In certain situations windows can have their input field set to false
but still expect to receive input focus by passively listening to key
presses via a parent window. The ICCCM specification outlines how focus
should be given to clients.
Further reading: https://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7
Relates to #2604
This allows a compositor to get a KMS connector object ID from a
wlr_output. The compositor can then query more information about
the connector via libdrm.
This gives more freedom to compositors and allows them to read
KMS properties that wlroots doesn't know about. For instance,
they could read the EDID or the suggested_{X,Y} properties and
change their output configuration based on that.
Value is now an enum with a new value ("on-demand") that compositors can use to allow "normal" keyboard focus semantics regardless of the layer the client surface is on. An error is sent for invalid keyboard interactivity values. The old behavior is retained for clients using the previous version of the protocol.
Also adjusted the layer-shell example program to use the new keyboard interactivity options.
This function is inferior to wlr_xdg_surface_for_each_popup_surface()
for rendering as it does not iterate over subsurfaces. Furthermore,
no compositor is known to use this to iterate popups for any purpose
other than rendering. Therefore remove the function, which may of course
be reintroduced at a later date if a use-case is found.
This function will allow compositors to implement input handling in a
way consistent with rendering more easily.
Calling wlr_layer_surface_v1_surface_at() and checking if the result is
a wlr_xdg_popup is flawed as there may be subsurfaces in the popup tree.
This function will allow compositors to implement input handling in a
way consistent with rendering more easily.
Calling wlr_xdg_surface_surface_at() and checking if the result is a
wlr_xdg_popup is flawed as there may be subsurfaces in the popup tree.
Sometimes wlr_session_find_gpus will encounter an error. This is
different from finding zero GPUs.
On error, wlr_session_find_gpus already returns -1. However, this is
casted to size_t, so callers uncorrectly assume this is a success.
Instead, make wlr_session_find_gpus return a ssize_t and allow callers
to handle the error accordingly.
This callback allowed compositors to customize the EGL config used by
the renderer. However with renderer v6 EGL configs aren't used anymore.
Instead, buffers are allocated via GBM and GL FBOs are rendered to. So
customizing the EGL config is a no-op.
Rename wlr_renderer_get_dmabuf_formats to
wlr_renderer_get_dmabuf_texture_formats. This makes it clear the formats
are only suitable for creating wlr_textures.
wlr_surface_send_enter now stores outputs that have been entered.
Combined with a new 'bind' event on wlr_output, this allows us to delay
enter events as necessary until the respective wl_output global has been
bound.
Closes: https://github.com/swaywm/wlroots/issues/2466
Wait for a DRM device if none is found in wlr_session_find_gpus. This
can happen if the compositor is loaded before the display kernel driver.
This supersedes the logind CanGraphical property.
To test, e.g. with i915 and sway:
rmmod -f i915
sway &
modprobe i915
Closes: https://github.com/swaywm/wlroots/issues/2093
Instead of operating on FDs in {open,close}_device, operate on
wlr_devices. This avoids the device lookup in wlr_session and allows
callers to have access to wlr_device fields.
For now, we use it to remove wlr_session_signal_add and replace it with
a more idiomatic wlr_session.events.change field. In the future, other
events will be added.
We were previously exporting DMA-BUFs when receiving the capture_output
request, and sending a done event on wlr_output.events.precommit. Instead,
export and send done on wlr_output.events.commit.
The resource field of wlr_xdg_positioner is never initialized or
accessed within wlroots. The wl_resource for this interface is stored
in the wlr_xdg_positioner_resource struct.
This brings the layer-shell api in line with that of xdg-shell and
avoids reimplementing this function in every compositor in order to
render layer shell popups correctly.
This event contains a `committed` bitfield, which allows callers to know
which output fields changed during the commit.
This allows users to setup a single atomic commit listener, instead of
setting up one listener for each event (mode, scale, transform, and so
on).
References: https://github.com/swaywm/wlroots/issues/2098
These states are distinct in the time period between the ack_configure
and the next commit on the surface. Splitting these states avoids the
following race for example:
- client starts at 1000x1000
- wlr_xdg_toplevel_set_size 500x500
- size is different -> configure sent
- client acks the configure
- wlr_xdg_toplevel_set_size 1000x1000
- compare_xdg_toplevel_state returns true since there is no pending
configure and the currently committed size is still 1000x1000
- no new configure is sent
- client commits at the size it last acked, 500x500
The output backend API is now mostly state-less thanks to the atomic
hooks (commit and test). There is one exception though: attach_render.
This function makes the rendering context current. However sometimes the
compositor might decide not to render after attach_render (e.g. when
there's nothing new to render to the back buffer). Thus
wlr_output_rollback has been introduced to revert the pending state.
Because the output backend API is mostly state-less, the only thing
wlr_output_impl.rollback needs to do is revert the current rendering
context. Rename the function to rollback_render to make this clear. Add
a check in the common wlr_output code to only call rollback_render when
attach_buffer has been previously called.
On the long term, we'll be able to remove attach_render and
rollback_render together.
This is necessary for some grabs, which currently have no way of knowing
when the pointer/keyboard focus has left a surface. For example, without
this, a drag-and-drop grab can erroneously drop into a window that the
cursor is no longer over.
This is the plumbing needed to properly fix swaywm/sway#5220. The
existing fix, swaywm/sway#5222, relies on every grab's `enter()` hook
allowing a `NULL` surface. This is not guaranteed by the API and, in
fact, is not the case for the xdg-shell popup grab and results in a
crash when the cursor leaves a surface and does not immediately enter
another one while a popup is open (#2161).
This fix also adds an assertion to wlr_seat_pointer_notify_enter() that
ensures it's never called with a `NULL` surface. This will make Sway
crash much more until it fixes its usage of the API, so we should land
this at the same time as a fix in Sway (which I haven't posted yet).
I found the previous wording a bit confusing when I first read it.
Reword these comments to explicitly say that the grab-respecting
variants should be used in most cases.
This change has no functional effect.
These three APIs are very similar to one another, but they all had
slightly different function orderings. For consistency, always declare
the non_`notify` functions first, then the `notify` functions, then
`{start,end,has}_grab`.
This change has no functional effect.
This introduces the enter and leave events for wlr_keyboard_group.
The enter event is emitted when a keyboard is added to the group while a
key is pressed that is not pressed by any other keyboard in the group.
The data is a wl_array of the pressed key codes unique to the keyboard
that should now be considered pressed.
Similarly the leave event is emitted when a keyboard is removed from the
group while at least one key is pressed that is not pressed by any other
keyboard in the group. The data is a wl_array of the pressed key codes
unique to the keyboard that should now be considered released.
The purpose of these events are to allow the compositor to update its
state to avoid corruption. Additionally, for the leave event, the
focused surface may have been notified of a key press for some or all of
the key codes and needs to be notified of a key release to avoid state
corruption.
These were previously emitted as normal key events, but they are not
normal key events. There is no actual key press or release associated
with the events. It's purely for state keeping purposes. Emitting them
as separate events allows the compositor to handle them differently.
Since these are purely for state keeping purposes and are not associated
with an actual key being pressed or released, bindings should not be
triggered as a result of these events.
We should throw a protocol error if the relevant capability has never
existed when get_(pointer|keyboard|touch) is called. Otherwise, it
should succeed, even if the capability is not currently present.
This follows the spec, and avoids possible races with the client when
capabilities are lost.
Closes: https://github.com/swaywm/wlroots/issues/2227
This function can be called after wlr_egl_make_current to cleanup the
EGL context. This avoids having lingering EGL contexts that make things
work by chance.
Closes: https://github.com/swaywm/wlroots/issues/2197
This is currently inconsistent with the rest of the library and a bit of
a footgun for new compositors. However, this breaks the API in a very
unfortunate way for existing compositors.
This is necessary so that sway can determine when to start emulating
pointer events -- it shouldn't start doing so during an implicit grab,
even if the pen is over a surface that doesn't bind tablet input.
Refs swaywm/sway#5302.
This patch will make the EGL renderer work on any EGL/GLESv2 driver
providing the EGL_WL_bind_wayland_display extensions.
Mesa used to declare provisional EGL_WL_bind_wayland_display directly
in <EGL/eglext.h>. Then, all unofficial extensions were moved to
<EGL/eglmesaext.h>, to have a cleaner implementation. See:
ab7bb10a2a
The extension was then approved at Khronos Group, and reached the
official <EGL/eglext.h>. See:
https://www.khronos.org/registry/EGL/extensions/WL/EGL_WL_bind_wayland_display.txtaa9b63f3ab
In order to make sure the renderer will work on any version of any
implementation providing the extension, only include the mesa-specific
header if it's present.
Signed-off-by: Julien Olivain <juju@cotds.org>
Instead of requiring compositors to call wlr_texture_get_size each time
they want to access the texture's size, expose this information as
wlr_texture fields.
Most of the pending output state is not forwarded to the backend prior
to an output commit. For instance, wlr_output_set_mode just stashes the
mode without calling any wlr_output_impl function.
wlr_output_impl.commit is responsible for applying the pending mode.
However, there are exceptions to this rule. The first one is
wlr_output_attach_render. It won't go away before renderer v6 is
complete, because it needs to set the current EGL surface.
The second one is wlr_output_attach_buffer.
wlr_output_impl.attach_buffer is removed in [1].
When wlr_output_rollback is called, all pending state is supposed to be
cleared. This works for all the state except the two exceptions
mentionned above. To fix this, introduce wlr_output_impl.rollback.
Right now, the backend resets the current EGL surface. This prevents GL
commands from affecting the output after wlr_output_rollback.
This patch is required for FBO-based outputs to work properly. The
compositor might be using FBOs for its own purposes [2], having leftover
FBO state can have bad consequences.
[1]: https://github.com/swaywm/wlroots/pull/2097
[2]: https://github.com/swaywm/wlroots/pull/2063#issuecomment-597614312
Check that buffer can be scanned out in wlr_output_test instead of
wlr_output_attach_buffer. This allows the backend to have access to the
whole pending state when performing the check.
This brings the wlr_output API more in line with the KMS API.
This removes the need for wlr_output_attach_buffer to return a value,
and for wlr_output_impl.attach_buffer.
Consumers call wlr_buffer_lock. Once all consumers are done with the
buffer, only the producer should have a reference to the buffer. In this
case, we can release the buffer (and let the producer re-use it).
This makes it easier for the user of this library to properly handle
failure of this function.
The signature of wlr_renderer_impl.init_wl_display was also modified to
allow for proper error propagation.
This patch disambiguates the needs_frame event by uncoupling it from
damage. A new separate damage event is emitted when the backend damages
the output (this happens e.g. VT is changed or software cursors are
used). The event specifies the damaged region.
The wlr_output.damage field is removed. wlr_output is no longer
responsible for tracking its own damage, this is wlr_output_damage's
job.
This is a breaking change, but wlr_output_damage users shouldn't need an
update.
Bugs fixed:
- Screen flashes on VT switch
- Cursor damage issues on the X11 and headless backends
Closes: https://github.com/swaywm/sway/issues/5086
Split out the client/resource handling out of wlr_buffer by introducing
wlr_client_buffer. Make wlr_buffer an interface so that compositors can
create their own wlr_buffers (e.g. backed by GBM, like glider [1]).
[1]: c66847dd1c/include/gbm_allocator.h (L7)
This function allowed backends to provide a custom function for frame
scheduling. Before resuming the rendering loop, the DRM and Wayland
backends would wait for vsync.
There isn't a clear benefit of doing this. The only upside is that we
get more stable timings: the delay between two repaints doesn't change too
much and is close to a mutliple of the refresh rate.
However this introduces latency, especially when a client misses a
frame. For instance a fullscreen game missing vblank will need to wait
more than a whole frame before being able to display new content. This
worst case scenario happens as follows:
- Client is still rendering its frame and cannot submit it in time
- Deadline is reached
- Compositor decides to stop the rendering loop since nothing changed on
screen
- Client finally manages to render its frame, submits it
- Compositor calls wlr_output_schedule_frame
- DRM backend waits for next vblank
- The wlr_output frame event is fired, compositor draws new content on screen
- On the second next vblank, the new content reaches the screen
With this patch, the wlr_output frame event is fired immediately when
the client submits its late frame.
This change also makes it easier to support variable refresh rate, since
VRR is all about being able to present too-late frames earlier.
References: https://github.com/swaywm/wlroots/issues/1925
The keyboard shortcuts inhibitor protocol is useful for remote desktop
and virtualization software in order to request all keyboard events to
be passed to it and (almost) none being resonded to by the compositor.
This allows the session at the other end of the remote desktop
connection or inside the virtual machine to be interacted with as usual
(e.g. Alt+Tab to switch windows on the remote system instead of
locally).
Add the wayland protocol to the meson build files.
Copy'n'search'n'replace the very similar idle inhibit protocol
implementation. This already provides all the basic functionality:
- creating and destroying inhibitors upon request by a client,
- destruction in reaction to destruction of surfaces or displays,
- a list of inhibitors to search through for existing ones as well as
- a signal to be sent to the compositor upon registration of a new
inhibitor.
Beyond that we add the active and inactive events to be sent to the
client and wire those to activate and deactivate functions for the
compositor to call in confirmation of activation of a new inhibitor or
(un-)suspending of an existing inhibitor e.g. in response to a special
key combination entered by the user as suggested by the protocol.
As mandated by the protocol, we check the existance of an inhibitor for
a given surface and seat upon creation and return the error provided by
the protocol for that purpose.
Signed-off-by: Michael Weiser <michael.weiser@gmx.de>
Closes: https://github.com/swaywm/wlroots/issues/1817
Previously, if the current configuration contains an output X which is
destroyed, its head is automatically removed. If the compositor submits
the new configuration after X was removed, the current output
configuration is incorrectly detected to be the same as the previous
one, and no done event is sent. To prevent this, we can just keep track
of whether the current configuration is dirty, i.e whether we have sent
a done event for it.
Add a wlr_renderer.rendering bool, set it to true between
wlr_renderer_begin() and wlr_renderer_end(). Assert we're rendering when
calling functions that render.
Since [1], the xdg-output description is mutable. Listen to output
description changes and send the new output description when updated.
[1]: 048102f21a
wlr_output.description is a string containing a human-readable string
identifying the output. Compositors can customise it via
wlr_output_set_description, for instance to make the name more
user-friendly.
References: https://github.com/swaywm/wlroots/issues/1623
Bumps minimum version to 0.51.0
- Remove all intermediate static libraries.
They serve no purpose and are just add a bunch of boilerplate for
managing dependencies and options. It's now managed as a list of
files which are compiled into libwlroots directly.
- Use install_subdir instead of installing headers individually.
I've changed my mind since I did that. Listing them out is annoying as
hell, and it's easy to forget to do it.
- Add not_found_message for all of our optional dependencies that have a
meson option. It gives some hints about what option to pass and what
the optional dependency is for.
- Move all backend subdirectories into their own meson.build. This
keeps some of the backend-specific build logic (especially rdp and
session) more neatly separated off.
- Don't overlink example clients with code they're not using.
This was done by merging the protocol dictionaries and setting some
variables containing the code and client header file.
Example clients now explicitly mention what extension protocols they
want to link to.
- Split compositor example logic from client example logic.
- Minor formatting changes
Remove glapi.sh code generation, replace it with hand-written loading
code that checks extension strings before calling eglGetProcAddress.
The GLES2 renderer still uses global state because of:
- {PUSH,POP}_GLES2_DEBUG macros
- wlr_gles2_texture_from_* taking a wlr_egl instead of the renderer
Some globals are static and it doesn't make sense to destroy them before
the wl_display. For instance, wl_compositor should be created before the
display is started and shouldn't be destroyed.
For these globals, we can simplify the code by removing the destructor
and stop keeping track of wl_resources (these will be destroyed with the
wl_display by libwayland).
Most of the time, compositors just display the surface's current buffer
on an output. Add an helper to make it easy to support presentation-time
in this case.
The wlr_presentation_feedback struct now tracks presentation feedback
for multiple resources (but still a single surface content update). This
allows the compositor to properly send presentation events even when
there is more than one frame of latency or when it references a
surface's buffer.
This is set to the value of wlr_output.commit_seq when the frame has
been submitted. This allows tracking presentation with more then 1 full
frame of latency.
References: https://github.com/swaywm/wlroots/issues/1917
Expose the remote wl_display, wl_surface and wl_seat used by the Wayland
backend.
This allows compositors to customize the Wayland backend and to have
more freedom. For instance a compositor might want to handle clipboard
and drag-and-drop from the remote Wayland compositor. Another compositor
might want to setup pointer constraints.
Prior to this commit, compositors needed to render the texture to an
intermediate off-screen buffer using wlr_renderer APIs if they wanted to
use a custom rendering path (e.g. render to a 3D scene).
A new wlr_gles2_texture_get_attribs exposes the GL texture target and ID
so that compositors can render wlr_textures with their own shaders. An
example of a compositor doing so is available at [1].
[1]: 3db905b784/src/render.c (L227)
A wlr_keyboard_group allows for multiple keyboard devices to be
combined into one logical keyboard. Each keyboard device can only be
added to one keyboard group. This helps with the situation where one
physical keyboard is exposed as multiple keyboard devices. It is up to
the compositors on how they group keyboards together, if at all.
Since a wlr_keyboard_group is one logical keyboard, the keys are a set.
This means that if a key is pressed on multiple keyboard devices, the
key event will only be emitted once, but the internal state will count
the number of devices that the key is pressed on. Likewise, the key
release will not be emitted until the key is released from all devices.
If the compositor wants access to which keys are pressed and released
on each keyboard device, the events for those devices can be listened
to, as they currently are, in addition to the group keyboard's events.
Also, all keyboard devices in the group must share the same keymap. If
the keymap's differ, the keyboard device will not be able to be added
to the group. Once in the group, if the keymap or effective layout for
one keyboard device changes, it will be synced to all keyboard devices
in the group. The repeat info and keyboard modifiers are also synced
Without this information, compositors have no way to tell whether
or not to consider the position information valid. Most notably,
a compositor needs to know if it should pick a position for the
surface or use the position sent in the configure request.
Since e26217c51e3a5e1d7dfc95a8a76299e056497981, touchpoints can outlive
surfaces. This works fine as long as the client stays around, but fails
horribly otherwise; therefore we have to make sure that touchpoints don't
outlive their clients.
Fixes#1788
From the xdg-shell specification:
If the parent is unmapped then its children are managed as
though the parent of the now-unmapped parent has become the
parent of this surface. If no parent exists for the now-unmapped
parent then the children are managed as though they have no
parent surface.
This commit makes more output properties (mode, enabled, scale and transform)
atomic. This means that they are double-buffered and only applied on commit.
Compositors now need to call wlr_output_commit after setting any of those
properties.
Internally, backends still apply properties sequentially. The behaviour should
be exactly the same as before. Future commits will update some backends to take
advantage of the atomic interface. Some backends are non-atomic by design, e.g.
the X11 backend or the legacy DRM backend.
Updates: https://github.com/swaywm/wlroots/issues/1640
This prevents screencopy applications from hanging because a failed
event never got sent when the output was disconnected or disabled after
the call to buffer().
The documentation for wayland-server.h says:
> Use of this header file is discouraged. Prefer including
> wayland-server-core.h instead, which does not include the server protocol
> header and as such only defines the library PI, excluding the deprecated API
> below.
Replacing wayland-server.h with wayland-server-core.h allows us to drop the
WL_HIDE_DEPRECATED declaration.
AFAIK this was always set to zero. Instead, compute wl_output mode flags on the
fly.
Technically this is a breaking change, but I don't think anybody uses this
field.
This commit matches sway's 2dc4978d8af326c310057ca8fd22a4c7f5d09335.
To help ensure a reproducible build (when debug info is disabled),
the meson build script now uses the -fmacro-prefix-map command line
argument supported by GCC to strip the build-path dependent bytes
of each __FILE__ string used by wlr_log and related functions.
A rather ugly algorithm is used to compute the relative path between
the build and source folders, because meson has no specific function
for this.
When the compiler does not support -fmacro-prefix-map, fall back
to shifting the start of each __FILE__ string by the length of the
relative path to the source directory.
This change tracks, for each wlr_seat_client, the most recent serial
numbers which were sent to the client. When the client makes a
selection request, wlroots now verifies that the serial number
associated with the selection request was actually provided to that
specific client. This ensures that the client that was most
recently interacted with always has priority for its copy selection
requests, and that no other clients can incorrectly use a larger serial
value and "steal" the role of having the copy selection.
Also, the code used to determine when a given selection is superseded
by a newer request uses < instead of <= to allow clients to make
multiple selection requests with the same serial number and have the
last one hold.
To limit memory use, a ring buffer is used to store runs of sequential
serial numbers, and all serial numbers earlier than the start of the
ring buffer are assumed to be valid. Faking very old serials is
unlikely to be disruptive.
Assuming all clients are correctly written, the only additional
constraint which this patch should impose is that serial numbers
are now bound to seats: clients may not receive a serial number
from an input event on one seat and then use that to request
copy-selection on another seat.
The backend doesn't need to handle transform changes, since everything is done
in software. In fact, all of the implementations were all identical and just
set the transform.
We could add support for hardware transforms, but:
- This would require a different field (something like hardware_transform)
- Not all combinations are possible because there often are hardware
limitations
- The Wayland protocol isn't ready for this (in particular xdg-output, see [1])
This belongs to a different patch series anyway.
[1]: https://patchwork.freedesktop.org/series/52324/
In addition to `button_count`, we keep track of the current buttons
pressed just as in `wlr_keyboard`.
Add `set_add` and `set_remove` to assist with this. These functions can
only be used with values greater than 0 (such as the button/key masks
for keyboards and pointers).
Partially addresses:
- https://github.com/swaywm/wlroots/issues/1716
- https://github.com/swaywm/wlroots/issues/1593
This commit introduces wlr_output_schedule_done and refactors the mechanism
used to send wl_output events to clients.
wlr_output_schedule_done schedules a wl_output.done event. This allows clients
to see wlr_output property changes as atomic.
This function is also useful for add-on interfaces like xdg_output which need
to trigger a wl_output.done event to apply their new state.
wlr_output_damage_make_current has been renamed to
wlr_output_damage_attach_render, since it's just a wrapper for
wlr_output_attach_render.
wlr_output_damage_swap_buffers has been removed completely. Instead,
wlr_output_damage now listens to successful wlr_output commits and updates its
internal state accordingly.
This updates the backend part of the output API. This is mostly renaming:
make_current becomes attach_render and swap_buffers becomes commit.
This also fixes the RDP backend to support NULL damage.
This is necessary for direct scan-out and other upcoming features. This patch
changes the output API to look like the wl_surface API.
Outputs now have some double-buffered state: the frame to be submitted
(currently only wlr_renderer frames are supported) and the damaged region.
To attach a pending frame, use wlr_output_attach_render. To set the pending
damaged region, use wlr_output_set_damage.
To submit the pending state, call wlr_output_commit. This will submit the
pending frame to the backend.
To migrate from the old API to the new one:
- Replace wlr_output_make_current calls by wlr_output_attach_render
- Replace wlr_output_swap_buffers calls by wlr_output_set_damage and
wlr_output_commit
* idle: enable the compositors to add custom idle timeouts
* idle: add a private constructor which also creates the resource
* idle: move resource creation to the idle implementation callback
This types adds a container for formats + modifiers.
A list that is of [format [modifier]] was chosen instead of
[format modifer] because that is how GBM accepts them.
Co-Authored-By: emersion <contact@emersion.fr>
Since the fullscreen request may be made before the toplevel's surface
is mapped, the requested fullscreen output needs to be stored so it
can be retrieved on map (along with the existing fullscreen property).
This commit makes the required changes for wlr_xdg_toplevel_v6.
Since the fullscreen request may be made before the toplevel's surface
is mapped, the requested fullscreen output needs to be stored so it
can be retrieved on map (along with the existing fullscreen property).
This commit makes the required changes for wlr_xdg_toplevel.
* wlr_output: Indicate modes link
* wlr_output: Introduce preferred flag
This indicates an outputs preferred mode.
* drm: Set preferred flag for an outputs preferred mode
data-control: separate out a data_offer struct
This is a prerequisite to adding primary selection support.
data-control: separate out data_control_source
This is a prerequisite to adding primary selection support, since that
doesn't use wlr_data_source, but rather wlr_primary_selection_source.
Update the data-control protocol
data-control: add primary selection support
Merge create_offer and create_primary_offer
Extract code into data_control_source_destroy()
Fix pointer style
Move resource neutralization to destructor
Store wl_resource in the data_offer
Extract data_offer destruction into a function
Frame events group logically connected pointer events. It makes sense to make
the backend responsible for sending frame events, since once the events are
split (ie. once the frame events are stripped) it's not easy to figure out
which events belongs to which frame again.
This is also how Weston handles frame events.
Fixes https://github.com/swaywm/wlroots/issues/1468
This makes compositors able to block and/or customize set_selection requests
coming from clients. For instance, it's possible for a compositor to disable
rich selection content (by removing all MIME types except text/plain). This
commit implements the design proposed in [1].
Two new events are added to wlr_seat: request_set_selection and
request_set_primary_selection. Compositors need to listen to these events and
either destroy the source or effectively set the selection.
Fixes https://github.com/swaywm/wlroots/issues/1138
[1]: https://github.com/swaywm/wlroots/issues/1367#issuecomment-442403454
