Shading method and shading apparatus for computer graphics

Abstract

A method and apparatus for shading images by approximating a three-dimensional curved surface for computer graphics. Shading of a two-dimensional surface is provided by varying pixel brightness values to indicate a depth dimension of the two-dimensional surface. A plurality of polygons are employed, with each polygon being used to approximate a portion of the curved surface. A coordinate grid is provided extending in horizontal and vertical directions. The polygons are plotted on this coordinate grid. Coordinate grid points of the coordinate grid each represent respective pixels whose brightness is to be varied for the graphics. Scanning occurs across scan lines in a horizontal direction across the grid from grid point to grid point. Vertices of the polygons are provided on the coordinate grid, which vertices may not necessarily lie directly on a grid point. Brightness values at each vertex of the polygon are provided. Using these brightness values, by a process known as sub-pixel addressing, brightness values at the pixels at the grid points of the coordinate grid lying inside of the polygons are determined by linear interpolation based on brightness values at locations where pixels are not provided on sides of the polygon.