RenderMan - Shading Language: Concepts -
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
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; }
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 output
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
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];
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 Surface Graphics State Variables
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); ) { ... } 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, 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
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, attribute, 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; )
1.Polygons A.Polygon B.GeneralPolygon C.PointsPolygons D.PointsGeneralPolygons 2.Patches A.Basis B.Patch C.PatchMesh D.NuPatch E.TrimCurve 3.Subdivision Surfaces A.SubdivisionMesh 4.Quadrics A.Sphere B.Cone C.Cylinder D.Hyperboloid E.Paraboloid F.Disk G. Torus Homework
