highly parallel computing in physics-based...

HIGHLY PARALLEL COMPUTING IN PHYSICS-BASED RENDERINGOpenCL Raytracing BasedThibaut PRADOSOPTISReal-Time & Virtual Reality Manager

3 | Highly Parallel Computing in Physics-based Rendering | June 13th, 2011

INTRODUCTION WHO WE ARE


INTRODUCTION | WHO WE ARE

OPTIS is a world leading provider of software solutions for physics based simulation of optics, light and human vision, used throughout the world’s leading vehicle, aerospace, lighting and LCD manufacturers.OPTIS SPEOS solutions are unique in being fully integrated into leading CAD platforms and take into account real measured light sources, materials, surfaces , human vision and international standards.



Founded in 1989 OPTIS now employs over 80 people in 5 countries, with over 1600 customers and 6000 licenses in use worldwide.

TOKYOTOULON

STUTTGART

DETROIT

SHANGHAI



SoftwareStandard developmentSoftware customization Services

Training

Measurement (optical properties of materials,

light sources)

Consulting projects(> 800 Engineering

studies)

HardwareDevelopment of optical surface measurement systems (OMS)


INTRODUCTION | REFERENCES

http://www.baesystems.com/index.htm


INTRODUCTION WHAT DOES PHYSICS-BASED MEAN ?


INTRODUCTION | WHAT DOES PHYSICS BASED MEAN ?

Classical Rendering Physical Rendering256 contrast levels High Dynamic Range Images

RGB colors Full spectral rendering (IR, visible, UV), CIE Standards

Simple sources definition Measured intensity diagrams, Spectra (Black bodies, Fluorescent, …), Radiometric power (Watt), LCD, …

Simple shading models Measured BRDF (spectral, polarized, …)

Alpha blending Complex material handling (spectral refraction, dispersion,diffusion, complex material indices…)

Pinhole camera Radiance sensor models including cameras and physiological model of human eye, glare, depth of field, …

Non exploitable image Physics and measurable accurate radiance simulation

Addresses sRGB screen All output screens (HDR, High gamut, projectors, …), calibrated (ICC profiles).



Used algorithms should ensure physics laws compliance :– Radiometric power conservation– Full spectrum (from IR to UV)– Correct Light sources data (spectrum, intensity)– Correct BRDF data…



BRDF defines the way that a surface reflects the light :

To ensure BRDF correctness, OPTIS measure most of BRDF using its own measurement device (OMS).

BidirectionalRefectanceDistributionFunction

Lambertian

GaussianSpecular

Measured



Rendering equation (Kajiya, Immel, 1986)

Reflected luminance

EmittedLuminancedue to surface

Incomingluminance

BRDF

Integral over all incoming light directions


OPENCL RAYTRACER | PRINCIPLES

Raytracing: principles

Propagate a ray from the eye through the scene for each pixel


OPENCL RAYTRACEREXPERIENCE FEEDBACK


OPENCL RAYTRACER | RAYTRACING ON GPU

Raytracing is a highly parallel task that suits GPU architecture

Single Program

Multiple Data

Vector computing

– Only one propagation law (optical law)Ray emissionGeometry intersection (ray hit)Surface interaction (ray reflection/refraction)Eye integration & tone mapping

– Huge number of pixels (~billion rays)– Each ray propagation is independent of the others

– Linear algebraHomogeneous vectorSpectral colors


OPENCL RAYTRACER | RAYTRACING ON GPU

GPU Raytracing drawbacks :

– Acceleration structure traversal is hard to “vectorize”Use of a Kd-tree like structure (1-dimension at each node)

– Raytracing algorithm is very divergentRays from second bound could be spread in all the 3D spaceKd-tree traversal could differs from one interaction to the otherTo avoid this, one can merge coherent rays in separated pass


OPENCL RAYTRACER | TECHNOLOGIES USED IN REAL-TIME

We are loading most data on GPU at the beginning into Buffers and Textures– GPU embedded data :

GeometryBRDFSpectraAcceleration structures

– GPU embedded source code PropagationSurface InteractionHuman vision algorithms and post process (ICC profiles)


OPENCL RAYTRACER | CUDA TO OPENCL CONVERSION FEEDBACK

Similar languages (~ 2 months for conversion)CUDA advantages

– Supports template types– Good development framework– Source code confidentiality

OpenCL advantages:– Source code portability– Hardware management and scalability– Improves vector operations


OPENCL RAYTRACER | CUDA TO OPENCL CONVERSION FEEDBACK

CUDA drawbacks:– Platform dependent– Proprietary language– No vector types– Thread distribution (grid, block, thread)

OpenCL drawbacks:– Confidentiality issues (needs embedded source code to be compiled before use)– No global parameters for all kernels

Easier to convert from CUDA to OpenCL than the opposite.


VISUAL ERGONOMICSCPU SOLUTION


INTRODUCTION | UNIQUE PROCESS

Human Vision Lab

Geometry

• Spectral sources• Natural (night and day)• Artificial (LEDs, displays…)• Physics Based• Materials

Optical properties

SimulationsSpectral radiance ( W/(m².sr.nm))

Human Vision Lab : Spectral luminance and perceived color computation (CIE recommendations).

Full CAD integration-Large assemblies-Libraries and catalogs

http://www.monarchatlanta.com/images/samples/Red leather.jpg


VISUAL ERGONOMICS SOLUTION | APPLICATIONS

Lit and unlit appearanceHuman vision perceptionQuantify critical reflections


VISUAL ERGONOMICS | SOME RESULTS


VRLAB | VIDEO (LIVE DEMO IS AVAILABLE IN THE EXPERIENCE ZONE)


VISUAL ERGONOMICS | INVOLVED TECHNOLOGIES

C++Multi-CPU architectureMulti-cores CPUMulti-threaded applications– No critical section– Only interlocked instructions– 100% CPU use of each core without kernel time

Cluster Distributed computingInnovative acceleration structure for intersections computing


VISUAL ERGONOMICS SOLUTION | KEY BENEFITS

Result analysis: light levels, contrast, uniformity, color (physics), visibility, legibility.

Now : SPEOS RTVE3 Real-time simulation technology integration

Calibrated displays (dynamics, color gamut)Uniquely based on human vision modelImmersive and interactive capabilities Product Lifecycle Management integration in CAD


REAL-TIME | WHY USE REAL-TIME ?

The notion of time is important for:Easily detecting hotspots (high frequency specular peaks)Understanding reflection phenomenaAddressing non-specialists (non-physicists)Ensuring interaction in immersive environments (CAVE)


REAL-TIME | VIDEO (LIVE DEMO IS AVAILABLE IN THE EXPERIENCE ZONE)


AMD FUSIONEXPECTED BENEFITS


AMD FUSION | EXPECTED BENEFITS

More powerful–CPU Fusion–GPU Fusion–Extra GPU(s)

Enhanced memory access (Virtual Texturing)Specialized computingScalable computingHybrid computing GPU/CPUExtra graphics

Shared memory

Accelerated Processor Unit

CPU

GPUDDR3

PC

Ie Graphic card

GPU

THANK YOU FOR YOUR ATTENTIONAny questions ?Thibaut [email protected]


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