Comparative Analysis of Real-Time Global Illumination Techniques in Current Game Engines

Abstract

The most important component of photorealism in Computer Graphics is given by a physically correct approximation of the light transport. Besides the direct illumination from light sources, there is an indirect illumination, produced by the reflections of the light rays on other surfaces of the scene. In Computer Graphics, the process of computing the illumination of a surface by considering both the direct and the indirect illumination is widely known as global illumination. This paper describes several classes of real-time global illumination techniques used in current game engines together with our own implementations of these approaches. All implementations were made in our own framework, specially designed with a multi-pass rendering architecture that allows fast implementation of rendering techniques and the reuse of functionalities. We analyze these classes based on the following criteria: the visual results produced by the indirect diffuse lighting, the ability to produce glossy reflections, shadows, ambient occlusion, subsurface scattering, translucency and volumetric lighting as well as the ability to simulate area lights. We present the quantitative results of our implementations, obtained with the same external parameters for all techniques, thanks to the unified implementations in the same framework. An important observation is that our analysis is focused on the techniques that are based on the rasterization pipeline, thus, the comparison does not include the techniques designed entirely for the ray-tracing pipeline.

A Framework for Learning and Rapid Implementation of Real-Time Global Illumination Methods

“…Among the real-time global illumination methods, there are several approaches that use certain data structures to store the light transport information, as presented by Ritschel et al [2] and more recently by Lambru et al [3]. This research field is complex and goes beyond the scope of this paper, so for a comprehensive analysis, the work cited above can be consulted.…”

“…There are several approaches [2,3] that process these data structures after the acquisition stage. Moreover, there is a wide range of techniques that sample them.…”

“…Subsequently, several real-time global illumination methods have been proposed [2,3]. Research in the field of development frameworks for these methods has been directed towards proprietary and commercial game engines.…”

“…This situation in which a rendering pass is used in several pipelines is quite necessary for the real-time rendering methods and also applies to real-time global illumination ones. This can be seen in our previous work [3], where the generation of G-buffers [49] and RSMs [6] is required for several techniques, so the rendering passes that produce these data structures are reused in several pipelines. Furthermore, the post-processing effects, implemented in rendering passes, can be reused in several rendering pipelines.…”

“…This result is called global illumination [1]. Several methods [2,3] have been proposed to produce the result in real time or have been adapted to achieve real-time performance as the GPU capabilities have grown.…”