Editing Ray casting (section)

=== Shaded Pictures ===
To make a shaded picture, again cast one ray per pixel in the screen. This time, however, use the visible surface pointer S[1] at each pixel to access the description of the surface. From this, compute the surface normal at the visible point ''t''[1]. The pixel’s value, the displayable light intensity, is proportional to the cosine of the angle formed by the surface normal and the light-source-to-surface vector. Processing all pixels this way produces a raster-type picture of the scene.