小米互娱VR技术专家房燕良-虚幻4渲染系统架构解析

2020-02-27 534浏览

1.虚幻4渲染系统结构解析房燕良 2016年9月
2.Overview • 自我介绍 • 3D引擎渲染系统概述 • 虚幻4渲染系统架构 – 游戏线程&渲染线程 – 场景管理与渲染数据管理 – Deferred Shading Scene Renderer • 虚幻4的VR渲染 – 以Google VR HMD插件为例
3.3D引擎渲染系统概述 • 渲染系统架构 – 场景管理与渲染器 – 核心问题是管理复杂度和效率 Scene/Level Management Render Pipeline Resource System （Meshes、Textures） Material System Graphic API（D3D、OpenGL、Metal、Valukan）
4.虚幻4渲染系统概述：Modules • Engine\Source\Runtime • 核心代码模块 – RenderCore – Renderer • RHI抽象层 – RHI：Render Hardware Interface – 基于D3D 11设计 • RHI实现层 – EmptyRHI – Windows\D3D11RHI – Apple\MetalRHI – OpenGLDrv、VulkanRHI
5.虚幻4渲染系统概述：渲染线程 • 从虚幻3开始引入了渲染线程—Gemini • 渲染线程对效率的提升 – 最耗时的系统：渲染、游戏逻辑/脚本、物理模拟 – 没有渲染线程 Game Render Frame 1 Game Render Frame 2 Game Render Frame 3 – 使用渲染线程 Game Render Frame 1 Game Render Frame 2 Game Render Frame 3
6.虚幻4渲染系统概述：渲染线程 • 主线程领先2帧 – Front Buffer：N，Render Thread：N+1，GameThread:N+2 – Render Command Fence：防止Game Thread跑太快 • 场景数据管理 – 主线程管理场景数据；渲染线程使用Proxy对象； – 渲染线程管理一份当前帧的拷贝 Main Thread Main Thread Fence Render Command Queue Rendering Thread Render Hardware Interface Render Thread
7.虚幻4渲染系统概述：核心类的静态结构
8.虚幻4渲染系统概述：核心类的静态结构
9.虚幻4基本渲染流程 • Game线程 voidUGameEngine::Tick(float DeltaSeconds, bool bIdleMode ) {UGameEngine::RedrawViewports(){ voidFViewport::Draw(bool bShouldPresent) { voidUGameViewportClient::Draw(){ //-- 计算ViewFamily、View的各种属性ULocalPlayer::CalcSceneView();//-- 发送渲染命令：FDrawSceneCommandFRendererModule::BeginRenderingViewFamily()//-- Draw HUD PlayerController->MyHUD->PostRender(); } }}} FrameEndSync.Sync();
10.虚幻4基本渲染流程 • Game线程 voidFRendererModule::BeginRenderingViewFamily(){ // render proxies update World->SendAllEndOfFrameUpdates(); // Construct the scene renderer. // This copies the view family attributes // into its own structures. FSceneRenderer* SceneRenderer =FSceneRenderer::CreateSceneRenderer(ViewFamily);ENQUEUE_UNIQUE_RENDER_COMMAND_ONEPARAMETER( FDrawSceneCommand, FSceneRenderer*,SceneRenderer,SceneRenderer, { RenderViewFamily_RenderThread(RHICmdList, SceneRenderer); FlushPendingDeleteRHIResources_RenderThread(); }); }
11.虚幻4基本渲染流程 • 渲染线程 – RenderViewFamily_RenderThread() –FSceneRenderer::Render()– InitViews() • Primitive Visibility Determination：Frustum Cull+Occlusion Cull • Light Visibility：Frustum Cull • 透明物体排序：Back to Front • 不透明物体排序：Front to Back – 渲染Scene Color – Post Process
12.虚幻4的延迟渲染 • FDeferredShadingSceneRenderer –GBuffers:class FSceneRenderTargets – DeferredShadingCommon.usf Name GBufferA GBufferB GBufferC Format PF_A2B10G10R10 PF_B8G8R8A8 PF_B8G8R8A8 Usage WorldNormal：xyz Metallic：r Specular：g Roughness：b ShadingModelID：a BaseColor：rgb GBufferAO：a
13.虚幻4的延迟渲染 • FDeferredShadingSceneRenderer
14.虚幻4的延迟渲染 voidFDeferredShadingSceneRenderer::Render(){ boolFDeferredShadingSceneRenderer::InitViews(){ //-- Visibility determination. voidFSceneRenderer::ComputeViewVisibility(){ FrustumCull(); OcclusionCull(); } //-- 透明对象排序：back to frontFTranslucentPrimSet::SortPrimitives();//determine visibility of each light DoFrustumCullForLights(); //-- Base Pass对象排序：front to back voidFDeferredShadingSceneRenderer::SortBasePassStaticData();} // 下页继续 }
15.虚幻4的延迟渲染 voidFDeferredShadingSceneRenderer::Render(){ //-- EarlyZPassFDeferredShadingSceneRenderer::RenderPrePass();RenderOcclusion(); //-- Build Gbuffers SetAndClearViewGBuffer();FDeferredShadingSceneRenderer::RenderBasePass();FSceneRenderTargets::FinishRenderingGBuffer();//-- Lighting stage RenderLights(); RenderDynamicSkyLighting(); RenderAtmosphere(); RenderFog(); RenderTranslucency(); RenderDistortion(); //-- post processing SceneContext.ResolveSceneColor();FPostProcessing::Process();FDeferredShadingSceneRenderer::RenderFinish();}
16.虚幻4的延迟渲染 voidFDeferredShadingSceneRenderer::RenderLights(){ foreach(FLightSceneInfoCompact light IN Scene->Lights) { voidFDeferredShadingSceneRenderer::RenderLight(Light){ RHICmdList.SetBlendState(Additive Blending); // DeferredLightVertexShaders.usf VertexShader = TDeferredLightVS; // DeferredLightPixelShaders.usf PixelShader = TDeferredLightPS; switch(Light Type) { case LightType_Directional:DrawFullScreenRectangle(); case LightType_Point:StencilingGeometry::DrawSphere();case LightType_Spot:StencilingGeometry::DrawCone();} } } }
17.虚幻4的VR渲染 • 虚幻4的渲染系统与Unity3D的架构不同 – 在Unity3D中，Camera管理一个渲染管线 – 虚幻4将VR渲染流程整合进引擎底层 – Scene View Family、Scene View • Case Study：Google VR HMD插件 – 代码目录：Plugins/Runtime/GoogleVR/GoogleVRHMD – VR渲染系统的静态结构 – VR渲染流程概述
18.虚幻4的VR渲染
19.虚幻4的VR渲染 • 创建HMD Device //-- 在引擎启动时，会创建所有的HMD设备 voidUEngine::Init(){ boolUEngine::InitializeHMDDevice(){ for (auto HMDModuleIt = HMDModules.CreateIterator(); HMDModuleIt; ++HMDModuleIt) { IHeadMountedDisplayModule* HMDModule = *HMDModuleIt; HMDDevice = HMDModule->CreateHeadMountedDisplay(); } } }
20.虚幻4的VR渲染 • 绘制流程入口 //-- 在View绘制时，如果是Stereo则绘制两个View voidUGameViewportClient::Draw(){ const bool bEnableStereo = GEngine->IsStereoscopic3D(InViewport); int32 NumViews = bEnableStereo ? 2 : 1; for (int32 i = 0; i < NumViews; ++i) { } }
21.虚幻4的VR渲染 • IStereoRendering接口调用 voidUGameViewportClient::Draw(){ULocalPlayer::CalcSceneView(){ULocalPlayer::GetProjectionData(){ GEngine->StereoRenderingDevice->AdjustViewRect(StereoPass); GEngine->StereoRenderingDevice->CalculateStereoViewOffset(StereoPass); ProjectionData.ProjectionMatrix = GEngine->StereoRenderingDevice ->GetStereoProjectionMatrix(StereoPass); } } }
22.虚幻4的VR渲染 • GoogleVRHMD实现 voidFGoogleVRHMD::AdjustViewRect(StereoPass,int32& X, int32& Y, uint32& SizeX, uint32& SizeY) const { SizeX = SizeX / 2; if( StereoPass == eSSP_RIGHT_EYE ) X += SizeX; } voidFGoogleVRHMD::CalculateStereoViewOffset(){ const float EyeOffset = (GetInterpupillaryDistance() * 0.5f) * WorldToMeters; const float PassOffset = (StereoPassType == eSSP_LEFT_EYE) ? -EyeOffset : EyeOffset; ViewLocation += ViewRotation.Quaternion().RotateVector(FVector(0,PassOffset,0 )); }
23.虚幻4的VR渲染 • GoogleVRHMD实现 voidFGoogleVRHMD::RenderTexture_RenderThread(){ gvr_distort_to_screen(GVRAPI, SrcTexture->GetNativeResource(), CachedDistortedRenderTextureParams, &CachedPose, &CachedFuturePoseTime); }
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