p.CollisionParticlesPerObjectFractionDefault

p.CollisionParticlesPerObjectFractionDefault

#Overview

name: p.CollisionParticlesPerObjectFractionDefault

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

• type: Var
• help: Fraction of verts

It is referenced in 4 C++ source files.

#Summary

#Usage in the C++ source code

The purpose of p.CollisionParticlesPerObjectFractionDefault is to control the fraction of vertices used for collision detection in Geometry Collection objects within Unreal Engine 5’s Chaos physics system.

• This setting variable is part of the Chaos physics system, specifically for Geometry Collection objects.
• The Chaos physics module and the Geometry Collection system rely on this setting variable.
• The value of this variable is set as a console variable, which means it can be changed at runtime or through configuration files.
• It interacts with the CollisionParticlesPerObjectFraction variable, which is initialized using this default value.
• Developers must be aware that this variable affects the performance and accuracy of collision detection for Geometry Collection objects. A higher value means more vertices are used for collision, increasing accuracy but potentially impacting performance.
• Best practices when using this variable include:
  1. Adjusting it based on the complexity of your Geometry Collection objects and performance requirements.
  2. Testing different values to find the optimal balance between collision accuracy and performance.
  3. Considering using different values for different levels of detail or based on the object’s distance from the camera.

Regarding the associated variable CollisionParticlesPerObjectFractionDefault:

• Its purpose is to store the actual value used by the physics system for collision particle fraction.
• It’s initialized with the value of p.CollisionParticlesPerObjectFractionDefault.
• It’s used in the FGeometryCollectionPhysicsProxy constructor to set the CollisionParticlesPerObjectFraction member variable.
• In the Initialize function of FGeometryCollectionPhysicsProxy, it’s combined with the CollisionSampleFraction parameter to calculate the final CollisionParticlesPerObjectFraction.
• Developers should be aware that changes to p.CollisionParticlesPerObjectFractionDefault will affect newly created Geometry Collection objects, but won’t immediately affect existing ones.
• Best practices include:
  1. Monitoring this value when debugging collision issues with Geometry Collection objects.
  2. Considering it when optimizing performance, as it directly affects the number of collision particles used.
  3. Potentially exposing it as a configurable parameter for artists or level designers to fine-tune collision behavior.

#References in C++ code

#Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/PhysicsProxy/GeometryCollectionPhysicsProxy.cpp:73

Scope: file

Source code excerpt:

float CollisionParticlesPerObjectFractionDefault = 1.0f;
FAutoConsoleVariableRef CVarCollisionParticlesPerObjectFractionDefault(
	TEXT("p.CollisionParticlesPerObjectFractionDefault"), 
	CollisionParticlesPerObjectFractionDefault, 
	TEXT("Fraction of verts"));

bool DisableGeometryCollectionGravity = false;
FAutoConsoleVariableRef CVarGeometryCollectionDisableGravity(
	TEXT("p.GeometryCollectionDisableGravity"),

#Associated Variable and Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/PhysicsProxy/GeometryCollectionPhysicsProxy.cpp:71

Scope: file

Source code excerpt:

}

float CollisionParticlesPerObjectFractionDefault = 1.0f;
FAutoConsoleVariableRef CVarCollisionParticlesPerObjectFractionDefault(
	TEXT("p.CollisionParticlesPerObjectFractionDefault"), 
	CollisionParticlesPerObjectFractionDefault, 
	TEXT("Fraction of verts"));

bool DisableGeometryCollectionGravity = false;
FAutoConsoleVariableRef CVarGeometryCollectionDisableGravity(
	TEXT("p.GeometryCollectionDisableGravity"),
	DisableGeometryCollectionGravity,

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/PhysicsProxy/GeometryCollectionPhysicsProxy.cpp:523

Scope (from outer to inner):

file
function     FGeometryCollectionPhysicsProxy::FGeometryCollectionPhysicsProxy

Source code excerpt:

	, LastSyncCountGT(MAX_uint32)
#endif
	, CollisionParticlesPerObjectFraction(CollisionParticlesPerObjectFractionDefault)
	, PhysicsThreadCollection(Parameters.RestCollection)
	, GameThreadCollection(GameThreadCollectionIn)
	, WorldTransform_External(FTransform::Identity)
	, bIsGameThreadWorldTransformDirty(false)
	, bHasBuiltGeometryOnPT(false)
	, bHasBuiltGeometryOnGT(false)

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/PhysicsProxy/GeometryCollectionPhysicsProxy.cpp:612

Scope (from outer to inner):

file
function     void FGeometryCollectionPhysicsProxy::Initialize

Source code excerpt:

	// Collision vertices down sampling validation.  
	//
	CollisionParticlesPerObjectFraction = Parameters.CollisionSampleFraction * CollisionParticlesPerObjectFractionDefault;
	if (ReportHighParticleFraction > 0)
	{
		for (const FSharedSimulationSizeSpecificData& Data : Parameters.Shared.SizeSpecificData)
		{
			if (ensure(Data.CollisionShapesData.Num()))
			{