Figure pick-up system

Claim 1

A graphic form extracting system for a graphic processor in which three-dimensional graphic data is clipped in accordance with a view volume set corresponding to a visual point, straight line data is generated corresponding to the plane of a graphic form contained in the view volume, and a graphic form is displayed, on a display screen, by straight lines extracted from the straight line data by reference to a depth value set in a depth buffer, characterized by: means for setting a window about a specified point on the display screen; means for appending identification data to each three-dimensional graphic data; and a pick buffer for storing the identification data; wherein the three-dimensional graphic data is clipped corresponding to the set window; the graphic form contained in the view volume corresponding to the window and its identification data are extracted and the identification data is stored in the pick buffer; a depth value of each of the straight lines generated corresponding to the plane of the extracted graphic form is compared with the depth value set in the depth buffer and when they coincide, the identification data of the graphic form to which the straight line belongs is read out of the pick buffer; and the graphic data corresponding to the read-out identification data is read out for extracting a graphic form corresponding to the specified point.