We were crashing in the error codepath [1] when
wlr_drm_create_lease() fails.
To fix this, delay the creation of the wlr_drm_lease_v1 until the
request is granted. Previously we were allocating that struct early
without populating the drm_lease field. However that means we ended
up with a half-constructed struct in the error codepath which is
annoying to handle.
[1]: https://github.com/swaywm/sway/issues/7204#issuecomment-1269797356
This field becomes stale too easily: for instance, see 6adca4089c
("backend/drm: don't unconditionally set desired_enabled").
Additionally, drm_connector_alloc_crtc() needs to do some weird
dance, restoring its previous value.
Instead, add a connector arg to realloc_crtcs() to indicate a new
connector we want to enable.
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
Instead of using low-level wl_shm_buffer and wlr_dmabuf_v1_buffer
APIs, use the unified wlr_buffer APIs. That way it doesn't matter
what the exact wlr_buffer implementation is used, any which provides
the necessary capabilities (data_ptr or dmabuf) would work.
Simplifies the logic a bit, and will make the transition to wlr_shm
easier.
CTA-861-H defines a picture aspect ratio which may be attached to
each mode. This affects the way the sink will display the image.
See annexes H.1 and H.2 for examples.
See the spec at [1]. tl;dr EGL has terrible defaults: eglTerminate()
may have side-effects on completely unrelated EGLDisplay objects.
This extension allows us to opt-in to get the sane behavior:
eglTerminate() only free's our own EGLDisplay without affecting
others.
[1]: https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_display_reference.txt
wlr_buffer.c is difficult to read because it contains a mixed bag
of unrelated things: base buffer type, buffer implementations,
buffer resource factory, and client buffer.
Split each of these into their own file.
dac040f87f mistakenly renamed
xdg_surface_destroy listener, which was listening to *unmap* events, to
xdg_surface_unmap. The actual fix, however, is to listen to destroy
events. This fixes various crashes.
Previously, adaptive sync was just a hint and wouldn't make any
atomic commit fail if the backend didn't support it. The main reason
is wlr_output_test wasn't supported at the time.
Now that we have a way for compositors to test whether a change can
work, let's remove the exception for adaptive sync and convert it to
a regular output state field.
array_realloc will grow the array for the target size like wl_insert_add, but
will also shrink the array if the target size is sufficiently smaller than the
current allocation.
This lets the renderer handle the wlr_buffer directly, just like it
does in texture_from_buffer. This also allows the renderer to batch
the rectangle updates, and update more than the damage region if
desirable (e.g. too many rects), so can be more efficient.
We were firing the new_input signal on backend initialization,
before the compositor had the chance to add a listener for it.
Mimick what's done for wl_keyboard: if the backend hasn't been
started, delay wl_touch initialization.
Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3473
When the client doesn't support high-resolution scroll, accumulate
deltas until we can notify a discrete event.
Some mice have a free spinning wheel, making possible to lock the wheel
when the accumulator value is not 0. To avoid synchronization issues
between the mouse wheel and the accumulators, store the last delta and
when the scroll direction changes, reset the accumulator.
On newer versions of libinput, the event LIBINPUT_EVENT_POINTER_AXIS
has been deprecated in favour of LIBINPUT_EVENT_POINTER_SCROLL_WHEEL,
LIBINPUT_EVENT_POINTER_SCROLL_FINGER and
LIBINPUT_EVENT_POINTER_SCROLL_CONTINUOUS.
Where new events are provided by the backend, ignore
LIBINPUT_EVENT_POINTER_AXIS, receive high-resolution scroll events from
libinput and emit the appropiate wlr_pointer signal.
Currently, the "wlr_event_pointer_axis" event stores low-resolution
values in its "delta_discrete" field. Low-resolution values are always
multiples of one, i.e., 1 for one wheel detent, 2 for two wheel
detents, etc.
In order to simplify internal handling of events, always transform in
the backend from the low-resolution value into the high-resolution
value.
The transformation is performed by multiplying by 120. The 120 magic
number is used by the kernel and it is exposed to clients in the
"WLR_POINTER_AXIS_DISCRETE_STEP" constant.
wlr_xdg_surface_from_wlr_surface() for example may return NULL even if
the surface has the xdg surface role if the corresponding xdg surface
has been destroyed.
"max bpc" is a maximum value, the driver is free to choose a
smaller value depending on the bandwidth available.
Some faulty monitors misbehave with higher bpc values. We'll add
a workaround if users get hit by these in practice.
References: https://gitlab.freedesktop.org/wayland/weston/-/issues/612
Whether a texture is opaque or not doesn't depend on the renderer
at all, it just depends on the source buffer. Instead of forcing
all renderers to implement wlr_texture_impl.is_opaque, let's move
this in common code and use the wlr_buffer format to know whether
a texture will be opaque.
This refactors output_ensure_buffer() to not mutate the state passed,
making the previous subtle behavior much more explicit.
Fixes: d483dd2f ("output: add wlr_output_commit_state")
Closes: #3442
CTA-861-G says that "graphics" is used to indicate non-analog (ie,
digital) content. With that bit set, the sink should turn off analog
reconstruction and other related filtering.
This commit ensures that outputs that weren't created by the output
layout helper aren't destroyed on the output layout change.
Consider the following piece of logic:
// struct wlr_output *o1, *o2;
// struct wlr_scene *scene;
// struct wlr_output_layout *layout;
wlr_scene_attach_output_layout(scene, layout);
wlr_output_layout_add_auto(layout, o1);
struct wlr_scene_output *so2 = wlr_scene_output_create(scene, o2);
wlr_output_layout_move(layout, o1, 100, 200);
// so2 is invalid now
Now that the DRM backend no longer depends on GBM, we can make it
optional. The GLES2 renderer still depends on it because of our EGL
device selection.
This is useful for compositors with their own renderers, and for
compositors using the Vulkan renderer.
This allows the make/model/serial to be NULL when unset, and allows
them to be longer than the hardcoded array length.
This is a breaking change: compositors need to handle the new NULL
case, and we stop setting make/model to useless "headless" or
"wayland" strings.
These are trivial wrappers around eglMakeCurrent and
eglGetCurrentContext. Compositors which need to call these
functions will also call other EGL or GL functions anyways. Let's
reduce our API surface a bit by making them private.
This will display red translucent rectangles on the screen regions that
have been damaged. These rectangles will fade out over the span of 250
msecs. If the area is damaged again while the region is fading out,
the timer is reset.
Let's also disable direct scan out when this option is enabled, or else
we won't be able to render the highlight damage regions.
After cancelation we destroy the touch points associated with this
surface as the Wayland spec says:
No further events are sent to the clients from that particular gesture.
Touch cancellation applies to all touch points currently active on this
client's surface. The client is responsible for finalizing the touch
points, future touch points on this surface may re-use the touch point
ID.
Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/2999
This function sidesteps damage tracking and output awareness on
buffers/surfaces. This function isn't a great fit for the API.
Let's also inline the function and simplify it.
There were a couple places this was missing
- on mode change of an output. If the resolution changes for example
nodes may fall out of the view.
- on commits on an output for scale or transform changes
- when the transform of a buffer is changed. If the dest size is not
set, the buffer may have been rotated potentially changing its size
if the buffer width != height
With protocol additions such as [1], compositors currently have no
way to opt out of the version upgrade. The protocol upgrade will
always be backwards-compatible but may require new compositor
features.
The status quo doesn't make it possible to ship a protocol addition
without breaking the wlroots API. This will be an issue for API
stabilization [2].
To address this, let compositors provide a maximum version in the
function creating the global. We need to support all previous versions
of the interface anyways because of older clients.
This mechanism works the same way as Wayland clients passing a version
in wl_global.bind.
[1]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3514
[2]: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/1008
References: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3397
Maintaining our internal table up-to-date is tedious: one needs to
manually go through the PnP ID registry [1] and check whether we're
missing any entry.
udev_hwdb already has an API to fetch a manufacturer name from its
PnP ID. Use that instead.
[1]: https://uefi.org/pnp_id_list
These formats require EXT_texture_norm16, which in turn needs OpenGL
ES 3.1. The EXT_texture_norm16 extension does not support passing
gl_internalformat = GL_RGBA to glTexImage2D, as can be done for
formats available in OpenGL ES 2.0, so this commit adds a field to
wlr_gles2_pixel_format to provide a more specific internalformat
parameter to glTexImage2D.
The original commit introduced a bug by transposing the order of
some of the fields in xcb_size_hints_t. Since XCB ICCCM support is
required now, we can just eliminate the duplicate structs.
With minor changes:
- Remove #ifdef HAS_XCB_ICCCM guards
- Fix #includes
- Fix references to local size_hints struct
This reverts commit 12b9b1a4bd.
All the code logic related to the pointer has been moved to its own file.
The seat is responsible for the lifetime of its wlr_wl_pointer(s), and assigning
them to the relevant wlr_wl_output. The wlr_wl_pointer becomes a simple helper
to manager the wlr_pointer associated to the seat's wl_pointer and its lifetime.
This was originally added in 810c7b7 for use in rootston's input config
handling. It has never actually been part of the wlroots API and
shouldn't exist.
The destroy callback in wlr_touch_impl has been removed. The function
`wlr_touch_finish` has been introduced to clean up the resources owned by a
wlr_touch.
`wlr_input_device_destroy` no longer destroys the wlr_touch, attempting to
destroy a wlr_touch will result in a no-op.
The field `name` has been added to the wlr_touch_impl to be able to identify
a given wlr_touch device.
The destroy callback in wlr_tablet_tool_impl has been removed. The function
`wlr_tablet_tool_finish` has been introduced to clean up the resources owned by
a wlr_tablet_tool.
`wlr_input_device_destroy` no longer destroys the wlr_tablet_tool, attempting to
destroy a wlr_tablet_tool will result in a no-op.
The field `name` has been added to the wlr_tablet_tool_impl to be able to
identify a given wlr_tablet_tool device.
The destroy callback in wlr_tablet_pad_impl has been removed. The function
`wlr_tablet_pad_finish` has been introduced to clean up the resources owned by a
wlr_tablet_pad.
`wlr_input_device_destroy` no longer destroys the wlr_tablet_pad, attempting to
destroy a wlr_tablet_pad will result in a no-op.
The field `name` has been added to the wlr_tablet_pad_impl to be able to identify
a given wlr_tablet_pad device.
The destroy callback in wlr_switch_impl has been removed. The function
`wlr_switch_finish` has been introduced to clean up the resources owned by a
wlr_switch.
`wlr_input_device_destroy` no longer destroys the wlr_switch, attempting to
destroy a wlr_switch will result in a no-op.
The field `name` has been added to the wlr_switch_impl to be able to identify
a given wlr_switch device.
The destroy callback in wlr_pointer_impl has been removed. The function
`wlr_pointer_finish` has been introduced to clean up the resources owned by a
wlr_pointer.
`wlr_input_device_destroy` no longer destroys the wlr_pointer, attempting to
destroy a wlr_pointer will result in a no-op.
The field `name` has been added to the wlr_pointer_impl to be able to identify
a given wlr_pointer device.
The destroy member in wlr_keyboard_impl has been removed. The function
`wlr_keyboard_finish` has been introduce to clean up the resources owned by a
wlr_keyboard.
`wlr_input_device_destroy` no longer destroys the wlr_keyboard, attempting to
destroy a wlr_keyboard will result in a no-op.
The field `name` has been added to the wlr_keyboard_impl to be able to identify
a given wlr_keyboard device.
This removes an artificial limitation in form of an assert that disallowed the
creation of textures while the renderer is rendering.
A consumer might run its own rendering pipeline and after start of the renderer
still want to create textures for internal usage.
To be consistent with other wlr_xdg_* structs,
wlr_xdg_positioner_resource is renamed to wlr_xdg_positioner and made
public, and wlr_xdg_positioner is renamed to wlr_xdg_positioner_rules.
Functions which operated on wlr_xdg_positioner were renamed and updated
accordingly.
In case the `wlr_input_device` is not owned by a specialized input device, the
function will finish the wlr_input_device and call it's implementation destroy
function if an implementation has been supplied, or simply free it.
The wlroots APIs currently don't allow importing/uploading a buffer
during rendering operations. Scene-graph buffer nodes need to turn
their wlr_buffer into a wlr_texture at some point. It's not always
possible to do so at wlr_scene_buffer creation time because the
scene-graph may have zero outputs at this point, thus no way to
grab a wlr_renderer.
Instead, add scene-graph buffers to a pending list and try to import
them in wlr_scene_output_commit.
References: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3354
Currently the output enter event is never sent if the client has not
yet bound the output, which happens every time the compositor creates a
new output.
To fix this, listen for the output bind event and inform clients as
if needed.
Allows the compositor to submit tokens to the pool of
currently active tokens. This can be useful when the
launcher doesn't use or support xdg-activation-v1 by
itself - e.g. when it is X11 based or use gtk_shell1.
This doesn't work if scene outputs are not used as the primary output of
scene surfaces will always be NULL.
Therefore, take a wlr_scene_output instead of separate wlr_scene and
wlr_output arguments and rename the function to
wlr_scene_output_send_frame_done().
The actual behavior of the function is unchanged.
This allows compositors to avoid sending multiple frame done events
to a surface that is rendered on multiple outputs at once. This may
also be used in the same way for presentation feedback.
wlroots picks names for all outputs, but it might be desirable for
compositor to override it.
For instance, Sway will use a headless output as a fallback in
case no outputs are connected. Sway wants to clearly label the
fallback output as such and label "real" headless outputs starting
from HEADLESS-1.
Implement a basic version of linux-dmabuf-unstable-v1 version 4.
Only default hints are implemented.
The new wlr_linux_dmabuf_feedback_v1 data structure will allow
compositors to define their own custom hints in the future. This
data structure makes it easy to describe feedback metadata.
It's converted to a "compiled" form suitable for marshalling over
the Wayland socket via feedback_compile.
This allows output commit listeners to access the newly committed
buffer. Currently wlr_output.front_buffer is used but it'll get
removed in the next commit.
This intersects two DRM format sets. This is useful for implementing
DMA-BUF feedback in compositors, see e.g. the Sway PR [1].
[1]: https://github.com/swaywm/sway/pull/6313
Support for EXT_image_dma_buf_import_modifiers doesn't necessarily
indicate support for modifiers. For instance, Mesa will advertise
EXT_image_dma_buf_import_modifiers for all drivers. This is a trick
to allow EGL clients to enumerate supported formats (something
EXT_image_dma_buf_import is missing). For more information, see [1].
Add a new wlr_egl.has_modifiers flag which indicates whether
modifiers are supported. It's set to true if any
eglQueryDmaBufModifiersEXT query returned a non-empty list.
Use that flag to figure out whether the buffer modifier should be
passed to the EGL implementation on import.
[1]: https://github.com/KhronosGroup/EGL-Registry/issues/142
This allows creating a wlr_egl from an already-existing EGL display
and context. This is useful to allow compositors to choose the exact
EGL initialization parameters.
This allows getting a wlr_scene_output from a wlr_output. Since an
output can only be added once to a scene-graph there's no ambiguity.
This is useful for compositors using wlr_scene_attach_output_layout:
the output layout integration automatically creates a scene-graph
output for each wlr_output added to the layout.
This allows compositors to get primary formats without manually
calling wlr_output_impl.get_primary_formats.
For example, the Sway patch for linux-dmabuf feedback [1] needs
this.
[1]: https://github.com/swaywm/sway/pull/6313
This allows compositors to easily add an xdg_surface to the
scene-graph while retaining the ability to unconstraint popups
and decide their final position.
Compositors can handle new popups with the wlr_xdg_shell.new_surface
event, get the parent scene-graph node via wlr_xdg_popup.parent.data,
create a new scene-graph node via wlr_scene_xdg_surface_tree_create,
and unconstraint the popup if they want to.
The headless backend no longer needs a parent renderer: it no longer
needs to return it in wlr_backend_impl.get_renderer, nor does it
need to return its DRM FD in wlr_backend_impl.get_drm_fd. Drop this
function altogether since it now behaves exactly like
wlr_headless_backend_create.
Sometimes the headless backend is used standalone with the Pixman
renderer, sometimes it's used together with another backend which
has already picked a DRM FD. In both of these cases it doesn't make
sense to pick a DRM FD.
Broadly speaking the headless backend doesn't really care which DRM
device is used for the buffers it receives. So it doesn't really
make sense to tie it to a particular DRM device.
Let the backend users (e.g. wlr_renderer_autocreate) open an arbitrary
DRM FD as needed instead.
This field's ownership is unclear: it's in wlr_input_device, but
it's not managed by the common code, it's up to each individual
backend to use it and clean it up.
Since this is a backend implementation detail, move it to the
backend-specific structs.
There's no guarantee that the parent Wayland compositor uses
CLOCK_MONOTONIC for reporting presentation timestamps, they could
be using e.g. CLOCK_MONOTONIC_RAW or another system-specific clock.
Forward the value via wlr_backend_impl.get_presentation_clock.
References: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3254#note_1143061
The parameters are used when the client is in the process of
building a buffer. There's no reason why this internal
implementation detail should be exposed in our public header.
This change introduces new double buffered state to the wlr_output,
corresponding to the buffer format to render to.
The format being rendered to does not control the bit depth of colors
being sent to the display; it does generally determine the format with
which screenshot data is provided. The DRM backend _may_ sent higher
bit depths if the render format depth is increased, but hardware and
other limitations may apply.
This makes it possible for the two functions using output_pick_format
(output_pick_cursor_format and output_create_swapchain) to select
different buffer formats.
They are never used in practice, which makes all of our flag
handling effectively dead code. Also, APIs such as KMS don't
provide a good way to deal with the flags. Let's just fail the
DMA-BUF import when clients provide flags.
The protocol uses a signed integer here, which is also what the
wlr_input_method_v2_preedit_string struct provides to compositors from
the input method protocol. Sway currently just passes those int32_t
values directly to this function leading to an implicit conversion.
The data field is useful to track metadata about a token. The destroy
events are useful for compositors that track application startup to
let them know they can stop doing that.
These new functions allow a compositor to request new managed tokens
without participating in the xdg-activation procedure as a wayland
client.
This enables the compositor itself to behave as a launcher
application.
The BO handle table exists to avoid double-closing a BO handle,
which aren't reference-counted by the kernel. But if we can
guarantee that there is only ever a single ref for each BO handle,
then we don't need the BO handle table anymore.
This is possible if we create the handle right before the ADDFB2
IOCTL, and close the handle right after. The handles are very
short-lived and we don't need to track their lifetime.
Because of multi-planar FBs, we need to be a bit careful: some
FB planes might share the same handle. But with a small check, it's
easy to avoid double-closing the same handle (which wouldn't be a
big deal anyways).
There's one gotcha though: drmModeSetCursor2 takes a BO handle as
input. Saving the handles until drmModeSetCursor2 time would require
us to track BO handle lifetimes, so we wouldn't be able to get rid
of the BO handle table. As a workaround, use drmModeGetFB to turn the
FB ID back to a BO handle, call drmModeSetCursor2 and then immediately
close the BO handle. The overhead should be minimal since these IOCTLs
are pretty cheap.
Closes: https://github.com/swaywm/wlroots/issues/3164
This organizes the wlr_output implementation into separate files.
This avoids having a single mega-file with lots of unrelated parts
and makes it more obvious what the interactions between all the
parts are.
No functional changes, just moving code around.
This new renderer is implemented with the existing wlr_renderer API
(which is known to be sub-optimal for some operations). It's not
used by default, but users can opt-in by setting WLR_RENDERER=vulkan.
The renderer depends on VK_EXT_image_drm_format_modifier and
VK_EXT_physical_device_drm.
Co-authored-by: Simon Ser <contact@emersion.fr>
Co-authored-by: Jan Beich <jbeich@FreeBSD.org>
Currently these functions remove the node from the scene if the sibling
argument is the same node as the node. To prevent confusion when
misusing this API, assert that the nodes are distinct and document this.
These functions are used mostly for rendering, where including unmapped
surfaces is undesired.
This is a breaking change. However, few to no usages will have to be
updated.
struct wlr_xdg_surface_state is introduced to hold the geometry
and configure serial to be applied on next wl_surface.commit.
This commit fixes our handling for ack_configure: instead of making
the request mutate our current state, it mutates the pending state
only.
Co-authored-by: Simon Ser <contact@emersion.fr>
As touchpad touches are generally fully abstracted, a client cannot
currently know when a user is interacting with the touchpad without
moving. This is solved by hold gestures.
Hold gestures are notifications about one or more fingers being held
down on the touchpad without significant movement.
Hold gestures are primarily designed for two interactions:
- Hold to interact: where a hold gesture is active for some time a
menu could pop up, some object could be selected, etc.
- Hold to cancel: where e.g. kinetic scrolling is currently active,
the start of a hold gesture can be used to stop the scroll.
Unlike swipe and pinch, hold gestures, by definition, do not have
movement, so there is no need for an "update" stage in the gesture.
Create two structs, wlr_event_pointer_hold_begin and
wlr_event_pointer_hold_end, to represent hold gesture events and the
signals to emit them: wlr_pointer->pointer.hold_begin/hold_end.
Expose the panel orientation with wlr_drm_connector_get_panel_orientation.
Leave it to the compositor to consume this information and configure the
output accordingly.
Closes: https://github.com/swaywm/wlroots/issues/1581
This commit removes any checks whether a configure will change anything
and makes configures be sent unconditionally. Additionally, configures
are scheduled on xdg_toplevel.{un,}set_{maximized,fullscreen} events.
Previously, `wlr_xdg_toplevel` didn't follow the usual "current state +
pending state" pattern and instead had confusingly named
`client_pending` and `server_pending`. This commit removes them, and
instead introduces `wlr_xdg_toplevel.scheduled` to store the properties
that are yet to be sent to a client, and `wlr_xdg_toplevel.requested`
to store the properties that a client has requested. They have different
types to emphasize that they aren't actual states.
A launchee notifies with a "remove"¹ message when done starting up.
Catch these and forward to the compositor. This allows the compositor to
end the startup sequence that might have been started by another
protocol like xdg-activation.
We don't handle other messages since we expect the launcher to use a
wayland protocol like xdg-activation.
While `_NET_STARTUP_ID` helps to associate toplevels with startup-ids
this signals the end of the startup sequence.
1) https://specifications.freedesktop.org/startup-notification-spec/startup-notification-latest.txt
This allows callers to specify the operations they'll perform on
the returned data pointer. The motivations for this are:
- The upcoming Linux MAP_NOSIGBUS flag may only be usable on
read-only mappings.
- gbm_bo_map with GBM_BO_TRANSFER_READ hurts performance.
Previously, we were copying wlr_output_state on the stack and
patching it up to be guaranteed to have a proper drmModeModeInfo
stored in it (and not a custom mode). Also, we had a bunch of
helpers deriving DRM-specific information from the generic
wlr_output_state.
Copying the wlr_output_state worked fine so far, but with output
layers we'll be getting a wl_list in there. An empty wl_list stores
two pointers to itself, copying it on the stack blindly results in
infinite loops in wl_list_for_each.
To fix this, rework our DRM backend to stop copying wlr_output_state,
instead add a new struct wlr_drm_connector_state which holds both
the wlr_output_state and additional DRM-specific information.
This function behaves like allocate_shm_file, except it also
returns a read-only FD. This is useful to share the same segment
of memory with many Wayland clients.
With the addition of a non-surface node type, it was unclear how such
nodes should interact with scene_node_surface_at(). For example, if the
topmost node at the given point is a RECT, should the function treat
that node as transparent and continue searching, or as opaque and return
(probably) NULL?
Instead, replace the function with one returning a scene_node, which
will allow for more consistent behavior across different node types.
Compositors can downcast scene_surface nodes via the now-public
wlr_scene_surface_from_node() if they need access to the surface itself.
RECT is a solid-colored rectangle, useful for simple borders or other
decoration. This can be rendered directly using the wlr_renderer,
without needing to create a surface.
