1. A computer graphics system for generating an image of a scene from a representation to which at least one instantiated phenomenon has been attached, said instantiated phenomenon comprising an encapsulated shader DAG comprising at least one shader node, the computer graphics system comprising: A. a pre-processor configured to determine whether the at least one instantiated phenomenon requires a pre-processing operation in connection with said representation, and, if so, performing said pre-processing operation to generate a pre-processed representation of the scene; and B. a renderer configured to generate a rendered image from said pre-processed representation of the scene.