Advanced Computer Graphics: Rendering Hair and Fur, Slides of Computer Graphics

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Advanced Topics in

Computer Graphics

Rendering Hair and Fur

Introduction

Humans used to seeing faces, hair

Hair

tough to render right ƒ Takes over ¼ of rendering time of manycharacters

Hair Rendering

Background

Jim Blinn, SIGGRAPH 1982

Render volume densities ƒ Homogeneous volume of microscopic spheres ƒ Kajiya and Von Herzen, SIGGRAPH 1984 ƒ Generalized Blinn model to non-homogeneous media

Kajiya and Von Herzen: Volume Densities ƒ For each ray through the volume… ƒ Find the transparency of the surface ƒ Find the brightness of the surface

Kajiya and Kay (1989): Texels ƒ Replace volume densities with

texels

ƒ 3D array containing microsurface data ƒ Texels: replace all integrals with sums ƒ Transparency equation becomes ƒ Brightness equation becomes

Kajiy and Kay: Fur

Rendering

Four steps to rendering fur:

Create fur texel ƒ Map texels to world space ƒ Shoot rays into texel ƒ Calculate lighting Rendering time: 2 hours

Marschner et al,

SIGGRAPH 2003

Model as elliptical scales which form cylinder ƒ Model sub-surface scattering as before ƒ R, TRT (highlights) successively less bright

Marschner et al,

SIGGRAPH 2003

Tilted scales: R direction and TRT direction meansdifferent shape of secondary highlights ƒ Elliptical cross-section: simply rotating hair about axischanges distance between R, TRT

Compare Kajiya, Marschner and Real ƒ Marschner model shows more secondary, tertiaryhighlights, etc Kajiya Marschner Real Hair

Final Words

Moon and Marschner, SIGGRAPH 2006 ƒ Interreflections from hair is highly directional ƒ Irradiance caching approach for interreflections ƒ Sped up light calculations ƒ Marschner 2008 ƒ Used spherical harmonics to speed up rendering