Rendering Material in Slate

class FSlateRenderTarget : public FRenderTarget
{
public:
    /** FRenderTarget interface */
    virtual FIntPoint GetSizeXY() const override
    {
        return FIntPoint(ClippingRect.GetSize().X, ClippingRect.GetSize().Y);
    }

    /** Sets the texture that this target renders to */
    void SetRenderTargetTexture(FTexture2DRHIRef& InRHIRef)
    {
        RenderTargetTextureRHI = InRHIRef;
    }

    /** Clears the render target texture */
    void ClearRenderTargetTexture()
    {
        RenderTargetTextureRHI.SafeRelease();
    }

    const FSlateRect& GetClippingRect() const
    {
        return ClippingRect;
    }

    void SetClippingRect(const FSlateRect& InClippingRect)
    {
        ClippingRect = InClippingRect;
    }

    const FSlateRenderTransform& GetRenderTransform() const
    {
        return RenderTransform;
    }

    void SetRenderTransform(const FSlateRenderTransform& InRenderTransform)
    {
        RenderTransform = InRenderTransform;
    }
private:
    FSlateRect ClippingRect;
    FSlateRenderTransform RenderTransform;
};

class FSlateElement : public ICustomSlateElement
{
public:
    FSlateElement(UTexture* InTexture)
        : Material(FindMaterialInstance())
        , Texture(InTexture)
        , RenderTarget(new FSlateRenderTarget)
    {
        Material->SetTextureParameterValue(TEXT("Texture"), InTexture);
        Size.X = Texture->GetSurfaceWidth();
        Size.Y = Texture->GetSurfaceHeight();
    }

    void DrawRenderThread(FRHICommandListImmediate& RHICmdList, const void* InWindowBackBuffer) override
    {
        if (!Texture || !Texture->Resource)
            return;

        auto RenderTransform = RenderTarget->GetRenderTransform();
        FVector2D Origin = RenderTransform.TransformPoint(FVector2D(0, 0));
        auto ClippingRect = RenderTarget->GetClippingRect().OffsetBy(Origin);

        RHICmdList.SetScissorRect(false, 0, 0, 0, 0);
        RenderTarget->SetRenderTargetTexture(*(FTexture2DRHIRef*)InWindowBackBuffer);
        {
            float CurrentTime = FApp::GetCurrentTime() - GStartTime;
            float DeltaTime = FApp::GetDeltaTime();
            FCanvas Canvas(RenderTarget.Get(), NULL, CurrentTime, CurrentTime, DeltaTime, GMaxRHIFeatureLevel);
            {
                FCanvasTileItem Tile(Origin,
                    Material->GetRenderProxy(false),
                    Size);

                Tile.BlendMode = SE_BLEND_AlphaComposite;
                Tile.UV0.Y = 0.0f;
                Tile.UV1.Y = 1.0f;
                Canvas.DrawItem(Tile);
            }
            Canvas.Flush_RenderThread(RHICmdList, true);
        }
        RenderTarget->ClearRenderTargetTexture();
    }

    TUniquePtr<FSlateRenderTarget> RenderTarget;
private:
    FVector2D Size;
    TUniquePtr<UMaterialInstanceDynamic> Material;
    UTexture* Texture;
};

void SMyWidget::Construct(const FArguments& InArgs)
{
    // Initialize Stuff, create the texture
    SlateElement = MakeShareable(new FSlateElement(Texture));
}

FVector2D SMyWidget::ComputeDesiredSize() const
{
    return Size;
}

int32 SMyWidget::OnPaint(const FPaintArgs& Args, const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 LayerId, const FWidgetStyle& InWidgetStyle, bool bParentEnabled) const
{
    SlateElement->RenderTarget->SetClippingRect(MyClippingRect);
    SlateElement->RenderTarget->SetRenderTransform(AllottedGeometry.ToPaintGeometry().GetAccumulatedRenderTransform());
    FSlateDrawElement::MakeCustom(OutDrawElements, LayerId, SlateElement);
    return LayerId;
}