CG for Vision Research

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CG for Vision Research

• Lecture 1
• Winter Term 05-06
• Quoc Vuong, Franck Caniard, MPI

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OpenGL Projections Transformations Graphics
Primitives Textures Lighting Material Properties
Vision Research Viewpoint Effect Structure from X
(Motion, Shading, Stereo) Active
Exploration Navigation
GLUT Window Management Input Devices Event
Loop Timing
Fun/Advanced Modeling Animations Mapping (bumps,
terrains) Physics Simulation Sound (OpenAL)
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Viewing Objects
The Ambassadors, Hans Holbein, 1533
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Setting the SceneThe Camera Analogy
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Coordinate Systems

• Three coordinate systems
• World (Fixed)
• Camera/Eye
• Object
• Relative position and orientation of eye and
  objects within world space inter-related
• Modelview transformation
• Eye also has projection
• Projection transformation

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Projections

• Define viewing volume
• Determines how an object is projected onto screen
  (2-D image plane)
• Determines what is visible (view clipping)

top
left
viewing volume
right
bottom
near
far
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Perspective glFrustum() gluPerspective()
Orthographic glOrtho() gluOrtho2D()
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• Perspective
• Parallel lines in 3-D not parallel in 2-D
  (foreshortening)
• Distortions larger at closer distances
• VP vanishing point

• Orthographic
• Parallel lines in 3-D remain parallel in 2-D
• Approximated by very distant objects
• Vanishing point at infinity

PlaneView3D www.mtsu.edu/csjudy/planeview3D/tuto
rial.html
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Transformations

• Three classes of model transformations
• Translation glTranslate()
• Rotation glRotate()
• Scaling glScale()
• gluLookAt()
• Combines all 3 transformations

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Move eye or object?
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Which transformation first? (matrix
multiplication is non-commutative AM ? MA)
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3-D Object Geometry

• 3-D object collection of vertices
• Position
• Surface Normal
• Normal is
• Object-centered
• Specifies orientation of points on surface, with
  respect to object coordinate system

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Surface Normals

• Vector perpendicular to tangent plane
• Has a direction (sign)!
• Used for calculating
• Shading angle between light ray and surface
  normal
• Visibility sign of direction with respect to eye
• Two methods to calculate normals (Appendix E in
  Redbook)
• Analytic solution If you know the surface
  function, you can calculate the normal exactly
• Polygonal approximation Calculate normal of
  polygon from 3 vertices

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Ballard Brown 82, Chap 3
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Projections and Transformations in OpenGL

• Redbook, Chap 3

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Enter the Matrix

• Projections and transformations are implemented
  as 4 x 4 matrices
• Eye and object transformations combined into
  modelview matrix
• Only one active current matrix
• Must switch between projection matrix and
  modelview matrix
• OpenGL functions to set current matrix
• Calls to glRotate(), glTranslate(), glScale(),
  etc. change values of active matrix
• Can directly change values of current matrix
• Can save and restore current matrix using Matrix
  Stack

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Transformation Matrix Multiplication
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Matrix Commands
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Modelview Matrix
Redbook, Appendix F
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Modelview Matrix
Scaling
glScalef(x,y,z)
Translation
glTranslatef(x,y,z)
Redbook, Appendix F
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Projection Matrix
Perspective
glFrustum()
Orthographic
glOrtho()
Redbook, Appendix F
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Matrix Stack

glPushMatrix()
glPopMatrix()
Top (current matrix)

• Keep track of matrix states (undoes)
• Hierarchical transformations

Bottom 2 projection 32 modelview
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Look At That!
gluLookAt(x, y, z, 0, 0, 0, 0, 1, 0)
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Rendering Pipeline(2nd pass)
3D Vertex Data
Vertex Evaluation
Frame Buffer
2D Pixel Data
Pixel Operation
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Translate Rotate Scale
3D Vertex Data
Vertex Evaluation
Modelview Matrix
(x, y, z)
Projection Matrix
Viewport Transf.
Frame Buffer
Perspective Orthographic
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Rendering Pipeline
MV
Pro
View port
3D Vertex Data
Vertex Evaluation
Frame Buffer
2D Pixel Data
Pixel Operation
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Template Code 1
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Basic Structure
Add libraries
Model Reader
Own/other libraries
Global variables Function prototypes
Initialization functions
Lighting
OpenGL States
Your functions here!
Model Renderer
Main function Infinite loop
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Header Files

• Interface between your program and libraries
• Data structures
• Functions
• Copies code in header file at include point
• Be careful not to duplicate variables or function
  names
• Standard directory paths for standard header
  files
• Accessed with ltgt (triangle brackets)
• Local directory for header files
• Accessed with (double-quotes)

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More on OpenGL States

• OpenGL states can be changed any where in your
  program
• Remember that states have default values!
• Sometimes comes in pairs
• glBegin() glEnd()
• glEnable() glDisable()
• glPushMatrix() glPopMatrix()
• Rule of thumb
• If you explicitly change a state, change it back
• If a state only needs to be changed once (e.g.,
  lighting), then set the state once in OpenGL
  initialization

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www.opengl.org/resources/code/basics/redbook/index
.html

• Add hand with additional fingers
• Animate robotic arm

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