If you don't have a xdg-desktop-portal backend then pipewire wont init,
however on exit we unconditionally deinit which can crash in pipewire
which does not handle this gracefully.
With the version 4 of the screencast portal, it is now possible
to request and use restore tokens [1] so that apps can restore a
previously configured screencast session without user interaction.
Add the corresponding code to linux-capture's PipeWire source.
Store the restore token in the source data, since each restore
token corresponds to an OBS source, and use it as soon as we try
to create a new session. Implement the obs_source_info.save vfunc,
and save the restore token when it's received by the Start()
response using obs_source_save().
[1] https://github.com/flatpak/xdg-desktop-portal/pull/638
Right now we just assume that every compositor and portal implementation
exposes both window and monitor captures, but that's not true, and in fact
the Desktop portal provides a simple mechanism to check which source types
are available: a D-Bus property called "AvailableSourceTypes".
Read this D-Bus property, and use it to conditionally register the desktop
and the window captures.
Related: https://github.com/obsproject/obs-studio/issues/4815
Add a new Linux capture based on PipeWire [1] and the Desktop portal [2].
This new capture starts by asking the Desktop portal for a screencapture session.
There are quite a few D-Bus calls involved in this, but the key points are:
1. A connection to org.freedesktop.portal.ScreenCast is estabilished, and the
available cursor modes are updated.
2. CreateSession() is called. This is the first step of the negotiation.
3. SelectSources() is called. This is when a system dialog pops up asking the
user to either select a monitor (desktop capture) or a window (window capture).
4. Start() is called. This signals the compositor that it can setup a PipeWire
stream, and start sending buffers.
The reply to this fourth call gives OBS Studio the PipeWire fd, and the id of the
PipeWire node where the buffers are being sent to. This allows creating a consumer
PipeWire stream, and receive the buffers.
Metadata cursor is always preferred, but on the lack of it, we ask the stream for
an embedded cursor (i.e. the cursor is drawn at the buffer, and OBS Studio has no
control over it.)
Window capturing is implemented as a crop operation on the buffer. Compositors
can send big buffers, and a crop rectangle, and this is used to paint a subregion
of the buffer in the scene.
The new capture is only loaded when running on EGL, since it depends on EGL to
call gs_texture_create_from_dmabuf().
[1] https://pipewire.org/
[2] https://github.com/flatpak/xdg-desktop-portal/
