p.CollisionParticlesBVHDepth

p.CollisionParticlesBVHDepth

#Overview

name: p.CollisionParticlesBVHDepth

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

• type: Var
• help: The maximum depth for collision particles bvh

It is referenced in 6 C++ source files.

#Summary

#Usage in the C++ source code

The purpose of p.CollisionParticlesBVHDepth is to control the maximum depth for the Bounding Volume Hierarchy (BVH) used in collision detection for particles in Unreal Engine’s Chaos physics system.

• This setting variable is primarily used in the Chaos physics system, which is part of Unreal Engine’s experimental physics framework.

• Based on the callsites, this variable is utilized in the Chaos namespace, specifically in the PBDCollisionConstraints and BVHParticles modules.

• The value of this variable is set using an FAutoConsoleVariableRef, which allows it to be modified at runtime through the console. Its default value is 4.

• This variable interacts closely with the CollisionParticlesBVHDepth variable, which shares the same value. It’s used in the construction of TBoundingVolumeHierarchy objects within the FBVHParticles class.

• Developers should be aware that modifying this value affects the performance and accuracy of collision detection for particles. A higher value may increase accuracy but at the cost of performance, while a lower value may improve performance but potentially reduce collision accuracy.

• Best practices when using this variable include:

  1. Experimenting with different values to find the optimal balance between performance and collision accuracy for your specific use case.
  2. Monitoring performance metrics when adjusting this value, especially in scenes with many particles.
  3. Considering the complexity of your scene and the number of particles when setting this value.

Regarding the associated variable CollisionParticlesBVHDepth:

• It serves the same purpose as p.CollisionParticlesBVHDepth, controlling the maximum depth of the BVH for collision particles.

• This variable is used directly in the Chaos physics system, particularly in the FBVHParticles class constructor and when rebuilding the BVH.

• Its value is set by the console variable p.CollisionParticlesBVHDepth.

• It’s used as a parameter when constructing TBoundingVolumeHierarchy objects, which are crucial for efficient collision detection.

• Developers should be aware that this variable directly affects the structure of the BVH used for collision detection, impacting both performance and accuracy.

• Best practices include:

  1. Ensuring that any changes to p.CollisionParticlesBVHDepth are reflected in the behavior of systems using CollisionParticlesBVHDepth.
  2. Considering the impact on memory usage when adjusting this value, as deeper BVHs will consume more memory.
  3. Testing thoroughly after making changes, as this variable can significantly affect collision behavior throughout the physics simulation.

#References in C++ code

#Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/Chaos/PBDCollisionConstraints.cpp:37

Scope (from outer to inner):

file
namespace    Chaos

Source code excerpt:

	int32 CollisionParticlesBVHDepth = 4;
	FAutoConsoleVariableRef CVarCollisionParticlesBVHDepth(TEXT("p.CollisionParticlesBVHDepth"), CollisionParticlesBVHDepth, TEXT("The maximum depth for collision particles bvh"));

	int32 ConstraintBPBVHDepth = 2;
	FAutoConsoleVariableRef CVarConstraintBPBVHDepth(TEXT("p.ConstraintBPBVHDepth"), ConstraintBPBVHDepth, TEXT("The maximum depth for constraint bvh"));

	int32 BPTreeOfGrids = 1;
	FAutoConsoleVariableRef CVarBPTreeOfGrids(TEXT("p.BPTreeOfGrids"), BPTreeOfGrids, TEXT("Whether to use a seperate tree of grids for bp"));

#Associated Variable and Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/Chaos/BVHParticles.cpp:7

Scope (from outer to inner):

file
namespace    Chaos
function     FBVHParticles::FBVHParticles

Source code excerpt:

	FBVHParticles::FBVHParticles()
		: FParticles()
		, MBVH(new TBoundingVolumeHierarchy<FParticles, TArray<int32>>(*this, CollisionParticlesBVHDepth))
	{}

	FBVHParticles::FBVHParticles(FBVHParticles&& Other)
		: FParticles(MoveTemp(Other))
		, MBVH(new TBoundingVolumeHierarchy<FParticles, TArray<int32>>(MoveTemp(*Other.MBVH)))
	{}

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/Chaos/BVHParticles.cpp:17

Scope (from outer to inner):

file
namespace    Chaos
function     FBVHParticles::FBVHParticles

Source code excerpt:

	FBVHParticles::FBVHParticles(FParticles&& Other)
		: FParticles(MoveTemp(Other))
		, MBVH(new TBoundingVolumeHierarchy<FParticles, TArray<int32>>(*this, CollisionParticlesBVHDepth))
	{}

	FBVHParticles::~FBVHParticles()
	{
		delete MBVH;
	}

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/Chaos/BVHParticles.cpp:46

Scope (from outer to inner):

file
namespace    Chaos
function     FBVHParticles::FBVHParticles

Source code excerpt:

			SetX(i, Other.GetX(i));
		}
		MBVH = new TBoundingVolumeHierarchy<FParticles, TArray<int32>>(*this, CollisionParticlesBVHDepth);
	}

	void FBVHParticles::UpdateAccelerationStructures()
	{
		MBVH->UpdateHierarchy();
	}

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Private/Chaos/PBDCollisionConstraints.cpp:36

Scope (from outer to inner):

file
namespace    Chaos

Source code excerpt:

	}

	int32 CollisionParticlesBVHDepth = 4;
	FAutoConsoleVariableRef CVarCollisionParticlesBVHDepth(TEXT("p.CollisionParticlesBVHDepth"), CollisionParticlesBVHDepth, TEXT("The maximum depth for collision particles bvh"));

	int32 ConstraintBPBVHDepth = 2;
	FAutoConsoleVariableRef CVarConstraintBPBVHDepth(TEXT("p.ConstraintBPBVHDepth"), ConstraintBPBVHDepth, TEXT("The maximum depth for constraint bvh"));

	int32 BPTreeOfGrids = 1;
	FAutoConsoleVariableRef CVarBPTreeOfGrids(TEXT("p.BPTreeOfGrids"), BPTreeOfGrids, TEXT("Whether to use a seperate tree of grids for bp"));

#Loc: <Workspace>/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/BVHParticles.h:8

Scope (from outer to inner):

file
namespace    Chaos

Source code excerpt:

namespace Chaos
{
	extern int32 CHAOS_API CollisionParticlesBVHDepth;

    template<class OBJECT_ARRAY, class LEAF_TYPE, class T, int d>
    class TBoundingVolumeHierarchy;


    template<class OBJECT_ARRAY, class LEAF_TYPE, class T, int d>