r.SupportDepthOnlyIndexBuffers

r.SupportDepthOnlyIndexBuffers

#Overview

name: r.SupportDepthOnlyIndexBuffers

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

• type: Var
• help: Enables depth-only index buffers. Saves a little time at the expense of doubling the size of index buffers.

It is referenced in 5 C++ source files.

#Summary

#Usage in the C++ source code

The purpose of r.SupportDepthOnlyIndexBuffers is to enable or disable the use of depth-only index buffers in Unreal Engine’s rendering system. This setting is primarily related to the rendering optimization for static meshes.

• The r.SupportDepthOnlyIndexBuffers setting is used in the Engine module, specifically within the StaticMesh rendering system.

• The value of this variable is set through a console variable (CVar) system. It is initialized with a default value of 1 (enabled) and can be changed at runtime through console commands.

• This variable interacts closely with CVarSupportDepthOnlyIndexBuffers, which is the associated console variable that stores and manages the actual value.

• Developers should be aware that enabling this feature (set to 1) can save rendering time but at the cost of doubling the size of index buffers. This trade-off between performance and memory usage should be considered based on the specific needs of the project.

• Best practices when using this variable include:

  1. Evaluating the performance impact in your specific use case.
  2. Considering the memory implications, especially for projects with memory constraints.
  3. Testing thoroughly with both enabled and disabled states to ensure optimal performance.

Regarding the associated variable CVarSupportDepthOnlyIndexBuffers:

• The purpose of CVarSupportDepthOnlyIndexBuffers is to store and manage the actual value of the r.SupportDepthOnlyIndexBuffers setting.

• It is used in the same Engine module and StaticMesh rendering system.

• The value is set at initialization and can be accessed through GetValueOnAnyThread() method calls.

• This variable directly influences the behavior of static mesh rendering, particularly in the calculation of buffer sizes and the serialization of static mesh data.

• Developers should be aware that this variable is marked as read-only and render thread safe, meaning its value should not be changed frequently during runtime.

• Best practices for using this variable include:

  1. Accessing its value through the provided GetValueOnAnyThread() method.
  2. Considering its impact on static mesh loading and rendering when modifying related systems.
  3. Being cautious about changing its value during runtime, as it may affect ongoing rendering processes.

#References in C++ code

#Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/StaticMesh.cpp:131

Scope: file

Source code excerpt:

static TAutoConsoleVariable<int32> CVarSupportDepthOnlyIndexBuffers(
	TEXT("r.SupportDepthOnlyIndexBuffers"),
	1,
	TEXT("Enables depth-only index buffers. Saves a little time at the expense of doubling the size of index buffers."),
	ECVF_ReadOnly | ECVF_RenderThreadSafe);

static TAutoConsoleVariable<int32> CVarSupportReversedIndexBuffers(
	TEXT("r.SupportReversedIndexBuffers"),

#Associated Variable and Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/StaticMesh.cpp:130

Scope: file

Source code excerpt:

	TEXT("If non-zero, mobile setting for MinLOD will be stored in the cooked data for desktop platforms"));

static TAutoConsoleVariable<int32> CVarSupportDepthOnlyIndexBuffers(
	TEXT("r.SupportDepthOnlyIndexBuffers"),
	1,
	TEXT("Enables depth-only index buffers. Saves a little time at the expense of doubling the size of index buffers."),
	ECVF_ReadOnly | ECVF_RenderThreadSafe);

static TAutoConsoleVariable<int32> CVarSupportReversedIndexBuffers(

#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/StaticMesh.cpp:460

Scope (from outer to inner):

file
function     uint32 FStaticMeshLODResources::FStaticMeshBuffersSize::CalcBuffersSize

Source code excerpt:

{
	// Assumes these two cvars don't change at runtime
	const bool bEnableDepthOnlyIndexBuffer = !!CVarSupportDepthOnlyIndexBuffers.GetValueOnAnyThread();
	const bool bEnableReversedIndexBuffer = !!CVarSupportReversedIndexBuffers.GetValueOnAnyThread();
	return SerializedBuffersSize
		- (bEnableDepthOnlyIndexBuffer ? 0 : DepthOnlyIBSize)
		- (bEnableReversedIndexBuffer ? 0 : ReversedIBsSize);
}

#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/StaticMesh.cpp:472

Scope (from outer to inner):

file
function     void FStaticMeshLODResources::SerializeBuffers

Source code excerpt:

	// If the index buffers have already been initialized, do not change the behavior since the RHI resource pointer may have been cached somewhere already.
	const bool bEnableDepthOnlyIndexBuffer = bHasDepthOnlyIndices || (CVarSupportDepthOnlyIndexBuffers.GetValueOnAnyThread() == 1);
	const bool bEnableReversedIndexBuffer = bHasReversedIndices || bHasReversedDepthOnlyIndices || (CVarSupportReversedIndexBuffers.GetValueOnAnyThread() == 1);

	// See if the mesh wants to keep resources CPU accessible
	bool bMeshCPUAcces = OwnerStaticMesh ? OwnerStaticMesh->bAllowCPUAccess : false;

	// Note: this is all derived data, native versioning is not needed, but be sure to bump STATICMESH_DERIVEDDATA_VER when modifying!

#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/StaticMesh.cpp:598

Scope (from outer to inner):

file
function     void FStaticMeshLODResources::SerializeAvailabilityInfo

Source code excerpt:

	Ar.UsingCustomVersion(FUE5ReleaseStreamObjectVersion::GUID);
	bool bHasAdjacencyInfo = false;
	const bool bEnableDepthOnlyIndexBuffer = !!CVarSupportDepthOnlyIndexBuffers.GetValueOnAnyThread();
	const bool bEnableReversedIndexBuffer = !!CVarSupportReversedIndexBuffers.GetValueOnAnyThread();

	Ar << DepthOnlyNumTriangles;
	uint32 Packed;
#if WITH_EDITOR
	if (Ar.IsSaving())