Graphics routines

Colors
Locking and pixel formats
Bitmap creation
Bitmap properties
Drawing operations
Blending modes
Clipping
- al_get_clipping_rectangle
- al_set_clipping_rectangle
Graphics utility functions
- al_convert_mask_to_alpha
Deferred drawing
- al_hold_bitmap_drawing
- al_is_bitmap_drawing_held
Image I/O

These functions are declared in the main Allegro header file:

#include <allegro5/allegro.h>

Colors

ALLEGRO_COLOR

typedef struct ALLEGRO_COLOR ALLEGRO_COLOR;

An ALLEGRO_COLOR structure describes a color in a device independant way. Use al_map_rgb et al. and al_unmap_rgb et al. to translate from and to various color representations.

al_map_rgb

ALLEGRO_COLOR al_map_rgb(
   unsigned char r, unsigned char g, unsigned char b)

Convert r, g, b (ranging from 0-255) into an ALLEGRO_COLOR, using 255 for alpha.

al_map_rgb_f

ALLEGRO_COLOR al_map_rgb_f(float r, float g, float b)

Convert r, g, b, (ranging from 0.0f-1.0f) into an ALLEGRO_COLOR, using 1.0f for alpha.

al_map_rgba

ALLEGRO_COLOR al_map_rgba(
   unsigned char r, unsigned char g, unsigned char b, unsigned char a)

Convert r, g, b, a (ranging from 0-255) into an ALLEGRO_COLOR.

al_map_rgba_f

ALLEGRO_COLOR al_map_rgba_f(float r, float g, float b, float a)

Convert r, g, b, a (ranging from 0.0f-1.0f) into an ALLEGRO_COLOR.

al_unmap_rgb

void al_unmap_rgb(ALLEGRO_COLOR color,
   unsigned char *r, unsigned char *g, unsigned char *b)

Retrieves components of an ALLEGRO_COLOR, ignoring alpha Components will range from 0-255.

al_unmap_rgb_f

void al_unmap_rgb_f(ALLEGRO_COLOR color, float *r, float *g, float *b)

Retrieves components of an ALLEGRO_COLOR, ignoring alpha. Components will range from 0.0f-1.0f.

al_unmap_rgba

void al_unmap_rgba(ALLEGRO_COLOR color,
   unsigned char *r, unsigned char *g, unsigned char *b, unsigned char *a)

Retrieves components of an ALLEGRO_COLOR. Components will range from 0-255.

al_unmap_rgba_f

void al_unmap_rgba_f(ALLEGRO_COLOR color,
   float *r, float *g, float *b, float *a)

Retrieves components of an ALLEGRO_COLOR. Components will range from 0.0f-1.0f.

Locking and pixel formats

ALLEGRO_LOCKED_REGION

typedef struct ALLEGRO_LOCKED_REGION ALLEGRO_LOCKED_REGION;

Users who wish to manually edit or read from a bitmap are required to lock it first. The ALLEGRO_LOCKED_REGION structure represents the locked region of the bitmap. This call will work with any bitmap, including memory bitmaps.

typedef struct ALLEGRO_LOCKED_REGION {
    void *data;
    int format;
    int pitch;
    int pixel_size;
} ALLEGRO_LOCKED_REGION;

data points to the leftmost pixel of the first row (row 0) of the locked region.
format indicates the pixel format of the data.
pitch gives the size in bytes of a single row (also known as the stride). The pitch may be greater than width * pixel_size due to padding; this is not uncommon. It is also not uncommon for the pitch to be negative (the bitmap may be upside down).
pixel_size is the number of bytes used to represent a single pixel.

ALLEGRO_PIXEL_FORMAT

typedef enum ALLEGRO_PIXEL_FORMAT

Pixel formats. Each pixel format specifies the exact size and bit layout of a pixel in memory. Components are specified from high bits to low bits, so for example a fully opaque red pixel in ARGB_8888 format is 0xFFFF0000.

Note:
The pixel format is independent of endianness. That is, in the above example you can always get the red component with
(pixel & 0x00ff0000) >> 16
But you can not rely on this code:
*(pixel + 2)

It will return the red component on little endian systems, but the green component on big endian systems.

Also note that Allegro's naming is different from OpenGL naming here, where a format of GL_RGBA8 merely defines the component order and the exact layout including endianness treatment is specified separately. Usually GL_RGBA8 will correspond to ALLEGRO_PIXEL_ABGR_8888 though on little endian systems, so care must be taken (note the reversal of RGBA <-> ABGR).

The only exception to this ALLEGRO_PIXEL_FORMAT_ABGR_8888_LE which will always have the components as 4 bytes corresponding to red, green, blue and alpha, in this order, independent of the endianness.

ALLEGRO_PIXEL_FORMAT_ANY - Let the driver choose a format. This is the default format at program start.
ALLEGRO_PIXEL_FORMAT_ANY_NO_ALPHA - Let the driver choose a format without alpha.
ALLEGRO_PIXEL_FORMAT_ANY_WITH_ALPHA - Let the driver choose a format with alpha.
ALLEGRO_PIXEL_FORMAT_ANY_15_NO_ALPHA - Let the driver choose a 15 bit format without alpha.
ALLEGRO_PIXEL_FORMAT_ANY_15_WITH_ALPHA - Let the driver choose a 15 bit format with alpha.
ALLEGRO_PIXEL_FORMAT_ANY_16_NO_ALPHA - Let the driver choose a 16 bit format without alpha.
ALLEGRO_PIXEL_FORMAT_ANY_16_WITH_ALPHA - Let the driver choose a 16 bit format with alpha.
ALLEGRO_PIXEL_FORMAT_ANY_24_NO_ALPHA - Let the driver choose a 24 bit format without alpha.
ALLEGRO_PIXEL_FORMAT_ANY_24_WITH_ALPHA - Let the driver choose a 24 bit format with alpha.
ALLEGRO_PIXEL_FORMAT_ANY_32_NO_ALPHA - Let the driver choose a 32 bit format without alpha.
ALLEGRO_PIXEL_FORMAT_ANY_32_WITH_ALPHA - Let the driver choose a 32 bit format with alpha.
ALLEGRO_PIXEL_FORMAT_ARGB_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_RGBA_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_ARGB_4444 - 16 bit
ALLEGRO_PIXEL_FORMAT_RGB_888 - 24 bit
ALLEGRO_PIXEL_FORMAT_RGB_565 - 16 bit
ALLEGRO_PIXEL_FORMAT_RGB_555 - 15 bit
ALLEGRO_PIXEL_FORMAT_RGBA_5551 - 16 bit
ALLEGRO_PIXEL_FORMAT_ARGB_1555 - 16 bit
ALLEGRO_PIXEL_FORMAT_ABGR_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_XBGR_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_BGR_888 - 24 bit
ALLEGRO_PIXEL_FORMAT_BGR_565 - 16 bit
ALLEGRO_PIXEL_FORMAT_BGR_555 - 15 bit
ALLEGRO_PIXEL_FORMAT_RGBX_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_XRGB_8888 - 32 bit
ALLEGRO_PIXEL_FORMAT_ABGR_F32 - 128 bit
ALLEGRO_PIXEL_FORMAT_ABGR_8888_LE - Like the version without _LE, but the component order is guaranteed to be red, green, blue, alpha. This only makes a difference on big endian systems, on little endian it is just an alias.

al_get_pixel_size

int al_get_pixel_size(int format)

Return the number of bytes that a pixel of the given format occupies.

al_get_pixel_format_bits

int al_get_pixel_format_bits(int format)

Return the number of bits that a pixel of the given format occupies.

al_lock_bitmap

ALLEGRO_LOCKED_REGION *al_lock_bitmap(ALLEGRO_BITMAP *bitmap,
   int format, int flags)

Lock an entire bitmap for reading or writing. If the bitmap is a display bitmap it will be updated from system memory after the bitmap is unlocked (unless locked read only). Returns NULL if the bitmap cannot be locked, e.g. the bitmap was locked previously and not unlocked.

Flags are:

ALLEGRO_LOCK_READONLY - The locked region will not be written to. This can be faster if the bitmap is a video texture, as it can be discarded after the lock instead of uploaded back to the card.
ALLEGRO_LOCK_WRITEONLY - The locked region will not be read from. This can be faster if the bitmap is a video texture, as no data need to be read from the video card. You are required to fill in all pixels before unlocking the bitmap again, so be careful when using this flag.
ALLEGRO_LOCK_READWRITE - The locked region can be written to and read from.

'format' indicates the pixel format that the returned buffer will be in. To lock in the same format as the bitmap stores it's data internally, call with al_get_bitmap_format(bitmap) as the format or use ALLEGRO_PIXEL_FORMAT_ANY. Locking in the native format will usually be faster.

Note: While a bitmap is locked, you can not use any drawing operations on it (with the sole exception of al_put_pixel and al_put_blended_pixel).

al_lock_bitmap_region

ALLEGRO_LOCKED_REGION *al_lock_bitmap_region(ALLEGRO_BITMAP *bitmap,
   int x, int y, int width, int height, int format, int flags)

Like al_lock_bitmap, but only locks a specific area of the bitmap. If the bitmap is a display bitmap, only that area of the texture will be updated when it is unlocked. Locking only the region you indend to modify will be faster than locking the whole bitmap.

al_unlock_bitmap

void al_unlock_bitmap(ALLEGRO_BITMAP *bitmap)

Unlock a previously locked bitmap or bitmap region. If the bitmap is a display bitmap, the texture will be updated to match the system memory copy (unless it was locked read only).

Bitmap creation

ALLEGRO_BITMAP

typedef struct ALLEGRO_BITMAP ALLEGRO_BITMAP;

Abstract type representing a bitmap (2D image).

al_create_bitmap

ALLEGRO_BITMAP *al_create_bitmap(int w, int h)

Creates a new bitmap using the bitmap format and flags for the current thread. Blitting between bitmaps of differing formats, or blitting between memory bitmaps and display bitmaps may be slow.

Unless you set the ALLEGRO_MEMORY_BITMAP flag, the bitmap is created for the current display. Blitting to another display may be slow.

If a display bitmap is created, there may be limitations on the allowed dimensions. For example a DirectX or OpenGL backend usually has a maximum allowed texture size - so if bitmap creation fails for very large dimensions, you may want to re-try with a smaller bitmap.

al_create_sub_bitmap

ALLEGRO_BITMAP *al_create_sub_bitmap(ALLEGRO_BITMAP *parent,
   int x, int y, int w, int h)

Creates a sub-bitmap of the parent, at the specified coordinates and of the specified size. A sub-bitmap is a bitmap that shares drawing memory with a pre-existing (parent) bitmap, but possibly with a different size and clipping settings.

The sub-bitmap may originate off or extend past the parent bitmap.

See the discussion in al_get_backbuffer about using sub-bitmaps of the backbuffer.

The parent bitmap's clipping rectangles are ignored.

If a sub-bitmap was not or cannot be created then NULL is returned.

Note that destroying parents of sub-bitmaps will not destroy the sub-bitmaps; instead the sub-bitmaps become invalid and should no longer be used.

al_clone_bitmap

ALLEGRO_BITMAP *al_clone_bitmap(ALLEGRO_BITMAP *bitmap)

Create a new bitmap with al_create_bitmap, and copy the pixel data from the old bitmap across.

al_destroy_bitmap

void al_destroy_bitmap(ALLEGRO_BITMAP *bitmap)

Destroys the given bitmap, freeing all resources used by it. Does nothing if given the null pointer.

al_get_new_bitmap_flags

int al_get_new_bitmap_flags(void)

Returns the flags used for newly created bitmaps.

al_get_new_bitmap_format

int al_get_new_bitmap_format(void)

Returns the format used for newly created bitmaps.

al_set_new_bitmap_flags

void al_set_new_bitmap_flags(int flags)

Sets the flags to use for newly created bitmaps. Valid flags are:

ALLEGRO_VIDEO_BITMAP

Creates a bitmap that resides in the video card memory. These types of bitmaps receive the greatest benefit from hardware acceleration. al_set_new_bitmap_flags will implicitly set this flag unless ALLEGRO_MEMORY_BITMAP is present.

ALLEGRO_MEMORY_BITMAP

Create a bitmap residing in system memory. Operations on, and with, memory bitmaps will not be hardware accelerated. However, direct pixel access can be relatively quick compared to video bitmaps, which depend on the display driver in use.

Note: Allegro's software rendering routines are currently very unoptimised.

ALLEGRO_KEEP_BITMAP_FORMAT

Only used when loading bitmaps from disk files, forces the resulting ALLEGRO_BITMAP to use the same format as the file.

This is not yet honoured.

ALLEGRO_FORCE_LOCKING

When drawing to a bitmap with this flag set, always use pixel locking and draw to it using Allegro's software drawing primitives. This should never be used if you plan to draw to the bitmap using Allegro's graphics primitives as it would cause severe performance penalties. However if you know that the bitmap will only ever be accessed by locking it, no unneeded FBOs will be created for it in the OpenGL drivers.

ALLEGRO_NO_PRESERVE_TEXTURE

Normally, every effort is taken to preserve the contents of bitmaps, since Direct3D may forget them. This can take extra processing time. If you know it doesn't matter if a bitmap keeps its pixel data, for example its a temporary buffer, use this flag to tell Allegro not to attempt to preserve its contents. This can increase performance of your game or application, but there is a catch. See ALLEGRO_EVENT_DISPLAY_LOST for further information.

ALLEGRO_ALPHA_TEST

This is a driver hint only. It tells the graphics driver to do alpha testing instead of alpha blending on bitmaps created with this flag. Alpha testing is usually faster and preferred if your bitmaps have only one level of alpha (0). This flag is currently not widely implemented (i.e., only for memory bitmaps).

ALLEGRO_MIN_LINEAR

When drawing a scaled down version of the bitmap, use linear filtering. This usually looks better. You can also combine it with the MIPMAP flag for even better quality.

ALLEGRO_MAG_LINEAR

When drawing a magnified version of a bitmap, use linear filtering. This will cause the picture to get blurry instead of creating a big rectangle for each pixel. It depends on how you want things to look like whether you want to use this or not.

ALLEGRO_MIPMAP

This can only be used for bitmaps whose width and height is a power of two. In that case, it will generate mipmaps and use them when drawing scaled down versions. For example if the bitmap is 64x64, then extra bitmaps of sizes 32x32, 16x16, 8x8, 4x4, 2x2 and 1x1 will be created always containing a scaled down version of the original.

ALLEGRO_NO_PREMULTIPLIED_ALPHA

By default, Allegro pre-multiplies the alpha channel of an image with the images color data when it loads it. Typically that would look something like this:

r = get_float_byte();
g = get_float_byte();
b = get_float_byte();
a = get_float_byte();

r = r * a;
g = g * a;
b = b * a;

set_image_pixel(x, y, r, g, b, a);

The reason for this can be seen in the Allegro example ex_premulalpha, ie, using pre-multiplied alpha gives more accurate color results in some cases. To use alpha blending with images loaded with pre-multiplied alpha, you would use the default blending mode, which is set with al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_INVERSE_ALPHA).

The ALLEGRO_NO_PREMULTIPLIED_ALPHA flag being set will ensure that images are not loaded with alpha pre-multiplied, but are loaded with color values direct from the image. That looks like this:

r = get_float_byte();
g = get_float_byte();
b = get_float_byte();
a = get_float_byte();

set_image_pixel(x, y, r, g, b, a);

To draw such an image using regular alpha blending, you would use al_set_blender(ALLEGRO_ADD, ALLEGRO_ALPHA, ALLEGRO_INVERSE_ALPHA) to set the correct blender. This has some caveats. First, as mentioned above, drawing such an image can result in less accurate color blending (when drawing an image with linear filtering on, the edges will be darker than they should be). Second, the behaviour is somewhat confusing, which is explained in the example below.

// Load and create bitmaps with an alpha channel
al_set_new_bitmap_format(ALLEGRO_PIXEL_FORMAT_ANY_32_WITH_ALPHA);
// Load some bitmap with alpha in it
bmp = al_load_bitmap("some_alpha_bitmap.png");
// We will draw to this buffer and then draw this buffer to the screen
tmp_buffer = al_create_bitmap(SCREEN_W, SCREEN_H);
// Set the buffer as the target and clear it
al_set_target_bitmap(tmp_buffer);
al_clear_to_color(al_map_rgba_f(0, 0, 0, 1));
// Draw the bitmap to the temporary buffer
al_draw_bitmap(bmp, 0, 0, 0);
// Finally, draw the buffer to the screen
// The output will look incorrect (may take close inspection
// depending on the bitmap -- it may also be very obvious)
al_set_target_bitmap(al_get_backbuffer(display));
al_draw_bitmap(tmp_buffer, 0, 0, 0);

To explain further, if you have a pixel with 0.5 alpha, and you're using (ALLEGRO_ADD, ALLEGRO_ALPHA, ALLEGRO_INVERSE_ALPHA) for blending, the formula is:

    a = da * dst + sa * src

Expands to:

    result_a = dst_a * (1-0.5) + 0.5 * 0.5;

So if you draw the image to the temporary buffer, it is blended once resulting in 0.75 alpha, then drawn again to the screen, blended in the same way, resulting in a pixel has 0.1875 as an alpha value.

al_add_new_bitmap_flag

void al_add_new_bitmap_flag(int flag)

A convenience function which does the same as

al_set_new_bitmap_flags(al_get_new_bitmap_flags() | flag);

al_set_new_bitmap_format

void al_set_new_bitmap_format(int format)

Sets the pixel format for newly created bitmaps. The default format is 0 and means the display driver will choose the best format.

Bitmap properties

al_get_bitmap_flags

int al_get_bitmap_flags(ALLEGRO_BITMAP *bitmap)

Return the flags user to create the bitmap.

al_get_bitmap_format

int al_get_bitmap_format(ALLEGRO_BITMAP *bitmap)

Returns the pixel format of a bitmap.

al_get_bitmap_height

int al_get_bitmap_height(ALLEGRO_BITMAP *bitmap)

Returns the height of a bitmap in pixels.

al_get_bitmap_width

int al_get_bitmap_width(ALLEGRO_BITMAP *bitmap)

Returns the width of a bitmap in pixels.

al_get_pixel

ALLEGRO_COLOR al_get_pixel(ALLEGRO_BITMAP *bitmap, int x, int y)

Get a pixel's color value from the specified bitmap. This operation is slow on non-memory bitmaps. Consider locking the bitmap if you are going to use this function multiple times on the same bitmap.

al_is_bitmap_locked

bool al_is_bitmap_locked(ALLEGRO_BITMAP *bitmap)

Returns whether or not a bitmap is already locked.

al_is_compatible_bitmap

bool al_is_compatible_bitmap(ALLEGRO_BITMAP *bitmap)

D3D and OpenGL allow sharing a texture in a way so it can be used for multiple windows. Each ALLEGRO_BITMAP created with al_create_bitmap however is usually tied to a single ALLEGRO_DISPLAY. This function can be used to know if the bitmap is compatible with the given display, even if it is a different display to the one it was created with. It returns true if the bitmap is compatible (things like a cached texture version can be used) and false otherwise (blitting in the current display will be slow).

The only time this function is useful is if you are using multiple windows and need accelerated blitting of the same bitmaps to both.

Returns true if the bitmap is compatible with the current display, false otherwise. If there is no current display, false is returned.

al_is_sub_bitmap

bool al_is_sub_bitmap(ALLEGRO_BITMAP *bitmap)

Returns true if the specified bitmap is a sub-bitmap, false otherwise.

Drawing operations

All drawing operations draw to the current "target bitmap" of the current thread. Initially, the target bitmap will be the backbuffer of the last display created in a thread.

al_clear_to_color

void al_clear_to_color(ALLEGRO_COLOR color)

Clear the complete target bitmap, but confined by the clipping rectangle.

al_draw_bitmap

void al_draw_bitmap(ALLEGRO_BITMAP *bitmap, float dx, float dy, int flags)

Draws an unscaled, unrotated bitmap at the given position to the current target bitmap (see al_set_target_bitmap).

flags can be a combination of:

ALLEGRO_FLIP_HORIZONTAL - flip the bitmap about the y-axis
ALLEGRO_FLIP_VERTICAL - flip the bitmap about the x-axis

Note: The current target bitmap must be a different bitmap. Drawing a bitmap to itself (or to a sub-bitmap of itself) or drawing a sub-bitmap to its parent (or another sub-bitmap of its parent) are not currently supported. To copy part of a bitmap into the same bitmap simply use a temporary bitmap instead.

Note: The backbuffer (or a sub-bitmap thereof) can not be transformed, blended or tinted. If you need to draw the backbuffer draw it to a temporary bitmap first with no active transformation (except translation). Blending and tinting settings/parameters will be ignored. This does not apply when drawing into a memory bitmap.

al_draw_tinted_bitmap

void al_draw_tinted_bitmap(ALLEGRO_BITMAP *bitmap, ALLEGRO_COLOR tint,
   float dx, float dy, int flags)

Like al_draw_bitmap but multiplies all colors in the bitmap with the given color. For example:

al_draw_tinted_bitmap(bitmap, al_map_rgba_f(1, 1, 1, 0.5), x, y, 0);

The above will draw the bitmap 50% transparently.

al_draw_tinted_bitmap(bitmap, al_map_rgba_f(1, 0, 0, 1), x, y, 0);

The above will only draw the red component of the bitmap.

al_draw_bitmap_region

void al_draw_bitmap_region(ALLEGRO_BITMAP *bitmap,
   float sx, float sy, float sw, float sh, float dx, float dy, int flags)

Draws a region of the given bitmap to the target bitmap.

sx - source x
sy - source y
sw - source width (width of region to blit)
sh - source height (height of region to blit)
dx - destination x
dy - destination y
flags - same as for al_draw_bitmap

al_draw_tinted_bitmap_region

void al_draw_tinted_bitmap_region(ALLEGRO_BITMAP *bitmap,
   ALLEGRO_COLOR tint,
   float sx, float sy, float sw, float sh, float dx, float dy,
   int flags)

Like al_draw_bitmap_region but multiplies all colors in the bitmap with the given color.

See also: al_draw_tinted_bitmap

al_draw_pixel

void al_draw_pixel(float x, float y, ALLEGRO_COLOR color)

Draws a single pixel at x, y. This function, unlike al_put_pixel, does blending and, unlike al_put_blended_pixel, respects the transformations. This function can be slow if called often; if you need to draw a lot of pixels consider using the primitives addon.

x - destination x
y - destination y
color - color of the pixel

Note: This function may not draw exactly where you expect it to. See the pixel-precise output section on the primitives addon documentation for details on how to control exactly where the pixel is drawn.

al_draw_rotated_bitmap

void al_draw_rotated_bitmap(ALLEGRO_BITMAP *bitmap,
   float cx, float cy, float dx, float dy, float angle, int flags)

Draws a rotated version of the given bitmap to the target bitmap. The bitmap is rotated by 'angle' radians clockwise.

The point at cx/cy inside the bitmap will be drawn at dx/dy and the bitmap is rotated around this point.

cx - center x
cy - center y
dx - destination x
dy - destination y
angle - angle by which to rotate
flags - same as for al_draw_bitmap

al_draw_tinted_rotated_bitmap

void al_draw_tinted_rotated_bitmap(ALLEGRO_BITMAP *bitmap,
   ALLEGRO_COLOR tint,
   float cx, float cy, float dx, float dy, float angle, int flags)

Like al_draw_rotated_bitmap but multiplies all colors in the bitmap with the given color.

See also: al_draw_tinted_bitmap

al_draw_scaled_rotated_bitmap

void al_draw_scaled_rotated_bitmap(ALLEGRO_BITMAP *bitmap,
   float cx, float cy, float dx, float dy, float xscale, float yscale,
   float angle, int flags)

Like al_draw_rotated_bitmap, but can also scale the bitmap.

The point at cx/cy in the bitmap will be drawn at dx/dy and the bitmap is rotated and scaled around this point.

cx - center x
cy - center y
dx - destination x
dy - destination y
xscale - how much to scale on the x-axis (e.g. 2 for twice the size)
yscale - how much to scale on the y-axis
angle - angle by which to rotate
flags - same as for al_draw_bitmap

al_draw_tinted_scaled_rotated_bitmap

void al_draw_tinted_scaled_rotated_bitmap(ALLEGRO_BITMAP *bitmap,
   ALLEGRO_COLOR tint,
   float cx, float cy, float dx, float dy, float xscale, float yscale,
   float angle, int flags)

Like al_draw_scaled_rotated_bitmap but multiplies all colors in the bitmap with the given color.

See also: al_draw_tinted_bitmap

al_draw_scaled_bitmap

void al_draw_scaled_bitmap(ALLEGRO_BITMAP *bitmap,
   float sx, float sy, float sw, float sh,
   float dx, float dy, float dw, float dh, int flags)

Draws a scaled version of the given bitmap to the target bitmap.

sx - source x
sy - source y
sw - source width
sh - source height
dx - destination x
dy - destination y
dw - destination width
dh - destination height
flags - same as for al_draw_bitmap

al_draw_tinted_scaled_bitmap

void al_draw_tinted_scaled_bitmap(ALLEGRO_BITMAP *bitmap,
   ALLEGRO_COLOR tint,
   float sx, float sy, float sw, float sh,
   float dx, float dy, float dw, float dh, int flags)

Like al_draw_scaled_bitmap but multiplies all colors in the bitmap with the given color.

See also: al_draw_tinted_bitmap

al_get_target_bitmap

ALLEGRO_BITMAP *al_get_target_bitmap(void)

Return the target bitmap of the calling thread.

al_put_pixel

void al_put_pixel(int x, int y, ALLEGRO_COLOR color)

Draw a single pixel on the target bitmap. This operation is slow on non-memory bitmaps. Consider locking the bitmap if you are going to use this function multiple times on the same bitmap. This function is not affected by the transformations or the color blenders.

al_put_blended_pixel

void al_put_blended_pixel(int x, int y, ALLEGRO_COLOR color)

Like al_put_pixel, but the pixel color is blended using the current blenders before being drawn.

al_set_target_bitmap

void al_set_target_bitmap(ALLEGRO_BITMAP *bitmap)

Select the bitmap to which all subsequent drawing operations in the calling thread will draw. Select the backbuffer (see al_get_backbuffer) to return to drawing to the screen normally.

Each video bitmap is tied to a display. When a video bitmap is set to as the target bitmap, the display that the bitmap belongs to is automatically made "current" for the calling thread (if it is not current already). Then drawing other bitmaps which are tied to the same display can be hardware accelerated.

A single display cannot be current for multiple threads simultaneously. If you need to release a display, so it is not current for the calling thread, call al_set_target_bitmap(NULL);

Setting a memory bitmap as the target bitmap will not change which display is current for the calling thread.

OpenGL note:

Framebuffer objects (FBOs) allow OpenGL to directly draw to a bitmap, which is very fast. When using an OpenGL display, if all of the following conditions are met an FBO will be created for use with the bitmap:

The GL_EXT_framebuffer_object OpenGL extension is available.
The bitmap is not a memory bitmap.
The bitmap is not currently locked.

In Allegro 5.0.0, you had to be careful as an FBO would be kept around until the bitmap is destroyed or you explicitly called al_remove_opengl_fbo on the bitmap, wasting resources. In newer versions, FBOs will be freed automatically when the bitmap is no longer the target bitmap, unless you have called al_get_opengl_fbo to retrieve the FBO id.

In the following example, no FBO will be created:

lock = al_lock_bitmap(bitmap);
al_set_target_bitmap(bitmap);
al_put_pixel(x, y, color);
al_unlock_bitmap(bitmap);

The above allows using al_put_pixel on a locked bitmap without creating an FBO.

In this example an FBO is created however:

al_set_target_bitmap(bitmap);
al_draw_line(x1, y1, x2, y2, color, 0);

An OpenGL command will be used to directly draw the line into the bitmap's associated texture.

al_set_target_backbuffer

void al_set_target_backbuffer(ALLEGRO_DISPLAY *display)

Same as al_set_target_bitmap(al_get_backbuffer(display));

al_get_current_display

ALLEGRO_DISPLAY *al_get_current_display(void)

Return the display that is "current" for the calling thread, or NULL if there is none.

Blending modes

al_get_blender

void al_get_blender(int *op, int *src, int *dst)

Returns the active blender for the current thread. You can pass NULL for values you are not interested in.

al_get_separate_blender

void al_get_separate_blender(int *op, int *src, int *dst,
   int *alpha_op, int *alpha_src, int *alpha_dst)

Returns the active blender for the current thread. You can pass NULL for values you are not interested in.

al_set_blender

void al_set_blender(int op, int src, int dst)

Sets the function to use for blending for the current thread.

Blending means, the source and destination colors are combined in drawing operations.

Assume the source color (e.g. color of a rectangle to draw, or pixel of a bitmap to draw) is given as its red/green/blue/alpha components (if the bitmap has no alpha it always is assumed to be fully opaque, so 255 for 8-bit or 1.0 for floating point): sr, sg, sb, sa. And this color is drawn to a destination, which already has a color: dr, dg, db, da.

The conceptional formula used by Allegro to draw any pixel then depends on the op parameter:

ALLEGRO_ADD

 r = dr * dst + sr * src
 g = dg * dst + sg * src
 b = db * dst + sb * src
 a = da * dst + sa * src

ALLEGRO_DEST_MINUS_SRC

 r = dr * dst - sr * src
 g = dg * dst - sg * src
 b = db * dst - sb * src
 a = da * dst - sa * src

ALLEGRO_SRC_MINUS_DEST

 r = sr * src - dr * dst
 g = sg * src - dg * dst
 b = sb * src - db * dst
 a = sa * src - da * dst

Valid values for src and dst passed to this function are

ALLEGRO_ZERO
```
 src = 0
 dst = 0
```
ALLEGRO_ONE
```
 src = 1
 dst = 1
```
ALLEGRO_ALPHA
```
 src = sa
 dst = sa
```
ALLEGRO_INVERSE_ALPHA
```
 src = 1 - sa
 dst = 1 - sa
```

Blending examples:

So for example, to restore the default of using premultiplied alpha blending, you would use (pseudo code)

al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_INVERSE_ALPHA)

If you are using non-pre-multiplied alpha, you could use

al_set_blender(ALLEGRO_ADD, ALLEGRO_ALPHA, ALLEGRO_INVERSE_ALPHA)

Additive blending would be achieved with

al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_ONE)

Copying the source to the destination (including alpha) unmodified

al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_ZERO)

al_set_separate_blender

void al_set_separate_blender(int op, int src, int dst,
   int alpha_op, int alpha_src, int alpha_dst)

Like al_set_blender, but allows specifying a separate blending operation for the alpha channel. This is useful if your target bitmap also has an alpha channel and the two alpha channels need to be combined in a different way than the color components.

Clipping

al_get_clipping_rectangle

void al_get_clipping_rectangle(int *x, int *y, int *w, int *h)

Gets the clipping rectangle of the target bitmap.

al_set_clipping_rectangle

void al_set_clipping_rectangle(int x, int y, int width, int height)

Set the region of the target bitmap or display that pixels get clipped to. The default is to clip pixels to the entire bitmap.

Graphics utility functions

al_convert_mask_to_alpha

void al_convert_mask_to_alpha(ALLEGRO_BITMAP *bitmap, ALLEGRO_COLOR mask_color)

Convert the given mask color to an alpha channel in the bitmap. Can be used to convert older 4.2-style bitmaps with magic pink to alpha-ready bitmaps.

Deferred drawing

al_hold_bitmap_drawing

void al_hold_bitmap_drawing(bool hold)

Enables or disables deferred bitmap drawing. This allows for efficient drawing of many bitmaps that share a parent bitmap, such as sub-bitmaps from a tilesheet or simply identical bitmaps. Drawing bitmaps that do not share a parent is less efficient, so it is advisable to stagger bitmap drawing calls such that the parent bitmap is the same for large number of those calls. While deferred bitmap drawing is enabled, the only functions that can be used are the bitmap drawing functions and font drawing functions. Changing the state such as the blending modes will result in undefined behaviour. One exception to this rule are the transformations. It is possible to set a new transformation while the drawing is held.

No drawing is guaranteed to take place until you disable the hold. Thus, the idiom of this function's usage is to enable the deferred bitmap drawing, draw as many bitmaps as possible, taking care to stagger bitmaps that share parent bitmaps, and then disable deferred drawing. As mentioned above, this function also works with bitmap and truetype fonts, so if multiple lines of text need to be drawn, this function can speed things up.

al_is_bitmap_drawing_held

bool al_is_bitmap_drawing_held(void)

Returns whether the deferred bitmap drawing mode is turned on or off.

Image I/O

al_register_bitmap_loader

bool al_register_bitmap_loader(const char *extension,
   ALLEGRO_BITMAP *(*loader)(const char *filename))

Register a handler for al_load_bitmap. The given function will be used to handle the loading of bitmaps files with the given extension.

The extension should include the leading dot ('.') character. It will be matched case-insensitively.

The loader argument may be NULL to unregister an entry.

Returns true on success, false on error. Returns false if unregistering an entry that doesn't exist.

al_register_bitmap_saver

bool al_register_bitmap_saver(const char *extension,
   bool (*saver)(const char *filename, ALLEGRO_BITMAP *bmp))

Register a handler for al_save_bitmap. The given function will be used to handle the loading of bitmaps files with the given extension.

The extension should include the leading dot ('.') character. It will be matched case-insensitively.

The saver argument may be NULL to unregister an entry.

Returns true on success, false on error. Returns false if unregistering an entry that doesn't exist.

al_register_bitmap_loader_f

bool al_register_bitmap_loader_f(const char *extension,
   ALLEGRO_BITMAP *(*loader_f)(ALLEGRO_FILE *fp))

Register a handler for al_load_bitmap_f. The given function will be used to handle the loading of bitmaps files with the given extension.

The extension should include the leading dot ('.') character. It will be matched case-insensitively.

The fs_loader argument may be NULL to unregister an entry.

Returns true on success, false on error. Returns false if unregistering an entry that doesn't exist.

al_register_bitmap_saver_f

bool al_register_bitmap_saver_f(const char *extension,
   bool (*saver_f)(ALLEGRO_FILE *fp, ALLEGRO_BITMAP *bmp))

Register a handler for al_save_bitmap_f. The given function will be used to handle the loading of bitmaps files with the given extension.

The extension should include the leading dot ('.') character. It will be matched case-insensitively.

The saver_f argument may be NULL to unregister an entry.

Returns true on success, false on error. Returns false if unregistering an entry that doesn't exist.

al_load_bitmap

ALLEGRO_BITMAP *al_load_bitmap(const char *filename)

Loads an image file into an ALLEGRO_BITMAP. The file type is determined by the extension.

Returns NULL on error.

Note: the core Allegro library does not support any image file formats by default. You must use the allegro_image addon, or register your own format handler.

al_load_bitmap_f

ALLEGRO_BITMAP *al_load_bitmap_f(ALLEGRO_FILE *fp, const char *ident)

Loads an image from an ALLEGRO_FILE stream into an ALLEGRO_BITMAP. The file type is determined by the passed 'ident' parameter, which is a file name extension including the leading dot.

Returns NULL on error. The file remains open afterwards.

Note: the core Allegro library does not support any image file formats by default. You must use the allegro_image addon, or register your own format handler.

al_save_bitmap

bool al_save_bitmap(const char *filename, ALLEGRO_BITMAP *bitmap)

Saves an ALLEGRO_BITMAP to an image file. The file type is determined by the extension.

Returns true on success, false on error.

Note: the core Allegro library does not support any image file formats by default. You must use the allegro_image addon, or register your own format handler.

al_save_bitmap_f

bool al_save_bitmap_f(ALLEGRO_FILE *fp, const char *ident,
   ALLEGRO_BITMAP *bitmap)

Saves an ALLEGRO_BITMAP to an ALLEGRO_FILE stream. The file type is determined by the passed 'ident' parameter, which is a file name extension including the leading dot.

Returns true on success, false on error. The file remains open afterwards.

Note: the core Allegro library does not support any image file formats by default. You must use the allegro_image addon, or register your own format handler.

Allegro version 5.0.1 - Last updated: 2011-03-13 23:14:15 UTC