Ownership rules for graphics objects

Overview

Type	Global/Singleton	Owned by	Notes
Renderer	Yes	Engine
Shader manager	Yes	Renderer	Con-/destruction by renderer
Shader descr.	No	Shader manager	Con-/destruction by shader manager
Vertex array	No	Mesh/Room/Global	Only owned by exactly one object at a time.

Note: Vertex arrays for GUI elements are global. This is extremely ugly, should be replaced by some Gui object owned by renderer. Code in Room should be cleaned up, too.

General Rules

Objects come in two categories. Type one is global, with lifetime from initializion at app startup to app exit. There is no need for cleaning them up them (though the code does it anyway; not sure why). The other is owned by the currently loaded level. Lifetime is either from level loading to level unload (for level transition or app end), or from specific gameplay events (Lua) to another one of those. There is no need for any shared ownership.