GRAPHIC PROCESSOR

PURPOSE:To eliminate the necessity of obtaining the Z component of a normal vector from the coordinate value of a surface by a graphic processing means and to speed up front/rear decision by giving additionally normal vector data to surface data to be stored in a segment buffer. CONSTITUTION:A graphic processing means 3 fetches the normal vector of the surface from a segment buffer 2 and executes a coordinate transformation. Next, the Z direction component of the normal after the coordinate transformation is decided and the front or the rear of the surface is determined. When the decision result shows the rear, the number of vertexes and vertex coordinates are thrown away after a single reading and a processing is terminated. When it is the front, the number of the vertexes is fetched, after that, the coordinates of a first vertex are fetched and the vertex coordinates are transformed. Next, whether or not the processings of all the vertexes are terminated is checked, when they are not yet terminated, it is returned to the preceding processing and the coordinates of a next second vertex are fetched. Like this, the processing is repeated by the number of the vertexes. When the processings of all the vertexes are terminated, the color of the obverse of the surface is obtained from the normal vector and the display color and the Z value of respective picture elements are written into a frame buffer and a Z buffer in a display 4.