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Abstract

A technique for representing a visual scene as a directed acyclic graph of data and operators that generates a sequence of image frames over specified time intervals. The graph specifies temporal and spatial values for associated visual elements of the scene. Time is modeled in the inheritance properties explicitly defined within the scene graph hierarchy, by assigning temporal attributes to each media element. Branch nodes of the graph specify transforms for the temporal and spatial coordinate systems. To evaluate the appearance or behavior of the scene and in particular the global time values of particular elements at a given time instant, the graph is traversed in a direction from a root node down toward the leaf nodes, thereby causing temporal transformations specified along the branches of the graph to modify time parameters of the scene data at the nodes. Child nodes are preferably evaluated after being transformed, to determine the extent to which they contribute the data to the final scene. Temporal transformations may include translation operations that offset temporal event times; scaling operations that change the rate at which time passes; or clipping operations, that restrict the range of time parameters to exclude the evaluation of parts of the graph.

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