RenderMan(Shading Language: Concepts)

RenderMan Interface

Conventional Shading System

Fixed parameter shading system Disadvantages

Built-in shading model is NOT enough New shading model

• Realistic shading model

• NPR

Can be inefficient

Flexible, extensible system is needed

New Shading System

Turner Whitted & David M. Weimer 1980, Shading dispatch table

Robert Cook 1984, Shade Trees

Ken Perlin 1985, Pixel Stream

Pat Hanrahan & Jim Lawson 1990, Shading Language

Parameterized shading model

Phong illumination model

Does not change the fundamental form of the shading equation Narrow range of appearances

Simple analytic model: Diffuse reflection + Specular reflection + Emission + “Ambient”

))()((1

nispecs

nlights

iiidiffdambaoutput RVCKClLNCKCKC

Diffuse Reflection

Assume surface reflects equally in all directions Example: chalk, clay

Diffuse Reflection

Lambertian model Cosine law (dot product)

Specular Reflection

Reflection is strongest near mirror angle Examples: mirrors, metals

Specular Reflection

Phong Model cos (n : This is a physically-motivated hack!

Ambient Term

Represents reflection of all indirect illumination This is a total hack

• Avoid complexity of global illumination

ALAA IKI

Surface Illumination Calculation

))()((1

nispecs

nlights

iiidiffdambaoutput RVCKClLNCKCKC

Types of shaders

Surface shaders Appearance of surface How they react to the lights

Displacement shaders How wrinkle or bump

Light shaders Directions, amounts, and colors of illumination

Volume shaders How light is affected as it passes through a participating medium

Imager shaders Describe color transformation make to final pixel values before the are outp

ut

Shading Language data type

Built-in types Floats Colors Points, Vectors, Normals Matrices Strings

SL has no double or int types SL does not support user-defined structures or pointer of a

ny kind

Shading Language Variables

Global variables graphics state variables

[class] type variablename [=initializer] Static 1D arrays are allowed

e.g.) float a; uniform float b; float c = 1; float d = b*a; float e[10];

Surface Graphics State Variables

P Surface position N Shading normal Ng Geometric normal I Incident vector E Vantage(eye) point Cs Surface color

Os Surface Opacity s,t Texture coordinates L,Cl Light vector and color u,v Parametric coordinates du,dv Change in coordinates dPdu,dPdv Surface tangents

Geometry at the Surface

Surface shader, Light shader

Shader Parameters

surface pitted (float Ka = 1, Kd = 1, Ks = 0.5;

float angle = radiances(30);

color spotcolor = 0;

color strpicolor = color (.5, .5, .75);

string texturename = "";

string dispmapname = "mydisp.tx";

vector up = vector "shader" (0, 0, 1);

varying point Pref = point (0, 0, 0);

)

{

...

}cd

Decalre "Kd" "float"

Declare "stripecolor" "color"

Surface "pitted" "Kd" [0.8] "stripecolor" [.2 .3 .8]

Sphere 1 -1 1 360

expressions

Unary – Binary + * - / ^ . ^ and .

– Operators only work for vectors and normals– ^ (vector cross product)– . (vector dot product)

* and / for matrix type– * (matrix multiplication)– / (matrix multiplication by the inverse)

Type casts Ternary operator ? : Function calls

Built-in functions

Angles & Trigonometry Exponentials, etc. Miscellaneous simple scalar functions Color operations Geometric functions Strings Matrix functions

Built-in functions

수학함수 PI, radians, degree, sin, asin, cos, acos, tan, atan, pow, exp, sqrt, inversesq

rt, log, mod, abs, sign, min, max, clamp, mix, floor, ceil, round, step, smoothstep, filterstep, spline, Du, Dv, Deriv, random, noise, pnoise, cellnoise,

기하함수 xcomp, ycomp, zcomp, setxcomp, setycomp, setzcomp, length, normalize,

distance, ptlined, rotate, area, faceforward, reflect, refract, fresnel, transform, vtransform, ntransform, depth, calculatenormal

색함수 comp, setcomp, mix, ctransform

행렬함수 comp, setcomp, determinant

Built-in functions

문자열함수 concat, printf, format, match,

쉐이딩과 라이팅 함수 ambient, diffuse, specular, specularbrdf, phong, trace,

텍스쳐 매핑함수 texture, environment, shadow, textureinfo

메시지 전달 및 정보함수 atmosphere, displacement, lightsource, surface, incident, opposite, attribut

e, option, rendererinfo, shadername 추가된 함수

gather, occlusion, indirectdiffuse, photonmap, iradiancecache, caustic, transmission, gridpattern, ambience, trace

Writing SL functions

Only one return statement is allowed per function Call by reference mechanism You may not compile functions separately from the body of

your shader

returntype functionname(params)

{

do some computations;

...

return return_value;

}

float myfunc ( float f; output float g;

)

My First Shader

Surface Shader Cs, Os: input color and opacity Ci, Oi: output color and opacity

Compile: slc first.sl

surface first()

{

Oi=Os;

Ci=Cs*Oi;

}

Display "first.tiff" "file" "rgb"

Projection "perspective" "fov" [45]

LightSource "ambientlight" 1 "intensity" [0.2]

LightSource "spotlight" 2 "from" [-1 1 0 ]

"to" [0 0 3] "intensity" [3]

Translate 0 0 3

WorldBegin

Color [1 0 0]

Surface "first"

Sphere 1 -1 1 360

WorldEnd

My Second Shader

faceforward(N,I) Face forward surface normal Shade the back just the same as the front N : Shading normal I : Incident vector

diffuse(N) Dot Product: Nf, L (=Light vector)

surface second (float Ka = 1;float Kd = 1;)

{ normal Nf = faceforward (normalize(N),I);

Oi = Os; Ci = Cs * diffuse(Nf) * Oi;}

Display “second.tiff" "tiff" "rgba"Format 320 240 1Projection "perspective" "fov" [45]LightSource "ambientlight" 1 "intensity" [0.2]LightSource "spotlight" 2 "from" [-1 1 0 ]

"to" [0 0 3] "intensity" [3]Translate 0 0 3WorldBeginColor [1 0 0]Surface “second"Sphere 1 -1 1 360WorldEnd

My Third Shader

specular(N,V,0.1) Dot product: R, V V: invert I R: Reflection vectorLight(L) and Normal(N) 0.1: roughness

surface third (){ normal Nf = faceforward (normalize(N),I); vector V = -normalize(I);

Oi = Os; Ci = Oi * Cs * specular(Nf,V,0.1);}

Display “third.tiff" "tiff" "rgba"Format 320 240 1Projection "perspective" "fov" [45]LightSource "ambientlight" 1 "intensity" [0.2]LightSource "spotlight" 2 "from" [-1 1 0 ]

"to" [0 0 3] "intensity" [3]Translate 0 0 3WorldBeginColor [1 0 0]Surface “third"Sphere 1 -1 1 360WorldEnd

Quick tour of a Shader

surface

plastic(float Ka = 1, Kd = 1, Ks = 0.5, roughness = 0.1;

color specularcolor = 1;)

{

/* simple plastic-like reflection model */

normal Nf = faceforward(normalize(N), I);

vector V = -normalize(I);

Ci = Cs * (Ka*ambient() + Kd*diffuse(Nf))

+ Ks*specularcolor*specular(Nf, V, roughness);

Oi = Os;

Ci *= Oi;

}