Current amp Future Johan Andersson Rendering Architect 25 Agenda Goal Share and discuss current amp future graphics use cases in our games and implications for graphics hardware Areas Engine overview ID: 933329
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Slide1
The Intersection of
Game Engines & GPUs:Current & Future
Johan AnderssonRendering Architect
2.5
Slide2Agenda
GoalShare and discuss current & future graphics use cases in our games and implications for graphics hardwareAreasEngine overviewShadersParallelizationTexturingRaytracingGPU computeConclusionsQ & A
Slide3Frostbite
DICE proprietary engineXbox 360PS3Windows (Direct3D 10)FocusLarge outdoor environmentsSingleplayer & multiplayerDestruction!New: Content workflows
Slide4BFBC screenshot
Slide5BFBC screenshot
Slide6Slide7Graph-based surface shaders
Artist-friendly Easy to create, tweak & manageFlexibleProgrammers & artists can extend & expose featuresData-centricEncapsulates resourcesTransformable
Rich high-level shading frameworkUsed by all content & systems
Slide8Slide9Shader permutations
Generate shader permutationsFor each used combination of features/dataHLSL vertex & pixel shadersMany features = permutation explosionShader graphs, lighting, geometryBalance perf. vs permutations vs featuresDynamic branchingLive with many permutations
Slide10Shader subroutines
Next step: Static subroutine linkingInline in all subroutines at call siteSimilar to a switch statementReduces # permutations Implementation moved to driver or GPUDoesn’t work with instancingFuture step: Dynamic subroutinesControl function pointers inside shaderProblem solved, but coherency important
Slide11Rendering & Parallelization
Slide12Jobs
Must utilize multi-core6 HW threads on Xbox 3606 SPUs on PS32-8 cores on PCJob definitionFully independent stateless functionPS3 SPU requirementGraph dependenciesTask-parallel and data-parallel
Slide13Rendering jobs
Refactor rendering systems to jobsMost will move to GPUEventuallyOne-way data flowCompute shaders & stream outputJobsDecal projectionParticle simulationTerrain geometry processingUndergrowth generation [2]Frustum cullingOcclusion culling
Command buffer generationPS3: Triangle culling
Slide14Parallel command buffer recording
Dispatch draw calls and state to multiple command buffers in parallelScales linearly with # cores1500-4000 draw calls per frameSuper-important for all platforms, used on:Xbox 360PS3 (SPU-based)No support in DX10!
Slide15DX10 parallel command buffer rec.
Single most important DX10 issue For us and many others (in the future)Until future API supportReduce draw calls with instancingTrade GPU performance for CPU performanceReduce state & constant updatesSlow dynamic constant path Manual software command buffers Difficult to update dynamic resources efficiently in parallel due to API
Slide16PS3 geometry processing (1/2)
Slow GPU triangle & vertex setup Unique situation with ”free” processorsNot fully utilizedSolution: SPU triangle cullingTrade SPU time for GPU performanceCull back faces, micro-triangles, frustumSony PS3 EDGE library5 jobs processes frame geometry in parallelOutput is new index buffer for each draw call
Slide17PS3 geometry processing (2/2)
Great flexibility and programmability!Custom processingPartition bounding box cullingTriangle part cullingClip plane triangle trivial accept & rejectTriangle cull volumes (inverse clip planes)Future: No vertex & geometry shadersDIY compute shaders with fixed-func tesselation and triangle setup unitsOutput buffer streaming still important
Slide18Occlusion culling
Buildings occlude objectsTons of objectsDifficult to implementBuilding destructionDynamic occludeesHeavy GPU occlusion queriesInvisible objects still have toUpdate logic & animationsGenerate command bufferProcessed on CPU & GPU
Slide19Software occlusion culling
Solution: Rasterize course zbuffer on SPU/CPULow-poly occluder meshes100m view distanceMax 10000 vertices/frameManually conservative256x114 float z-bufferCreated for PS3, now on allCull all objects against zbufferBefore passed to all other systems = big savingsScreen-space bbox test
Slide20GPU occlusion culling
Want GPU rasterization & testing, but:Occlusion queries introduces overhead & latencyCan be manageable, not idealConditional rendering only helps GPUNot CPU, frame memory or draw callsFuture1: Low-latency extra GPU exec contextRasterization and testing done on GPULockstep with CPUFuture2: Move entire cull & rendering to GPUScene graph, cull, systems, dispatch. End goal.
Slide21Texturing
Slide22Texture formats
UsingDXT1/5 color maps, sRGBBC5 (3Dc) normal mapsBC4 (DXT5A) for grayscale maskssRGB support for BC4/5 would be niceDXT1 replacement neededLow quality565 color bleedingRG/RGB masks compresses badlyHDR envmaps & lightmaps
RGB DXT1 mask
DXT color bleed
Slide23Slide24Future texture sampling
Texture sampling derivatives1st order texel derivatives2nd order as well?Implement in sampler unitBad performance or quality with shader sampling Artifacts with ddx/ddy techniqueReplace normalmaps with easily compressed bumpmapsBicubic upsamplingTerrain masks
Terrain heightmap
Derived normals [2]
Slide25Slide26Current sparse textures
Save memory for terrainStatic quadtree mask textureDynamic sparse destruction maskImplementationIndirection texture lookup in atlasArrays too small, want 8192 slicesCorrect bilinear filtering by bordersSiggraph’07 course for details [2]
Source mask
Atlas texture
Slide27HW sparse textures
Virtual textureHW texture filtering & mipmappingFallback on non-resident tile access Lower mipmap, default value or shader boolAt least 32k x 32k, fp issues with larger?Application-controlled tile commit/free~128 x 128 tilesFeedback mechanism for referenced tilesEasy view-dependent allocationFuture: Latency-free allocation & generationAlt1. CPU thread callback & blockAlt2. Keep everything on GPU. ”Command” shader?
Slide28Cached Procedural Unique Texturing
Unique dynamic sparse texture on all objects Defined by texture shader graphCombine procedurals, compositing, streaming and uv-space geometryDynamically commit & render visible tilesHighly complex compositingThanks to high frame-to-frame coherencyUpsample and refineNew dynamic effects made possibleAffect every surface
Slide29Raytracing
Slide30Raytracing
Much recent debate & interest in RTRTWhat we are interested in:Performance!! Rasterization for primary raysDeterministicEasy integration into enginesJust another method for certain effects & objectsNot replace whole pipeline Efficient dynamic geometryProcedural & manual animation (foliage, characters)Destruction (foliage, buildings, objects)
Slide31Mirror’s Edge
Slide32Raytraced reflections wanted
Glass & metalMostly planar surfacesReflection localityCorrect reflections for important objectsMain characterSimplified world geometry & shading for restCommon for gamesBrickmaps? [3]
Slide33Soft reflections
Mirror’s Edge
Slide34GPGPU
Slide35GPGPU uses
Effect physicsParticle vs world soft collisionAI pathfindingAI visibilityView rasterization. Obstruction from smoke & foliageProcedural animationTrees, undergrowth, hairPost-processing
Slide36CUDA DOF post-process filter
Circle of confusion mapThesis work at DICE [4]Test CUDA and performancePoisson disc blur
Multi-passed diffusionSeperable diffusionGood:Easy to learn (C)Map complex algorithmsThread & memory controlBad:Performance vs shaders
Beta interopVendor-specific
Output
Slide37GPU Compute programming model
Wanted:Easy & efficient Direct3D 10 interopLow-latency Compute tasksVendor-independent base interfaceOpenCL?Efficient CPU multi-core backendServer, older GPUs, debuggingMCUDA [5]Eventually platform-independentFuture consoles
Slide38Conclusions
Shader subroutinesMore software-controlled pipelineMore texture sampler functionalityLimited-case raytracingGPU compute for games
Slide39Questions?
Contact: johan.andersson@dice.se
Slide40References
[1] Tartarchuk, Natasha & Andersson, Johan. ”Rendering Architecture and Real-time Procedural Shading & Texturing Techniques”. GDC 2007. Link[2] Andersson, Johan. ”Terrain Rendering in Frostbite using Procedural Shader Splatting”. Siggraph 2007. Link[3] Christensen, Per H. & Batali, Dana. "An Irradiance Atlas for Global Illumination in Complex Production Scenes“. Eurographics Symposium on Rendering 2004. Link
[4] Lonroth, Per & Unger, Mattias. ”Advanced Real-time Post-Processing using GPGPU techniques”. Master thesis, 2008.[5] John Stratton, Sam Stone, Wen-mei Hwu. "MCUDA: An Efficient Implementation of CUDA Kernels on Multi-cores". Technical report, University of Illinois at Urbana-Champaign, IMPACT-08-01, March, 2008.
Slide41Bonus slides
Slide42Real-time REYES
Very interestingDisplacement mapping & proceduralsStochastic samplingPotentially more efficient & generalCompared to maxed out rasterization & tessellation on everything = pixel-sized trianglesButNo experience More research & experimentation needed
Slide43Terrain detail
Deriving normal from heightfield good in distanceFuture: HW tessellation & procedural displacement shaders for up close ground detail
Slide44Texture arrays
Use cases:Everything!Rich parameterized shadersVary slice index per instance, triangle or texel Instancing without comprimising on variation or perf.Cascaded shadow mapsHW PCF only in DX 10.1 Stable Cascaded Bounding Box Shadow MapsSparse texturesMore slices plzFor tile pools. 64x64x8192
Slide45Other raytracing uses
Global Illumination & Ambient OcclusionIncremental Photon Mapping?Async collision raycastsAI pathfinding, gameplay, sound obstructionSeperate collision world from visual worldCPU job-based now