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

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1

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:

GEngine->GameViewport->GetGameViewport()->GetRenderTargetTexture().GetReference();

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?

2

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
3

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?

4

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…

5

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 >.<

6

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
7

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

8

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!
M

10

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

11

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"

/**
 * 
 */
UCLASS()
class SCENARIOSYSTEM_API URQ_GameViewportClient : public UGameViewportClient
{
	GENERATED_BODY()

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

	void CopyViewportToRenderTarget(UTextureRenderTarget2D* RenderTarget);

	UPROPERTY()
	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)
{
	

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

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

[/Script/Engine.Engine]
GameViewportClientClassName=/Script/ScenarioSystem.RQ_GameViewportClient

RenderTarget2D is using RTF_RGB10A2 pixel format