Meet the Ray Tracing Gems Team - Live AMA July 28, 2022

Welcome to our first Connect with Experts - AMA, an exclusive benefit of the NVIDIA Developer Program
The team behind the popular Ray Tracing Gems will be here live on July 28, 2022 at 10am (PDT) to 11am

Eric Haines, Adam Marrs, Peter Shirley and Ingo Wald,

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Hello, I was wondering if you had any tips for someone who has read a few Ray Tracing books and wants to dive into “real” examples and get coding. So far I have been playing with the foundations built in Ray Tracing in One Weekend (really enjoyed these tutorial), and looking at open-source such as Q2 RTX . Any other suggestions, or pointers to cool open-source examples, would be greatly appreciated!

You could also look at my OWL project (GitHub - owl-project/owl) - it’s using OptiX, and has a lot of little examples that might be good to starting points to take and extend upon. Then you could take this, for example, to then add something similar to the RTGems2 Sample Path Tracer chapter if you want to get started.

I agree, Ingo’s OWL project hides a lot of the verbose bits of OptiX itself and has nice examples. The OptiX SDK itself has still more examples - me, I dissected the Whitted sample when I was first learning OptiX, which was a simple enough example to figure out, but one that shows some of the key concepts, such as the Shader Binding Table.

I have a bunch of general resources listed here Ray Tracing Resources Page which may be a help. That page could use some updating (suggestions welcome), but points at some key resources.

Could you please talk about how raytracing and RTX could help realistic sound in sound-oriented games, in the context of the gameplay of the original Thief game, to give a concrete example? Effects such as realistic reverberation, sound occlusion, the carrying of sound by continuous surfaces, and others are all of benefit here. Are there current approaches to such problems which will still allow raytracing the graphics at the same time?

Here is an example of gameplay: Thief Gold | 1080p60 | Longplay Full Game Walkthrough No Commentary - YouTube

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First off: “IRL” sound is important to judge directions - you can absolutely hear what direction something is coming from - so simulating that better in a game should help make this game “feel” more realistic, and better. On the technical side, sound transport and light transport are - conceptually - actually very similar; though there’s differences in “how” things reflect you still need frequent “line of sight” computations, which are exactly what ray tracing does - so yes, having fast ray tracing should help in making sound simulation better/more accurate.

Eric notes two things: VRWorks - Audio | NVIDIA Developer is from NVIDIA and may be just what the poster wants. For more on research in the area, a good place to start might be “Guided Multiview Ray Tracing for Fast Auralization” by Micah Taylor, Anish Chandak, Qi Mo, Christian Lauterbach, Carl Schissler, and Dinesh Manocha, 2012

Response from Tony Scudiero:

There’s a good history of ray tracing in audio: there are a number of commercial products that use ray methods for generating synthetic room impulse response filters. RTX technology is actually very good for acoustic simulations, as the material interactions of sounds are usually modeled at a coarser granularity than interactions of material and light. Acoustic simulations tend to have simple shaders, making their performance fundamentally a function of ray-scene queries, which RTX accelerates quite well!

One of the fundamental challenges of ray tracing acoustic energy is that the wavelengths in question are about 1 million times longer than visible light. Wavelengths can be on the order of a meter, which is the same order of magnitude as many objects. The consequence is that many effects must be treated over a cross-sectional area of the wavefront: the interaction of sound energy with a surface cannot be accurately modeled only at an infinitesimal point. That said, there has been some research on how these effects can be treated using ray tracing techniques. The ‘right’ approach usually depends on your goals: accuracy or speed.

From a technological perspective, there’s absolutely nothing standing in the way of writing a real-time acoustics simulation using ray tracing graphics APIs like DXR or VkRay to do sound propagation simulation in tandem with ray tracing graphics. The available ray-tracing power of current-generation GPUs should be able to handle a moderately complex acoustic simulation in tandem with graphics. Depending on how the graphics rendering engine is designed, primary rays could be used for both purposes, further economizing the simulation. While this is perfectly possible, I’m not aware of anyone that has actually done this in one of the graphics APIs.

NVIDIA’s VRWorks Audio, which is a relatively simple acoustics simulation intended for interactive experiences, uses OptiX. Version 2.0 of that SDK can make use of RTX hardware when available.

How do you see ray tracing in real-time applications evolving over the next few years? Do you think key advancements will come in the form of incremental improvements to techniques that are already well known, or could there be more uncommon advancements?

Thanks for doing this AMA!

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I hope to be surprised! What’s great about the area of real-time graphics is that GPUs have changed the game, making particular slow things fast. Researchers and developers figure out ways to use features, often in unexpected ways. The great thing is realtime ray tracing is now here to stay.

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