How to change Z-order between UMG widgets and "draw elements" from OnPaint/NativePaint?

Development Programming & Scripting UI
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1

I have a UMG widget class inheriting from UUserWidget. In this widget, I am drawing some elements by overriding the NativePaint function (also known as OnPaint in Blueprint).

The drawing code is something very standard like this (simplified for readability):

int32 UMyWidget::NativePaint(const FPaintArgs& Args, const FGeometry& AllottedGeometry, const FSlateRect& MyCullingRect, FSlateWindowElementList& OutDrawElements, int32 LayerId, const FWidgetStyle& InWidgetStyle, bool bParentEnabled) const
{
	// Draw some curves on the AllotedGeometry
	for (/* some loop */) FSlateDrawElement::MakeSpline(OutDrawElements, LayerId, AllottedGeometry.ToPaintGeometry(), /* the rest doesn't matter */ );
	++LayerId

	return Super::NativePaint(/* same args */);
}

This works fine, and the draw elements show up. The problem is, they are always drawn on top of widgets I add to this widget in UMG (so, all UMG widgets are are behind all DrawElements).

I assume something like the Z-Order, or the LayerID variable, could be responsible for this? Or is the graphics pipeline hard-coded to draw UMG first, and the OnPaint stuff second?

Is it possible to order these Draw Elements behind the rest of the UMG elements?

2

Did you ever figure this out? I’m having the same issue. I tried subtracting from the LayerId which works but it sometimes causes asserts in the rendering code, so it must not be safe.

3

I just had the same problem and this is how I solved it: I moved paint code into another widget, place that widget into original widget under widget I wanted it to draw under.