动画更新率优化URO（Update Rate Optimization）

https://gameinstitute.qq.com/course/detail/10131

引用来自Epic Games 工程师王祢语录：

URO（Update Rate Optimization），我们其实没有必要对所有的角色在每一帧都做骨骼计算。比如画面中一个角色的POSE上半身动作是怎么样，下半身动作是怎么样，是否需要融合，什么频率融合，中间是不是要插值，这些设置可以非常大程度决定骨骼更新的计算量。大家可以看到下面的图，左一是每一帧都更新；左边二是每四帧更新一次，中间用插值；第三张图是每十帧更新一次，中间用插值；最后一张图是每四帧更新一次，不用插值。大家可以看到当角色占屏面积比较小，离得比较远的时候其实是没有大差别的。

找到对应相关关键代码，抛砖引玉：

SkinnedMeshComponent如下代码

// Update Rate
   /** if TRUE, Owner will determine how often animation will be updated and evaluated. See AnimUpdateRateTick()
   * This allows to skip frames for performance. (For example based on visibility and size on screen). */
   UPROPERTY(EditAnywhere, AdvancedDisplay, BlueprintReadWrite, Category=Optimization)
   uint8 bEnableUpdateRateOptimizations:1;

bool ShouldUseUpdateRateOptimizations() const;//是否使用更新率优化基于这个函数跟进代码会看到很多内容

/** Animation Update Rate optimization parameters. */
struct FAnimUpdateRateParameters* AnimUpdateRateParams;//重点：动画更新结构体参数，可以修改里面的参数优化

//以下控制台查看命令

static TAutoConsoleVariable<int32> CVarEnableAnimRateOptimization(
   TEXT("a.URO.Enable"),
   1,
   TEXT("True to anim rate optimization."));

static TAutoConsoleVariable<int32> CVarDrawAnimRateOptimization(
   TEXT("a.URO.Draw"),
   0,
   TEXT("True to draw color coded boxes for anim rate."));

SkeletalMeshComponent如下代码

   /** @return whether we should tick animation (we may want to skip it due to URO) */
   bool ShouldTickAnimation() const;

   /** Used to scale speed of all animations on this skeletal mesh. */
   UPROPERTY(EditAnywhere, AdvancedDisplay, BlueprintReadWrite, Category=Animation)
   float GlobalAnimRateScale;

void USkeletalMeshComponent::TickAnimation(float DeltaTime, bool bNeedsValidRootMotion)
{
   SCOPED_NAMED_EVENT(USkeletalMeshComponent_TickAnimation, FColor::Yellow);
   SCOPE_CYCLE_COUNTER(STAT_AnimGameThreadTime);
   SCOPE_CYCLE_COUNTER(STAT_AnimTickTime);
   if (SkeletalMesh != nullptr)
   {
       // We're about to UpdateAnimation, this will potentially queue events that we'll need to dispatch.
       bNeedsQueuedAnimEventsDispatched = true;

       // We update sub instances first incase we're using either root motion or non-threaded update.
       // This ensures that we go through the pre update process and initialize the proxies correctly.
       for(UAnimInstance* SubInstance : SubInstances)
       {
           SubInstance->UpdateAnimation(DeltaTime * GlobalAnimRateScale, false);
       }

       if (AnimScriptInstance != nullptr)
       {
           // Tick the animation
           AnimScriptInstance->UpdateAnimation(DeltaTime * GlobalAnimRateScale, bNeedsValidRootMotion);
       }

       if(ShouldUpdatePostProcessInstance())
       {
           PostProcessAnimInstance->UpdateAnimation(DeltaTime * GlobalAnimRateScale, false);
       }

       /**
           If we're called directly for autonomous proxies, TickComponent is not guaranteed to get called.
           So dispatch all queued events here if we're doing MontageOnly ticking.
       */
       if (ShouldOnlyTickMontages(DeltaTime))
       {
           ConditionallyDispatchQueuedAnimEvents();
       }
   }
}

void USkeletalMeshComponent::TickPose(float DeltaTime, bool bNeedsValidRootMotion)
{
Super::TickPose(DeltaTime, bNeedsValidRootMotion);

   if (ShouldTickAnimation())
   {
       // Don't care about roll over, just care about uniqueness (and 32-bits should give plenty).
       LastPoseTickFrame = static_cast<uint32>(GFrameCounter);

       const bool bUseUpdateRateOptimizations = ShouldUseUpdateRateOptimizations();
       float TimeAdjustment = bUseUpdateRateOptimizations ? AnimUpdateRateParams->GetTimeAdjustment() : 0.0f;
       TickAnimation(DeltaTime + TimeAdjustment, bNeedsValidRootMotion);
       if (CVarSpewAnimRateOptimization.GetValueOnGameThread() > 0 && Ticked.Increment()==500)
       {
           UE_LOG(LogTemp, Display, TEXT("%d Ticked %d NotTicked"), Ticked.GetValue(), NotTicked.GetValue());
           Ticked.Reset();
           NotTicked.Reset();
       }
   }
   else
   {
       if (AnimScriptInstance)
       {
           AnimScriptInstance->OnUROSkipTickAnimation();
       }

       for(UAnimInstance* SubInstance : SubInstances)
       {
           SubInstance->OnUROSkipTickAnimation();
       }

       if(PostProcessAnimInstance)
       {
           PostProcessAnimInstance->OnUROSkipTickAnimation();
       }

       if (CVarSpewAnimRateOptimization.GetValueOnGameThread())
       {
           NotTicked.Increment();
       }
   }
}

AnimUpdateRateParams结构体内容优化，动态改写

动画更新率优化URO（Update Rate Optimization）

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