Enable scene-tree direct scanout of a single buffer with various options
for scaling and source crop. This is intended to support direct scanout
for fullscreen video with/without scaling, letterboxing/pillarboxing
(e.g. 4:3 content on a 16:9 display), and source crop (e.g. when
1920x1088 planes are used for 1920x1080 video).
This works by explicitly specifying the source crop and destination box
for the primary buffer in the output state. DRM atomic and libliftoff
backends will turn this into a crop and scale of the plane (assuming the
hardware supports that). For the Wayland/X11/DRM-legacy backends I just
reject this so scanout will be disabled.
The previous behaviour is preserved if buffer_src_box and buffer_dst_box
are unset: the buffer is displayed at native size at the top-left of the
output with no crop.
The change to `struct wlr_output_state` makes this a binary breaking
change (but this works transparently for scene-tree compositors like
labwc after a recompile).
The name "allow_artifacts" and associated description is very vague, and
theoretically allow for tearing behavior. Clarify that we only intend to
mean artifacts related to output configuration (e.g., modesets).
References: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3740
This changes the semantics of wlr_output_state. Instead of having
fields with uninitialized memory when missing from the committed
bitflag, all fields are always initialized (and maybe NULL/empty),
just like we do in wlr_surface_state. This reduces the chances of
footguns when reading a field, and removes the need to check for
the committed bitfield everywhere.
A new wlr_output_state_init() function takes care of initializing
the Pixman region.
When starting up, the compositor might call wlr_output_set_mode()
with a mode which is already the current one. wlroots will detect
this and make the wlr_output_set_mode() call a no-op. During the
next wlr_output_commit() call, wlroots will perform an atomic
commit without the ALLOW_MODESET flag.
This is an issue, because some drivers need ALLOW_MODESET even if
the mode is the same. For instance, if the FB stride or modifier
changed, some drivers require a modeset.
Add a new flag "allow_artifacts" which is set when the compositor
calls mode-setting functions. Use this flag to figure out whether
we want to perform atomic commits with ALLOW_MODESET.
(The name "allow_artifacts" is picked because ALLOW_MODESET is a
misnomer, see [1].)
[1]: https://patchwork.freedesktop.org/patch/505107/
Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3499
David Turner
Simon Ser
Kenny Levinsen
Alexander Orzechowski