What is Ray Tracing?

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What is Ray Tracing?

• In computer graphics, an advanced technique for
  adding realism to an image by including
  variations in shade, color intensity, and shadows
  that would be produced by having one or more
  light sources. Webopedia

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What is Ray Tracing?

• A rendering method that simulates light
  reflections, refractions and shadows. It follows
  a light path from a specific source and computes
  each pixel in the image to simulate the effect of
  the light. It is a very process-intensive
  operation. PCmag Encyclopedia

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What is raytracing?

• Its a graphics technique for rendering very
  realistic scenes.
• And a method of creating highly unreal scenes
  that look plausible, too.
• Each pixels colour is calculated from a
  reasonably accurate physics model.
• The path of a notional light ray is traced from
  the screen out into the scene.

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Tracing the path of a ray...

• The colour of a pixel is calculated by tracing
  the ray from the viewpoint, through the pixel
  until an intersection is found.
• Further rays may be generated and they are
  traced, and so on.
• Dull, opaque objects tend to stop a ray, but
  shiny objects reflect and transparent objects can
  generate extra rays.

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Tracing the path of a ray...
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Limitations

• Perfect parallel mirrors are an obvious problem -
  most ray-tracers have a fixed cut-off depth.
• Some ray tracers add a glow to all objects to
  help simulate ambient lighting.
• Complex scenes may require a lot of memory and an
  enormous amount of time to process.
• Real-time ray-tracing is a big research topic.
  See http//www.youtube.com/watch?vmtHDSG2wNh

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Performance

• In a scene of 100 primitive objects, rendered at
  a resolution of 640 by 480 pixels, the minimum
  number of intersection tests (using the simplest
  ray tracing algorithm) is in excess of 30
  million.
• In practice, objects are bound by spheres or
  boxes to simplify intersection tests. Only if the
  ray intersects with the bounding shape is it
  worth testing the complex shape.

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Constructive Solid Geometry

• Primitive shapes (spheres, boxes, cones,
  cylinders) are not terribly useful on their own.
• CSG gives us a way to build complicated shapes by
  merging, joining and subtracting primitives.
• You can weld shapes together or use one shape to
  take a chunk out of another with CSG.

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CSG types

• union (and merge)objects glued together - may
  overlap. Merging loses the edges inside the
  composite object.
• intersectionthe new object exists only where all
  the original shapes overlapped.
• differenceremoves a shape from another.

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Boolean Set Operators

• Union -edges maintained

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Boolean Set Operators

• Merge -edges lost

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Boolean Set Operators

• Intersection

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Boolean Set Operators

• Difference

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Practicalities

• Ray tracing procedures have to be modified to
  determine the surfaces of the CSG objects
• Surfaces are generated for a CSG object by using
  the texture of the primitive that formed that
  surface

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References Reading

• Ray Tracing, G. Scott Owen, SIGgraphhttp//www.si
  ggraph.org/education/materials/HyperGraph/raytrace
  /rtrace0.htm
• The Internet Raytracing Competitionhttp//www.irt
  c.org/
• Simple Nature Chapter 12, Opticshttp//www.lig
  htandmatter.com/html_books/0sn/ch12/ch12.html