With Parallaxcorrected Cubemap Sébastien Lagarde Antoine Zanuttini DONTNOD Entertainment Imagebased Lighting Distant IBL Infinite cubemap Distant lighting No position Hand authored Camerabased ID: 1024561
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2. Local Image-based LightingWith Parallax-corrected CubemapSébastien Lagarde, Antoine ZanuttiniDONTNOD Entertainment
3. Image-based Lighting
4. Distant IBLInfinite cubemapDistant lightingNo positionHand authoredCamera-basedContributes to all objectsSmooth lighting transitionOfflineRuntime
5. Local IBLLocal cubemapLocal lightingPositionIn-engine generatedObject-basedContribute to nearest objectsLighting seamsParallax issueRuntimeOffline
6. Local IBLLighting seamsParallax issue
7. Our Local Image-based Lighting Approach
8. Our Local IBL ApproachMix of local cubemapsPositionLocal lightingIn-engine generatedPoint of interest -basedContribute to all objectsNo lighting seamsStill parallax issueOfflineRuntime
9. Our Local IBL ApproachNo lighting seams anymoreBut still have parallax issueAnd introduce error with distant objects
10. Parallax-corrected Cubemapin Object’s shader
11. Parallax-corrected Cubemap
12. Parallax-corrected CubemapSimple algorithm to minimize parallax issue on GPUArtists define box volumeIntersect a volume and correct the reflection vectorWe just reinvented the wheel!Kevin Bjorke, GPU GemsBartosz Czuba, Gamedev.net forums
13. Parallax-corrected CubemapWorks well on all kind of surfaces but…costlyOBB geometry proxy : ~21 instructionsFor one parallax-corrected cubemapCheaper approximation existsNVIDIA / ATI demoPseudo code D = normalize(K * (Pp - C) + R)
14. Parallax-corrected Cubemap
15. Parallax-corrected CubemapScene renderingObject’s Shader with cubemaps parallax correctionObject’shaderScene renderingMixing step with cubemaps parallax correction
16. Parallax-corrected CubemapMixing Step
17. Parallax-corrected CubemapNo pixel positionsAdd a reflection planeParallax correction is based on camera, geometry proxy and reflection planeFor current point of view
18. Parallax-corrected Cubemap // Intersection with OBB convert to unit box spacefloat3 RayWS = normalize(GetCubeDir(...)); // Current directionfloat3 RayLS = mul((float3x3)WorldToLocal, RayWS);float3 ReflCameraLS = mul(WorldToLocal, ReflCameraWS); // Can be precalc// Same code as before but for ReflCameraLS and with unit boxfloat3 Unitary = float3(1.0f, 1.0f, 1.0f);float3 FirstPlaneIntersect = (Unitary - ReflCameraLS) / RayLS;float3 SecondPlaneIntersect = (-Unitary - ReflCameraLS) / RayLS;float3 FurthestPlane = max(FirstPlaneIntersect, SecondPlaneIntersect);float Distance = min(FurthestPlane.x, min(FurthestPlane.y, FurthestPlane.z));// Use Distance in WS directly to recover intersectionfloat3 IntersectPositionWS = ReflCameraWS + RayWS * Distance;float3 ReflDirectionWS = IntersectPositionWS - CubemapPositionWS;return texCUBE(envMap, ReflDirectionWS);
19. Parallax-corrected CubemapTop-Dow view of a corridor with 3 local cubemaps
20. Parallax-corrected CubemapVideo
21. Parallax-corrected CubemapWith glossy material : Enlarge geometry proxy
22. Parallax-corrected CubemapReferenceDistortion with glossy materialOur approximation
23. Parallax-corrected CubemapImprovementRasterizing parallax corrected cubemapDraw the textured box volume from reflected camera positionNo longer restricted to box/sphere volume!Tools for artists to define any convex volume
24. Parallax-corrected Cubemap
25. Parallax-corrected Cubemap // C++Matrix Mirror = CreateMirrorMatrix(ReflectionPlaneWS);Vector ReflectedViewPositionWS = Mirror.TransformVector(ViewPositionWS);Matrix View = CalcCubeFaceViewMatrix(FaceIndex, ReflectedViewPositionWS);Matrix ViewProjection = View * Projection; // ShaderVertexMain() {float4 PositionWS = mul(LocalToWorld, InPositionOS); float4 PositionSS = mul(ViewProjectionMatrix, PositionWS);OutPosition = PositionSS; OutDirection = PositionWS.xyz - CubemapPositionWS.xyz; // Current direction}PixelMain() { OutColor = texCUBE(CubeTexture, OutDirection);}
26. Sum up : Parallax-corrected CubemapPlanar objects onlyConvex volumesScalable with number of cubemapGeneralCheap approximationPer pixel correctionSimple volume (Box/Sphere)# CubePS3 (ms)X360 (ms)10.140.2920.230.4130.310.52Measures for 128x128x6 DXT1 cubemapMeasures for 25% / 75% screen coverage# CubePS3 (ms)X360 (ms)10.24 / 0.750.19 / 0.4520.48 / 1.270.44 / 1.2130.72/ 2.260.61 / 2.27
27. Caveats
28. Caveats - Distant lighting issuesAccuracy decreases with distance from POIProvide different solutions to artistsUse ambient lighting information at objects positionMix with cubemap based on POI distanceFade cubemap contribution with distanceHelps with performance too Override cubemap by objects
29. Conclusion
30. TakeawaysNew local IBL approachCheapReplace costly real-time IBLSeveral tools in the hands of the artistsTo ease smooth lighting transitionTo get accurate lighting
31. FutureThese tools are not enoughWe developed othersDescribed in upcoming GPU pro 4 book to be released at GDC 2013
32. AcknowledgmentsFrédéric Cros (Lighting artist) for his invaluable help on testing, using and mastering our toolsDONTNOD teamNaty Hoffman for his help with the submission processThanks to all my reviewersGabriel Ware, Stephen Hill, Laury Michel, Sam Hocevar, Jérôme Banal, Nicolas Serouart, Michel Koch, Brian Karis, Colin Barré-Brisebois
33. Questions?Slides available at http://seblagarde.wordpress.com/Twitter: @SebLagardeEmail: Lagardese@hotmail.fr
34. ReferencesMcTaggart, “Half-Life 2 Valve Source Shading” http://www2.ati.com/developer/gdc/D3DTutorial10_Half-Life2_Shading.pdfBjorke, “Image based lighting”, http://http.developer.nvidia.com/GPUGems/gpugems_ch19.htmlBehc, “Box projected cubemap environment mapping” http://www.gamedev.net/topic/568829-box-projected-cubemap-environment-mapping/
35. ReferencesMad Mod Mike demo, “The Naked Truth Behind NVIDIA’s Demos”, ftp.up.ac.za/mirrors/www.nvidia.com/developer/presentations/2005/SIGGRAPH/Truth_About_NVIDIA_Demos.pdfBrennan, “Accurate Environment Mapped Reflections and Refractions by Adjusting for Object Distance”, http://developer.amd.com/media/gpu_assets/ShaderX_CubeEnvironmentMapCorrection.pdf
36. Bonus slides
37. Our Local IBL ApproachPoint of interest (POI)?Context dependentCameraPlayerAny characterDummy locationAnimated by a track
38. Our Local IBL approachInfluence volume link to local cubemapBox or sphereMust overlapGather local cubemapsBased on POI locationBased on cubemap influence volumeTake N nearest volumesTop view
39. Blending algorithmBlending weights rules100% influence at boundary of inner range0% influence at boundary of outer rangeSmaller influence more importantNo overlap of inner range
40. Blending algorithm – Pseudo code for (int i = 0; i < NumPrimitive; ++i) { if (In inner range) EarlyOut; if (In outer range) SelectedPrimitive.Add(CurrentPrimitive.GetInfluenceWeights(LocationPOI));}SelectedPrimitive.Sort();for (int i = 0; i < NumSelectedPrimitive; ++i) { SumIW += SelectedPrimitive[i]; InvSumIW += (1.0f - SelectedPrimitive[i]);}for (int i = 0; i < NumSelectedPrimitive; ++i) { BlendFactor[i] = (1.0f - (SelectedPrimitive[i] / SumIW)) / (NumSelectedPrimitive - 1); BlendFactor[i] *= ((1.0f - SelectedPrimitive[i]) / InvSumIW); SumBlendFactor += BlendFactor[i];}// Normalize BlendFactor (...)
41. Blending algorithm
42. Blending algorithmCombined on GPUMultiple shadersBy faceBy cubemap numberBlend all mipmapsFor preconcolved cubemapUse knowledge of hardware texture layout128^2 DXT1PS3 (ms)X360 (ms) 10.080.2020.090.2630.100.3440.110.41256^2 DXT1PS3 (ms)X360 (ms)10.290.4820.400.6130.540.7840.680.99
43. Parallax-corrected Cubemap float3 DirectionWS = PositionWS - CameraWS;float3 ReflDirectionWS = reflect(DirectionWS, NormalWS); // Find the ray intersection with box planefloat3 FirstPlaneIntersect = (BoxMax - PositionWS) / ReflDirectionWS;float3 SecondPlaneIntersect = (BoxMin - PositionWS) / ReflDirectionWS;// Get the furthest of these intersections along the ray (Ok because x/0 give +inf and -x/0 give –inf )float3 FurthestPlane = max(FirstPlaneIntersect, SecondPlaneIntersect);// Find the closest far intersectionfloat Distance = min(min(FurthestPlane.x, FurthestPlane.y), FurthestPlane.z);// Get the intersection positionfloat3 IntersectPositionWS = PositionWS + ReflDirectionWS * Distance;// Get corrected reflection ReflDirectionWS = IntersectPositionWS - CubemapPositionWS;return texCUBE(envMap, ReflDirectionWS);
44. Parallax-corrected cubemap
45. Parallax-corrected CubemapError analysisParallax-corrected cubemap only works for one normal
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