Shadow Mapping based Algorithms for Arbitrary 3D Scenes

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Shadow Mapping based Algorithms for Arbitrary 3D
Scenes
University of Rome Tor Vergata DEGREE IN COMPUTER
SCIENCE ENGINEERING
BACHELOR DEGREE THESIS

• Candidate
• Fabio Suriano
• Assistant Professor
• Prof. Roberto Basili
• Prof. Paolo Cignoni

ACADEMIC YEAR 2004/2005
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Summary

• What are shadows ?
• Shadows Usefulness in Computer Graphics
• Shadow Volumes (or Stencil Shadows)
• Standard Shadow Map
• Perspective Shadow Map
• Results

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What are shadows ?

• They are the concequence of interaction between
  an object, called occluder, and a light source

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What are shadows ?

• They are the concequence of interaction between
  an object, called occluder, and a light source

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Usefulness of Shadows in 3D Graphics

• They confer realism to 3D Scenes
• Videogames
• Doom3 of ID Software
• Digital Movies created with 3D rendering
  packages
• Renderman of Pixar Animation Studios

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Shadow Volumes

• They are based on occluder geometric volume
  description
• This volume is called Shadow Volume
• In order to compute the shadow volume we have to
  determine the object edge silhouette, extruding
  it at infinity. Moreover, we have to use the
  stencil buffer to find shadowed and not shadowed
  areas

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Shadow Volumes

• What happen in the Stencil Buffer ?

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Shadow Volumes

• Lit zones have elements 0
• Shadowed zones have elements gt 0

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Standard Shadow Map

• In the very beginning we consider two frame of
  reference systems
• Observer
• Light Source
• Algorithm
• From the light point of view we acquire z-buffer
  information (i.e. We acquire shadow map)
• A shadow map sample
• B a generic point in the observer space
• B TB (where T is a linear transformation that
  maps B from observer space to light space)
• From the observer point of view we transform the
  fragments in light space, performing the
  visibility test. Finally, we can render the scene

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What is the Shadow Map ?

• It is a texture that stores depth buffer
  information from light point of view

Light point of view
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What is the Shadow Map ?

• It is a texture that stores depth buffer
  information from light point of view

Light point of view
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Standard Shadow Map

• if then B is in shadow
• if then B is lit

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Standard Shadow Map

• In the first step of the algorithm we store the
  Shadow Map or, alternatively, the Depth Map in a
  texture
• In the second step we use the shadow map
  information to determine the shadowed and
  unshadowed regions, by a comparing operation

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Perspective Shadow Map

• Shadow aliasing reduction
• In order to obtain the shadow aliasing reduction,
  the shadow map is acquired in post-perspective
  space
• Therefore, we must
• Transform the light source in post-perspective
  space
• Determine the light frustum in post perspective
  space so that tightly fits the unit cube
• Store the shadow map in a texture

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Perspective Shadow Map

• How the space has been deformed, after
  perspective transformation P ?

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Perspective Shadow Map

• How the space has been deformed, after
  perspective transformation P ?

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Perspective Shadow Map

• Frustum computation for a light source in
  post-perspective space

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Results

• Standard Shadow Map

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Results

• Perspective Shadow Map

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Results

• Integrated Development Environment
• Microsoft Visual Studio .net 2003
• Programming Language
• C/C
• Graphics API
• OpenGL
• Code lines
• 7910