Inside Macintosh: QuickTime Components
Use the progress function request to assign a progress function for use by the standard dialog component. The progress function is a part of your application. The standard dialog component calls this function during time-consuming operations, and reports its progress. Your progress function can use the information it receives from the standard dialog component to keep the user informed about the progress of the operation.
You supply a pointer to an Image Compression Manager progress function structure (see the chapter "Image Compression Manager" in Inside Macintosh: QuickTime for information about the format and content of this structure, as well as complete information about progress functions). Set the pointer to nil to clear the current progress function; in this case, the standard dialog component does not report its progress to the user. Set the pointer to -1 to use the component's default progress function.