RealTime Hair Rendering Agenda Introduction Hair Geometry Hair

Real-Time Hair Rendering Гнатюк Денис

Agenda ü Introduction ü Hair Geometry ü Hair Shading

Introduction ü 4, 095 individual hairs ü 123, 000 vertices (just for the hair rendering)

Hair Geometry

Data Flow

Data Flow

Tessellation

Interpolation Barycentric coefficients: b. A + b B + b C = 1 Interpolated hair Y : Y = A x b. A + B x b. B + C x b. C

Interpolation

Interpolation

The Effect of Tessellation and Interpolation

Modulate density across scalp

Curly Hair

Hair Shading üa local reflectance model for hair üa method for computing self-shadowing between hairs

A Real-Time Reflectance Model for Hair The Marschner Reflectance Model S(f i , q i ; f o , q o ) S = SR + STT + STRT Sp = Mp (q i , q o ) x Np (q d , f d ) for P = R, TT, TRT q d = ½(q i – q o ), f d = f i – f o

Lookup Textures for the Marschner Hair Reflectance Model

Reflectance

Pseudocode Summarizing the Shaders // In the Vertex Shader: Sin. Theta. I = dot(light, tangent) ; Sin. Theta. O = dot(eye, tangent) ; Light. Perp = light – Sin. Theta. I * tangent ; eye. Perp = eye – Sin. Theta. O * tangent ; Cos. Phi. D = dot(eye. Perp, light. Perp) * (dot(eye. Perp, eye. Perp) * dot(light. Perp, light. Perp))^-0. 5 // In the Fragment Shader: (MR, MTT, MTRT, cos. Theta. D) = lookup 1(cos. Theta. I, cos. Theta. O) (NTT, NR) = lookup 2(Cos. Phi. D, cos. Theta. D) NTRT = lookup 3(Cos. Phi. D, cos. Theta. D) S = MR * NR + MTT * NTT + MTRT * NTRT

Real-Time Volumetric Shadows in Hair Ø Stencil Shadow Volumes Ø Shadow Maps ü Opacity Shadow Maps !

Opacity Shadow Maps - T(x, y, z) is the fraction of light penetrating to depth z - σ is called the opacity thickness - r(x, y, z) is the extinction coefficient

Opacity Shadow Maps To compute σ at a discrete set of z values z 0. . . z n-1 where z i < z i+1. - n = 16 - z 0 being the near plane of the hair in light space - z 15 being the far plane of the hair in light space - z i = z 0 + i dz, dz = (z 15 – z 0)/16

Opacity Shadow Maps

Results

Results

Q&A