Fragment Processing Features Rich instruction set



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Ray Tracing on Programmable GPUs


Graphics Pipeline



Fragment Processing Features

  • Rich instruction set

    • No branching yet (see PS 3.0 spec)
  • Floating point

    • Arithmetic
    • Texture memory
  • Dependent texturing

  • Multipass rendering flow control

    • NV_OCCLUSION_QUERY


The Ray Engine [Carr02]



Ray Engine – Main Idea

  • Ray-traingle intersection done by GPU

    • CPU-based renderer does everything else


Ray Engine Algorithm

  • Renderer sends ray textures to GPU

  • Renderer sends ‘triangles’ down pipeline

    • Vertex interpolants of a screen aligned quad
  • GPU performs ray-triangle intersection tests

    • Short fragment program
    • Framebuffer stores closest hit point
  • Renderer reads back closest hit



Pixel Shader 1.4 Implementation



Full Precision Simulations



Ray Engine Results



Ray Engine Summary

  • GPU performs ray-triangle intersection

    • CPU-based renderer does everything else
  • Raw ray-triangle intersection rate is faster than CPU based approach

    • Total rays processed per second is slower than CPU
  • Readback limited



Streaming Ray Tracer [Purcell02]



Streaming Ray Tracer – Main Ideas

  • Entire ray tracing computation can be done efficiently on the GPU

    • Minimal host interaction
  • Stream processor abstraction for programmable fragment processor



Streaming Ray Tracer



GPU Abstraction

  • Texture memory is memory

    • Think of dependent texture fetches as pointer dereferencing
  • Programmable fragment processor is a programmable stream processor

    • Think of multipass rendering as stream and kernel programming


Texture Memory Organization



Stream Programming Model

  • Programmable fragment processor is essentially a stream processor

  • Kernels and streams

    • Stream is a set of data records
    • Kernels operate on records
    • Streams connect kernels together
    • Kernels can read global memory


Streaming Flow Control



Multiple Rendering Passes



Multiple Rendering Passes



Multiple Rendering Passes



Multiple Rendering Passes



Multiple Rendering Passes



Multiple Rendering Passes



Demos



Demos



Demos



Demos



Streaming Ray Tracer Results

  • Simulations

    • 50M – 200M ray-triangle intersections/s
  • Radeon 9700 Pro Implementation

    • 100M ray-triangle intersections/s
    • 300K – 4.0M rays/s


Streaming Ray Tracer Summary

  • Entire ray tracing computation can be mapped efficiently to the GPU

  • Stream processor is a good abstraction for a programmable fragment processor



Dedicated Hardware Ray Tracing



Ray Tracing in Hardware

  • Volume Rendering

    • [Meissner98],[Pfister99]
  • Offline Rendering

    • [ART01],[ART02]
  • Interactive Rendering

    • [Schmittler02]


SaarCOR – Main Idea

  • Scalable and efficient real time hardware ray tracer

    • Implementation based on Saarland RTRT


SaarCOR Implementation

  • Packet based ray tracer

  • Several custom cores

    • Computational units
      • Traversal, intersection, ray generation and shading
    • Memory units
  • Multithreaded

  • Standard DRAM memory on board

  • Virtual memory support for large scenes

  • Support for programmable shading



SaarCOR Architecture



SaarCOR Test Scenes



Simulated Performance



Simulated Bandwidth Usage



SaarCOR Summary



Conclusions for Part I



Conclusions

  • Real time ray tracing advantages

    • Physically correct renderings
    • High geometric complexity
    • Shading flexibility
  • Several options for real time ray tracing

    • Software, GPU, Hardware


Backup



Acknowledgments

  • Ian Buck, Bill Mark, Pat Hanrahan

  • James ‘RTD’ Percy, Pradeep Sen, Eric Chan

  • Matt Papakipos, Kurt Akeley - NVIDIA

  • Bob Drebin, Mark Peercy – ATI

  • Sponsors

    • ATI, MERL, NVIDIA, Sony, Sun
    • DARPA


Ray-Triangle Intersection as a Crossbar



Rasterization as a Crossbar



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