Base abstract widgets, compositors, and bridge between UI, client and window. *
Internal. Operations on list of 2D boxes.
Home of UIBufferedElement, for non-opaque widgets. *
PBR rendering, custom rendering. *
UIContext holds global state for the whole UI (current selected widget, etc...). *
UIElement is the base class of all widgets. *
A GUIGraphics is the interface between a plugin client and a IWindow. *