This reads a rectangle of pixels from the given framebuffer where position (0, 0) is the top left.
The pixel at (x, y) is the first read, and a rectangle of pixels with the same size as the bitmap is read right and downwards from that point.
Currently Cogl assumes that the framebuffer is in a premultiplied format so if the format of
bitmap is non-premultiplied it
will convert it. To read the pixel values without any conversion you should either specify a format that doesn't use an alpha channel or
use one of the formats ending in PRE.
The x position to read from
The y position to read from
Identifies which auxillary buffer you want to read (only COGL_READ_PIXELS_COLOR_BUFFER supported currently)
The bitmap to store the results in.
true if the read succeeded or false otherwise. The function is only likely to fail if the bitmap points to a pixel buffer and it could not be mapped.