Defines the type of the function that gets called once the size of the loaded image is known.
The function is expected to set
height to the desired
size to which the image should be scaled. If a module has no efficient
way to achieve the desired scaling during the loading of the image, it may
either ignore the size request, or only approximate it - gdk-pixbuf will
then perform the required scaling on the completely loaded image.
If the function sets
height to zero, the module should interpret
this as a hint that it will be closed soon and shouldn’t allocate further
resources. This convention is used to implement gdk_pixbuf_get_file_info() efficiently.