[Question] UTextureRenderTarget2D and Canvas

Development Programming & Scripting C++
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1

Hi! I’m trying to figure out how to use a UTextureRenderTarget2D with canvas rendering (not a camera render target.) I’ve almost got it working, but the editor crashes (with absolutely no useful info in the Log or the crash reporter - I’ve even got the editor crashing without the error reporter coming up at all, just silently closing.)

Here’s what I’ve got so far… I have no idea if this is correct or not:

Class:

protected:

	UPROPERTY()
	UTextureRenderTarget2D* tRenderTarget;

	FCanvas* oCanvas;

	UPROPERTY()
	UCanvas* uoCanvas;

Method that creates texture:

	FVector2D v2Size = GetSize();
	
	if ( v2Size.X <= 0.f || v2Size.Y <= 0.f )
		return;

	tRenderTarget = NewObject<UTextureRenderTarget2D>( this );
	tRenderTarget->InitAutoFormat( FMath::Floor( v2Size.X ), FMath::Floor( v2Size.Y ) );
	tRenderTarget->ClearColor = FLinearColor( 0.f, 0.f, 0.f, 0.f );

	// Create canvas to draw on the render target.

	// FCanvas, not a UObject
	oCanvas = new FCanvas( tRenderTarget->GameThread_GetRenderTargetResource(), NULL, GetWorld() );

	// UCanvas UObject.
	uoCanvas = NewObject<UCanvas>( this );
	uoCanvas->Canvas = oCanvas;
	uoCanvas->Init( FMath::Floor( v2Size.X ), FMath::Floor( v2Size.Y ), NULL );

I use the uoCanvas->DrawItem to draw stuff to the render target (causes crash.)

I then use the tRenderTarget object as a texture in an FCanvasTileItem, which I draw to the hud within the DrawHUD() call (causes crash after I press Stop from doing a PIE (where a big green square is drawn on the screen.))

Does anyone have any experience with rendering to render targets with canvas? Would appreciate some tips!

2

Instead of creating UCanvas in my code I just use the FCanvas to make my draw calls.

_outline_canvas->DrawTile(_renderTarget_res_x*u - (STAMP_SIZE - (STAMP_SIZE/4.0)) ,
		_renderTarget_res_y*v - (STAMP_SIZE - (STAMP_SIZE/4.0)), 
		STAMP_SIZE, STAMP_SIZE, 
		0,0,1,1,
		FLinearColor::White, 
		_grassOutlineMaskSplotch->Resource,
		true);

Where the grassOutlineMaskSplotch is the texture I want to draw at the specified location on the rendertarget.

3

I believe a render target texture is green as default. It seems like nothing is being drawn to the render target.

4

Can you try to do this during construction

tRenderTarget ->ClearColor = FLinearColor::Black;

and see if its black then just to make sure you have the right handle and its just a draw issue ?

Where are you calling your draw BTW ?

5

Good.

Then how about setting the following during construction and trying the draw again ?

tRenderTarget ->bNeedsTwoCopies = false;

6

I tried something similar:

Constructor:

	static ConstructorHelpers::FObjectFinder<UTexture2D> tTextureFinder( TEXT( "Texture2D'/Game/Textures/Particles/comb.comb'" ) );
	this->tTexture2 = tTextureFinder.Object;

	UTextureRenderTarget2D* tRenderTarget = NewObject<UTextureRenderTarget2D>( this );
	tRenderTarget->InitAutoFormat( FMath::Floor( 512 ), FMath::Floor( 512 ) );

	FCanvas canvas = FCanvas( tRenderTarget->GameThread_GetRenderTargetResource(), NULL, GetWorld() );
	canvas.DrawTile( 0, 0, 512, 512, 0, 0, 1, 1, FLinearColor::White, this->tTexture2->Resource, true );

	this->tTexture = tRenderTarget;

DrawHUD:

	oCanvas->Canvas->DrawTile( 100, 100, 512, 512, 0, 0, 1, 1, FLinearColor::White, tTexture->Resource, false );
	oCanvas->Canvas->DrawTile( 620, 100, 512, 512, 0, 0, 1, 1, FLinearColor::White, tTexture2->Resource, false );

I end up with (see attached.)

I tried using a render target taken from the editor, but I got the same result. A big green square. Using an editor resource is not doable for this particular bit of code anyway because they need to be dynamically generated at runtime.

I also tried putting the render target draw calls into the DrawHUD call. Same result.

I tried using (FTextureRenderTarget2DResource*) tRenderTarget->Resource instead of the GameThread_… call, too. No luck.

It’s not crashing with this majorly simplified version, so I guess I’ve got something in my code causing that. However, I still don’t get why it’s green.

7

tRenderTarget->ClearColor = FLinearColor::Black;

causes the texture to become black.

It’s a custom class that derives from HUD. The initial set up of the textures is in the constructor (with PCIP etc), the second set of calls are in DrawHUD().

8

Still black. I’ll try moving the render target rendering back into drawhud for a try.

9

No luck :frowning:

10

Just as a test. Let’s say you create the render target through the editor and there you set the need two copies parameter to false. Does this still happen ? Because this works for me.

11

Np. Good luck !

12

Sadly, it doesn’t work :frowning:

UTextureRenderTarget2D* tRenderTarget = NewObject( this );

replaced with:

static ConstructorHelpers::FObjectFinder<UTextureRenderTarget2D> tRenderTargetFinder( TEXT( "TextureRenderTarget2D'/Game/Developers/RenderTargetTest2.RenderTargetTest2'" ) );
UTextureRenderTarget2D* tRenderTarget = tRenderTargetFinder.Object;

Same result. Black square :frowning:

Talking with James Tan in IRC, though, and he says he has some insight. If I find a fix, I’ll post!

Thanks for trying to help, though, darkZ.

13

This is a ScriptedTexture class that James wrote yesterday, for dynamically created render targets:

https://github.com/EpicGames/UnrealEngine/pull/24/files

Thanks, James!

14

https://github.com/EpicGames/UnrealEngine/pull/24/files

James Tan went to town on it. Everything you should need is here.