ALLEGRO_DISPLAY_ORIENTATION_FACE_DOWN
ALLEGRO_EVENT_DISPLAY_HALT_DRAWING
When a display receives this event it should stop doing any drawing and then call al_acknowledge_drawing_halt immediately.
This is currently only relevant for Android and iOS. It will be sent when the application is switched to background mode, in addition to ALLEGRO_EVENT_DISPLAY_SWITCH_OUT. The latter may also be sent in situations where the application is not active but still should continue drawing, for example when a popup is displayed in front of it.
Note: This event means that the next time you call a drawing function, your program will crash. So you must stop drawing and you must immediately reply with al_acknowledge_drawing_halt. Allegro sends this event because it cannot handle this automatically. Your program might be doing the drawing in a different thread from the event handling, in which case the drawing thread needs to be signaled to stop drawing before acknowledging this event.
Note: Mobile devices usually never quit an application, so to prevent the battery from draining while your application is halted it can be a good idea to call al_stop_timer on all your timers, otherwise they will keep generating events. If you are using audio, you can also stop all audio voices (or pass NULL to al_set_default_voice if you use the default mixer), otherwise Allegro will keep streaming silence to the voice even if the stream or mixer are stopped or detached.
Since: 5.1.0
See also: ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING
ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING
When a display receives this event, it may resume drawing again, and it must call al_acknowledge_drawing_resume immediately.
This is currently only relevant for Android and iOS. The event will be sent when an application returns from background mode and is allowed to draw to the display again, in addition to ALLEGRO_EVENT_DISPLAY_SWITCH_IN. The latter event may also be sent in a situation where the application is already active, for example when a popup in front of it closes.
Note: Unlike ALLEGRO_EVENT_DISPLAY_FOUND it is not necessary to reload any bitmaps when you receive this event.
Since: 5.1.0
See also: ALLEGRO_EVENT_DISPLAY_HALT_DRAWING
ALLEGRO_EVENT_DISPLAY_CONNECTED
This event is sent when a physical display is connected to the device Allegro runs on. Currently, on most platforms, Allegro supports only a single physical display. However, on iOS, a secondary physical display is supported.
- display.source (ALLEGRO_DISPLAY *)
- The display which was connected.
Since: 5.1.1
ALLEGRO_EVENT_DISPLAY_DISCONNECTED
This event is sent when a physical display is disconnected from the device Allegro runs on. Currently, on most platforms, Allegro supports only a single physical display. However, on iOS, a secondary physical display is supported.
- display.source (ALLEGRO_DISPLAY *)
- The display which was disconnected.
ALLEGRO_EVENT_DROP
If a display is created with the ALLEGRO_DRAG_AND_DROP flag it will generate ALLEGRO_EVENT_DROP events when files or text are dropped over the display.
- drop.x (int)
- X coordinate that something is being dragged to
- drop.y (int)
- Y coordinate that something is being dragged to
- drop.text (char *)
the filename or text that was dropped - this will be NULL while the item is being dragged and only set at the final drop.
Note: if the text field is not NULL ownership transfers to the event receiver and it must eventually be freed with al_free.
- drop.is_file (bool)
- if text is not NULL whether the text is a filename or just plain text.
- drop.row (int)
- if there is multiple files or multiple rows of text this will number them, starting with 0.
- drop.is_complete (bool)
- indicates that this event will be the last one sent for the drag&drop action. If is_complete is set before receiving an event where text was not NULL it means the user aborted the drag&drop.
Since: 5.2.9
Unstable API: This is an experimental feature and currently only works for the X11 backend.
ALLEGRO_USER_EVENT
typedef struct ALLEGRO_USER_EVENT ALLEGRO_USER_EVENT;An event structure that can be emitted by user event sources. These are the public fields:
- ALLEGRO_EVENT_SOURCE *source;
- intptr_t data1;
- intptr_t data2;
- intptr_t data3;
- intptr_t data4;
Like all other event types this structure is a part of the ALLEGRO_EVENT union. To access the fields in an ALLEGRO_EVENT variable ev, you would use:
- ev.user.source
- ev.user.data1
- ev.user.data2
- ev.user.data3
- ev.user.data4
To create a new user event you would do this:
ALLEGRO_EVENT_SOURCE my_event_source;
ALLEGRO_EVENT my_event;
float some_var;
al_init_user_event_source(&my_event_source);
my_event.user.type = ALLEGRO_GET_EVENT_TYPE('M','I','N','E');
my_event.user.data1 = 1;
my_event.user.data2 = &some_var;
al_emit_user_event(&my_event_source, &my_event, NULL);Event type identifiers for user events are assigned by the user. Please see the documentation for ALLEGRO_GET_EVENT_TYPE for the rules you should follow when assigning identifiers.
See also: al_emit_user_event, ALLEGRO_GET_EVENT_TYPE, al_init_user_event_source
Examples:
ALLEGRO_EVENT_QUEUE
typedef struct ALLEGRO_EVENT_QUEUE ALLEGRO_EVENT_QUEUE;An event queue holds events that have been generated by event sources that are registered with the queue. Events are stored in the order they are generated. Access is in a strictly FIFO (first-in-first-out) order.
See also: al_create_event_queue, al_destroy_event_queue
Examples:
ALLEGRO_EVENT_SOURCE
typedef struct ALLEGRO_EVENT_SOURCE ALLEGRO_EVENT_SOURCE;An event source is any object which can generate events. For example, an ALLEGRO_DISPLAY can generate events, and you can get the ALLEGRO_EVENT_SOURCE pointer from an ALLEGRO_DISPLAY with al_get_display_event_source.
You may create your own “user” event sources that emit custom events.
See also: ALLEGRO_EVENT, al_init_user_event_source, al_emit_user_event
Examples:
ALLEGRO_EVENT_TYPE
typedef unsigned int ALLEGRO_EVENT_TYPE;An integer used to distinguish between different types of events.
See also: ALLEGRO_EVENT, ALLEGRO_GET_EVENT_TYPE, ALLEGRO_EVENT_TYPE_IS_USER
ALLEGRO_GET_EVENT_TYPE
#define ALLEGRO_GET_EVENT_TYPE(a, b, c, d) AL_ID(a, b, c, d)Make an event type identifier, which is a 32-bit integer. Usually, but not necessarily, this will be made from four 8-bit character codes, for example:
Examples:
* [ex_user_events.c](https://github.com/liballeg/allegro5/blob/eb4d06a79610465091d129614c61d20e82c8ab35/examples/ex_user_events.c#L10)
* [ex_native_filechooser.c](https://github.com/liballeg/allegro5/blob/eb4d06a79610465091d129614c61d20e82c8ab35/examples/ex_native_filechooser.c#L24)
#defin MY_EVENT_TYPE ALLEGRO_GET_EVENT_TYPE('M','I','N','E')IDs less than 1024 are reserved for Allegro or its addons. Don’t use anything lower than ALLEGRO_GET_EVENT_TYPE(0, 0, 4, 0).
You should try to make your IDs unique so they don’t clash with any 3rd party code you may be using. Be creative. Numbering from 1024 is not creative.
If you need multiple identifiers, you could define them like this:
#defin BASE_EVENT ALLEGRO_GET_EVENT_TYPE('M','I','N','E')
#defin BARK_EVENT (BASE_EVENT + 0)
#defin MEOW_EVENT (BASE_EVENT + 1)
#defin SQUAWK_EVENT (BASE_EVENT + 2)
/* Alternatively */
enum {
BARK_EVENT = ALLEGRO_GET_EVENT_TYPE('M','I','N','E'),
MEOW_EVENT,
SQUAWK_EVENT
};See also: ALLEGRO_EVENT, ALLEGRO_USER_EVENT, ALLEGRO_EVENT_TYPE_IS_USER
ALLEGRO_EVENT_TYPE_IS_USER
#define ALLEGRO_EVENT_TYPE_IS_USER(t) ((t) >= 512)A macro which evaluates to true if the event type is not a builtin event type, i.e. one of those described in ALLEGRO_EVENT_TYPE.
al_create_event_queue
ALLEGRO_EVENT_QUEUE *al_create_event_queue(void)Create a new, empty event queue, returning a pointer to the newly created object if successful. Returns NULL on error.
See also: al_register_event_source, al_destroy_event_queue, ALLEGRO_EVENT_QUEUE
Examples:
al_destroy_event_queue
void al_destroy_event_queue(ALLEGRO_EVENT_QUEUE *queue)Destroy the event queue specified. All event sources currently registered with the queue will be automatically unregistered before the queue is destroyed.
This function does nothing if queue is NULL. (since 5.2.9)
See also: al_create_event_queue, ALLEGRO_EVENT_QUEUE
Examples:
al_register_event_source
void al_register_event_source(ALLEGRO_EVENT_QUEUE *queue,
ALLEGRO_EVENT_SOURCE *source)Register the event source with the event queue specified. An event source may be registered with any number of event queues simultaneously, or none. Trying to register an event source with the same event queue more than once does nothing.
See also: al_unregister_event_source, ALLEGRO_EVENT_SOURCE
Examples:
al_unregister_event_source
void al_unregister_event_source(ALLEGRO_EVENT_QUEUE *queue,
ALLEGRO_EVENT_SOURCE *source)Unregister an event source with an event queue. If the event source is not actually registered with the event queue, nothing happens.
If the queue had any events in it which originated from the event source, they will no longer be in the queue after this call.
See also: al_register_event_source
Examples:
al_is_event_source_registered
bool al_is_event_source_registered(ALLEGRO_EVENT_QUEUE *queue,
ALLEGRO_EVENT_SOURCE *source)Return true if the event source is registered.
See also: al_register_event_source
Since: 5.2.0
al_pause_event_queue
void al_pause_event_queue(ALLEGRO_EVENT_QUEUE *queue, bool pause)Pause or resume accepting new events into the event queue (to resume, pass false for pause). Events already in the queue are unaffected.
While a queue is paused, any events which would be entered into the queue are simply ignored. This is an alternative to unregistering then re-registering all event sources from the event queue, if you just need to prevent events piling up in the queue for a while.
See also: al_is_event_queue_paused
Since: 5.1.0
al_is_event_queue_paused
bool al_is_event_queue_paused(const ALLEGRO_EVENT_QUEUE *queue)Return true if the event queue is paused.
See also: al_pause_event_queue
Since: 5.1.0
al_is_event_queue_empty
bool al_is_event_queue_empty(ALLEGRO_EVENT_QUEUE *queue)Return true if the event queue specified is currently empty.
See also: al_get_next_event, al_peek_next_event
Examples:
al_get_next_event
bool al_get_next_event(ALLEGRO_EVENT_QUEUE *queue, ALLEGRO_EVENT *ret_event)Take the next event out of the event queue specified, and copy the contents into ret_event, returning true. The original event will be removed from the queue. If the event queue is empty, return false and the contents of ret_event are unspecified.
See also: ALLEGRO_EVENT, al_peek_next_event, al_wait_for_event
Examples:
al_peek_next_event
bool al_peek_next_event(ALLEGRO_EVENT_QUEUE *queue, ALLEGRO_EVENT *ret_event)Copy the contents of the next event in the event queue specified into ret_event and return true. The original event packet will remain at the head of the queue. If the event queue is actually empty, this function returns false and the contents of ret_event are unspecified.
See also: ALLEGRO_EVENT, al_get_next_event, al_drop_next_event
al_drop_next_event
bool al_drop_next_event(ALLEGRO_EVENT_QUEUE *queue)Drop (remove) the next event from the queue. If the queue is empty, nothing happens. Returns true if an event was dropped.
See also: al_flush_event_queue, al_is_event_queue_empty
al_flush_event_queue
void al_flush_event_queue(ALLEGRO_EVENT_QUEUE *queue)Drops all events, if any, from the queue.
See also: al_drop_next_event, al_is_event_queue_empty
Examples:
al_wait_for_event
void al_wait_for_event(ALLEGRO_EVENT_QUEUE *queue, ALLEGRO_EVENT *ret_event)Wait until the event queue specified is non-empty. If ret_event is not NULL, the first event in the queue will be copied into ret_event and removed from the queue. If ret_event is NULL the first event is left at the head of the queue.
See also: ALLEGRO_EVENT, al_wait_for_event_timed, al_wait_for_event_until, al_get_next_event
Examples:
al_wait_for_event_timed
bool al_wait_for_event_timed(ALLEGRO_EVENT_QUEUE *queue,
ALLEGRO_EVENT *ret_event, float secs)Wait until the event queue specified is non-empty. If ret_event is not NULL, the first event in the queue will be copied into ret_event and removed from the queue. If ret_event is NULL the first event is left at the head of the queue.
secs determines approximately how many seconds to wait. If the call times out, false is returned. Otherwise, if an event ocurred, true is returned.
For compatibility with all platforms, secs must be 2,147,483.647 seconds or less.
See also: ALLEGRO_EVENT, al_wait_for_event, al_wait_for_event_until
Examples:
al_wait_for_event_until
bool al_wait_for_event_until(ALLEGRO_EVENT_QUEUE *queue,
ALLEGRO_EVENT *ret_event, ALLEGRO_TIMEOUT *timeout)Wait until the event queue specified is non-empty. If ret_event is not NULL, the first event in the queue will be copied into ret_event and removed from the queue. If ret_event is NULL the first event is left at the head of the queue.
timeout determines how long to wait. If the call times out, false is returned. Otherwise, if an event ocurred, true is returned.
For compatibility with all platforms, timeout must be 2,147,483.647 seconds or less.
See also: ALLEGRO_EVENT, ALLEGRO_TIMEOUT, al_init_timeout, al_wait_for_event, al_wait_for_event_timed
Examples:
al_init_user_event_source
void al_init_user_event_source(ALLEGRO_EVENT_SOURCE *src)Initialise an event source for emitting user events. The space for the event source must already have been allocated.
One possible way of creating custom event sources is to derive other structures with ALLEGRO_EVENT_SOURCE at the head, e.g.
typedef struct THING THING;
struct THING {
ALLEGRO_EVENT_SOURCE event_source;
int field1;
int field2;
/* etc. */
};
THING *create_thing(void)
{
THING *thing = malloc(sizeof(THING));
if (thing) {
al_init_user_event_source(&thing->event_source);
thing->field1 = 0;
thing->field2 = 0;
}
return thing;
}The advantage here is that the THING pointer will be the same as the ALLEGRO_EVENT_SOURCE pointer. Events emitted by the event source will have the event source pointer as the source field, from which you can get a pointer to a THING by a simple cast (after ensuring checking the event is of the correct type).
However, it is only one technique and you are not obliged to use it.
The user event source will never be destroyed automatically. You must destroy it manually with al_destroy_user_event_source.
See also: ALLEGRO_EVENT_SOURCE, al_destroy_user_event_source, al_emit_user_event, ALLEGRO_USER_EVENT
Examples:
al_destroy_user_event_source
void al_destroy_user_event_source(ALLEGRO_EVENT_SOURCE *src)Destroy an event source initialised with al_init_user_event_source.
This does not free the memory, as that was user allocated to begin with.
See also: ALLEGRO_EVENT_SOURCE
Examples:
al_emit_user_event
bool al_emit_user_event(ALLEGRO_EVENT_SOURCE *src,
ALLEGRO_EVENT *event, void (*dtor)(ALLEGRO_USER_EVENT *))Emit an event from a user event source. The event source must have been initialised with al_init_user_event_source. Returns false if the event source isn’t registered with any queues, hence the event wouldn’t have been delivered into any queues.
Events are copied in and out of event queues, so after this function returns the memory pointed to by event may be freed or reused. Some fields of the event being passed in may be modified by the function.
Reference counting will be performed if dtor is not NULL. Whenever a copy of the event is made, the reference count increases. You need to call al_unref_user_event to decrease the reference count once you are done with a user event that you have received from al_get_next_event, al_peek_next_event, al_wait_for_event, etc.
Once the reference count drops to zero dtor will be called with a copy of the event as an argument. It should free the resources associated with the event, but not the event itself (since it is just a copy).
If dtor is NULL then reference counting will not be performed. It is safe, but unnecessary, to call al_unref_user_event on non-reference counted user events.
You can use al_emit_user_event to emit both user and non-user events from your user event source. Note that emitting input events will not update the corresponding input device states. For example, you may emit an event of type ALLEGRO_EVENT_KEY_DOWN, but it will not update the ALLEGRO_KEYBOARD_STATE returned by al_get_keyboard_state.
See also: ALLEGRO_USER_EVENT, al_unref_user_event
Examples:
al_unref_user_event
void al_unref_user_event(ALLEGRO_USER_EVENT *event)Decrease the reference count of a user-defined event. This must be called on any user event that you get from al_get_next_event, al_peek_next_event, al_wait_for_event, etc. which is reference counted. This function does nothing if the event is not reference counted.
See also: al_emit_user_event, ALLEGRO_USER_EVENT
Examples:
al_get_event_source_data
intptr_t al_get_event_source_data(const ALLEGRO_EVENT_SOURCE *source)Returns the abstract user data associated with the event source. If no data was previously set, returns NULL.
See also: al_set_event_source_data
al_set_event_source_data
void al_set_event_source_data(ALLEGRO_EVENT_SOURCE *source, intptr_t data)Assign the abstract user data to the event source. Allegro does not use the data internally for anything; it is simply meant as a convenient way to associate your own data or objects with events.
See also: al_get_event_source_data