Ubuntu Manpage: ALLEGRO_PIXEL_FORMAT

NAME

       ALLEGRO_PIXEL_FORMAT - Allegro 5 API

SYNOPSIS

              #include <allegro5/allegro.h>

              typedef enum ALLEGRO_PIXEL_FORMAT

DESCRIPTION

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

Some of the pixel formats represent compressed bitmap formats. Compressed bitmaps take up less space in
the GPU memory than bitmaps with regular (uncompressed) pixel formats. This smaller footprint means that
you can load more resources into GPU memory, and they will be drawn somewhat faster. The compression is
lossy, however, so it is not appropriate for all graphical styles: it tends to work best for images with
smooth color gradations. It is possible to compress bitmaps at runtime by passing the appropriate bitmap
format in al_set_new_bitmap_format and then creating, loading, cloning or converting a non-compressed
bitmap. This, however, is not recommended as the compression quality differs between different GPU dri‐
vers. It is recommended to compress these bitmaps ahead of time using external tools and then load them
compressed.

Unlike regular pixel formats, compressed pixel formats are not laid out in memory one pixel row at a
time. Instead, the bitmap is subdivided into rectangular blocks of pixels that are then laid out in
block rows. This means that regular locking functions cannot use compressed pixel formats as the desti‐
nation format. Instead, you can use the blocked versions of the bitmap locking functions which do sup‐
port these formats.

It is not recommended to use compressed bitmaps as target bitmaps, as that operation cannot be hardware
accelerated. Due to proprietary algorithms used, it is typically impossible to create compressed memory
bitmaps.

• 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_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_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.

• ALLEGRO_PIXEL_FORMAT_RGBA_4444 - 16bit

• ALLEGRO_PIXEL_FORMAT_SINGLE_CHANNEL_8 - A single 8-bit channel. A pixel value maps onto the red chan‐
nel when displayed, but it is undefined how it maps onto green, blue and alpha channels. When drawing
to bitmaps of this format, only the red channel is taken into account. Allegro may have to use fall‐
back methods to render to bitmaps of this format. This pixel format is mainly intended for storing the
color indices of an indexed (paletted) image, usually in conjunction with a pixel shader that maps in‐
dices to RGBA values. Since 5.1.2.

• ALLEGRO_PIXEL_FORMAT_COMPRESSED_RGBA_DXT1 - Compressed using the DXT1 compression algorithm. Each 4x4
pixel block is encoded in 64 bytes, resulting in 6-8x compression ratio. Only a single bit of alpha
per pixel is supported. Since 5.1.9.

• ALLEGRO_PIXEL_FORMAT_COMPRESSED_RGBA_DXT3 - Compressed using the DXT3 compression algorithm. Each 4x4
pixel block is encoded in 128 bytes, resulting in 4x compression ratio. This format supports sharp al‐
pha transitions. Since 5.1.9.

• ALLEGRO_PIXEL_FORMAT_COMPRESSED_RGBA_DXT5 - Compressed using the DXT5 compression algorithm. Each 4x4
pixel block is encoded in 128 bytes, resulting in 4x compression ratio. This format supports smooth
alpha transitions. Since 5.1.9.

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO