GeglMetadataStoregenerate_value

This method is called to optionally generate a value to be written to and image file. If no generator is available it returns FALSE and the registered mapping is used. If a generator is available it should create a suitable value to be written to the image file and return TRUE. The default method checks if a signal handler is registered for the generate-value signal with the variable name as the detail parameter. If a handler is registered it emits the signal with an initialised GValue to receive the file metadata and returns TRUE otherwise FALSE. parse_value and generate_value are provided to handle the case where some file formats overload, for example, image comments. A typical case is formatting many values into a TIFF file’s ImageDescription field.