Autostereoscopic displays enable unencumbered immersive virtual reality, but at a significant computational expense. This expense impacts the feasibility of autostereo displays in high-performance real-time interactive applications. A new autostereo rendering algorithm named Autostereo Combiner addresses this problem using the programmable vertex and fragment pipelines of modern graphics processing units (GPUs). This algorithm is applied to the Varrier, a large-scale, head-tracked, parallax barrier autostereo virtual reality platform. In this capacity, the Combiner algorithm has shown performance gains of 4x over traditional parallax barrier rendering algorithms. It has enabled high-performance rendering at sub-pixel scales, affording a 2x increase in resolution and showing a 1.4x improvement in visual acuity.