# Cache and Bandwidth Aware Real-time Subsurface Scattering

University of Maryland, Baltimore County
Figure 1: MetaHuman rendered with our proposed subsurface scattering algorithm in Unreal Engine in real time.

Abstract: Photo-realistic subsurface scattering is a demanding feature in many real-time applications, especially in next-generation games and virtual productions where the uncanny valley needs to be addressed for real-time human skin rendering. Most importantly, it must be addressed in milliseconds or less without visible quality compromise. These quality and performance demands are prohibitively expensive when using Monte Carlo sampling for subsurface scattering. Moreover, real-time rendering is limited by hardware capability and GPU cache architectures. This dissertation explores novel algorithms for high-quality photo-realistic real-time subsurface scattering with cache incoherence and limited bandwidth.
To achieve this, a new generic taxonomy is proposed for heterogeneous realtime rendering to identify techniques that can improve bandwidth and cache utilization. A single pass, variance guided, and generic O(1) real-time adaptive sampling technique is proposed to minimize bandwidth demands and improve cache utilization. This adaptive sampling pass works with different global temporal accumulation techniques (e.g., Temporal Anti-Aliasing and Deep Learning Super Sampling) to further improve quality. We propose a new technique, adaptive filtered importance sampling (AFIS), based on our single pass adaptive sampling technique and filtered importance sampling. A hybrid AFIS and the separable approximation technique allows the user to balance quality and performance. To deal with instability during dynamic lighting, a novel use of Control Variates (CV) in the sample domain instead of shading domain is proposed.
Our algorithm induces as little as one texture overhead to a real-time rendering engine, and has been battle tested in the Unreal Engine, a commercial game engine.

#### News

• 2020.12.31: Dissertation is included in SIGGRAPH PhD Thesis Fast Forward 2021!

#### Hooding Narrative

Dr. Xie developed approximations to the fundamental mathematics of subsurface scattering to address the uncanny valley of skin rendering of digital humans in metaverse and games. He is currently working as a rendering programmer at Epic Games.

#### BibTex

@phdthesis{xie2021cache,
title={Cache and Bandwidth Aware Real-Time Subsurface Scattering},
author={Xie, Tiantian},
year={2021},
school={University of Maryland, Baltimore County}
}