Ray Tracing Variants

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Ray Tracing Variants

• Distributed ray tracing
• Generalized rays
• Cone Tracing
• Beam Tracing
• Pencil Tracing
• Constructive solid geometry
• Acceleration methods

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Distributed Ray Tracing

• General term for shoot a bunch-o-extra rays
• Solution for fuzzy phenomena

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Examples

• Distributing reflected rays according to specular
  distribution function (blurry reflection)
• Distributing transmitted rays (blurry
  transparency)
• Distributing shadow feelers (penumbra)
• Distributing ray origins over camera lens (depth
  of field)
• Distributing rays in time (motion blur)

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Whats the matter with ray tracing?

• ?

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Whats the matter with ray tracing?

• Infinitesimally small rays are point sampling our
  space
• We generally fix this using more rays
• Contributes to exponential blowups
• We dont take advantage of coherence

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Generalized Rays

• Rays that have a shape of some kind
• Cone for example
• Why?

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Cone Tracing

• Apex
• Spread angle
• Center line

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Partial Intersections
What do we do?
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Cone tracing

• Intersection test is more complicated
• Complex surface geometry is very difficult
• How do we do
• Reflections?
• Shadow feelers?

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Beam Tracing

• Rays with polygonal cross sections

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How arbitrary are the cross sections?
Non-convex? Holes? How big should initial beam be?
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How to?

• Shadows
• Penumbra
• Reflections

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Beam Trees

• Each beam can generate additional beams due to
• Continuing past object
• Splitting around object
• Shadow feelers
• Reflections
• These form a tree

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Beam Tracing Big Advantage

• Takes advantage of spatial coherence!

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Pencil Tracing

• Pencil
• Centered axial ray
• Set of paraxial rays
• Closely aligned to axial ray
• Infinite set (not actually represented)
• Uses paraxial theory of optics
• Optics can be approximated using linear
  transformations in the small
• 4 x 4 transformation matrix for each pencil
  intersection, concatenate matrices

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A fast ray tracer using pencil tracing

• Use rays around the edges and pencils in large
  (multiple pixel) shaded areas
• Order of magnitude improvement
• Approximation, though.

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Constructive Solid Geometry

• Ray tracing is very natural for CSG
• How?

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Ray Tracing Acceleration Techniques
Acceleration Techniques
Faster Intersections
Fewer Rays
Generalized Rays
Fewer ray-object intersections
Faster ray-object intersections
Adaptive tree-depth Adaptive sampling
Volume hierarchies Spatial subdivision Directional
techniques
Beam tracing Cone tracing Pencil tracing
Bounding volumes Efficient surfaces