Some issues adding a Blur to the Ambient Occlusion Pass [C++]

Development Rendering
1

Hi!

A while ago I implemented a screen space blur for the SSAO pass. However since 4.11 this has been broken. I recently started working on getting it to work properly again, and I am almost there.

The only issue is… it turns everything… red?

Like this:

Imgur

So, yes. Very red.

Does anyone have any ideas as to what is even going on here?! xD

Thanks,
.

Edit: Sorry, it just occured I should probably reference some code in here:

So! Right now the Blur code looks like this:


static FRenderingCompositeOutputRef BlurSSAOBuffer(FPostprocessContext& Context, FSceneRenderTargets& SceneContext, FRenderingCompositeOutputRef AO)
{
	FRenderingCompositePass* SSAO = Context.Graph.RegisterPass(new(FMemStack::Get()) FRCPassPostProcessInput(SceneContext.ScreenSpaceAO));

	FRCPassPostProcessWeightedSampleSumInputBlur* PostProcessBlurX = Context.Graph.RegisterPass(new(FMemStack::Get())
		FRCPassPostProcessWeightedSampleSumInputBlur(EFS_Horiz,
			EFCM_Weighted,
			CVarAmbientOcclusionBlurRadius.GetValueOnRenderThread(),
			TEXT("SSAO Blur X")));

	PostProcessBlurX->SetInput(ePId_Input0, SSAO);
	PostProcessBlurX->AddDependency(AO);

	FRCPassPostProcessWeightedSampleSumInputBlur* PostProcessBlurY = Context.Graph.RegisterPass(new(FMemStack::Get())
		FRCPassPostProcessWeightedSampleSumInputBlur(
			EFS_Vert,
			EFCM_Weighted,
			CVarAmbientOcclusionBlurRadius.GetValueOnRenderThread(),
			TEXT("SSAO Blur Y")));

	PostProcessBlurY->SetInput(ePId_Input0, SSAO);

	PostProcessBlurY->AddDependency(PostProcessBlurX);
	return PostProcessBlurY;
}

This function is called here:


FRenderingCompositePass* AmbientOcclusionPassMip0 = Context.Graph.RegisterPass(new(FMemStack::Get()) FRCPassPostProcessAmbientOcclusion(Context.View, FullResAOType, false));
	AmbientOcclusionPassMip0->SetInput(ePId_Input0, GBufferA);
	AmbientOcclusionPassMip0->SetInput(ePId_Input1, AmbientOcclusionInMip1);
	AmbientOcclusionPassMip0->SetInput(ePId_Input2, AmbientOcclusionPassMip1);
	AmbientOcclusionPassMip0->SetInput(ePId_Input3, HZBInput);

	// to make sure this pass is processed as well (before), needed to make process decals before computing AO
	if(AmbientOcclusionInMip1)
	{
		AmbientOcclusionInMip1->AddDependency(Context.FinalOutput);
	}
	else
	{
		AmbientOcclusionPassMip0->AddDependency(Context.FinalOutput);
	}
	
	FRenderingCompositeOutputRef BluredAO = FRenderingCompositeOutputRef(BlurSSAOBuffer(Context, SceneContext, FRenderingCompositeOutputRef(AmbientOcclusionPassMip0)));
	Context.FinalOutput = BluredAO;// FRenderingCompositeOutputRef(AmbientOcclusionPassMip0);
	

	SceneContext.bScreenSpaceAOIsValid = true;

	return BluredAO;

The “FRCPassPostProcessWeightedSampleSumInputBlur” is a slightly modified version of WeightedSampleSum. The Main difference is instead of this:

FRCPassPostProcessWeightedSampleSum:


Context.RHICmdList.CopyToResolveTarget(DestRenderTarget.TargetableTexture, DestRenderTarget.ShaderResourceTexture, false, FResolveParams());

FRCPassPostProcessWeightedSampleSumInputBlur:


Context.RHICmdList.CopyToResolveTarget(DestRenderTarget.TargetableTexture, InputPooledElement->GetRenderTargetItem().TargetableTexture, false, FResolveParams());
	Context.RHICmdList.CopyToResolveTarget(DestRenderTarget.TargetableTexture, InputPooledElement->GetRenderTargetItem().ShaderResourceTexture, false, FResolveParams());
2

Update: So, I’ve found a work around, though I don’t really understand why. I’ve turned up the “Static Fraction” value to be non-zero, which has fixed the red. Really confused about this, since we aren’t using static lighting at all in our game (Custom lighting solution).

3

I’ve replicated all of your blur code based on your pull request and this fix posted here and I too get the red effect if I have Static Fraction set to 0 (we also use 100 percent dynamic lighting). The blur effect is great - you saved our console users from grainy AO!