Ray-tracing hardware explained

Ray-tracing hardware is special-purpose computer hardware designed for accelerating ray tracing calculations.

Introduction: Ray tracing and rasterization

The problem of rendering 3D graphics can be conceptually presented as finding all intersections between a set of "primitives" (typically triangles or polygons) and a set of "rays" (typically one or more per pixel).^[1]

Up to 2010, all typical graphic acceleration boards, called graphics processing units (GPUs), used rasterization algorithms. The ray tracing algorithm solves the rendering problem in a different way. In each step, it finds all intersections of a ray with a set of relevant primitives of the scene.

Both approaches have their own benefits and drawbacks. Rasterization can be performed using devices based on a stream computing model, one triangle at the time, and access to the complete scene is needed only once. The drawback of rasterization is that non-local effects, required for an accurate simulation of a scene, such as reflections and shadows are difficult; and refractions^[2] nearly impossible to compute.

The ray tracing algorithm is inherently suitable for scaling by parallelization of individual ray renders.^[3] However, anything other than ray casting requires recursion of the ray tracing algorithm (and random access to the scene graph) to complete their analysis,^[4] since reflected, refracted, and scattered rays require that various parts of the scene be re-accessed in a way not easily predicted. But it can easily compute various kinds of physically correct effects, providing much more realistic impression than rasterization.

The complexity of a well implemented ray tracing algorithm scales logarithmically; this is due to objects (triangles and collections of triangles) being placed into BSP trees or similar structures, and only being analyzed if a ray intersects with the bounding volume of the binary space partition.^[5]

Implementations

Various implementations of ray tracing hardware have been created, both experimental and commercial:

• (1995) Advanced Rendering Technology (ART) founded^[6] in Cambridge, UK, based on a 1994 PhD thesis, to produce dedicated ray tracing silicon (initially the "AR250" chip, which accelerated ray-triangle intersection, bounding box traversal and shading), using a "RenderDrive" networked accelerator for off-line rendering.^[7] Products were first shipped to customers in 1998.^[8] Software provided integration with Autodesk Maya and Max data formats, and utilized the Renderman scene description language for sending data to the processors (the .RIB or Renderman Interface Bytestream file format).^[9] ART was re-founded as ART-VPS in 2002. As of 2010, ART-VPS no longer produces ray tracing hardware but continues to produce rendering software.^[10]
• (1996) Researchers at Princeton university proposed using DSPs to build a hardware unit for ray tracing acceleration, named "TigerSHARK".^[11]
• Implementations of volume rendering using ray tracing algorithms on custom hardware were carried out in 1999 by Hanspeter Pfister^[12] and researchers at Mitsubishi Electric Research Laboratories.^[13] with the vg500 / VolumePro ASIC based system and in 2002 with FPGAs by researchers at the University of Tübingen with VIZARD II^[14]
• (2002) The computer graphics laboratory at Saarland University headed by Dr.-Ing. Philipp Slusallek has produced prototype ray tracing hardware including the FPGA based fixed function data driven SaarCOR (Saarbrücken's Coherence Optimized Ray Tracer) chip^{[15] [16] [17]} and a more advanced programmable (2005) processor, the Ray Processing Unit (RPU)^[18]
• (2009–2010) Intel^[19] showcased their prototype "Larrabee" GPU and Knights Ferry MIC at the Intel Developer Forum in 2009 with a demonstration of real-time ray-tracing.
• Caustic Graphics^[20] produced a plug in card, the "CausticOne" (2009),^[21] that accelerated global illumination and other ray based rendering processes when coupled to a PC CPU and GPU. The hardware is designed to organize scattered rays (typically produced by global illumination problems) into more coherent sets (lower spatial or angular spread) for further processing by an external processor.^[22]
• Siliconarts^[23] developed a dedicated real-time ray tracing hardware (2010). RayCore (2011), which is the world's first real-time ray tracing semiconductor IP, was announced.
• In August 2013 Imagination Technologies, after acquiring Caustic Graphics, produced the Caustic Professional's R2500 and R2100 plug in cards containing RT2 ray trace units (RTUs). Each RTU was capable of calculating up to 50 million incoherent rays per second.^[24]
• In January 2018, Nvidia, partnering with Microsoft DirectX, announced the Nvidia RTX developer library,^[25] which promised fast GPU software ray tracing solutions in the Volta-generation GPUs.^[26]
• In September 2018, Nvidia introduced their GeForce RTX and Quadro RTX GPUs, based on the Turing architecture, with hardware-accelerated ray tracing using a separate functional block, publicly called an "RT core". This unit is somewhat comparable to a texture unit in size, latency, and interface to the processor core. The unit features BVH traversal, compressed BVH node decompression, ray-AABB intersection testing, and ray-triangle intersection testing.^[27] The GeForce RTX 2080 and 2080 Ti became the first consumer-oriented brand of graphics card that can perform ray tracing in real time,.^[28]
• In October 2020, AMD announced further information regarding the "refresh" of the RDNA micro-architecture. According to the company, the RDNA 2 micro-architecture supports real-time hardware accelerated ray tracing, consisting of BVH node decoding, ray-AABB intersection testing, and ray-triangle intersection testing.^{[29] [30]}
• Intel released Arc Alchemist GPU in 2022,^{[31] [32] [33]} in which the GPU featured ray tracing acceleration core that are performing comparatively with RTX 3000 series mid-range GPU.^[34]
• On 4 November 2021, Imagination Technologies announced their IMG CXT GPU with hardware-accelerated ray tracing.^{[35] [36]}
• On January 18, 2022, Samsung announced their Exynos 2200 AP SoC with hardware-accelerated ray tracing based on the AMD RDNA2 GPU architecture.^[37]
• On June 28, 2022, Arm announced their Immortalis-G715 with hardware-accelerated ray tracing.^[38]
• On November 16, 2022, Qualcomm announced their Snapdragon 8 Gen 2 with hardware-accelerated ray tracing.^{[39] [40]}
• On September 12, 2023, Apple announced their Apple A17 with hardware-accelerated ray tracing.^[41]

Further reading

• State of the Art in Interactive Ray Tracing Ingo Wald and Philipp Slusallek, Computer Graphics Group, Saarland University, Review article to year 2001

Notes and References

1. https://graphics.cg.uni-saarland.de/fileadmin/cguds/courses/old_courses/OpenRT/Siggraph0f5/Slusallek_Intro.ppt Introduction to real time raytracing
2. http://www.cs.uiowa.edu/~cwyman/publications/projects/refractions.html Chris Wyman's Research: Interactive Refractions
3. SaarCOR —A Hardware Architecture for Ray Tracing, Jörg Schmittler, Ingo Wald, Philipp Slusallek, Section 2, "Previous work"
4. SaarCOR —A Hardware Architecture for Ray Tracing, Jörg Schmittler, Ingo Wald, Philipp Slusallek, Section 3, "The Ray Tracing Algorithm"
5. http://www.pcper.com/article.php?aid=506&type=expert&pid=3 Ray Tracing and Gaming - One Year Later
6. https://highperformancegraphics.org/wp-content/uploads/2018/Hot3D/HPG2018_RenderDrive.pdf Cold Chips: ART's RenderDrive
7. http://www.art.co.uk ART company website
8. http://www.art.co.uk/press/releases/980121_ar250.html ART press release
9. http://www.protograph.co.uk/artvps.html ALL ABOUT ARTVPS, PURE CARDS, RENDERDRIVES and RAYBOX
10. https://web.archive.org/web/20090607034740/http://www.artvps.com/content/artvps About ArtVPS
11. http://cscott.net/Publications/tigershark-thesis.pdf A Hardware Accelerated Ray-tracing Engine
12. http://www.hotchips.org/archives/hc11/3_Tue/hc99.s5.4.Pfister.pdf The vg500 Real-Time Ray-Casting ASIC
13. The VolumePro Real-Time Ray-Casting System . Hanspeter Pfister . Jan Hardenbergh . Jim Knittely . Hugh Lauery . Larry Seiler . Mitsubishi Electric . April 1999 . 10.1.1.69.4091 . 2010-02-27 . https://web.archive.org/web/20110616202224/http://people.csail.mit.edu/fredo/Book/Stuff/volumePro.pdf . 2011-06-16 .
14. http://www.doggetts.org/michael/Meissner-2002-VIZARDII.pdf VIZARD II: An FPGA-based Interactive Volume Rendering System
15. SaarCOR - A Hardware Architekture for Ray Tracing .
16. SaarCOR —A Hardware Architecture for Ray Tracing . Graphics Hardware . 2002 . 1–11 . Jörg . Schmittler . Ingo . Wald . Philipp . Slusallek . Computer Graphics Group, Saarland University . Germany . PDF . 2011-11-22 . https://web.archive.org/web/20110814155510/http://graphics.cg.uni-saarland.de/fileadmin/cguds/papers/2002/gh02/Schmittler-AHardwareArchitectureForRayTracing.pdf . 2011-08-14 .
17. Realtime Ray Tracing of Dynamic Scenes on an FPGA Chip . 10.1.1.72.2947 . Graphics Hardware . 2004 . Jörg Schmittler . Sven Woop . Daniel Wagner . Wolfgang J. Paul . Philipp Slusallek . Computer Science, Saarland University, Germany .
18. RPU: A Programmable Ray Processing Unit for Realtime Ray Tracing . Sven Woop . Jorg Schmittler . Philipp Slusallek . Saarland University . 2011-11-22 . https://web.archive.org/web/20120415113958/http://graphics.cg.uni-saarland.de/fileadmin/cguds/papers/2005/rpu_siggraph/RPU_SIGGRAPH05.pdf . 2012-04-15 .
19. Web site: Sean Maloney's IDF 2009 Larrabee graphics demo - YouTube. https://ghostarchive.org/varchive/youtube/20211221/G-FKBMct21g . 2021-12-21 . live. 2021-01-06. www.youtube.com.
20. http://www.caustic.com/ Caustic Graphics company website
21. Web site: 2009-04-20 . Caustic Graphics Ray Tracing Acceleration Technology Review - PC Perspective . 2022-08-05 . pcper.com . en-US.
22. http://www.drdobbs.com/hpc-high-performance-computing/218500694 Reinventing Ray Tracing
23. http://www.siliconarts.com Siliconarts company website
24. Web site: The future of ray tracing, reviewed: Caustic's R2500 accelerator finally moves us towards real-time ray tracing ExtremeTech. 2013-08-01. ExtremeTech. 2015-10-05.
25. News: NVIDIA RTX™ Technology. 2018-03-06. NVIDIA Developer. 2018-04-20. en.
26. News: NVIDIA Announces RTX Technology: Real Time Ray Tracing Acceleration for Volta GPUs and Later. Oh. Nate. 2018-04-20.
27. Web site: NVIDIA Turing Architecture In-Depth. Kilgariff. Emmett. Moreton. Henry. Stam. Nick. Bell. Brandon. Nvidia Developer. 2018-09-14. 2022-11-13. https://web.archive.org/web/20221113010753/https://developer.nvidia.com/blog/nvidia-turing-architecture-in-depth/. 2022-11-13. live.
28. Web site: Nvidia unveils GeForce RTX graphics chips for real-time ray tracing games. Takahashi. Dean. VentureBeat. 2018-08-20. 2022-11-13. https://web.archive.org/web/20221113013850/https://venturebeat.com/games/nvidia-unveils-geforce-rtx-graphics-chips-for-real-time-ray-tracing-games. 2022-11-13. live.
29. Web site: AMD unveils three Radeon 6000 graphics cards with ray tracing and RTX-beating performance. Judd. Will. Eurogamer. October 28, 2020. October 28, 2020.
30. Web site: AMD Announces Ryzen "Zen 3" and Radeon "RDNA2" Presentations for October: A New Journey Begins. anandtech.com. AnandTech. 2020-09-09. 2020-10-25.
31. Web site: Intel officially launches Arc A380 desktop graphics card in China, costs 153 USD . 2022-12-13 . VideoCardz.com . en-US.
32. Web site: updated . Mark Tyson last . 2022-09-28 . Intel Arc A310 Graphics Card Quietly Goes Official . 2022-12-13 . Tom's Hardware . en.
33. News: 2022-10-12 . Intel Arc A770 and Arc A750 graphics cards now available to buy from $289 . en-US . XDA Developers . 2022-12-13.
34. Web site: 2022-10-08 . Does ray tracing work on the Intel Arc GPUs? . 2022-12-13 . Digital Trends . en.
35. Web site: 93digital . 2021-11-04 . Imagination launches the most advanced ray tracing GPU . 2023-09-17 . Imagination . en-GB.
36. Web site: Ray Tracing . 2023-09-17 . Imagination . en-GB.
37. Web site: Samsung Introduces Game Changing Exynos 2200 Processor With Xclipse GPU Powered by AMD RDNA 2 Architecture . 2023-09-17 . news.samsung.com . en.
38. Web site: 2022-06-28 . Gaming Performance Unleashed with Arm's new GPUs - Announcements - Arm Community blogs - Arm Community . 2023-09-17 . community.arm.com . en.
39. Web site: Snapdragon 8 Gen 2 Defines a New Standard for Premium Smartphones . 2023-09-17 . www.qualcomm.com . en.
40. Web site: New, Snapdragon 8 Gen 2: 8 extraordinary mobile experiences, unveiled . 2023-09-17 . www.qualcomm.com . en.
41. Web site: Bonshor . Ryan Smith, Gavin . The Apple 2023 Fall iPhone Event Live Blog (Starts at 10am PT/17:00 UTC) . 2023-09-17 . www.anandtech.com.