- Display creation
- Display operations
- Display size and position
- Display settings
- Drawing halts
These functions are declared in the main Allegro header file:
All drawing operations end up being visible on a display which is the same as a window in windowed environments. Thus, before anything is displayed, a display needs to be created.
Before creating a display with al_create_display, flags and options can be set with al_set_new_display_flags and al_set_new_display_option. For example, you can enable the use of shaders or choose between the OpenGL and Direct3D backends (on platforms that support both) with al_set_new_display_flags. Display options are rather optional settings that do not affect Allegro itself, e.g. they allow you to specify whether you want a depth buffer or enable multisampling.
The actual properties of a display that has been successfully created can be queried via al_get_display_option, al_get_display_flags, al_get_display_width etc. Note that you can query some additional read-only properties such as the maximum allowed bitmap (i.e. texture) size via al_get_display_option.
Each display has a backbuffer associated to it which is the default target for any drawing operations. In order to make visible what has been drawn previously, you have to to call al_flip_display. Note that it is generally advisable to redraw the whole screen (or clear it in advance) to avoid artefacts of uninitialised memory becoming visible with some drivers.
You don't have to use Allegro's drawing routines, however: since creating a display implies the creation of an OpenGL context or Direct3D device respectively, you can use these APIs directly if you prefer to do so. Allegro provides integration for both (see the OpenGL / Direct3D sections), so you can retrieve the underlying textures of ALLEGRO_BITMAPs, for example.
typedef struct ALLEGRO_DISPLAY ALLEGRO_DISPLAY;
An opaque type representing an open display or window.
ALLEGRO_DISPLAY *al_create_display(int w, int h)
Create a display, or window, with the specified dimensions. The parameters of the display are determined by the last calls to al_set_new_display_*. Default parameters are used if none are set explicitly. Creating a new display will automatically make it the active one, with the backbuffer selected for drawing.
Returns NULL on error.
Each display that uses OpenGL as a backend has a distinct OpenGL rendering context associated with it. See al_set_target_bitmap for the discussion about rendering contexts.
void al_destroy_display(ALLEGRO_DISPLAY *display)
Destroy a display.
If the target bitmap of the calling thread is tied to the display, then it implies a call to "al_set_target_bitmap(NULL);" before the display is destroyed.
That special case notwithstanding, you should make sure no threads are currently targeting a bitmap which is tied to the display before you destroy it.
See also: al_set_target_bitmap
Get the display flags to be used when creating new displays on the calling thread.
void al_set_new_display_flags(int flags)
Sets various flags to be used when creating new displays on the calling thread. flags is a bitfield containing any reasonable combination of the following:
Prefer a windowed mode.
Under multi-head X (not XRandR/TwinView), the use of more than one adapter is impossible due to bugs in X and GLX. al_create_display will fail if more than one adapter is attempted to be used.
Make the window span the entire screen. Unlike ALLEGRO_FULLSCREEN this will never attempt to modify the screen resolution. Instead the pixel dimensions of the created display will be the same as the desktop.
The passed width and height are only used if the window is switched out of fullscreen mode later but will be ignored initially.
Under Windows and X11 a fullscreen display created with this flag will behave differently from one created with the ALLEGRO_FULLSCREEN flag - even if the ALLEGRO_FULLSCREEN display is passed the desktop dimensions. The exact difference is platform dependent, but some things which may be different is how alt-tab works, how fast you can toggle between fullscreen/windowed mode or how additional monitors behave while your display is in fullscreen mode.
Additionally under X, the use of more than one adapter in multi-head mode or with true Xinerama enabled is impossible due to bugs in X/GLX, creation will fail if more than one adapter is attempted to be used.
Prefer a fullscreen mode.
Under X the use of more than one FULLSCREEN display when using multi-head X, or true Xinerama is not possible due to bugs in X and GLX, display creation will fail if more than one adapter is attempted to be used.
Note: Prefer using ALLEGRO_FULLSCREEN_WINDOW as it typically provides a better user experience as the monitor doesn't change resolution and switching away from your game via Alt-Tab works smoothly. ALLEGRO_FULLSCREEN is typically less well supported compared to ALLEGRO_FULLSCREEN_WINDOW.
- The display is resizable (only applicable if combined with ALLEGRO_WINDOWED).
- The display window will be maximized (only applicable if combined with ALLEGRO_RESIZABLE). Since: 5.1.12
- Require the driver to provide an initialized OpenGL context after returning successfully.
- Require the driver to provide an initialized OpenGL context compatible with OpenGL version 3.0.
- If this flag is set, the OpenGL context created with ALLEGRO_OPENGL_3_0 will be forward compatible only, meaning that all of the OpenGL API declared deprecated in OpenGL 3.0 will not be supported. Currently, a display created with this flag will not be compatible with Allegro drawing routines; the display option ALLEGRO_COMPATIBLE_DISPLAY will be set to false.
- Used together with ALLEGRO_OPENGL, requests that the OpenGL context uses the OpenGL ES profile. A specific version can be requested with al_set_new_display_option. Note: Currently this is only supported by the X11/GLX driver. Since: 5.1.13
- Require the driver to do rendering with Direct3D and provide a Direct3D device.
- Require a programmable graphics pipeline. This flag is required to use ALLEGRO_SHADER objects. Since: 5.1.6
- Try to create a window without a frame (i.e. no border or titlebar). This usually does nothing for fullscreen modes, and even in windowed modes it depends on the underlying platform whether it is supported or not. Since: 5.0.7, 5.1.2
- Original name for ALLEGRO_FRAMELESS. This works with older versions of Allegro.
- Let the display generate expose events.
- Create a GTK toplevel window for the display, on X. This flag is conditionally defined by the native dialog addon. You must call al_init_native_dialog_addon for it to succeed. ALLEGRO_GTK_TOPLEVEL is incompatible with ALLEGRO_FULLSCREEN. Since: 5.1.5
0 can be used for default values.
int al_get_new_display_option(int option, int *importance)
Retrieve an extra display setting which was previously set with al_set_new_display_option.
void al_set_new_display_option(int option, int value, int importance)
Set an extra display option, to be used when creating new displays on the calling thread. Display options differ from display flags, and specify some details of the context to be created within the window itself. These mainly have no effect on Allegro itself, but you may want to specify them, for example if you want to use multisampling.
The 'importance' parameter can be either:
- ALLEGRO_REQUIRE - The display will not be created if the setting can not be met.
- ALLEGRO_SUGGEST - If the setting is not available, the display will be created anyway with a setting as close as possible to the requested one. You can query the actual value used in that case by calling al_get_display_option after the display has been created.
- ALLEGRO_DONTCARE - If you added a display option with one of the above two settings before, it will be removed again. Else this does nothing.
The supported options are:
- This can be used to ask for a specific bit depth. For example to force a 16-bit framebuffer set this to 16.
- ALLEGRO_RED_SIZE, ALLEGRO_GREEN_SIZE, ALLEGRO_BLUE_SIZE, ALLEGRO_ALPHA_SIZE
- Individual color component size in bits.
- ALLEGRO_RED_SHIFT, ALLEGRO_GREEN_SHIFT, ALLEGRO_BLUE_SHIFT, ALLEGRO_ALPHA_SHIFT
- Together with the previous settings these can be used to specify the exact pixel layout the display should use. Normally there is no reason to use these.
- ALLEGRO_ACC_RED_SIZE, ALLEGRO_ACC_GREEN_SIZE, ALLEGRO_ACC_BLUE_SIZE, ALLEGRO_ACC_ALPHA_SIZE
- This can be used to define the required accumulation buffer size.
- Whether the display is a stereo display.
- Number of auxiliary buffers the display should have.
- How many depth buffer (z-buffer) bits to use.
- How many bits to use for the stencil buffer.
- Whether to use multisampling (1) or not (0).
- If the above is 1, the number of samples to use per pixel. Else 0.
- 0 if hardware acceleration is not used with this display.
- Whether to use floating point color components.
- Whether to use a floating point depth buffer.
- Whether the display uses a single buffer (1) or another update method (0).
- If the above is 0, this is set to 1 to indicate the display is using a copying method to make the next buffer in the flip chain available, or to 2 to indicate a flipping or other method.
- Indicates if Allegro's graphics functions can use this display. If you request a display not useable by Allegro, you can still use for example OpenGL to draw graphics.
- Set to 1 if the display is capable of updating just a region, and 0 if calling al_update_display_region is equivalent to al_flip_display.
- Set to 1 to tell the driver to wait for vsync in al_flip_display, or to 2 to force vsync off. The default of 0 means that Allegro does not try to modify the vsync behavior so it may be on or off. Note that even in the case of 1 or 2 it is possible to override the vsync behavior in the graphics driver so you should not rely on it.
- When queried this returns the maximum size (width as well as height) a bitmap can have for this display. Calls to al_create_bitmap or al_load_bitmap for bitmaps larger than this size will fail. It does not apply to memory bitmaps which always can have arbitrary size (but are slow for drawing).
- Set to 1 if textures used for bitmaps on this display can have a size which is not a power of two. This is mostly useful if you use Allegro to load textures as otherwise only power-of-two textures will be used internally as bitmap storage.
- Set to 1 if you can use al_set_target_bitmap on bitmaps of this display to draw into them. If this is not the case software emulation will be used when drawing into display bitmaps (which can be very slow).
- This is set to 1 if the al_set_separate_blender function is supported. Otherwise the alpha parameters will be ignored.
This is on by default. It causes any existing memory bitmaps with the ALLEGRO_CONVERT_BITMAP flag to be converted to a display bitmap of the newly created display with the option set.
This is a bit-combination of the orientations supported by the application. The orientations are the same as for al_get_display_orientation with the additional possibilities:
PORTRAIT means only the two portrait orientations are supported, LANDSCAPE means only the two landscape orientations and ALL allows all four orientations. When the orientation changes between a portrait and a landscape orientation the display needs to be resized. This is done by sending an ALLEGRO_EVENT_DISPLAY_RESIZE message which should be handled by calling al_acknowledge_resize.
Request a specific OpenGL major version.
Request a specific OpenGL minor version.
This undoes any previous call to al_set_new_display_option on the calling thread.
void al_get_new_window_position(int *x, int *y)
Get the position where new non-fullscreen displays created by the calling thread will be placed.
See also: al_set_new_window_position
void al_set_new_window_position(int x, int y)
Sets where the top left pixel of the client area of newly created windows (non-fullscreen) will be on screen, for displays created by the calling thread. Negative values are allowed on some multihead systems.
To reset to the default behaviour, pass (INT_MAX, INT_MAX).
See also: al_get_new_window_position
Get the requested refresh rate to be used when creating new displays on the calling thread.
See also: al_set_new_display_refresh_rate
void al_set_new_display_refresh_rate(int refresh_rate)
Sets the refresh rate to use when creating new displays on the calling thread. If the refresh rate is not available, al_create_display will fail. A list of modes with refresh rates can be found with al_get_num_display_modes and al_get_display_mode.
The default setting is zero (don't care).
See also: al_get_new_display_refresh_rate
ALLEGRO_EVENT_SOURCE *al_get_display_event_source(ALLEGRO_DISPLAY *display)
Retrieve the associated event source. See the documentation on events for a list of the events displays will generate.
ALLEGRO_BITMAP *al_get_backbuffer(ALLEGRO_DISPLAY *display)
Return a special bitmap representing the back-buffer of the display.
Care should be taken when using the backbuffer bitmap (and its sub-bitmaps) as the source bitmap (e.g as the bitmap argument to al_draw_bitmap). Only untransformed operations are hardware accelerated. These consist of al_draw_bitmap and al_draw_bitmap_region when the current transformation is the identity. If the tranformation is not the identity, or some other drawing operation is used, the call will be routed through the memory bitmap routines, which are slow. If you need those operations to be accelerated, then first copy a region of the backbuffer into a temporary bitmap (via the al_draw_bitmap and al_draw_bitmap_region), and then use that temporary bitmap as the source bitmap.
Copies or updates the front and back buffers so that what has been drawn previously on the currently selected display becomes visible on screen. Pointers to the special back buffer bitmap remain valid and retain their semantics as the back buffer, although the contents may have changed.
Several display options change how this function behaves:
With ALLEGRO_SINGLE_BUFFER, no flipping is done. You still have to call this function to display graphics, depending on how the used graphics system works.
The ALLEGRO_SWAP_METHOD option may have additional information about what kind of operation is used internally to flip the front and back buffers.
If ALLEGRO_VSYNC is 1, this function will force waiting for vsync. If ALLEGRO_VSYNC is 2, this function will not wait for vsync. With many drivers the vsync behavior is controlled by the user and not the application, and ALLEGRO_VSYNC will not be set; in this case al_flip_display will wait for vsync depending on the settings set in the system's graphics preferences.
void al_update_display_region(int x, int y, int width, int height)
Does the same as al_flip_display, but tries to update only the specified region. With many drivers this is not possible, but for some it can improve performance. If this is not supported, this function falls back to the behavior of al_flip_display. You can query the support for this function using
Wait for the beginning of a vertical retrace. Some driver/card/monitor combinations may not be capable of this.
Note how al_flip_display usually already waits for the vertical retrace, so unless you are doing something special, there is no reason to call this function.
Returns false if not possible, true if successful.
See also: al_flip_display
Display size and position
int al_get_display_width(ALLEGRO_DISPLAY *display)
Gets the width of the display. This is like SCREEN_W in Allegro 4.x.
See also: al_get_display_height
int al_get_display_height(ALLEGRO_DISPLAY *display)
Gets the height of the display. This is like SCREEN_H in Allegro 4.x.
See also: al_get_display_width
bool al_resize_display(ALLEGRO_DISPLAY *display, int width, int height)
Resize the display. Returns true on success, or false on error. This works on both fullscreen and windowed displays, regardless of the ALLEGRO_RESIZABLE flag.
Adjusts the clipping rectangle to the full size of the backbuffer.
See also: al_acknowledge_resize
bool al_acknowledge_resize(ALLEGRO_DISPLAY *display)
When the user receives a resize event from a resizable display, if they wish the display to be resized they must call this function to let the graphics driver know that it can now resize the display. Returns true on success.
Adjusts the clipping rectangle to the full size of the backbuffer. This also resets the backbuffers projection transform to default orthographic transform (see al_use_projection_transform).
Note that a resize event may be outdated by the time you acknowledge it; there could be further resize events generated in the meantime.
void al_get_window_position(ALLEGRO_DISPLAY *display, int *x, int *y)
Gets the position of a non-fullscreen display.
See also: al_set_window_position
void al_set_window_position(ALLEGRO_DISPLAY *display, int x, int y)
Sets the position on screen of a non-fullscreen display.
See also: al_get_window_position
bool al_get_window_constraints(ALLEGRO_DISPLAY *display, int *min_w, int *min_h, int *max_w, int *max_h)
Gets the constraints for a non-fullscreen resizable display.
See also: al_set_window_constraints
bool al_set_window_constraints(ALLEGRO_DISPLAY *display, int min_w, int min_h, int max_w, int max_h)
Constrains a non-fullscreen resizable display. The constraints are a hint only, and are not necessarily respected by the window environment. A value of 0 for any of the parameters indicates no constraint for that parameter.
See also: al_get_window_constraints
int al_get_display_flags(ALLEGRO_DISPLAY *display)
Gets the flags of the display.
In addition to the flags set for the display at creation time with al_set_new_display_flags it can also have the ALLEGRO_MINIMIZED flag set, indicating that the window is currently minimized. This flag is very platform-dependent as even a minimized application may still render a preview version so normally you should not care whether it is minimized or not.
bool al_set_display_flag(ALLEGRO_DISPLAY *display, int flag, bool onoff)
Enable or disable one of the display flags. The flags are the same as for al_set_new_display_flags. The only flags that can be changed after creation are:
Returns true if the driver supports toggling the specified flag else false. You can use al_get_display_flags to query whether the given display property actually changed.
Since: 5.0.7, 5.1.2
int al_get_display_option(ALLEGRO_DISPLAY *display, int option)
Return an extra display setting of the display.
See also: al_set_new_display_option
void al_set_display_option(ALLEGRO_DISPLAY *display, int option, int value)
Change an option that was previously set for a display. After displays are created, they take on the options set with al_set_new_display_option. Calling al_set_new_display_option subsequently only changes options for newly created displays, and doesn't touch the options of already created displays. al_set_display_option allows changing some of these values. Not all display options can be changed or changing them will have no effect. Changing options other than those listed below is undefined.
- ALLEGRO_SUPPORTED_ORIENTATIONS - This can be changed to allow new or restrict previously enabled orientations of the screen/device. See al_set_new_display_option for more information on this option.
See also: al_set_new_display_option
int al_get_display_format(ALLEGRO_DISPLAY *display)
Gets the pixel format of the display.
See also: ALLEGRO_PIXEL_FORMAT
int al_get_display_orientation(ALLEGRO_DISPLAY* display)
Return the display orientation, which can be one of the following:
int al_get_display_refresh_rate(ALLEGRO_DISPLAY *display)
Gets the refresh rate of the display.
See also: al_set_new_display_refresh_rate
void al_set_window_title(ALLEGRO_DISPLAY *display, const char *title)
Set the title on a display.
void al_set_new_window_title(const char *title)
Set the title that will be used when a new display is created. Allegro uses a static buffer of ALLEGRO_NEW_WINDOW_TITLE_MAX_SIZE to store this, so the length of the titme you set must be less than this.
#define ALLEGRO_NEW_WINDOW_TITLE_MAX_SIZE 255
This is the maximum size of the title that can be set with al_set_new_window_title.
See also: al_set_new_window_title
const char *al_get_new_window_title(void)
Returns the title that will be used when a new display is created. This returns the value that al_set_window_title was called with. If that function wasn't called yet, the value of al_get_app_name is returned as a default. The current implementation returns a pointer to a static buffer of which you should make a copy if you want to modify it.
void al_set_display_icon(ALLEGRO_DISPLAY *display, ALLEGRO_BITMAP *icon)
Changes the icon associated with the display (window). Same as al_set_display_icons with one icon.
void al_set_display_icons(ALLEGRO_DISPLAY *display, int num_icons, ALLEGRO_BITMAP *icons)
Changes the icons associated with the display (window). Multiple icons can be provided for use in different contexts, e.g. window frame, taskbar, alt-tab popup. The number of icons must be at least one.
Note: If the underlying OS requires an icon of a size not provided then one of the bitmaps will be scaled up or down to the required size. The choice of bitmap is implementation dependent.
Since: 5.0.9, 5.1.5
void al_acknowledge_drawing_halt(ALLEGRO_DISPLAY *display)
Call this in response to the ALLEGRO_EVENT_DISPLAY_HALT_DRAWING event. This is currently necessary for Android and iOS as you are not allowed to draw to your display while it is not being shown. If you do not call this function to let the operating system know that you have stopped drawing or if you call it to late the application likely will be considered misbehaving and get terminated.
See also: ALLEGRO_EVENT_DISPLAY_HALT_DRAWING
void al_acknowledge_drawing_resume(ALLEGRO_DISPLAY *display)
Call this in response to the ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING event.
See also: ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING
bool al_inhibit_screensaver(bool inhibit)
This function allows the user to stop the system screensaver from starting up if true is passed, or resets the system back to the default state (the state at program start) if false is passed. It returns true if the state was set successfully, otherwise false.
With the clipboard API of Allegro, text can be copied from and to the clipboard. Currentlly, only UTF8 encoded text is supported. It currently works on Linux, Windows, OSX, Android and IOS.
char *al_get_clipboard_text(ALLEGRO_DISPLAY *display)
This function returns a pointer to a string, allocated with al_malloc with the text contents of the clipboard if available. If no text is available on the clipboard then this function returns NULL. You must call al_free on the returned pointer when you don't need it anymore.
Beware that text on the clipboard on Windows may be in Windows format, that is, it may have carriage return newline combinations for the line endings instead of regular newlines for the line endings on Linux or OSX.
bool al_set_clipboard_text(ALLEGRO_DISPLAY *display, const char *text)
This function pastes the text given as an argument to the clipboard.
bool al_clipboard_has_text(ALLEGRO_DISPLAY *display)
This function returns true if and only if the clipboard has text available.