PURPOSE:To surely project a texture original image even if a mapping area on a display device surface is a butterfly face, by performing the line interpolation of two sides and subjecting obtained segments to line interpolation. CONSTITUTION:In a processor 62, apex data corresponding to start and end points of two sides to be subjected to side interpolation are supplied to side interpolating circuits 11, 12...16 and side interpolating circuits 21, 22...26 on the basis of plural transmitted apex data. Division number data of side interpolation is calculated on the basis of the length of the side determined by a pair of apex data and is supplied to circuits 11...16 and 21...26. In each side interpolating circuit, the length of the side is divided by division number data and the divided value is successively accumulatively added to one apex data to obtain side interpolating data, and this data is sent to segment interpolating circuits 31 and 32. Graphic data in a mapping memory 41 is projected on picture element coordinates obtained by circuits 31 and 32 to display data, which corresponds to the graphic pattern subjected to texture mapping, through a frame memory.
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