FCanvas and UTextureRenderTarget2D: Draw functions not working

Development Rendering
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1

Greetings.

I have rigged up a FCanvas with UTextureRenderTarget2D to draw texture in realtime via code. Render target is applied to dynamic material instance. Problem is: canvas->clear function is working(can change clear color at any moment), but drawing functions(DrawItem, DrawNGon) produce no visual result.

Canvas and RenderTarget initialization:

 material = UMaterialInstanceDynamic::Create(gridMesh->GetMaterial(0), GetWorld());
    gridMesh->SetMaterial(0, material);
    
    gridTexture = (UTextureRenderTarget2D*)StaticConstructObject(UTextureRenderTarget2D::StaticClass());
    gridTexture->bNeedsTwoCopies = false;
    gridTexture->bHDR = false;
    gridTexture->ClearColor = FLinearColor::Black;
    gridTexture->InitAutoFormat(1024, 1024);
    gridTexture->UpdateResourceImmediate();
    
    FTextureRenderTarget2DResource* gridTexResource = (FTextureRenderTarget2DResource*)gridTexture->Resource;
    gridCanvas = new FCanvas(gridTexResource, NULL, 0, 0, 0, ERHIFeatureLevel::ES2);
    gridCanvas->Clear(FLinearColor::Black);
    gridTexture->UpdateResourceImmediate(false);
    material->SetTextureParameterValue(TEXT("TTarget2D"), gridTexture);

And drawing:

 void ASoliField::UpdateField(){
    
    	gridCanvas->Clear(FLinearColor(0.5,0.5,0.5,1)); //Works fine
    
    	FCanvasBoxItem box(FVector2D(512, 512), FVector2D(256, 256));
    	box.LineThickness = 10;
    	box.SetColor(FLinearColor::Red);
    	box.BlendMode = SE_BLEND_Additive;
    
    	FCanvasLineItem line(FVector2D(0, 0), FVector2D(1024, 1024));
    	line.LineThickness = 50;
    	line.SetColor(FLinearColor::Green);
    	line.BlendMode = SE_BLEND_Opaque;
    
    	FCanvasLineItem line2(FVector2D(0, 1024), FVector2D(1024, 0));
    	line2.LineThickness = 2;
    	line2.SetColor(FLinearColor::Blue);
    	line2.BlendMode = SE_BLEND_Translucent;
    
    	gridCanvas->DrawItem(box); //Doesnt draw
    	gridCanvas->DrawItem(line);  //Doesnt draw
    	gridCanvas->DrawItem(line2);  //Doesnt draw
    
    }

Any insight on this problem will be appreciated. Thank you.

2

You should change your init code from :
gridCanvas = new FCanvas(gridTexResource, NULL, 0, 0, 0, ERHIFeatureLevel::ES2);
to :
gridCanvas = new FCanvas(gridTexResource, NULL, 0, 0, 0, GMaxRHIFeatureLevel);

AND

add the following code at the end of UpdateField():
gridCanvas->Flush_GameThread();

I had the same problem as you, now it works.

3

My great thanks to you. The root of this problem was in wrong feature level, because with ES2 enqueuing draws onto rendering thread with Flush_GameThread() caused crash. Setting feature level to auto(GMaxRHIFeatureLevel) solved this problem