a function that is called to save each block of data that the save routine generates.
user data to pass to the save function.
name of file format.
name of options to set, NULL-terminated
values for named options
whether an error was set
GException on failure.
2.4
Saves pixbuf to a callback in format type, which is currently "jpeg", "png", "tiff", "ico" or "bmp". If error is set, FALSE will be returned. See gdk_pixbuf_save_to_callback () for more details.