METHOD AND APPARATUS FOR COMPOSING LAYERED SYNTHETIC GRAPHICS FILTERS

A computerized two-dimensional illustration system composes an image of a scene with layered synthetic graphics filters or lenses. The scene is defined by an ordered list of shapes. Some of the shapes in the ordered list of shapes are lenses. Each lens is a shape that has a fill color which is an operator rather than a constant. The operator of a selected lens performs a filtering function on the shapes ordered below it in the list of shapes. To compose a selected lens in the scene, the system first computes an under-list of shapes for the selected lens. The under-list of shapes is used to identify those shapes in the ordered list of shapes to which the filtering function of the selected lens may apply. Depending on the filtering function of a lens, the lens composes in either a back-to-front order or a front-to-back order. A lens composes in a back-to-front order by freezing lenses in the under-list before applying the filtering function of the lens to shapes in the under-list. In contrast, a lens composes in a front-to-back order by applying the filtering function of the lens to the under-list of shapes before freezing lenses in the under-list. When a lens is frozen, it is replaced with a cluster of shapes that are formed independently of other shapes in the list of shapes.