World Space - LGUI Renderer

World Space - LGUI Renderer use LGUI's render pipeline, elements render direct to viewport after UnrealEngine render the world, not affected by post-process.

Create

Select "LGUI Editor Tools"->"Basic Setup"->"World Space - LGUI Renderer":

Then a "WorldSpaceUIRoot_LGUIRenderer" will be created.:

Select LGUICanvas component, you will see the "Render Mode" is "World Space - LGUI Renderer":

Blend depth with existing scene objects

LGUI can take depth buffer texture, sample it and compare with current rendering UI elements's depth value, and do depth blend. Create a Sphere object, move and scale it so that it can occlude with existing UI elements, and create a light to make the level look better. By default this feature is enabled, so you can see the UI is occluded by the sphere:

Select LGUICanvas component, change "Blend Depth" parameter value to 1.0:

So the "Blend Depth" parameter can control how much visible if UI elements is occluded by a scene object. This feature only support opaque object, and not work on mobile platform.