| 摘要 |
A computerized two-dimensional illustration system composes an image of a scene with layered synthetic graphics filters or lenses. The scene is d efined by an ordered list of shapes. Some of the shapes in the ordered list of shap es 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 functi on on the shapes ordered below it in the list of shapes. To compose a selected len s inthe scene, the system computes an under-list of shap es for the selected lens. The under-list of shapes identifies shapes in the ordered list of shapes to which the filtering function of the selected lens may apply. After computing the u nder-list for a selected lens, the system freezes the shapes in the under-list and applies the filtering function of the selected lens to the shapes in the und er-list. When a lens is frozen, it is replaced with a list of shapes that are formed independently of other shapes in the list of shapes. The scope of operation of the selected lens can be reduced by grouping the selected lens with other shapes in the scene as either a lens-in cluster or a lens-out cluster. A len s-incluster limits the scope of operation of the selecte d lens by operating on only those shapes in the cluster, while a lens-out cluster limits the scope of op eration of the lens by operating on only those shapes outside the cluster. As a resu lt of limiting the scope of operation, grouping lenses with other objects in a sce ne enables the creation of different visual effects. In addition, depending on whether a lens is grouped as a lens-in or a lens-out cluster, the computed under-lis t ofthe selected lens may have a reduced number of shape s, thereby reducing the computational complexity of composing an image of the scene.
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