Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics CIS 636/736 Computer Graphics Lecture 12 of 42 William H. Hsu Department of Computing and Information Sciences, KSU KSOL course pages: Course web site: Instructor home page: Readings: All slides from SIGGRAPH 2000 tutorial on OpenGL, Shreiner, Angel, Shreiner: Sections 2.6, 3.1, 20.3 – 20.13, Eberly 2 e – see NeHe tutorials: 6 – 10, Article: Surface Detail 5: Pixel and Vertex Programs

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Lecture Outline Based in part on OpenGL Tutorials from SIGGRAPH 2000 Vicki Shreiner: Animation and Depth Buffering  Double buffering  Illumination: light positioning, light models, attenuation  Material properties  Animation basics in OpenGL Vicki Shreiner: Imaging and Raster Primitives Ed Angel: Texture Mapping Dave Shreiner: Advanced Topics  Display lists and vertex arrays  Accumulation buffer  Fog  Stencil buffering  Fragment programs (to be concluded in Tutorial 3)

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Lighting Dave Shreiner

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Lighting Principles Lighting simulates how objects reflect light  material composition of object  light’s color and position  global lighting parameters  ambient light  two sided lighting  available in both color index and RGBA mode

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Surface Normals Normals define how a surface reflects light glNormal3f( x, y, z )  Current normal is used to compute vertex’s color  Use unit normals for proper lighting  scaling affects a normal’s length glEnable( GL_NORMALIZE ) or glEnable( GL_RESCALE_NORMAL ) CPU DL Poly. Per Vertex Per Vertex Raster Frag FB Pixel Texture

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Light Properties glLightfv( light, property, value );  light specifies which light  multiple lights, starting with GL_LIGHT0 glGetIntegerv( GL_MAX_LIGHTS, &n );  properties  colors  position and type  attenuation

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Light Sources Light color properties  GL_AMBIENT  GL_DIFFUSE  GL_SPECULAR

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Turning on the Lights Flip each light’s switch glEnable( GL_LIGHT n ); Turn on power glEnable( GL_LIGHTING );

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Light Material Tutorial

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Controlling a Light’s Position Modelview matrix affects a light’s position  Different effects based on when position is specified  eye coordinates  world coordinates  model coordinates  Push and pop matrices to uniquely control a light’s position

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Light Position Tutorial

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Frame Buffer Rasterization (including Pixel Zoom) Per Fragment Operations TextureM emory Pixel-Transfer Operations (and Pixel Map) CPU Pixel Storage Modes glReadPixels(), glCopyPixels() glBitmap(), glDrawPixels() glCopyTex*Image(); Pixel Pipeline Programmable pixel storage and transfer operations CPU DL Poly. Per Vertex Per Vertex Raster Frag FB Pixel Texture

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Texture Mapping Ed Angel

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Texture Mapping CPU DL Poly. Per Vertex Per Vertex Raster Frag FB Pixel Texture Apply 1-D, 2-D, or 3-D image to geometric primitives Uses of Texturing  simulating materials  reducing geometric complexity  image warping  reflections

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Texture Mapping s t x y z image geometry screen

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Texture Mapping and OpenGL Pipeline geometry pipeline vertices pixel pipeline image rasterizer Images and geometry flow through separate pipelines that join at the rasterizer  “complex” textures do not affect geometric complexity

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Texture Example The texture (below) is a 256 x 256 image that has been mapped to a rectangular polygon which is viewed in perspective

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Three steps  specify texture  read or generate image  assign to texture  assign texture coordinates to vertices  specify texture parameters  wrapping, filtering Applying Textures [1]

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Applying Textures [2]  specify textures in texture objects  set texture filter  set texture function  set texture wrap mode  set optional perspective correction hint  bind texture object  enable texturing  supply texture coordinates for vertex  coordinates can also be generated

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Define a texture image from array of texels in CPU memory glTexImage2D( target, level, components, w, h, border, format, type, *texels );  dimensions of image must be powers of 2 Texel colors are processed by pixel pipeline  pixel scales, biases and lookups can be done Specify Texture Image CPU DL Poly. Per Vertex Per Vertex Raster Frag FB Pixel Texture

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Tutorial: Texture

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Summary OpenGL Tutorials from SIGGRAPH 2000 Vicki Shreiner: Animation and Depth Buffering  Double buffering  Illumination: light positioning, light models, attenuation  Material properties  Animation basics in OpenGL Vicki Schreiner: Imaging and Raster Primitives Ed Angel: Texture Mapping in OpenGL More in CG Basics 5: GL Primer 2 of 3

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Terminology Double Buffering Lighting Illumination Equation – describes light in scene  Ambient light – catch-all term for whole scene, all lights  Diffuse reflectance – omnidirectional, from matte surfaces  Specular reflectance – unidirectional, for highlights: shiny surfaces  Attenuation – how quickly light drops off as function of distance Pixel and Fragment Programs (“Pixel Shaders”) Vertex Shaders Texture Maps Other Mappings Discussed in Course  Bump aka displacement – perturb surface normal, calculate lighting  Reflection and transparency  Shadow  Environment

Computing & Information Sciences Kansas State University Lecture 12 of 42CIS 636/736: (Introduction to) Computer Graphics Next: Polygons, OpenGL Tutorial 3 Dave Shreiner: Advanced Topics (concluded)  Advanced Primitives: Cubic Curves, Bicubic Surfaces  More on Shadow Stencil Buffer  Alpha, Blending, Antialiasing  Accumulation Buffer, Fog, Jitter Using the OpenGL Shading Language  More on fragment programs  Demo: color interpolation  Example: Fast Phong shading Special Effects