GetRenderTargetTexture() on GameViewport works in editor mode, but returns 0 in standalone

I’m trying to get a native texture pointer to the content currently displayed on screen.

Using 4.8.3 and executing the following code on the render thread:


Returns the correct texture pointer when run in the editor, and everything works fine.

However, when I run my project as a standalone or after packaging, it returns a null pointer. I’m guessing the viewports and rendertargets are set up differently in standalone mode compared to regular mode. How can I achieve what I want, so it works in all cases?

Okay, so I managed to get non-null texture pointer, by moving the code to the Draw() method of a custom UGameViewportClient, but the texture I get is not being rendered to when playing as standalone (I get a completely black texture). The exact same code works fine in PIE-mode.

1 Like

So it seems that the viewport in PIE-mode creates a render texture with a format that is different from the one in standalone mode. I get:

  • PF_B8G8R8A8 in PIE-mode
  • PF_A2B10G10R10 in standalone-mode

Can I force the render texture format of standalone mode to be the same format?

Did you get anywhere with this?

I’m trying to enable the AVIWriter::StartCapture during a standalone build. Of course it gets a viewport with a null RenderTarget…

Hey Yu He!

I am working on a similar issue and like you can only get black video out. Did you end up finding a way to convert the Pixel Format?

Information on this stuff is so hard to find >.<

I did in fact solve this! To convert the pixel format, you can sample the backbuffer using a simple pixel shader and draw it on a new render target with the desired size and format. Seems to have close to zero impact on performance.

1 Like

hi Ye Hu, can you give some light on how did you solve this? Thanks alot, i’m having the same issue :frowning:

Hello @Yu He,

Similarly to Madlions, I was wondering if you could shed some more light on how you managed to get the texture from the viewport in standalone mode?

Many thanks!

I use RTF_RGB10A2 in PIE mode, works perfectly. Where did you get that it’s PF_B8G8R8A8 in PIE?

Ok, i made it work SOMEHOW.

.h file:

#pragma once

#include "CoreMinimal.h"
#include "UObject/Object.h"
#include "UnrealClient.h"
#include "RQ_GameViewportClient.generated.h"

class SCENARIOSYSTEM_API URQ_GameViewportClient : public UGameViewportClient

	virtual void Draw(FViewport* InViewport, FCanvas* Canvas) override;

	void CopyViewportToRenderTarget(UTextureRenderTarget2D* RenderTarget);

	UTextureRenderTarget2D* MyRenderTarget;
	bool PendingCopyViewportToRenderTarget;

	void CopyTextureRHI(FRenderTarget* MyViewRenderTarget, UTextureRenderTarget2D* DestRenderTarget);

and .cpp file:

#include "Core/RQ_GameViewportClient.h"
#include "Engine/TextureRenderTarget2D.h"
#include "Slate/SceneViewport.h"

void URQ_GameViewportClient::Draw(FViewport* InViewport, FCanvas* Canvas)
	Super::Draw(Viewport, Canvas);
	if (InViewport && PendingCopyViewportToRenderTarget)
		CopyTextureRHI(InViewport, MyRenderTarget);

void URQ_GameViewportClient::CopyViewportToRenderTarget(UTextureRenderTarget2D* RenderTarget)
	MyRenderTarget = RenderTarget;
	PendingCopyViewportToRenderTarget = true;

void URQ_GameViewportClient::CopyTextureRHI(FRenderTarget* MyViewRenderTarget, UTextureRenderTarget2D* DestRenderTarget)

		[MyViewRenderTarget, DestRenderTarget](FRHICommandListImmediate& RHICmdList)
			FTexture2DRHIRef destTexture = DestRenderTarget->GetRenderTargetResource()->GetRenderTargetTexture();
			FResolveParams ResolveParams;
			RHICmdList.CopyToResolveTarget(MyViewRenderTarget->GetRenderTargetTexture(), destTexture, ResolveParams);

This this custom viewoirt client, so don’t forget to tell UE5 to use it in DefaultEngine.ini:


RenderTarget2D is using RTF_RGB10A2 pixel format