This function returns the raw 32-bit pixel data of the image handle allocated
by hw_LoadImage(). The alpha byte will always be set, even
if the image doesn't contain an alpha channel. In that case the alpha byte will be
set to 255 (i.e. fully opaque) for every pixel. The pointer returned by this function
is valid until you call hw_FreeImage() on this image.
The pixel format can either be RGBA or ARGB, depending on the parameters passed
to hw_LoadImage().