Visibility computations, exhibiting a quadratic growth rate, are the bottleneck of high quality, real-time rendering of 3D models. In order to speed up visibility computations parallel or distributed-computing techniques can be used. Recent research demonstrates that scanline algorithms are suitable for balancing the workload and reducing the communication overhead of multiprocessor architectures. This paper summarizes known scanline algorithms and proposes a new one that takes time proportional to N log₂ N and storage space proportional to N in the worst case, where N is the number of input line segments. The advantages of the proposed algorithm include that it can take real values obtained by the intersection of a 3D scene with the plane of the scanline as input and that it is optimal under several models of computation.