Method and system for updating derived items in a view model which

Abstract

A computer graphics interface between an application program and device pipeline. The computer system implements a view model including a plurality of coordinate systems. An acyclic graph is stored, wherein the acyclic graph representing dependencies between various items in each of the plurality of coordinate systems. Upon a creation of an item in a first coordinate system of the plurality of coordinate systems, an object is associated with the item an object which associates all derived items from the item in others of the plurality of coordinate systems, wherein the object includes a first flag for indicating whether the item current item is valid within the first coordinate system. The object further includes a second flag for indicating that at least one of the derived items is not valid in its respective coordinate system. Upon requests for the item by the application program, it is determined whether the item is valid, and if not, then the acyclic graph is descended to determine when one of the derived items is valid. When one valid item is found, the item is calculated and it is indicated that the one item is valid. Then, the acyclic graph is ascended, calculating each derived item, and indicating that each derived item is valid until reaching the requested item. Then, the requested item is calculated, a flag is set indicating that it is valid and the requested item is presented to the application program. The storage of the object further allows entry of data from multiple coordinate systems, and provides a fast test to indicate that derived items are invalid.