Method for rendering silhouette and true edges of 3-d line drawings with occlusion

Abstract

A computer-implemented method for generating three dimensional line drawings in which only silhouette edges and true edges that are visible are displayed. The color, depth, and stencil buffers are respectively initialized to background color, farthest value, and zero. In a first pass, all polygons are rendered by filling all pixels within their boundaries. At each pixel, only its depth value is modified by selecting the nearer of either the current depth value or the new depth value. This creates a depth image in the depth buffer used for occlusion detection. In a second pass, all the polygons of a particular orientation are rendered by drawing lines from vertex to vertex for each of the polygons. The pixel values are modified only when the depth comparison passes (i.e., the pixel is visible and not occluded). Each time a particular pixel is modified, its corresponding stencil value is toggled from 0 to 1 or from 1 back to 0. Afterwards, the value of each pixel in the frame buffer is set to the line color if and only if its corresponding stencil value is 1. Lastly, all true edges are rendered. For the true edges, only those pixels which pass the depth comparison are modified by setting them to the line color. In the end, only the visible true edges and silhouette edges are drawn for display.