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Real-time path tracing using ahybrid deferred approach
GTC EUR 2017, Talk #23026
Thomas Schander@ThomasSchander
Clemens Musterle
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What stops us from real-time PT?
Unbiased qualityHigh performance
How can we create an intermediate, scalable solution?
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What is Enscape?
Real-time rendering plugin for architectural construction programs
Used by 78 of the Top 100 architecture companiesworld wide
The construction tool serves as the editorWYSIWYG for CAD model changesHuge projects, massive polycount, unpreparedfor renderingOffline quality without precalculation
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Problems of real-time GI
Light leaking Offscreen reflectionsIncompatible to complex BRDFs Indirect shadowsHigh frequency indirect lightingPrecomputation necessaryDo not scale to ground truthScene size assumptions
SSDO, Ritschel
Voxel Cone Tracing, Crassin
Light Field Probes, McGuire
LPVs, Kaplanyan
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Deferred Path TracingOverview for diffuse and specular
GBuffer
Last frame‘sreprojection
Decide if new ray isnecessary Trace in SS Trace in BVH Filter
BVH constructionRay queue
Radiance buffer
or
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Hybrid Approach
Rasterization techniques where possibleGbufferShadow MapsPost processing techniques
Complements rasterization renderingEliminates the need for primary rays
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Ray traversal scheme
Sample arbitrary BRDF with N number of rays per fragmentCheck for ray in screen space
If not, append to queue and traverse BVH laterTemporally accumulate per pixel radiance and recycle until fragment can‘t be reusedLazy request of new rays only when sampling density becomes too low
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BVH Construction
Async BVH construction and streaming with LOD based on scene locationCalculate a score for each object based on its occlusion relevance vs traversal costInclude the best objects until maximum BVHsize is reachedBake direct artificial light
Evaluate sun shading at traversal time to allowquick time of day changes
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Sample Accumulation
Calculate desired spp based on albedo, material parameters and direct light amount
Skip ray if spp is sufficientUse variable filter kernel depending on number of existing samples in sample accumulation bufferKeep accumulating for a while when camera stops before idling
Add more spp for powerful machines
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Sample Accumulation
Variance tile-based over the wholeimage to stop accumulating where wereached a sufficient noise level
𝜎 = 𝑎𝑣𝑔2 − 𝑎𝑣𝑔𝑆𝑞𝑟
Bicubic tile filtering for stenciling and erosion mask for passes that are thesource of a non-local filter kernel
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Ground Truth Comparison
Reliable in-app debug validation of indirect lighting resultsCPU based classic path tracerSame shading models as real-time rendererOutputs an HDR target which is theninjected into the normal post processingchain
Allows to toggle results immediately
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Ground Truth Comparison
EnscapeGround Truth
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Ground Truth Comparison
Ground Truth Enscape
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Results
Pass msGBuffer 0.7Direct Light 0.6Transparency 1.8Diffuse Rays 1.4Diffuse Filtering 2.5Specular Rays 1.6Specular Filtering 0.3Post Processing 1.6Total 10.5
Average Timings @1080p on GTX1080
Reaches stable real-time frameratesScalable for low spec machines & VR (spp, range) up to ground truthAsync BVH Update every 2 secondsScales well even to huge architectural projectsComplete diffuse & specular indirect light paths except for caustics and indirect specularAlmost no light leaking. Only cause are missingrelevant objects in BVH, which is rare.
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Thank you!
Contact us for licensing or APIWe‘re hiring for our office in Karlsruhe, Germany
www.enscape3d.com