file
class        class UEngine : public UObject , public FExec

	/** The amount of time a primitive is considered to be probably visible after it was last actually visible. */
	UPROPERTY(config)
	float PrimitiveProbablyVisibleTime;

	/** Max screen pixel fraction where retesting when unoccluded is worth the GPU time. */
	UPROPERTY(config)
	float MaxOcclusionPixelsFraction;

	/** Whether to pause the game if focus is lost. */

file
function     static void TrimAllOcclusionHistory

		{
			const double RealTimeSeconds = View.Family->Time.GetRealTimeSeconds();
			View.ViewState->TrimOcclusionHistory(RealTimeSeconds, RealTimeSeconds - GEngine->PrimitiveProbablyVisibleTime, RealTimeSeconds, View.ViewState->OcclusionFrameCounter);
		}
	}
}

static void AllocateOcclusionTests(FViewOcclusionQueriesPerView& QueriesPerView, const FScene* Scene, TArrayView<const FVisibleLightInfo> VisibleLightInfos, TArrayView<FViewInfo> Views)
{

file
function     static void AllocateOcclusionTests

			// Clear primitives which haven't been visible recently out of the occlusion history, and reset old pending occlusion queries.
			ViewState->TrimOcclusionHistory(ViewFamily.Time.GetRealTimeSeconds(), ViewFamily.Time.GetRealTimeSeconds() - GEngine->PrimitiveProbablyVisibleTime, ViewFamily.Time.GetRealTimeSeconds(), ViewState->OcclusionFrameCounter);

			// Give back all these occlusion queries to the pool.
			ShadowOcclusionQueryMap.Reset();

			if (FeatureLevel > ERHIFeatureLevel::ES3_1)
			{

file
function     FGPUOcclusionPacket::FGPUOcclusionPacket

	, ViewOrigin(View.ViewMatrices.GetViewOrigin())
	, OcclusionFrameCounter(ViewState.OcclusionFrameCounter)
	, PrimitiveProbablyVisibleTime(GEngine->PrimitiveProbablyVisibleTime)
	, CurrentRealTime(View.Family->Time.GetRealTimeSeconds())
	, NeverOcclusionTestDistanceSquared(GNeverOcclusionTestDistance* GNeverOcclusionTestDistance)
	, bUseOcclusionFeedback(OcclusionFeedback.IsInitialized())
	, bNewlyConsideredBBoxExpandActive(GExpandNewlyOcclusionTestedBBoxesAmount > 0.0f && GFramesToExpandNewlyOcclusionTestedBBoxes > 0 && GFramesNotOcclusionTestedToExpandBBoxes > 0)
{}

						{
							// If there's no occlusion query for the primitive, set it's visibility state to whether it has been unoccluded recently.
							bIsOccluded = (PrimitiveOcclusionHistory->LastProvenVisibleTime + GEngine->PrimitiveProbablyVisibleTime < CurrentRealTime);
							// the state was definite last frame, otherwise we would have ran a query
							bOcclusionStateIsDefinite = true;
						}
						if (bIsOccluded)
						{
							PrimitiveOcclusionHistory->LastPixelsPercentage = 0.0f;

							else
							{
								bRunQuery = CurrentRealTime - PrimitiveOcclusionHistory->LastProvenVisibleTime > PrimitiveProbablyVisibleTime * (0.5f * 0.25f * Rnd);
							}
						}
						else
						{
							bGroupedQuery = false;
							bRunQuery = true;

file
function     void FSceneRenderer::PrepareViewStateForVisibility

			// detect conditions where we should reset occlusion queries
			if (bFirstFrameOrTimeWasReset || 
				ViewState->LastRenderTime + GEngine->PrimitiveProbablyVisibleTime < View.Family->Time.GetRealTimeSeconds() ||
				View.bCameraCut ||
				View.bForceCameraVisibilityReset ||
				IsLargeCameraMovement(
					View, 
				    FMatrix(ViewState->PrevViewMatrixForOcclusionQuery), 
				    ViewState->PrevViewOriginForOcclusionQuery, 

file
class        class FGPUOcclusionPacket

	const FVector ViewOrigin;
	const uint32 OcclusionFrameCounter;
	const float PrimitiveProbablyVisibleTime;
	const float CurrentRealTime;
	const float NeverOcclusionTestDistanceSquared;
	const bool bUseOcclusionFeedback;
	const bool bNewlyConsideredBBoxExpandActive;
};