Real-time Raytracing and Screen-space Ambient Occlusion

Abstract: This paper investigates the advances in real-time ambient occlusion (AO). Topics discussed are state-of-the-art screen-space techniques and raytraced ambient occlusion. Methods compared are our screen-space ambient occlusion (SSAO) variant, horizon-based ambient occlusion(HBAO), Unity’s scalable AO (AlchemyAO), multi-scale volumetric AO (MSVO), and raytraced AO (RTAO). The methods were compared based on the errors produced in dynamic scenes, performance and similarity to reference scenes rendered by an offline raytracer. Important dynamic scene errors were highlighted, visual results were objectively evaluated using Structural Similarity Index (SSIM) and Unity engine was used as a common platform for all the methods in order to obtain performance metrics. RTAO managed to achieve a strikingly high SSIM score, while, MSVO traded some accuracy to be the fastest of all the methods. Further analysis of different implementations and their strengths and weaknesses are provided.