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4.8.3 Proxy Geometry

One method to reduce the amount of work done by the OpenGL pipeline during picking operations (for color buffer tagging or OpenGL selection) is to use a simplified form of the object in the picking computations. For example, individual objects can be replaced by geometry representing their bounding boxes. The accuracy of the picking operation is traded for increased speed. Some of the accuracy can be improved by adding a second pass in which the objects which are selected using their simplified geometry are reprocessed using their real geometry.