Real-time path tracing using a hybrid deferred approach, GTC EUR 2017
- 1. Real-time path tracing using a hybrid deferred approach GTC EUR 2017, Talk #23026 Thomas Schander @ThomasSchander Clemens Musterle
- 2. What stops us from real-time PT? Unbiased qualityHigh performance How can we create an intermediate, scalable solution?
- 3. What is Enscape? Real-time rendering plugin for architectural construction programs Used by 78 of the Top 100 architecture companies world wide The construction tool serves as the editor WYSIWYG for CAD model changes Huge projects, massive polycount, unprepared for rendering Offline quality without precalculation
- 7. Problems of real-time GI Light leaking Offscreen reflections Incompatible to complex BRDFs Indirect shadows High frequency indirect lighting Precomputation necessary Do not scale to ground truth Scene size assumptions SSDO, Ritschel Voxel Cone Tracing, Crassin Light Field Probes, McGuire LPVs, Kaplanyan
- 8. Deferred Path Tracing Overview for diffuse and specular GBuffer Last frame‘s reprojection Decide if new ray is necessary Trace in SS Trace in BVH Filter BVH constructionRay queue Radiance buffer or
- 9. Hybrid Approach Rasterization techniques where possible Gbuffer Shadow Maps Post processing techniques Complements rasterization rendering Eliminates the need for primary rays
- 10. Ray traversal scheme Sample arbitrary BRDF with N number of rays per fragment Check for ray in screen space If not, append to queue and traverse BVH later Temporally accumulate per pixel radiance and recycle until fragment can‘t be reused Lazy request of new rays only when sampling density becomes too low
- 11. BVH Construction Async BVH construction and streaming with LOD based on scene location Calculate a score for each object based on its occlusion relevance vs traversal cost Include the best objects until maximum BVH size is reached Bake direct artificial light Evaluate sun shading at traversal time to allow quick time of day changes
- 12. Sample Accumulation Calculate desired spp based on albedo, material parameters and direct light amount Skip ray if spp is sufficient Use variable filter kernel depending on number of existing samples in sample accumulation buffer Keep accumulating for a while when camera stops before idling Add more spp for powerful machines
- 13. Sample Accumulation Variance tile-based over the whole image to stop accumulating where we reached a sufficient noise level 𝜎 = 𝑎𝑣𝑔2 − 𝑎𝑣𝑔𝑆𝑞𝑟 Bicubic tile filtering for stenciling and erosion mask for passes that are the source of a non-local filter kernel
- 14. Ground Truth Comparison Reliable in-app debug validation of indirect lighting results CPU based classic path tracer Same shading models as real-time renderer Outputs an HDR target which is then injected into the normal post processing chain Allows to toggle results immediately
- 15. Ground Truth Comparison EnscapeGround Truth
- 16. Ground Truth Comparison Ground Truth Enscape
- 17. Results Pass ms GBuffer 0.7 Direct Light 0.6 Transparency 1.8 Diffuse Rays 1.4 Diffuse Filtering 2.5 Specular Rays 1.6 Specular Filtering 0.3 Post Processing 1.6 Total 10.5 Average Timings @1080p on GTX1080 Reaches stable real-time framerates Scalable for low spec machines & VR (spp, range) up to ground truth Async BVH Update every 2 seconds Scales well even to huge architectural projects Complete diffuse & specular indirect light paths except for caustics and indirect specular Almost no light leaking. Only cause are missing relevant objects in BVH, which is rare.
- 18. Thank you! Contact us for licensing or API We‘re hiring for our office in Karlsruhe, Germany www.enscape3d.com