Real-time Level-of-Detail Strand-based Hair Rendering

TL;DR

This paper presents a real-time strand-based hair rendering framework that ensures seamless level-of-detail transitions, maintains consistent appearance, and achieves significant speed improvements over traditional methods.

Contribution

It introduces an innovative LOD system using elliptical thick hairs and a novel BCSDF model for accurate, efficient hair rendering with seamless transitions.

Findings

Achieves up to 3x speedup in rendering performance.

Produces highly similar appearances to full geometries at various distances.

Ensures seamless LOD transitions with consistent hair appearance.

Abstract

Strand-based hair rendering has become increasingly popular in production for its realistic appearance. However, the prevailing level-of-detail solution employing hair cards for distant hair models introduces a significant discontinuity in dynamics and appearance during the transition from strands to cards. We introduce an innovative real-time framework for strand-based hair rendering that ensures seamless transitions between different levels of detail (LOD) while maintaining a consistent hair appearance. Our method uses elliptical thick hairs that contain multiple hair strands at each LOD to maintain the shapes of hair clusters. In addition to geometric fitting, we formulate an elliptical Bidirectional Curve Scattering Distribution Functions (BCSDF) model for a thick hair, accurately capturing single scattering and multiple scattering within the hair cluster, accommodating a spectrum from sparse to dense hair distributions. Our framework, tested on various hairstyles with dynamics as well as knits, shows that it can produce highly similar appearances to full hair geometries at different viewing distances with seamless LOD transitions, while achieving up to a 3x speedup.