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This presentation was held at the Digital Dragons 2014 conference.

Videos shown during the talk are available here: http://bglatzel.movingblocks.net/publications

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- 1. Volumetric Lighting for Many Lights in Lords of the Fallen Benjamin Glatzel Engine/Graphics Programmer Deck13 Interactive GmbH
- 2. Who are we? • One of Germany’s leading game studios • Currently working on “Lords of the Fallen” in cooperation with CI Games • We’re using our own proprietary multi-platform technology called “Fledge” • We’ve shipped numerous titles primarily on PC but also on Xbox 360, iOS and PS3 (maybe you know Jack Keane, Ankh, Venetica, Blood Knights or Tiger and Chicken)
- 3. Lords of the Fallen • Lords of the Fallen is a challenging Action-RPG for PC, Xbox One and PlayStation 4 • Will be released fall 2014 • For an in-depth view into the rendering guts of Fledge, visit Philips talk tomorrow
- 4. Who am I? • Engine/Graphics Programmer since 2 years • Mainly responsible for the GNM/PS4 version of “Fledge” • Apart from that I'm behind everything related to physics, our software rasterisation based culling system, our IK system, …
- 5. Introduction
- 6. Light Scattering Lightwaves Participating media
- 7. Motivation
- 8. Motivation • Simple light shafts as a screen space post-processing effect [1] sure are shiny, but…
- 9. Light shafts as a post-processing effect
- 10. Light shafts as a post-processing effect
- 11. Motivation • Billboards can be neat, but…
- 12. “Billboard volumetrics”
- 13. “Billboard volumetrics”
- 14. Motivation • We wanted something more dynamic and ﬂexible that could be tightly integrated into our lighting system • It should work with a lot of small to medium sized light sources • Our artists tend to place a whole lot of lights • Thus a negligible performance penalty on all supported platforms was critical
- 15. State of the Art
- 16. Deep Down Killzone 4 Crysis 3
- 17. State of the Art • Many recent implementations seem to be based on the work of Toth et. al. [2]: • Ray marching in light view space while evaluating the shadow map • Often combined with a special sampling approach to reduce the workload per fragment • Many other approaches/optimisations popped up over the recent years: Epipolar sampling [3], sampling planes shaded in light space [4], …
- 18. Our Approach
- 19. Our Approach • Loosely based on “Real-time Volumetric Lighting in Participating Media” (Toth et. al. [2]) • Straightforward ray marching • Usage of “Interleaved Sampling” to reduce the overall sample count needed per fragment • Utilises low-resolution rendering to reduce the fragment workload even further
- 20. Our Approach • Works with multiple lights and light types • Custom bilateral blurring and depth-aware up- sampling to work around the obvious artefacts • Various tweaks and optimisations per light type • Completely implemented using good old pixel and vertex shaders - no compute
- 21. Basic Algorithm
- 22. Radiative Transport Equation [2] ~x(s) = ~x0 + ~!s L(~x(s), ~!) ⌧ a P(~!0 , ~!) Ray equation, where ω is the direction of the ray Change of radiance along the ray Probability of collision Scattering probability after collision Phase function dL(~x(s), ~!) ds = ⌧L(~x(s), ~!) + ⌧a Z ⌦0 L(~x(s), ~!)P(~!0 , ~!)d!0
- 23. L(~x(s), ~!) = e ⌧s L(~x0, ~!) + Z s 0 Li(~x(l), ~!)e ⌧(s l) dl L(~x(s), ~!) ⇡ L(~x0, ~!)e ⌧s + NX n=0 Li(~x(ln), ~!)e ⌧(s ln) l Ignore multiple scattering Li(~x, ~!) = ⌧a 4⇡d2 v(~x)e ⌧d P(~!l, ~!) In-scattering term s Total ray marching distance d Distance to the light source l Traveled distance on the ray l Step size v(~x) Visibility function Source power of the light Direction from the ray position to the light source ~!l
- 24. Basic Algorithm • Let’s start with a simple fullscreen pass for a directional light • Start the ray marching on the position of the current fragment in light space • Evaluate and accumulate the in-scattering term for each of the n samples and march in equidistant steps towards the position of the viewer
- 25. #define NUM_SAMPLES 128! #define NUM_SAMPLES_RCP 0.0078125! ! FRAGMENT_OUT ps_main(VERTEX_OUTPUT f_in)! {! // Fallback if we can't find a tighter limit! float raymarchDistanceLimit = 999999.0 ;! ! [...]! ! // Reduce noisyness by truncating the starting position! float raymarchDistance = trunc ( clamp ( length ( cameraPositionLightVS . xyz - positionLightVS . xyz ) , ! 0.0, raymarchDistanceLimit ) ) ;! ! // Calculate the size of each step! float stepSize = raymarchDistance * NUM_SAMPLES_RCP ;! float3 rayPositionLightVS = positionLightVS . xyz ;! ! // The total light contribution accumulated along the ray! float3 VLI = 0.0 ;! ! // ... start the actual ray marching! [loop] for ( float l = raymarchDistance; l > stepSize ; l -= stepSize ) ! {! executeRaymarching(...) ;! }! ! f_out . color . rgb = light_color_diffuse . rgb * VLI ;! return f_out ;! }
- 26. #define TAU 0.0001! #define PHI 10000000.0! ! #define PI_RCP 0.31830988618379067153776752674503! ! void executeRaymarching(...)! {! rayPositionLightVS . xyz += stepSize * invViewDirLightVS . xyz ;! ! [...]! ! // Fetch whether the current position on the ray is visible form the light's perspective - or not! float3 shadowTerm = getShadowTerm ( shadowMapSampler, shadowMapSamplerState, rayPositionLightSS . xyz ) . xxx ;! ! // Distance to the current position on the ray in light view-space! float d = length ( rayPositionLightVS . xyz ) ; ;! float dRcp = rcp ( d ) ;! ! // Calculate the final light contribution for the sample on the ray...! float3 intens = TAU * ( shadowTerm * (phi * 0.25 * PI_RCP) * dRcp * dRcp ) * exp( -d * TAU ) * exp ( -l * TAU ) * stepSize ;! ! // ... and add it to the total contribution of the ray! VLI += intens ;! }
- 27. From One to Many
- 28. From One to Many • Render the back faces of the light volume for each volumetric light (depth test/ write disabled) • Start the ray marching on the fragment of the light geometry instead of the scene geometry • If the light volume intersects the scene geometry, the starting position gets clamped to the closest fragment position relatively to the viewer
- 29. From One to Many • Calculate the in-scattering term as depicted before • In addition to that evaluate the attenuation function for each given light type and “modulate” it with the in-scattering term • March the ray in light view and in world space in parallel - less costly than transforming between spaces for each step • Accumulate the volumetric lighting contribution for each visible light to an accumulation buffer using additive blending
- 30. From One to Many • Constrain the taken samples to the area inside the light volume to increase the precision • For box and point lights we simply clamp the total ray marching distance to the attenuation ranges of the lights • In the case of spotlights we actually calculate the intersection points between the current ray and the light volume and calculate the range in-between
- 31. Much slow Wow So sample How to Make it Fast
- 32. How to Make it Fast • Everything I told you so far needs far too many samples to achieve visually pleasing results • 128+ samples per fragment for each light rendered to a full resolution target does not sound like the ideal solution
- 33. How to Make it Fast • We ended up rendering all volumetrics to a half or quarter resolution target • We use an additional depth aware up-sampling pass to hide this fact - often referred to as ”Nearest Depth Up-Sampling“ [5]
- 34. Without depth-aware up-sampling
- 35. With depth-aware up-sampling
- 36. How to Make it Fast • Only using half-resolution rendering will not sufﬁce to make it fast enough for multiple light sources on the screen • We can “abuse” the fact that the in-scattered light value at a given fragment position is either equal or at least close to one or more of the surrounding values
- 37. How to Make it Fast • We spread the evaluation of the in-scattering term from a single pixel to multiple pixels • We ended up using 8x8 pixel tiles, where each pixel of a tile evaluates 16 samples • This makes a total of 8x8x16 = 1024 potential samples • Each pixel of one tile evaluates a different region of the ray vs.
- 38. How to Make it Fast • Assign an unique index i ∊ [0..64) to each pixel of the tile - the indices repeat for each tile • Reduce the total ray marching distance by one step • Offset the ray marching starting position for each pixel of the tile according to i • • Randomising the indices trades the obvious repetitive sampling pattern for some less noticeable noise ray = i stepSize 64
- 39. #define INTERLEAVED_GRID_SIZE 8! #define INTERLEAVED_GRID_SIZE_SQR 64! #define INTERLEAVED_GRID_SIZE_SQR_RCP 0.015625! ! [...]! ! // Calculate the offsets on the ray according to the interleaved sampling pattern! float2 interleavedPos = fmod ( f_in . position . xy, INTERLEAVED_GRID_SIZE ) ; ! ! #if defined (USE_RANDOM_RAY_SAMPLES)! float index = ( interleavedPos . y * INTERLEAVED_GRID_SIZE + interleavedPos . x ) ;! // light_volumetric_random_ray_samples contains the values 0..63 in a randomized order! // The indices are packed to float4s => { (0,1,2,3), (4,5,6,7), ... }! float rayStartOffset = light_volumetric_random_ray_samples [ index * 0.25 ] [ fmod ( index, 4.0 ) ] * ( stepSize * INTERLEAVED_GRID_SIZE_SQR_RCP ) ;! #else! float rayStartOffset = ( interleavedPos . y * INTERLEAVED_GRID_SIZE + interleavedPos . x ) * ( stepSize * INTERLEAVED_GRID_SIZE_SQR_RCP ) ;! #endif // USE_RANDOM_RAY_SAMPLES! ! float3 rayPositionLightVS = rayStartOffset * invViewDirLightVS . xyz + positionLightVS . xyz ;! ! [...]
- 40. Accumulation buffer before the gather pass
- 41. How to Make it Fast • To achieve the ﬁnal results we use an additional blur pass before the up-sampling pass • We use a simple bilateral blur ﬁlter to avoid bleeding over the edges of any geometry inside or behind the volumetrics
- 42. Accumulation buffer after the gather pass
- 43. Non-bilateral blur
- 44. Bilateral blur
- 45. Non-bilateral blur
- 46. Bilateral blur
- 47. Render light geometry for each volumetric and execute ray marching R11G11B10 1/2 Resolution Apply horizontal and vertical bilateral Gaussian Blur Accumulation Pass Gather Pass Apply depth-aware up- sampling Upscale Pass Composite Pass Add ﬁnal up-scaled buffer to the scene R11G11B10 Native Resolution Final Scene
- 48. Extending the System
- 49. 2D projector texture (gobo/cookie)
- 50. 3D noise texture
- 51. IES proﬁlesTop down perspective
- 52. Isostropic scattering
- 53. Anisotropic scattering (Henyey-Greenstein phase function) p(⇥) = 1 g2 (1 + g2 + 2g cos ⇥)1.5
- 54. Anisotropic scattering (Schlick phase function) p(⇥) = 1 k2 (1 + k cos ⇥)2 k ⇡ 1.55g 0.55g3
- 55. Without temporal re-projection
- 56. With temporal re-projection
- 57. Performance
- 58. Pass PC (GTX 700 Series GPU) PS4/GNM Accumulation* 0.362 ms 0.161 ms Gather 0.223 ms 0.375 ms Upscale 0.127 ms 0.321 ms = 0.712 ms = 0.857 ms *measured using a half resolution render target
- 59. Results
- 60. No volumetrics
- 61. Volumetrics active
- 62. No volumetrics
- 63. Volumetrics active
- 64. “Faked” multiple scattering
- 65. Thanks for listening! :) Questions?
- 66. Contact • Benjamin Glatzel <bglatzel@deck13.com> • @begla • http://www.deck13.com
- 67. References • [1] Volumetric Light Scattering as a Post-Process - http:// http.developer.nvidia.com/GPUGems3/gpugems3_ch13.html • [2] Real-time Volumetric Lighting in Participating Media - http:// sirkan.iit.bme.hu/~szirmay/lightshaft.pdf • [3] Epipolar Sampling for Shadows and Crepuscular Rays in Participating Media with Single Scattering - http://www.sfb716.uni-stuttgart.de/uploads/ tx_vispublications/espmss10.pdf • [4] Light Shafts - Rendering Shadows in Participating Media - http:// developer.amd.com/wordpress/media/2012/10/Mitchell_LightShafts.pdf • [5] Fast Rendering of Opacity Mapped Particles using DirectX 11 Tessellation and Mixed Resolutions - https://developer.nvidia.com/sites/default/ﬁles/akamai/ gamedev/ﬁles/sdk/11/OpacityMappingSDKWhitePaper.pdf
- 68. Bonus Slides
- 69. ½-Resolution accumulation buffer
- 70. ¼-Resolution accumulation buffer
- 71. static const float gauss_filter_weights[] = {! 0.14446445, 0.13543542, 0.11153505, 0.08055309, 0.05087564, 0.02798160, 0.01332457, 0.00545096! } ;! ! #define NUM_SAMPLES_HALF 7! #define BLUR_DEPTH_FALLOFF 1000.0! ! float4 gatherGauss ( in float2 blurDirection , in float2 uv )! {! [...]! ! [unroll]! for ( REAL r = -NUM_SAMPLES_HALF; r <= NUM_SAMPLES_HALF; ++r )! {! uvOffset = r * blurDirection * rendertarget_size . zw ;! kernelSample = SAMPLE ( inputSampler, uv + uvOffset ) . rgba ;! kernelDepth = getLinearDepth ( depthSampler, depthSamplerState, uv + uvOffset ) ;! ! // Simple depth-aware filtering! depthDiff = abs ( kernelDepth - centerDepth ) ;! r2 = BLUR_DEPTH_FALLOFF * depthDiff ;! g = exp ( -r2*r2 ) ;! weight = g * gauss_filter_weights [ abs ( r ) ] ;! ! accumResult += weight * kernelSample . rgb ;! ! accumWeights += weight ;! }! ! return float4 ( accumResult . rgb / accumWeights , 1.0 ) ;! }! ! float4 ps_gather_horz ( VERTEX_OUTPUT f_in ) : SV_Target! {! return gatherGauss ( float2 ( 1.0, 0.0 ), f_in . uv0 ) ;! }! ! [...]
- 72. float4 ps_upsample ( VERTEX_OUTPUT f_in ) : SV_Target! {! [...]! ! // Better choose something relative to the far clip distance here! const float upsampleDepthThreshold = 0.0001 ;! ! float minDepthDiff = 1.0 ;! uint nearestDepthIndex = 0 ;! ! float currentDepthDiff = abs ( sampleDownsampledDepth[0] - fullResDepth ) ;! bool rejectSample = currentDepthDiff < upsampleDepthThreshold ;! ! [branch]! if ( currentDepthDiff < minDepthDiff )! {! minDepthDiff = currentDepthDiff ;! nearestDepthIndex = 0 ;! }! ! currentDepthDiff = abs ( sampleDownsampledDepth[1] - fullResDepth ) ;! rejectSample = rejectSample && currentDepthDiff < upsampleDepthThreshold ; ! ! [branch]! if ( currentDepthDiff < minDepthDiff )! {! minDepthDiff = currentDepthDiff ;! nearestDepthIndex = 1 ;! }! ! // Repeat this for the remaining 2 samples! [...]! ! // Avoid blocky artefacts using edge detection! if (rejectSample)! return float4 ( SAMPLE ( inputSampler, f_in . uv0 ) . rgb, 1.0 ) ;! ! return float4 ( sampleR[nearestDepthIndex], sampleG[nearestDepthIndex], sampleB[nearestDepthIndex], 1.0 ) ;! }

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