Ray Tracing with Dynamic Spatial Decomposition using MPI

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Ray Tracing with Dynamic Spatial Decomposition
using MPI

• Rafal Zboinski

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Ray Tracing

• Basic Techniques
• Phong Shading Model
• Diffuse, Specular
• Reflection
• Refraction
• Beers law Percentage of light transmitted T
  e-(edc)
• (e absorbity, d distance, c
  concentration/density)
• Advanced Ray Tracing Techniques
• Shoot out multiple rays to produce more realistic
  effects
• Soft Shadows using spherical area light sources
• Motion Blur to produce realistic
  animation/movies
• Texture Mapping
• Bi-linear interpolation to smooth textures
• Bump-mapping to produce realistic surfaces
• Exploit Parallelism (using MPI)
• Embarrassingly Parallel
• Dynamically decompose scene into chunks of
  optimal size to render movies on lots of CPUs

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Basic Ray Tracer
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Textures
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Soft Shadows
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Bump Mapping
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Motion Blur
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Parallel Implementation
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Master - Worker Paradigm

• Renderer
• Basic Renderer for a one CPU implementation (No
  MPI)
• Handles both ray tracing and 2D output
• RendererMaster
• Only handles 2D and manages workers
• Doesnt touch ray tracing
• RendererWorker
• Only handles ray tracing computation doesnt
  know about windows, X, etc.

Renderer
RendererMaster
RendererWorker
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Algorithm Overview
Processing (hard to compute)
t 1
Current Frame
Ahead of the game
t 2
Overflow Frame
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Problems

• We dont have to wait on CPUs to finish but..
• Very small grid sizes with lots of CPUs require
  many overflow buffers
• approx buffers Processors/(Grids per frame)
• Only used 2 buffers
• Even worse when there is a complex data/slow
  nodes

Computationally Complex Nodes
Slow nodes
T 3
T 4
T 1
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Problem Pictures
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Grid Size and Effect on Performance

• Very fine grid causes increased bandwidth
  requirements
• Goal Adapt grid size to optimize performance
• Single Processor Times
• 8x8 Grid 11.8302 sec/frame
• 16x16 Grid 14.693 sec/frame

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8x8 Grid, 512x512 - Rohan
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16x16 Grid, 512x512 - Rohan
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Future Work

• Use more overflow buffers to prevent overwriting
  but..
• Attempt to load-balance per frame to prevent
  skipping ahead

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Movies and Questions
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Movies and Questions