Algebraic Smooth Occluding Contours

Computing occluding contours is a key building block of non-photorealistic rendering, but producing contours with consistent visibility has been notoriously challenging. This paper describes the first general-purpose smooth surface construction for which the occluding contours can be computed in closed form. For a given input mesh and camera viewpoint, we produce a $G^1$ piecewise-quadratic surface approximating the mesh. We show how the image-space occluding contours of this representation may then be described as piecewise rational curves. We show that this method produces smooth contours with consistent visibility much more efficiently than the state-of-the-art.