CS6230: Parallel Rendering

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CS6230 Parallel Rendering

• Andrew Hilton
• Brett Lucey

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What is Ray Tracing?

• Creates very high quality computer rendered
  images
• Rays are cast from the view plane (screen) into
  3D space until they hit an object
• The color of the object hit determines the color
  of the pixel

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What is Ray Tracing?

• When a ray hits an object, it may bounce. It
  will absorb some of the color, but continue
  onto another object. This creates reflections.

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Ray Tracing

• Every time a ray hits a reflective and/or
  transparent object, additional rays must be cast
  from that point.
• Every contact with an object must also result in
  checks for lights and lighting effects.
• More objects and lights/lighting effects become
  expensive quickly.
• Very parallelizable

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Example 1
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Example 2
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Who does Ray Tracing?

• Not Pixar! Pixar actually using shading, which
  is less computationally expensive, but the
  parallelization ideas are similar.
• Render farm with 1024 2.8GHz Xeon processors
  running Linux
• Average rendering time of 3 hours, 2 minutes per
  frame. (Would take 65 years to render on a
  single processor!)
• Sort-First Image Parallel Algorithm

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Our Approach

• Build a basic ray tracing engine
• Divide the image up into blocks and send those
  blocks to different processors
• Working on a region may allow a processor to
  cache the results of calculations. (Rays near to
  each other are likely to hit the same objects)
• Use MPI to manage parallelization with a
  Master-Slave method

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Example
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Experimentation Plans

• Vary sizes of chunks
• Smaller chunks would balance load more
  effectively, but have a high communication
  overhead.
• Larger chunks will have less communication, but
  will not balance the work as well.
• Overhead
• How effective is splitting the viewplane into
  blocks vs. by other means?

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Expectated Results

• Close to Linear Speed-up
• Blocks will be most effective division of work
• Moderately sized blocks (i.e. 10 pixels by 10
  pixels) will give the best results due to
  balanced communcation load and work

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For More Information...

• These slides
• http//www.lucey.org/cs6230/midpres.ppt
• Google
• Search for parallel ray tracing
• Email Us
• blucey_at_cc.gatech.edu
• adhilton_at_cc.gatech.edu