The ABGR Extension

The ABGR Extension

The ABGR extension, EXT_abgr, extends the list of host-memory color formats by an alternative to the RGBA format that uses reverse component order. The ABGR component order matches the cpack IRIS GL format on big-endian machines. This is the most convenient way to use an ABGR source image with OpenGL.

Note that the ABGR extension provides the best performance on the following graphics systems: Starter, XZ, Elan, XS24, Extreme.

To use this extension, call glDrawPixels(), glGetTexImage(), glReadPixels(), and glTexImage*() with GL_ABGR_EXT as the value of the format parameter.

The following code fragment illustrates the use of the extension:

/*
 *  draw a 32x32 pixel image at location 10, 10 using an ABGR source 
 *  image. "image" *should* point to a 32x32 ABGR UNSIGNED BYTE image
 */

{
    unsigned char *image;

    glRasterPos2f(10, 10);
    glDrawPixels(32, 32, GL_ABGR_EXT, GL_UNSIGNED_BYTE, image);
}