CIS736-Lecture-12-20080218

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CIS 636/736 Computer GraphicsLecture 12 of 42
Surface Detail 5 Pixel and Vertex Programs
William H. Hsu Department of Computing and
Information Sciences, KSU KSOL course pages
http//snipurl.com/1y5gc Course web site
http//www.kddresearch.org/Courses/CIS636 Instruct
or home page http//www.cis.ksu.edu/bhsu Readin
gs All slides from SIGGRAPH 2000 tutorial on
OpenGL, Shreiner, Angel, Shreiner
http//www.cs.unm.edu/angel/SIGGRAPH/ Sections
2.6, 3.1, 20.3 20.13, Eberly 2e see
http//snurl.com/1ye72 NeHe tutorials 6 10,
http//nehe.gamedev.net Article
http//www.kuro5hin.org/story/2003/10/28/9853/1617
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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)

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Lighting

• Dave Shreiner

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Lighting Principles

• Lighting simulates how objects reflect light
• material composition of object
• lights color and position
• global lighting parameters
• ambient light
• two sided lighting
• available in both color indexand RGBA mode

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Surface Normals

• Normals define how a surface reflects light
• glNormal3f( x, y, z )
• Current normal is used to compute vertexs color
• Use unit normals for proper lighting
• scaling affects a normals length
• glEnable( GL_NORMALIZE ) orglEnable(
  GL_RESCALE_NORMAL )

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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

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Light Sources

• Light color properties
• GL_AMBIENT
• GL_DIFFUSE
• GL_SPECULAR

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Turning on the Lights

• Flip each lights switch
• glEnable( GL_LIGHTn )
• Turn on power
• glEnable( GL_LIGHTING )

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Light Material Tutorial
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Controlling a Lights Position

• Modelview matrix affects a lights position
• Different effects based on when position is
  specified
• eye coordinates
• world coordinates
• model coordinates
• Push and pop matrices to uniquely control a
  lights position

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Light Position Tutorial
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Pixel Pipeline

• Programmable pixel storage and transfer
  operations

glBitmap(), glDrawPixels()
Rasterization (including Pixel Zoom)
Pixel-Transfer Operations (and Pixel Map)
Pixel Storage Modes
Per FragmentOperations
FrameBuffer
CPU
glCopyTexImage()
TextureMemory
glReadPixels(), glCopyPixels()
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Texture Mapping

• Ed Angel

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Texture Mapping

• Apply 1-D, 2-D, or 3-D image to geometric
  primitives
• Uses of Texturing
• simulating materials
• reducing geometric complexity
• image warping
• reflections

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Texture Mapping
screen
geometry
image
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Texture Mapping andOpenGL Pipeline

• Images and geometry flow through separate
  pipelines that join at the rasterizer
• complex textures do not affect geometric
  complexity

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Texture Example

• The texture (below) is a 256 x 256 image that
  has beenmapped to a rectangularpolygon which is
  viewed inperspective

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Applying Textures 1

• Three steps
• specify texture
• read or generate image
• assign to texture
• assign texture coordinates to vertices
• specify texture parameters
• wrapping, filtering

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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

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Specify Texture Image

• 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 bedone

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Tutorial Texture
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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

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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

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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