r.PostProcessing.DownsampleChainQuality

r.PostProcessing.DownsampleChainQuality

#Overview

name: r.PostProcessing.DownsampleChainQuality

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

• type: Var
• help: Defines the quality used for downsampling to the scene color in scene color chains.\n 0: low quality\n 1: high quality (default)\n

It is referenced in 3 C++ source files.

#Summary

#Usage in the C++ source code

The purpose of r.PostProcessing.DownsampleChainQuality is to define the quality used for downsampling the scene color in scene color chains. This setting variable is used in the post-processing pipeline of Unreal Engine 5.

• The Unreal Engine rendering system, specifically the post-processing module, relies on this setting variable.

• The value of this variable is set through a console variable (CVarDownsampleChainQuality) defined earlier in the code.

• This variable interacts with the GetDownsampleQuality function, which likely translates the integer value into an enumeration representing the quality level.

• Developers should be aware that this variable affects the quality of downsampling operations in the post-processing chain, which can impact both visual quality and performance.

• Best practices when using this variable include:

  1. Adjusting it based on the target hardware capabilities and performance requirements.
  2. Testing different values to find the optimal balance between visual quality and performance.
  3. Considering its impact on the entire post-processing pipeline, as it may affect subsequent operations.

Regarding the associated variable CVarDownsampleChainQuality:

• It’s a TAutoConsoleVariable, which means it’s an integer console variable that can be changed at runtime.
• It’s initialized with a default value of 1, which corresponds to high quality.
• It has options for low quality (0) and high quality (1).
• This console variable is marked with ECVF_Scalability and ECVF_RenderThreadSafe flags, indicating it’s used for scalability settings and is safe to access from the render thread.
• Developers can modify this variable through console commands or project settings to adjust the downsampling quality dynamically.

In summary, r.PostProcessing.DownsampleChainQuality and its associated console variable CVarDownsampleChainQuality provide a way to control the quality of downsampling operations in the post-processing pipeline, allowing developers to balance visual quality and performance in their Unreal Engine 5 projects.

#References in C++ code

#Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Renderer/Private/PostProcess/PostProcessing.cpp:130

Scope (from outer to inner):

file
namespace    anonymous

Source code excerpt:

TAutoConsoleVariable<int32> CVarDownsampleChainQuality(
	TEXT("r.PostProcessing.DownsampleChainQuality"), 1,
	TEXT("Defines the quality used for downsampling to the scene color in scene color chains.\n")
	TEXT(" 0: low quality\n")
	TEXT(" 1: high quality (default)\n"),
	ECVF_Scalability | ECVF_RenderThreadSafe);

#if !(UE_BUILD_SHIPPING)

#Associated Variable and Callsites

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

#Loc: <Workspace>/Engine/Source/Runtime/Renderer/Private/PostProcess/PostProcessing.cpp:129

Scope (from outer to inner):

file
namespace    anonymous

Source code excerpt:

	ECVF_Scalability | ECVF_RenderThreadSafe);

TAutoConsoleVariable<int32> CVarDownsampleChainQuality(
	TEXT("r.PostProcessing.DownsampleChainQuality"), 1,
	TEXT("Defines the quality used for downsampling to the scene color in scene color chains.\n")
	TEXT(" 0: low quality\n")
	TEXT(" 1: high quality (default)\n"),
	ECVF_Scalability | ECVF_RenderThreadSafe);

#Loc: <Workspace>/Engine/Source/Runtime/Renderer/Private/PostProcess/PostProcessing.cpp:591

Scope (from outer to inner):

file
function     void AddPostProcessingPasses

Source code excerpt:

		const EAntiAliasingMethod AntiAliasingMethod = !bVisualizeDepthOfField ? View.AntiAliasingMethod : AAM_None;
		const EDownsampleQuality DownsampleQuality = GetDownsampleQuality(CVarDownsampleQuality);
		const EDownsampleQuality DownsampleChainQuality = GetDownsampleQuality(CVarDownsampleChainQuality);
		const EPixelFormat DownsampleOverrideFormat = PF_FloatRGB;

		// Previous transforms are nonsensical on camera cuts, unless motion vector simulation is enabled (providing FrameN+1 transforms to FrameN+0)
		const bool bMotionBlurValid = FMotionVectorSimulation::IsEnabled() || (!View.bCameraCut && !View.bPrevTransformsReset);

		// Motion blur gets replaced by the visualization pass.