Final exam effects Final exam effects Lighting Neon lights - PDF document

Announcement  Lots of CS Scholarship opportunities Textures I  Deadline: April 15, 2008. Final exam effects Final exam effects  Lighting  Neon lights  Textures / refelction  Strawberry  Snapple bottle  Water surface  CD surface  Volumetric  PET scan visualization  Postprocessing  “Classic” film look  Impressionistic painting Final exam effects Final exam effects  Grads  Please register your preference  Research and implementation plan  Mycourses quiz.  Teams  Implementation  RenderMan  GLSL  Documentations 1

Notes for Lab 1 Notes for Lab 1  GLSL coordinate spaces  In Renderman, premultiply opacity…I.e. world eye clip Os = Oi; object Model View Projection Cs = Ci * Os; transformation gl_ModelViewMatrix gl_ModelViewProjection Plan Texture Mapping Define surface characteristics of  Textures  an object using an image  This week Basic concept: associate value texture space (u,v)  at some coordinates in texture  Texture mapping (from files) with pixel at some coordinates in parameterization  Bump Mapping geometry Coordinate spaces used in  Environment Mapping object space (x o ,y o , z o )  texture mapping:  Simple Toon Shading Texture space (u, v) projection   Next week Object space (x o ,y o ,z o )  Screen space (x, y) screen space (x,y)  Procedural shading  Texture Mapping Texture Mapping y z x geometry screen v image u 2

Textures in shaders Texture pipeline  Textures are just data  Texture coordinates available to the shader  Global variable / semantic Akenine-Moller / Haines  Actual mapping determined by underlying scene model. Texture pipeline example Textures in shaders  Tasks:  Make texture data available to rendering  Grab texture data for a given point  Use texture coord from shading point  Indexed by some other means  Apply texture data as appropriate  Color, normal, opacity, whatever. Akenine-Moller / Haines Textures in RenderMan Texture mapping in RenderMan  Texture coordinates range from 0-1 in  Access texture values from file using the texture() function texture space  texture (filename, q, r) -- Return  Values of texture coords corresponding value(s) at texture coords (q,r) to P given in global parameters s and  texture (filename) -- Return value(s) t . at standard texture coords (s, t).  Filtered texture lookup  Free antialiasing. 3

Textures in RenderMan Textures in RenderMan  texture() function provides manual  Can access color or floating point values control over filtering from file  Blur  f = float texture (“foo.tex”);  Filter width  c = color texture (“bar.tex”);  Type of filter  Can access specific channels from file  Fill data (for missing channels)  f = texture (“foo.tex” [1]);  See Section 8.1.4 in text. Texture format Textures in RenderMan  prman has a proprietary format for textures. surface paintedplastic ( float Ka = 1, Kd = .5, Ks = .5, roughness = .1;  txmake [args] infile outfile color speccolor = 1; string texname = “”;)  Converts images into this format {  Args: color Ct = Cs; if (texname != “”)  -mode [black clamp periodic] Ct *= color texture (texname);  -smode, -tmode normal Nf = faceforward (normalize(N), I);  -short, -float vector V = -normalize (I);  -resize up- Ci = Ct * (Ka*ambient() + Kd*diffuse(Nf)) + speccolor * Ks * specular (Nf, V, roughness); Oi = Os; Ci *= Oi; } Textures in RenderMan Textures in GLSL  Questions?  Texture access in GLSL is almost as easy  EXCEPT…  Texture state must be set up in OpenGL program!  Places texture into texture memory for use by shaders 4

Setting up OpenGL Texture Setting up the OpenGL texture state state  Select a texture unit and make it active  Notes: ( glActiveTexture())  No need to enable texture (glEnable()) or  Create a tecture object and bind to the set the up the texture function active texture ( glBindTexture()). (glTexEnv())  Set texture parameters (wrapping,  Texture data must be read in by aux filtering etc) ( glTexParam()). functions.  Define the texture ( glTexImage()) Sample setup code Sample code setup  Initializing the texture  Using the texture glActiveTexture (GL_TEXTURE0) glBindTexture (GL_TEXTURE_2D, myTexName); Sample code setup On the shader side  Textures are grabbed from texture  Passing texture to a shader memory by use of samplers  sampler1D - 1D texture texLoc = glGetUniformLocation (myProgram,  sampler2D - 2D texture “paramname);  sampler3D - 3D texture glUniform1i (texLoc, 0);  samplerCube - cube map texture  samplerShadow1D/2D - shadow maps 5

Shader texture functions Texture access in GLSL  Access to texture values: use  texture1D  textureNNNN[proj/Lod] () functions  texture2D  shadowNNNN[proj/Lod] () functions  NNNN =  texture3D  1D / 2D / 3D - using texture coords (0-1)  textureCube  Cube - for environment mapping  [proj] - projective texture map  shadow1D  Proj = As if projected by slide projector/Useful in shadowing  Lod = Use of textures in vertex shaders  shadow2D  See section 5.7 for complete list Textures in GLSL Simple example  Projective texture mapping varying float Intensity; Uniform sampler2D myTexture; void main() { vec3 light = vec3 (texture2D (myTexture, glTexCoord [0].st; glFragColor = vec4 (light * Intensity, 1.0); } What you can do with texture Textures in GLSL maps  Textures are data  Color  Can be used as values  Bump Mapping  Individual components can be accessed via  Environment Mapping swizzling / masking  Toon Shading.  Questions / Break 6

Texture Mapping- Bump Mapping Texture Mapping- Bump Mapping  Perturbing surface normal  Adds roughness to surfaces  Texture map represents displacements from the  Quick way to add detail to normal an object  Use perturbed normal in illumination model  Polygon remains physically flat, but appears bumpy Jim Blinn Texture mapping – Bump Mapping Issues with Bump Mapping  How much to perturb  Common coordinate system  Using eye or even object may be cumbersome.  Normal map defined on object Tangent Space Bump mapping in RenderMan  Build a local coordinate system around  Performed using the displacement shader: the normal at a point  Modifies global variables P and N P+= bumpheight * normalize(N); N = calculatenormal (P);  Recall that displacement shaders are executed before surface shaders.  bumpheight can be read from a texture file, or generated procedurally, or both… 7

Bump mapping in RenderMan Bump vs displacement mapping  Displacement mapping  Bump mapping calculations should be done in “shader” space  Moves actual point P+= bumpheight * normalize(N); Coordinate Description N = calculatenormal (P); System  Bump mapping "shader" The coordinate system in which the shader was defined. This is the "object" coordinate  Just changes normal system when the shader is defined. N = calculatenormal (P + amp*normalize(N)); "current" The coordinate system in which the shading calculations are being performed. This is normally the "camera" or "world" coordinate system. Bump Mapping in Renderman Bump Mapping in GLSL vector Nshad = vtransform (“shader”, N);  No convenient displacement shader point Pshad = transform (“shader”, P);  Just vertex and fragment shaders Pshad += amp * normalize (Nshad); P = transform (“shader”, “current”, Pshad); N = calculatenormal (P);  Must be done in fragment shader  Works just as well (see Section 8.2.3 in text for derivation) vector Nn = normalize (N); P += Nn * (amp / length (vtransform(“shader”, Nn)); Phong as a Vertex Shader - Phong as a Vertex Shader - diffuse specular Lighthouse3d.com 8

Issues with Bump Mapping Tangent Space  How much to perturb  Build a local coordinate system around the normal at a point  Common coordinate system  Using eye or even object may be cumbersome.  Normal map defined on object GLSL does not have a calculatenormal() function Tangent Space Matrix Multiplication  Converting to tangent space � � � � � � S x T x T y T z O x � � � � � � S y = B x B y B z O y � � � � � � � � S x T x T y T z O x � � � � � � � � � � � � � S z � N x N y N z � O z � � � � � � � S y = B x B y B z O y � � � � � � � S z � � N x N y N z � � O z � � � � � S x = T x O x + T y O y + T z O z � � S - vector in tangent space  T - tangent vector   S x = T • O N - normal vector  B - binormal vector  S y = B • O  O - vector in object space   S z = N • O Bump Mapping Bump Mapping  For a modified Phong  For a modified Phong:  Vertex shader takes as args:  Fragment Shader will:  Normal (built-in)  Modify normal  Tangent (user defined)  Do lighting calculation.  Bi-normal (can be calculated)  Will pass to fragment:  Set fragment color.  Light vector  Eye position  BOTH IN Tangent Space 9