Replace the default master clock with multiple frame clocks, each
driving its own stage view. As each stage view represents one CRTC, this
means we draw each CRTC with its own designated frame clock,
disconnected from all the others.
For example this means we when using the native backend will never need
to wait for one monitor to vsync before painting another, so e.g. having
a 144 Hz monitor next to a 60 Hz monitor, things including both Wayland
and X11 applications and shell UI will be able to render at the
corresponding monitor refresh rate.
This also changes a warning about missed frames when sending
_NETWM_FRAME_TIMINGS messages to a debug log entry, as it's expected
that we'll start missing frames e.g. when a X11 window (via Xwayland) is
exclusively within a stage view that was not painted, while another one
was, still increasing the global frame clock.
Addititonally, this also requires the X11 window actor to schedule
timeouts for _NET_WM_FRAME_DRAWN/_NET_WM_FRAME_TIMINGS event emitting,
if the actor wasn't on any stage views, as now we'll only get the frame
callbacks on actors when they actually were painted, while in the past,
we'd invoke that vfunc when anything was painted.
Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/903
Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/3https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285
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.
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