1. RenderMan (Shading Language: Concepts)

2. RenderMan Interface

3. 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

4. New Shading System Turner Whitted & David M. Weimer Robert Cook
1980, Shading dispatch table
Robert Cook
1984, Shade Trees
Ken Perlin
1985, Pixel Stream
Pat Hanrahan & Jim Lawson
1990, Shading Language

5. 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”
Cdiff: texture mapping
N: bump mapping

6. Diffuse Reflection Assume surface reflects equally in all directions
Example: chalk, clay

7. Diffuse Reflection
Lambertian model
Cosine law (dot product)

8. Specular Reflection Reflection is strongest near mirror angle
Examples: mirrors, metals

9. Specular Reflection Phong Model
cos (a)n : This is a physically-motivated hack!

10. Ambient Term Represents reflection of all indirect illumination
This is a total hack
Avoid complexity of global illumination

11. Surface Illumination Calculation

12. Types of shaders Surface shaders Displacement shaders Light 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 output
Programmable imager shaders are supported by BMRT; but not by PRMan.

13. 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 any kind
Names of color spaces
“rgb”, “hsv”, “hsl”, “YIQ”, “xyz”, “xyY”
Names of predeclared geometric spaces
“current”, “object”, “shader”, “world”, “camera”, “screen”, “raster”, “NDC”

14. 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];
Class: uniform | varying(default)

15. 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

16. Geometry at the Surface

17. Surface shader, Light shader

18. 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" [ ]
Sphere

19. expressions Unary – Binary + * - / ^ . ^ and . * and / for matrix type
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

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

21. Built-in functions 수학함수 기하함수 색함수 행렬함수
PI, radians, degree, sin, asin, cos, acos, tan, atan, pow, exp, sqrt, inversesqrt, 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

22. Built-in functions 문자열함수 쉐이딩과 라이팅 함수 텍스쳐 매핑함수 메시지 전달 및 정보함수 추가된 함수
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, attribute, option, rendererinfo, shadername
추가된 함수
gather, occlusion, indirectdiffuse, photonmap, iradiancecache, caustic, transmission, gridpattern, ambience, trace

23. 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; )

24. My First Shader Surface Shader Cs, Os: input color and opacity
surface first() {
Oi=Os;
Ci=Cs*Oi; }
Surface Shader
Cs, Os: input color and opacity
Ci, Oi: output color and opacity
Compile: slc first.sl
Display "first.tiff" "file" "rgb"
Projection "perspective" "fov" [45]
LightSource "ambientlight" 1 "intensity" [0.2]
LightSource "spotlight" 2 "from" [ ]
"to" [0 0 3] "intensity" [3]
Translate 0 0 3
WorldBegin
Color [1 0 0]
Surface "first"
Sphere
WorldEnd

25. My Second Shader faceforward(N,I) diffuse(N)
surface second (
float Ka = 1;
float Kd = 1; ) {
normal Nf = faceforward (normalize(N),I);
Oi = Os;
Ci = Cs * diffuse(Nf) * Oi; }
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)
Display “second.tiff" "tiff" "rgba"
Format
Projection "perspective" "fov" [45]
LightSource "ambientlight" 1 "intensity" [0.2]
LightSource "spotlight" 2 "from" [ ]
"to" [0 0 3] "intensity" [3]
Translate 0 0 3
WorldBegin
Color [1 0 0]
Surface “second"
Sphere
WorldEnd

26. My Third Shader specular(N,V,0.1) Dot product: R, V V: invert I
surface third () {
normal Nf = faceforward (normalize(N),I);
vector V = -normalize(I);
Oi = Os;
Ci = Oi * Cs * specular(Nf,V,0.1); }
My Third Shader
specular(N,V,0.1)
Dot product: R, V
V: invert I
R: Reflection vectorLight(L) and Normal(N)
0.1: roughness
Display “third.tiff" "tiff" "rgba"
Format
Projection "perspective" "fov" [45]
LightSource "ambientlight" 1 "intensity" [0.2]
LightSource "spotlight" 2 "from" [ ]
"to" [0 0 3] "intensity" [3]
Translate 0 0 3
WorldBegin
Color [1 0 0]
Surface “third"
Sphere
WorldEnd

27. 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; }