Enabling immersive gaming experiences Intro to Ray Tracing

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2 Enabling immersive gaming experiences Intro to Ray Tracing

3 Overview What is Ray Tracing? Why Ray Tracing? PowerVR Wizard Architecture Example Content Unity Hybrid Rendering Demonstration 3

4 What is Ray Tracing? Ray Tracing is a model of the physics of light It s the primary technique used for Hollywood special effects rendering Ray tracing is the only way to achieve photorealism for interactive content without spending $millions per title to fake it! It allows the seamless blending of captured real life with computergenerated images Ray Tracing is the inevitable next step in the evolution of 3D graphics hardware 4

5 How it works Ray tracing allows the behaviour of light to be simulated 5

6 How it works Ray tracing allows the behaviour of light to be simulated 6

7 How it works Ray tracing allows the behaviour of light to be simulated 7

8 How it works Ray tracing allows the behavior of light to be simulated 8

9 How it works Ray tracing allows the behaviour of light to be simulated 9

10 Ray Tracing Starts with a pixel Perform geometry processing using a shader, exactly as in rasterization. Behind the scenes, the GPU assembles the triangles into a searchable database representing the 3D world. Run a shader for each pixel, which can cast rays into the 3D world. Behind the scenes, the GPU searches the database to determine which triangle is the closest intersection with the ray. Run a shader when a ray intersects a triangle. That shader can contribute color into the pixel, or cast additional rays. These secondary rays can, in turn, cause the execution of additional shaders. This is the key to the benefits of ray tracing. 10

11 Ray Tracing Usage Cases Hybrid Shadows, Reflections, etc. Augmented Reality Refraction Order-Independent Transparency Ambient Occlusion Asset creation / compression Global Illumination Physics & Collision Detection Virtual Reality Lens correction, Ultra-low latency rendering, Lenticular Displays A.I. / Line of Sight Rapid photoquality output 11

12 A continuum based on your ray budget Many options for Ray Tracing! Ray Traced Pre-Baked Light Maps e.g. Unity 5 Editor Hybrid Game Engine Ray Trace Everything, eg. Brigade & Arauna 2 Scalability 12

13 PowerVR Graphics GPU+RTU Architecture Series 6XT Wizard GPU+RTU Host CPU Bus Host CPU Interface Vertex Data Master Pixel Data Master Compute Data Master Ray Data Master Coarse Grain Scheduler Control and Register Bus Unified Shading Cluster Array USC0 USCn-1 Texture Unit Texture Unit USC1 USCn System Memory Interface Core Management Unit (META) Multi-level Memory Cache Unit System Memory Bus Doppler Ray Tracing Unit Ray Intersection Processor Coherency Engine Scene Hierarchy Generator Tiling Co-Processor Pixel Co-Processor Frame Accumulator Cache 2D Core (PTLA) System Memory Bus

14 Ray Tracing - Shadows For Each Pixel: Shoot a ray towards the light If the ray hits *anything* do nothing as the region is in shadow If they ray reaches the light source, calculate the illumination of the pixel Cost Low Simple traversal of hierarchy structure and intersection calculation Easy to extend & improve Multiple rays / Advanced Filtering 14

15 Ray Tracing Transparency For transparent pixel: Take incoming ray Send out new ray in same direction through the object surface Trivial to code Just works: No need to worry about render order Complex effects such as refractions are trivial to implement Cost: Low Just find the next object a ray hits 15

16 Ray Tracing - Reflections For each reflective pixel Take incoming ray Reflect versus surface normal Shoot out a new ray Trivial - uses 3 lines of shader code Just works Resolution not an issue Reflections inside reflections just work Cost: Low Simple traversal of hierarchy structure and intersection calculation & shade 16

17 The Final Frame Ray traced shadows and reflections in a rasterized game Correct soft shadows are created by tracing rays. Note the shadows sharply focused near the base of the fence, and soft towards the top. Accurate reflections will correctly display ALL objects with the correct perspective, including moving objects and selfreflecting objects. 17

18 Unity Hybrid Rendering Video Available online on YouTube 18

19 Conclusions IMG PowerVR bringing Ray Tracing to Mobile Traditional Rendering Many complex effects are being approximated with complex rendering algorithms Multiple geometry passes, multiple renders to texture, complex shaders using pre-calculated data Despite implementation complexity image quality and accuracy remains problematic Order dependent transparency, Single reflection bounce, Pixelation Issues (too low resolution) Ray Tracing Many complex effects become trivial due to the natural behaviour of ray tracing No need for complex approximations, simply implements real natural behaviour of light Limitations are not an issue No resolution dependency issues, no (practical) limits on bounces, no need to sort geometry Ray tracing is more efficiency in render cost and bandwidth for complex high quality effects 19

20 Confidential Subject to NDA PowerVR Ray Tracing Backup Slides Oct

21 Traditional Rendering - Shadows Cascaded Shadow Maps 21 Render Scene from Light Point of View Depth information Multi-resolution to ensure sensible quality at different distances Render Scene comparing a rendered pixel s distance from light with projected depth maps (above) Cost: Render Cascade of Depth Maps Submit scene geometry x 3 plus write images Render final scene Expensive shader selecting correct depth map for compare operation Higher quality = High Cost

22 Traditional Rendering - Reflections Render object environment to cubemap 6 renders per frame Difficult to judge required resolution Repeat for each reflective object Reflections inside reflections do not work Use cubemap on reflective object Cost: 22 6x geometry submission 6x render cost (full shader complexity) High resolution cubemap for quality

23 Traditional Rendering Transparency Transparency requires sorting Back to front render order Incorrect order = incorrect rendering Cost: High, typical sorted on CPU Often short cuts taken: Sort per object vs per triangle Sort per pixel required for correct results Limits the types of objects that can be drawn On left object which fails to render correct OIT implementations in shaders are very expensive e.g. depth peeling 23

24 PowerVR Ray Tracing How? September 2014

25 Ray Coherency Example Non Trivial Coherency between Rays 25

26 PowerVR Ray Tracing Unity Hybrid Rendering September 2014

27 The Hybrid Pipeline Rasterizer renders the scene into a G-buffer that stores which material, position, and normal values Ray Tracer traces reflection rays where needed to fill in reflection effect. All buffers combine to create final image with reflections and shadows. 27 Ray Tracer traces shadow rays to determine which parts of the scene are lit. This buffer can be filtered to eliminate artifacts.

28 Shadow Detail is Always Right for View Perspective No need for cascade shadow maps, etc. MIP Mapping on fence alpha-texture means shadow is mostly transparent from far away 28

29 Shadow Detail is Always Right for View Perspective No need for cascade shadow maps, etc. 29

30 Shadow Detail is Always Right for View Perspective No need for cascade shadow maps, etc. 30

31 Shadow Detail is Always Right for View Perspective No need for cascade shadow maps, etc. 31

32 Shadow Detail is Always Right for View Perspective No need for cascade shadow maps, etc. Very high levels of shadow detail are visible, looking closely at an object 32

33 Traditional Shadow Maps The same perspective, rendered with Unity s shadow map feature It is impossible to find a shadow map that looks good across all scene scales without wasting significant memory, bandwidth, and power. 33

34 Reflections Add Realism Another advantage of Hybrid Buildings are visible in visor Driver s visor is visible in mirror Mirror is visible in car body Tree and sky are visible in body 34

35 Multiple Shadow-Casting Lights No need to transform all geometry for each light, with ray traced shadows 3 lights are present in this scene, 2 headlights and the moon. Light samples can be determined on a pixel-by-pixel basis, so only the pixels within a light cone spend rays. Multiple shadow samples create a realistic look of a set of headlights. 35

36 Ray Traced Effects Layer Together Smoothly Reflections of the areas lit by the headlights can be seen in the car hood. 36

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