CG for Vision Research

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CG for Vision Research

• Lecture 2
• 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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Lighting Materials Properties
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Lighting ? Realism
www.cs.kuleuven.be/cwis/research/graphics/RENDERPA
RK/
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more render time
www.winosi.onlinehome.de/Gallery_t14_01.htm
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The Cornell Box Which is real and which is
synthesized?
Left is real!
www.graphics.cornell.edu/online/box/compare.html
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Lighting
Illumination/Lighting Model
Shading Model
Global
Local
Flat
Gouraud
Phong
Reflected
Ambient
Directed
Scattered
www.ntsc-uk.com/features/BeautyPixelDeep/GouraudPh
ong.jpg
Directional
Positional
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Illumination Model
surface normal
Diffuse Reflection
Specular Reflection
Specifies interaction between light ray and
material
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• Material properties defined by illumination model
• Materials have a separate ambient, diffuse and
  specular component

Mathworks 3-D Visualization
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en.wikipedia.org/wiki/Phong_shading
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Shading Model

• Specifies how illumination is applied locally to
  vertices and ultimately pixels
• Flat Compute the colour for a polygon, and use
  this colour for the entire polygon
• Gouraud Compute colour at vertices and
  interpolate these colours across the polygon
• Phong Compute colour by normal interpolation
  during rasterization (Not implement in OpenGL lt
  2.0)

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Flat
Gouraud
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Shape-from-Shading

• Three important components of shading models
• Position of light source
• Position of eye
• Surface normal

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Demos!

• Material properties (Lesson26_ball.exe)
• Shadows (Lesson27_shadows.exe)

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Culling

• For rendering efficiency, dont draw polygons
  that are not visible
• Culling or back-face elimination simple
  operation that compares surface normals of
  polygons to viewpoint and removes polygons that
  cannot be seen

viewing volume
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Lighting Mat. Prop. in OpenGL

• Redbook, Chap 4

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Lighting in 5 Easy Steps

• Initialize OpenGL for lighting
• Define Normal vectors at each vertex
• From model, analytically or by polygon
  approximation
• Create, select and position one or more light
  sources
• Create and select a lighting model
• Global ambient level
• Location of viewpoint
• Define material properties of each object
• Colour (ambient, diffuse and emission)
• Specularity and shininess

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Initialization
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Create Light Source
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Types of Light Sources
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Material Properties
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Template Code 2
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Basic Structure
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The Event Loop (GLUT)
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Event-driven Model

• Standard approach in graphical-user interfaces
• Every action of program is response to user
  events
• Nothing (idle)
• Press key button
• Press mouse button or move mouse (or both)
• Interactivity with user

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The glutMainLoop

• void glutMainLoop(void)
• // pseudo-code
• loop forever
• check event queue
• if (event)
• // user performed some action (e.g., pressed
  key)
• invoke appropriate callback function (e.g.,
  keyboard)
• else
• // user idle
• if (idle function exists)
• invoke idle function (e.g., display scene)
• else
• sleep for 1 time unit

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The Loop Thickens
GLUT Event Loop
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• Make stationary light source
• Make light source move with viewpoint
• Add at least another light source
• Combine movelight.c with material.c

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