Ambient occlusion volumes

Abstract

Kajalin 2009] [Szirmay-Kalos et al. 2009] Ray Traced Reference Ambient Occlusion Volumes 256 samples/pix 64 samples/pix 5000 samples/pix (analytic) 16 ms 61 ms 556228 ms 31 ms Figure 1: 1.4 M-triangle scene at 720p resolution on GeForce 280 GT using geometry from Marvel Ultimate Alliance 2 by Vicarious Visions/Activision. The new Ambient Occlusion Volume algorithm produces quality comparable to ray tracing, in real time and with no noise. In contrast, many alternative screen-space algorithms offer extremely fast AO approximations but cannot converge towards the correct result, even when extended to high sampling rates as shown here.Introduction Ambient illumination is an approximation to the light reflected from the sky and other objects in a scene. Ambient occlusion (AO) is the darkening that occurs when this illumination is locally blocked by another object or a nearby fold in a surface. Both ambient illumination and occlusion are qualitatively important to perception of shape and depth in the real world. Artists have long recognized AO, and specifically seek to reproduce the real phenomena such as corner darkening and contact shadows. Because AO is so important to shape perception, practitioners in many disciplines rely software that simulates AO to visualize structures. Ambientocclusion renderings of building facades, medical data, and engineering parts reveal the spatial relationship between complex details. CG artists also a prefer untextured, AO-only rendering as a method for visualizing geometry. While the problem of computing an explicit AO factor has been studied for over a decade, most previous AO algorithms seek extreme quality or extreme performance. Ray tracing methods are the gold standard for quality, but take minutes to evaluate. Recent screen space methods (e.g., [Mittring 2007;Kajalin 2009;Bavoil and Sainz 2009;Szirmay-Kalos et al. 2009]) are well suited to console games because they execute in only a few milliseconds at HD resolution. However, they sacrifice significant quality for that performance and do not improve under the higher sample rates possible on today's GPUs. We build on the screen space notion of AO as a deferred shading pass for performance, but develop and analytic solution inspired by radiosity and Crow's shadow volumes and thus yields higher quality. By enabling high-quality AO in real-time, it is well suited to modeling applications and CAD. With screen-space subsampling it can match the performance of screen space methods with high quality for games on contemporary GPUs.

Adaptively layered statistical volumetric obscurance

“…An alternative geometry-based approach was presented by McGuire in 2010 [7]. The technique is inspired by Shadow Volumes [8] and evaluates AO through a scattering process.…”

Voxel-Space Ambient Occlusion

“…Similar to McGuire's work, we let the light arriving from nearby objects be L n [McG10]. Light arriving from large distant objects (ambient light) be L a .…”

“…Recent work by McGuire [McG10] computes ambient occlusion by generating volumes around geometry, however geometry volume complexity increases with primitive count.…”

“…McGuire [McG10] and Laine and Karras [LK10] compute ambient occlusion similar to shadow volumes by extruding the polygons and applying an occlusion function with the extrusions.…”

“…We use a modification of the ambient occlusion formulation by McGuire [McG10] in Ambient occlusion volumes, where we derive an area formulation of ambient occlusion from the area rendering equation formulation.…”