Material Parameter Collection updates do not reflect at Runtime

Development Programming & Scripting
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1

In my game I have the following:

  • Material Parameter Collection (MPC) containing a scalar value “IrisSize”
  • Material Function (MF_Gobos) which utilizes “IrisSize” as an input, used for various calculations.
  • Material asset (M_LightCrossSection) which utilizes MF_Gobos to determine its emissive output.
  • A C++ function responsible for copying the contents of the dynamic material instance of M_LightCrossSection into a UTextureRenderTarget2D.

Observed Behavior: When updating IrisSize’s default value in-editor, I do see the UTextureRenderTarget2D update as expected. However, during gameplay, when I update “IrisSize” via sequencer or C++, I do not see any changes to the Render Target take place. Regardless of approach, the rendering portion always seems to utilize IrisSize’s default value, ignoring subsequent changes. My main questions are:

  1. Should I even be using MPCs in this context or is there a preferred approach?

  2. If so, I believe the issue may be with the rendering call itself. I am wondering if the CanvasPass detailed below is somehow unaware of the updates to Iris Size, or if the Scene View options may be interfering. I have pasted a snippet below. Any insights appreciated. Thanks!

void AStageLight::QueueRender()
{
	UMaterialInstanceDynamic* SafeMID = MID_LightCrossSection;
	UTextureRenderTarget2D* SafeRenderTarget = RT_CrossSectionTexture;
	UWorld* SafeWorld = GetWorld();

    //Note: Calling GetWorld(), getting MPC object, and  GetScalarParameterValues("IrisSize") here does print the correct value.


	ENQUEUE_RENDER_COMMAND(RenderRDGToTarget)(
		[SafeMID, SafeRenderTarget, SafeWorld, MyGameTime](FRHICommandListImmediate& RHICmdList)
		{
			FRDGBuilder GraphBuilder(RHICmdList);

			FRHITexture* RHITexture = SafeRenderTarget->GetRenderTargetResource()->GetRenderTargetTexture();
			FRDGTextureRef OutputRDG = GraphBuilder.RegisterExternalTexture(
				CreateRenderTarget(RHITexture, TEXT("RT_CrossSectionTextureOutput"))
			);

			FScreenPassRenderTarget Output(OutputRDG, ERenderTargetLoadAction::EClear);


			FSceneViewFamilyContext ViewFamily(
				FSceneViewFamily::ConstructionValues(nullptr, SafeWorld->Scene,
					FEngineShowFlags(ESFIM_Game)).SetTime(FGameTime::GetTimeSinceAppStart())); //FGameTime::GetTimeSinceAppStart();

			FSceneViewInitOptions ViewInitOptions;
			ViewInitOptions.ViewFamily = &ViewFamily;
			ViewInitOptions.ViewOrigin = FVector::ZeroVector;
			ViewInitOptions.ViewRotationMatrix = FMatrix::Identity;
			ViewInitOptions.ProjectionMatrix = FMatrix::Identity;
			//ViewInitOptions.SceneViewStateInterface = nullptr;
			ViewInitOptions.SetViewRectangle(FIntRect(0, 0, SafeRenderTarget->SizeX, SafeRenderTarget->SizeY)); // Need this SetView call in 5.3

			FSceneView* SceneView = new FSceneView(ViewInitOptions);
			ViewFamily.Views.Add(SceneView);

			// is this a different world?? without collection param?
			AddDrawCanvasPass(
				GraphBuilder,
				RDG_EVENT_NAME("DrawMID_LightCrossSection"),
				*SceneView,
				Output,
				[SafeMID, SafeRenderTarget](FCanvas& Canvas)
				{
					FCanvasTileItem Tile(FVector2D(0, 0), SafeMID->GetRenderProxy(), FVector2D(SafeRenderTarget->SizeX, SafeRenderTarget->SizeY));
					Tile.BlendMode = SE_BLEND_Opaque;
					Canvas.DrawItem(Tile);
				}
			);

			GraphBuilder.Execute();
		}
	);
}