SHADING SYSTEM BY Z-BUFFER ALGORITHM

PURPOSE:To enable a user to easily perform simple shading nearly without being conscious of a shading process by generating projection data on an output body with a certain light source by a projection data generating means, extracting and generating a shadow figure by a shadow generating means, and drawing the shadow figure by a shadow drawing means. CONSTITUTION:The projection data generating means 2 generates projection data on a projection surface in surface units (consisting of respective vertexes) of the output body by light sources. Data on the source surfaces (vertex coordinate value, RGB value, and vector), said projection data (vertex coordinate value), and information on the light sources are saved together. The shadow generating means 6 finds overlap surface data (coordinate value and vertex normal vector) when there is a body overlapping with the area of a shadow encircled with the saved source surface data and projection data. Further, the vertex coordinates of the above shadow figure are compared with Z values in a Z buffer to judge whether the above shadow figure is visible and delete invisible parts (size correction of shadow figure).