p.ChaosCloth.UseTimeStepSmoothing

p.ChaosCloth.UseTimeStepSmoothing

#Overview

name: p.ChaosCloth.UseTimeStepSmoothing

This variable is created as a Console Variable (cvar).

It is referenced in 7 C++ source files.

#Summary

#Usage in the C++ source code

The purpose of p.ChaosCloth.UseTimeStepSmoothing is to control time step smoothing in the Chaos Cloth simulation system to avoid jitter during drastic changes in time steps.

This setting variable is primarily used in the Chaos Cloth simulation system, which is part of the ChaosCloth plugin in Unreal Engine 5. It’s specifically utilized in the clothing simulation module.

The value of this variable is set through a console variable (CVar) system. It’s initialized with a default value of true in the ChaosClothingSimulation.cpp file.

The associated variable bClothUseTimeStepSmoothing interacts directly with p.ChaosCloth.UseTimeStepSmoothing. They share the same value, with bClothUseTimeStepSmoothing being used in the actual simulation code.

Developers must be aware that this variable affects the smoothness of cloth simulation, particularly when there are significant changes in time steps. Disabling it might lead to more apparent jitter in cloth movement during such changes.

Best practices when using this variable include:

  1. Keeping it enabled (true) for most scenarios to ensure smooth cloth simulation.
  2. Only disabling it if there’s a specific need for more responsive, albeit potentially jittery, cloth behavior.
  3. Being cautious when changing its value during runtime, as it could lead to noticeable changes in cloth behavior.

Regarding the associated variable bClothUseTimeStepSmoothing:

#References in C++ code

#Callsites

This variable is referenced in the following C++ source code:

#Loc: <Workspace>/Engine/Plugins/ChaosCloth/Source/ChaosCloth/Private/ChaosCloth/ChaosClothingSimulation.cpp:60

Scope: file

Source code excerpt:

{
bool bClothUseTimeStepSmoothing = true;
FAutoConsoleVariableRef CVarClothUseTimeStepSmoothing(TEXT("p.ChaosCloth.UseTimeStepSmoothing"), bClothUseTimeStepSmoothing, TEXT("Use time step smoothing to avoid jitter during drastic changes in time steps."));

#if CHAOS_DEBUG_DRAW
namespace ClothingSimulationCVar
{
	TAutoConsoleVariable<bool> DebugDrawLocalSpace          (TEXT("p.ChaosCloth.DebugDrawLocalSpace"          ), false, TEXT("Whether to debug draw the Chaos Cloth local space"), ECVF_Cheat);
	TAutoConsoleVariable<bool> DebugDrawBounds              (TEXT("p.ChaosCloth.DebugDrawBounds"              ), false, TEXT("Whether to debug draw the Chaos Cloth bounds"), ECVF_Cheat);

#Loc: <Workspace>/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Private/Graph/Nodes/MovieGraphGlobalGameOverrides.cpp:84

Scope (from outer to inner):

file
function     void UMovieGraphGlobalGameOverridesNode::BuildNewProcessCommandLineArgsImpl

Source code excerpt:

	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("p.Chaos.ImmPhys.MinStepTime=%d"), 0));
	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("r.SkipRedundantTransformUpdate=%d"), 0));
	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("p.ChaosCloth.UseTimeStepSmoothing=%d"), 0));
}

void UMovieGraphGlobalGameOverridesNode::ApplySettings(const bool bOverrideValues, UWorld* InWorld)
{
	// Apply the scalability settings
	if (bOverrideValues)

#Loc: <Workspace>/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Private/Graph/Nodes/MovieGraphGlobalGameOverrides.cpp:168

Scope (from outer to inner):

file
function     void UMovieGraphGlobalGameOverridesNode::ApplySettings

Source code excerpt:


		// Cloth's time step smoothing messes up the change in number of simulation substeps that fixes the cloth simulation behavior when using Temporal Samples.
		MOVIEPIPELINE_STORE_AND_OVERRIDE_CVAR_INT(PreviousChaosClothUseTimeStepSmoothing, TEXT("p.ChaosCloth.UseTimeStepSmoothing"), 0, bOverrideValues);

		// Water skips water info texture when the world's game viewport rendering is disabled so we need to prevent this from happening.
		MOVIEPIPELINE_STORE_AND_OVERRIDE_CVAR_INT_IF_EXIST(PreviousSkipWaterInfoTextureRenderWhenWorldRenderingDisabled, TEXT("r.Water.SkipWaterInfoTextureRenderWhenWorldRenderingDisabled"), 0, bOverrideValues);

	}

#Loc: <Workspace>/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Private/MoviePipelineGameOverrideSetting.cpp:135

Scope (from outer to inner):

file
function     void UMoviePipelineGameOverrideSetting::ApplyCVarSettings

Source code excerpt:


	// Cloth's time step smoothing messes up the change in number of simulation substeps that fixes the cloth simulation behavior when using Temporal Samples.
	MOVIEPIPELINE_STORE_AND_OVERRIDE_CVAR_INT(PreviousChaosClothUseTimeStepSmoothing, TEXT("p.ChaosCloth.UseTimeStepSmoothing"), 0, bOverrideValues);

	// Water skips water info texture when the world's game viewport rendering is disabled so we need to prevent this from happening.
	MOVIEPIPELINE_STORE_AND_OVERRIDE_CVAR_INT_IF_EXIST(PreviousSkipWaterInfoTextureRenderWhenWorldRenderingDisabled, TEXT("r.Water.SkipWaterInfoTextureRenderWhenWorldRenderingDisabled"), 0, bOverrideValues);

	// Must come after the above cvars so that if one of those cvars is also specified by the Scalability level, then we restore to the value in the original scalability level
	// not the value we cached in the Cinematic level (if applied).

#Loc: <Workspace>/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Private/MoviePipelineGameOverrideSetting.cpp:243

Scope (from outer to inner):

file
function     void UMoviePipelineGameOverrideSetting::BuildNewProcessCommandLineArgsImpl

Source code excerpt:

	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("p.Chaos.ImmPhys.MinStepTime=%d"), 0));
	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("r.SkipRedundantTransformUpdate=%d"), 0));
	InOutDeviceProfileCvars.Add(FString::Printf(TEXT("p.ChaosCloth.UseTimeStepSmoothing=%d"), 0));
}

#Associated Variable and Callsites

This variable is associated with another variable named bClothUseTimeStepSmoothing. They share the same value. See the following C++ source code.

#Loc: <Workspace>/Engine/Plugins/ChaosCloth/Source/ChaosCloth/Private/ChaosCloth/ChaosClothingSimulation.cpp:59

Scope: file

Source code excerpt:

namespace Chaos
{
bool bClothUseTimeStepSmoothing = true;
FAutoConsoleVariableRef CVarClothUseTimeStepSmoothing(TEXT("p.ChaosCloth.UseTimeStepSmoothing"), bClothUseTimeStepSmoothing, TEXT("Use time step smoothing to avoid jitter during drastic changes in time steps."));

#if CHAOS_DEBUG_DRAW
namespace ClothingSimulationCVar
{
	TAutoConsoleVariable<bool> DebugDrawLocalSpace          (TEXT("p.ChaosCloth.DebugDrawLocalSpace"          ), false, TEXT("Whether to debug draw the Chaos Cloth local space"), ECVF_Cheat);
	TAutoConsoleVariable<bool> DebugDrawBounds              (TEXT("p.ChaosCloth.DebugDrawBounds"              ), false, TEXT("Whether to debug draw the Chaos Cloth bounds"), ECVF_Cheat);

#Loc: <Workspace>/Engine/Plugins/ChaosCloth/Source/ChaosCloth/Private/ChaosCloth/ChaosClothingSimulation.cpp:494

Scope (from outer to inner):

file
function     void FClothingSimulation::Simulate

Source code excerpt:

		const Softs::FSolverReal DeltaTime = (Softs::FSolverReal)Context->DeltaSeconds;
		const Softs::FSolverReal PrevDeltaTime = Solver->GetDeltaTime();
		const Softs::FSolverReal SmoothedDeltaTime = bClothUseTimeStepSmoothing ?
			PrevDeltaTime + (DeltaTime - PrevDeltaTime) * DeltaTimeDecay :
			DeltaTime;

		const double StartTime = FPlatformTime::Seconds();
		const float PrevSimulationTime = SimulationTime;  // Copy the atomic to prevent a re-read