This document summarizes a presentation about real-time ray tracing. It discusses the history of ray tracing, compares rasterization and ray tracing approaches, demonstrates a basic ray tracing example in Unity using a Cornell box, and provides performance advice for ray tracing including keeping shaders simple, using acceleration structures correctly, and reducing ray counts and lengths. More resources on ray tracing and DirectX Raytracing (DXR) are also listed.

2. Real-Time Ray Tracing
Paulo Silva
Developer Technology Engineer, NVIDIA

3. Announcements
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• Target Audience:
• Engineers & Technical Artists
• Level:
• Beginner (no programming)
• Intermediate (some programming)
• Warning:
• This is Beta software and is still changing
• Slides will be available
• Session recording will also be available

4. Outline
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• History Of Ray-Tracing
• Rasterization vs Ray-Tracing
• Basic Example
• Scriptable Pipelines & DXR Details
• Performance Advice
• More Resources

5. History of Ray-Tracing
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6. What is Ray-Tracing?
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• Rendering method
• Simulates light path
• Most modern movies use it for SFX
• Photo-realistic rendering
• Car & Architecture visualization
Rendered in unity using real-time ray tracing

7. • Kajiya 1986
• Path Tracing
• Rendering Equation
• Diffuse Interreflections
• Caustics
• Cook 1984
• Fuzzy
• Motion Blur
• Soft Shadows
• Whitted 1980
• Shiny
• Reflections
• Refractions
• Shadows
History
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8. History
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• Kajiya 1986• Cook 1984• Whitted 1980

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Rasterization vs Ray-Tracing

10. Vertex Shader Rasterizer
Rasterization: Very Simplified
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Pixel Shader

11. Trace Rays Shade & TraceIntersection Test
Ray-Tracing: Very Simplified
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12. Rasterizer
Rasterization vs Ray-Tracing: Key Ideas
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Which pixel □ does triangle △ cover? Which triangles △ does pixel □ see?
Pixel □ in triangle △ Ray → triangle △ intersection
Question
Operation
Triangles △ Rays →Streaming
Overdraw △ Many → collisionsInefficiency
(Hierarchical) Z-buffering Bounding volume hierarchy BVH (AABBs)Speedups
Ray Tracing

13. SSRShadow MapsSSAO
Rasterization: Hacks
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14. SSAO
Rasterization vs Ray-Tracing: AO
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Ray-Tracing AO

15. Shadow Maps (No baked light maps)
Rasterization vs Ray-Tracing: Shadows
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Ray-Tracing Shadows

16. SSR
Rasterization vs Ray-Tracing: Reflections #1
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Ray-Tracing Reflections

17. SSR
Rasterization vs Ray-Tracing: Reflections #2
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Ray-Tracing Reflections

18. Basic Example
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19. Basic Example
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• No programming needed
• Setup needed to get started
• Shows off the main features
• Reflections
• Shadows
• Ambient Occlusion
• Global Illumination
• Compare to Rasterization
Cornell Box

20. System Requirements
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• RTX GPU for complex Ray Tracing Effects*
• Windows 10 v1809
• Unity 2019.3b1

21. Setup
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• In Player settings set:
• DirectX12 (Experimental)
• REALTIME_RAYTRACING_SUPPORT
• ENABLE_RAYTRACING

22. Basic Demo Scene
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• Let’s create a Cornell Box

23. Basic Demo: Add Ray Tracing
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• Add the Raytracing Environment

24. Basic Demo: Reflections
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Before After

25. Basic Demo – Shadows
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Before After

26. Basic Demo – Indirect Illumination
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Before After

27. Basic Demo: Raster vs Ray Tracing
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Raster (no baked lights) Ray-Tracing

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Scriptable Pipelines & DXR Details

29. Scriptable Pipelines & DXR Details
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Required for next section:
• DXR shader types
• Acceleration structures
DXR shaders in HDRP
What is DXR?
• DXR = D3D12 ray tracing
• HDRP uses Scriptable Pipelines
• These use DXR ray tracing

30. DXR Shaders
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DXR Shader Graph
• Ray Generation
• defines how rays start
• Closest-hit
• e.g.: calculate color
• Miss shader
• e.g.: sample skybox
• Any-hit
• run once per hit for transparency
• Intersection
• Intersect arbitrary shapes

31. Acceleration Structure
DXR Acceleration Structures
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Bounding Boxes are Axis Aligned (AABB)

32. Performance Advice
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33. • Smooth reflective surfaces are cheaper than rough surfaces
• Keep shaders simple when using rough surfaces
Performance Advice - Reflections
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Rough – Rays Diverge Smooth – Coherent Rays

34. • Keep Any-Hit shaders simple
• When possible make objects opaque (Use LOD)
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Transparent – many Any-Hits calls Opaque – No Any-Hit call
Performance Advice -Transparency

35. • Correctly tag objects as static, dynamic, animated
Performance Advice – Acceleration Structures
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Static Object Dynamic Rigid Body Animated Character

36. • Group geometry together when possible
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Separate Objects ☹ One Object ☺
AS AS AS
AS
Performance Advice – Acceleration Structures

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Performance Advice
Ray Count
Ray Length
Denoiser Quality
Small Transparent Objects
Performance Quality

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More Resources

39. More Resources
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• Ray-Tracing Gems (free pdf):
http://www.realtimerendering.com/raytracinggems/
• SIGGRAPH 2018 DXR Tutorial:
http://intro-to-dxr.cwyman.org/
• Gameworks Ray-Tracing:
https://developer.nvidia.com/gameworks-ray-tracing
• DXR Specification:
https://microsoft.github.io/DirectX-Specs/d3d/Raytracing.html
• Unity HDRP DXR Build:
get 2019.3b1 from unity hub, or download the following version
https://github.com/Unity-Technologies/Unity-Experimental-DXR

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Please try real-time ray tracing
and make something amazing!
Thank You