mutter/src/compositor

Intro
=====

In general, the compositor splits the window from the contents of
the window from the shape of the window. In other words, a window
has contents, and the contents of the window have a shape. This is
represented by the actor hierarchy:

 +--------------------------------------+
 | MetaWindowActor                      |
 | +----------------------------------+ |
 | | MetaSurfaceActor                 | |
 | | +------------------------------+ | |
 | | | MetaShapedTexture            | | |
 | | |                              | | |
 | | |                              | | |
 | | |                              | | |
 | | |                              | | |
 | | +------------------------------+ | |
 | +----------------------------------+ |
 +--------------------------------------+

Surfaces may also contain subsurfaces. The MetaWindowActor and
MetaSurfaceActor subclasses that will be created depend on the client
type, and the display server type.

## Subsurfaces

Additionally, there is also the case of subsurfaces: surfaces that
are child of other surfaces. That is also represented in the actor
hierarchy by having one or many MetaSurfaceActors (the subsurfaces)
added as children of a parent MetaSurfaceActor. There are no limits
to how many subsurfaces a surface may have. With subsurfaces, the
actor hierarchy looks like this:

 MetaWindowActor
  ↳ MetaSurfaceActor (surface)
     ↳ MetaShapedTexture
     ↳ MetaSurfaceActor (subsurface)
        ↳ MetaShapedTexture
        ↳ MetaSurfaceActor (sub-subsurface)
           ↳ MetaShapedTexture
     ↳ MetaSurfaceActor (subsurface)
        ↳ MetaShapedTexture

In this example, the main surface has 2 subsurfaces. One of these
subsurfaces contains a subsurface as well.

All MetaWindowActors contain at least one MetaSurfaceActor, and all
MetaSurfaceActors contain a MetaShapedTexture.

## Client and compositor

MetaWindowActor and its subclasses represent the client window's
type. A X11 client will have a MetaWindowActorX11 representing it,
and a Wayland client will have a MetaWindowActorWayland.

On the compositor side, the surface where the contents of the window
are drawn into are represented by MetaSurfaceActor subclasses. On a
Wayland session, windows are backed by a MetaSurfaceActorWayland
surface, whereas on X11 sessions, by MetaSurfaceActorX11.

XWayland windows are X11 client windows (MetaWindowActorX11) backed
by Wayland surfaces (MetaWindowActorWayland).


Env Vars
========

MUTTER_DISABLE_MIPMAPS - set to disable use of mipmaped windows.