LGUI render flow

Prepare render resource (game thread)

LGUIManagerActor is responsible for updating all LGUICanvas -> LGUICanvas to update all UIItem and UIBaseRenderable (renderable objects) -> UIBaseRenderable to create and update UIGeometry, UIPostProcessRenderProxy -> LGUICanvas to collect and create grids, textures, materials, merge drawcall -> LGUICanvas to create drawcall Rendering resources.

Rendering (rendering thread)

Screen space UI and world space UI rendered by LGUIRenderer

The LGUIRenderer renderer is extended from the ViewExtension of UE. It performs all rendering in the function XXX_RenderThread of the rendering thread and directly renders to the RenderTarget of the screen. It does not support UE's own post-production, lighting, anti-aliasing, etc.
The rendering process is similar to Slate. Set ViewUniformBuffer -> Specify RenderTarget -> Initialize GraphicsPipelineState -> foreach Drawcall -> Shader/Material -> SetGraphicsPipelineState -> DrawIndexedPrimitive -> foreach Drawcall

World Space UI

The world space UI uses UE's own rendering pipeline, and uses translucent materials by default to support UE's own post-production, lighting, anti-aliasing, etc.