Copyright © 2008-2011 Kristian Høgsberg Copyright © 2010-2011 Intel Corporation Copyright © 2012-2013 Collabora, Ltd. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. The core global object. This is a special singleton object. It is used for internal Wayland protocol features. The sync request asks the server to emit the 'done' event on the returned wl_callback object. Since requests are handled in-order and events are delivered in-order, this can be used as a barrier to ensure all previous requests and the resulting events have been handled. The object returned by this request will be destroyed by the compositor after the callback is fired and as such the client must not attempt to use it after that point. The callback_data passed in the callback is the event serial. This request creates a registry object that allows the client to list and bind the global objects available from the compositor. The error event is sent out when a fatal (non-recoverable) error has occurred. The object_id argument is the object where the error occurred, most often in response to a request to that object. The code identifies the error and is defined by the object interface. As such, each interface defines its own set of error codes. The message is a brief description of the error, for (debugging) convenience. These errors are global and can be emitted in response to any server request. This event is used internally by the object ID management logic. When a client deletes an object, the server will send this event to acknowledge that it has seen the delete request. When the client receives this event, it will know that it can safely reuse the object ID. The singleton global registry object. The server has a number of global objects that are available to all clients. These objects typically represent an actual object in the server (for example, an input device) or they are singleton objects that provide extension functionality. When a client creates a registry object, the registry object will emit a global event for each global currently in the registry. Globals come and go as a result of device or monitor hotplugs, reconfiguration or other events, and the registry will send out global and global_remove events to keep the client up to date with the changes. To mark the end of the initial burst of events, the client can use the wl_display.sync request immediately after calling wl_display.get_registry. A client can bind to a global object by using the bind request. This creates a client-side handle that lets the object emit events to the client and lets the client invoke requests on the object. Binds a new, client-created object to the server using the specified name as the identifier. Notify the client of global objects. The event notifies the client that a global object with the given name is now available, and it implements the given version of the given interface. Notify the client of removed global objects. This event notifies the client that the global identified by name is no longer available. If the client bound to the global using the bind request, the client should now destroy that object. The object remains valid and requests to the object will be ignored until the client destroys it, to avoid races between the global going away and a client sending a request to it. Clients can handle the 'done' event to get notified when the related request is done. Notify the client when the related request is done. A compositor. This object is a singleton global. The compositor is in charge of combining the contents of multiple surfaces into one displayable output. Ask the compositor to create a new surface. Ask the compositor to create a new region. The wl_shm_pool object encapsulates a piece of memory shared between the compositor and client. Through the wl_shm_pool object, the client can allocate shared memory wl_buffer objects. All objects created through the same pool share the same underlying mapped memory. Reusing the mapped memory avoids the setup/teardown overhead and is useful when interactively resizing a surface or for many small buffers. Create a wl_buffer object from the pool. The buffer is created offset bytes into the pool and has width and height as specified. The stride argument specifies the number of bytes from the beginning of one row to the beginning of the next. The format is the pixel format of the buffer and must be one of those advertised through the wl_shm.format event. A buffer will keep a reference to the pool it was created from so it is valid to destroy the pool immediately after creating a buffer from it. Destroy the shared memory pool. The mmapped memory will be released when all buffers that have been created from this pool are gone. This request will cause the server to remap the backing memory for the pool from the file descriptor passed when the pool was created, but using the new size. This request can only be used to make the pool bigger. A singleton global object that provides support for shared memory. Clients can create wl_shm_pool objects using the create_pool request. At connection setup time, the wl_shm object emits one or more format events to inform clients about the valid pixel formats that can be used for buffers. These errors can be emitted in response to wl_shm requests. This describes the memory layout of an individual pixel. All renderers should support argb8888 and xrgb8888 but any other formats are optional and may not be supported by the particular renderer in use. The drm format codes match the macros defined in drm_fourcc.h. The formats actually supported by the compositor will be reported by the format event. Create a new wl_shm_pool object. The pool can be used to create shared memory based buffer objects. The server will mmap size bytes of the passed file descriptor, to use as backing memory for the pool. Informs the client about a valid pixel format that can be used for buffers. Known formats include argb8888 and xrgb8888. A buffer provides the content for a wl_surface. Buffers are created through factory interfaces such as wl_drm, wl_shm or similar. It has a width and a height and can be attached to a wl_surface, but the mechanism by which a client provides and updates the contents is defined by the buffer factory interface. Destroy a buffer. If and how you need to release the backing storage is defined by the buffer factory interface. For possible side-effects to a surface, see wl_surface.attach. Sent when this wl_buffer is no longer used by the compositor. The client is now free to reuse or destroy this buffer and its backing storage. If a client receives a release event before the frame callback requested in the same wl_surface.commit that attaches this wl_buffer to a surface, then the client is immediately free to reuse the buffer and its backing storage, and does not need a second buffer for the next surface content update. Typically this is possible, when the compositor maintains a copy of the wl_surface contents, e.g. as a GL texture. This is an important optimization for GL(ES) compositors with wl_shm clients. A wl_data_offer represents a piece of data offered for transfer by another client (the source client). It is used by the copy-and-paste and drag-and-drop mechanisms. The offer describes the different mime types that the data can be converted to and provides the mechanism for transferring the data directly from the source client. Indicate that the client can accept the given mime type, or NULL for not accepted. For objects of version 2 or older, this request is used by the client to give feedback whether the client can receive the given mime type, or NULL if none is accepted; the feedback does not determine whether the drag-and-drop operation succeeds or not. For objects of version 3 or newer, this request determines the final result of the drag-and-drop operation. If the end result is that no mime types were accepted, the drag-and-drop operation will be cancelled and the corresponding drag source will receive wl_data_source.cancelled. Clients may still use this event in conjunction with wl_data_source.action for feedback. To transfer the offered data, the client issues this request and indicates the mime type it wants to receive. The transfer happens through the passed file descriptor (typically created with the pipe system call). The source client writes the data in the mime type representation requested and then closes the file descriptor. The receiving client reads from the read end of the pipe until EOF and then closes its end, at which point the transfer is complete. This request may happen multiple times for different mime types, both before and after wl_data_device.drop. Drag-and-drop destination clients may preemptively fetch data or examine it more closely to determine acceptance. Destroy the data offer. Sent immediately after creating the wl_data_offer object. One event per offered mime type. Notifies the compositor that the drag destination successfully finished the drag-and-drop operation. Upon receiving this request, the compositor will emit wl_data_source.dnd_finished on the drag source client. It is a client error to perform other requests than wl_data_offer.destroy after this one. It is also an error to perform this request after a NULL mime type has been set in wl_data_offer.accept or no action was received through wl_data_offer.action. Sets the actions that the destination side client supports for this operation. This request may trigger the emission of wl_data_source.action and wl_data_offer.action events if the compositor needs to change the selected action. This request can be called multiple times throughout the drag-and-drop operation, typically in response to wl_data_device.enter or wl_data_device.motion events. This request determines the final result of the drag-and-drop operation. If the end result is that no action is accepted, the drag source will receive wl_drag_source.cancelled. The dnd_actions argument must contain only values expressed in the wl_data_device_manager.dnd_actions enum, and the preferred_action argument must only contain one of those values set, otherwise it will result in a protocol error. While managing an "ask" action, the destination drag-and-drop client may perform further wl_data_offer.receive requests, and is expected to perform one last wl_data_offer.set_actions request with a preferred action other than "ask" (and optionally wl_data_offer.accept) before requesting wl_data_offer.finish, in order to convey the action selected by the user. If the preferred action is not in the wl_data_offer.source_actions mask, an error will be raised. If the "ask" action is dismissed (e.g. user cancellation), the client is expected to perform wl_data_offer.destroy right away. This request can only be made on drag-and-drop offers, a protocol error will be raised otherwise. This event indicates the actions offered by the data source. It will be sent right after wl_data_device.enter, or anytime the source side changes its offered actions through wl_data_source.set_actions. This event indicates the action selected by the compositor after matching the source/destination side actions. Only one action (or none) will be offered here. This event can be emitted multiple times during the drag-and-drop operation in response to destination side action changes through wl_data_offer.set_actions. This event will no longer be emitted after wl_data_device.drop happened on the drag-and-drop destination, the client must honor the last action received, or the last preferred one set through wl_data_offer.set_actions when handling an "ask" action. Compositors may also change the selected action on the fly, mainly in response to keyboard modifier changes during the drag-and-drop operation. The most recent action received is always the valid one. Prior to receiving wl_data_device.drop, the chosen action may change (e.g. due to keyboard modifiers being pressed). At the time of receiving wl_data_device.drop the drag-and-drop destination must honor the last action received. Action changes may still happen after wl_data_device.drop, especially on "ask" actions, where the drag-and-drop destination may choose another action afterwards. Action changes happening at this stage are always the result of inter-client negotiation, the compositor shall no longer be able to induce a different action. Upon "ask" actions, it is expected that the drag-and-drop destination may potentially choose a different action and/or mime type, based on wl_data_offer.source_actions and finally chosen by the user (e.g. popping up a menu with the available options). The final wl_data_offer.set_actions and wl_data_offer.accept requests must happen before the call to wl_data_offer.finish. The wl_data_source object is the source side of a wl_data_offer. It is created by the source client in a data transfer and provides a way to describe the offered data and a way to respond to requests to transfer the data. This request adds a mime type to the set of mime types advertised to targets. Can be called several times to offer multiple types. Destroy the data source. Sent when a target accepts pointer_focus or motion events. If a target does not accept any of the offered types, type is NULL. Used for feedback during drag-and-drop. Request for data from the client. Send the data as the specified mime type over the passed file descriptor, then close it. This data source is no longer valid. There are several reasons why this could happen: - The data source has been replaced by another data source. - The drag-and-drop operation was performed, but the drop destination did not accept any of the mime types offered through wl_data_source.target. - The drag-and-drop operation was performed, but the drop destination did not select any of the actions present in the mask offered through wl_data_source.action. - The drag-and-drop operation was performed but didn't happen over a surface. - The compositor cancelled the drag-and-drop operation (e.g. compositor dependent timeouts to avoid stale drag-and-drop transfers). The client should clean up and destroy this data source. For objects of version 2 or older, wl_data_source.cancelled will only be emitted if the data source was replaced by another data source. Sets the actions that the source side client supports for this operation. This request may trigger wl_data_source.action and wl_data_offer.action events if the compositor needs to change the selected action. The dnd_actions argument must contain only values expressed in the wl_data_device_manager.dnd_actions enum, otherwise it will result in a protocol error. This request must be made once only, and can only be made on sources used in drag-and-drop, so it must be performed before wl_data_device.start_drag. Attempting to use the source other than for drag-and-drop will raise a protocol error. The user performed the drop action. This event does not indicate acceptance, wl_data_source.cancelled may still be emitted afterwards if the drop destination does not accept any mime type. However, this event might however not be received if the compositor cancelled the drag-and-drop operation before this event could happen. Note that the data_source may still be used in the future and should not be destroyed here. The drop destination finished interoperating with this data source, so the client is now free to destroy this data source and free all associated data. If the action used to perform the operation was "move", the source can now delete the transferred data. This event indicates the action selected by the compositor after matching the source/destination side actions. Only one action (or none) will be offered here. This event can be emitted multiple times during the drag-and-drop operation, mainly in response to destination side changes through wl_data_offer.set_actions, and as the data device enters/leaves surfaces. It is only possible to receive this event after wl_data_source.dnd_drop_performed if the drag-and-drop operation ended in an "ask" action, in which case the final wl_data_source.action event will happen immediately before wl_data_source.dnd_finished. Compositors may also change the selected action on the fly, mainly in response to keyboard modifier changes during the drag-and-drop operation. The most recent action received is always the valid one. The chosen action may change alongside negotiation (e.g. an "ask" action can turn into a "move" operation), so the effects of the final action must always be applied in wl_data_offer.dnd_finished. Clients can trigger cursor surface changes from this point, so they reflect the current action. There is one wl_data_device per seat which can be obtained from the global wl_data_device_manager singleton. A wl_data_device provides access to inter-client data transfer mechanisms such as copy-and-paste and drag-and-drop. This request asks the compositor to start a drag-and-drop operation on behalf of the client. The source argument is the data source that provides the data for the eventual data transfer. If source is NULL, enter, leave and motion events are sent only to the client that initiated the drag and the client is expected to handle the data passing internally. The origin surface is the surface where the drag originates and the client must have an active implicit grab that matches the serial. The icon surface is an optional (can be NULL) surface that provides an icon to be moved around with the cursor. Initially, the top-left corner of the icon surface is placed at the cursor hotspot, but subsequent wl_surface.attach request can move the relative position. Attach requests must be confirmed with wl_surface.commit as usual. The icon surface is given the role of a drag-and-drop icon. If the icon surface already has another role, it raises a protocol error. The current and pending input regions of the icon wl_surface are cleared, and wl_surface.set_input_region is ignored until the wl_surface is no longer used as the icon surface. When the use as an icon ends, the current and pending input regions become undefined, and the wl_surface is unmapped. This request asks the compositor to set the selection to the data from the source on behalf of the client. To unset the selection, set the source to NULL. The data_offer event introduces a new wl_data_offer object, which will subsequently be used in either the data_device.enter event (for drag-and-drop) or the data_device.selection event (for selections). Immediately following the data_device_data_offer event, the new data_offer object will send out data_offer.offer events to describe the mime types it offers. This event is sent when an active drag-and-drop pointer enters a surface owned by the client. The position of the pointer at enter time is provided by the x and y arguments, in surface-local coordinates. This event is sent when the drag-and-drop pointer leaves the surface and the session ends. The client must destroy the wl_data_offer introduced at enter time at this point. This event is sent when the drag-and-drop pointer moves within the currently focused surface. The new position of the pointer is provided by the x and y arguments, in surface-local coordinates. The event is sent when a drag-and-drop operation is ended because the implicit grab is removed. The drag-and-drop destination is expected to honor the last action received through wl_data_offer.action, if the resulting action is "copy" or "move", the destination can still perform wl_data_offer.receive requests, and is expected to end all transfers with a wl_data_offer.finish request. If the resulting action is "ask", the action will not be considered final. The drag-and-drop destination is expected to perform one last wl_data_offer.set_actions request, or wl_data_offer.destroy in order to cancel the operation. The selection event is sent out to notify the client of a new wl_data_offer for the selection for this device. The data_device.data_offer and the data_offer.offer events are sent out immediately before this event to introduce the data offer object. The selection event is sent to a client immediately before receiving keyboard focus and when a new selection is set while the client has keyboard focus. The data_offer is valid until a new data_offer or NULL is received or until the client loses keyboard focus. The client must destroy the previous selection data_offer, if any, upon receiving this event. This request destroys the data device. The wl_data_device_manager is a singleton global object that provides access to inter-client data transfer mechanisms such as copy-and-paste and drag-and-drop. These mechanisms are tied to a wl_seat and this interface lets a client get a wl_data_device corresponding to a wl_seat. Depending on the version bound, the objects created from the bound wl_data_device_manager object will have different requirements for functioning properly. See wl_data_source.set_actions, wl_data_offer.accept and wl_data_offer.finish for details. Create a new data source. Create a new data device for a given seat. This is a bitmask of the available/preferred actions in a drag-and-drop operation. In the compositor, the selected action is a result of matching the actions offered by the source and destination sides. "action" events with a "none" action will be sent to both source and destination if there is no match. All further checks will effectively happen on (source actions ∩ destination actions). In addition, compositors may also pick different actions in reaction to key modifiers being pressed. One common design that is used in major toolkits (and the behavior recommended for compositors) is: - If no modifiers are pressed, the first match (in bit order) will be used. - Pressing Shift selects "move", if enabled in the mask. - Pressing Control selects "copy", if enabled in the mask. Behavior beyond that is considered implementation-dependent. Compositors may for example bind other modifiers (like Alt/Meta) or drags initiated with other buttons than BTN_LEFT to specific actions (e.g. "ask"). This interface is implemented by servers that provide desktop-style user interfaces. It allows clients to associate a wl_shell_surface with a basic surface. Create a shell surface for an existing surface. This gives the wl_surface the role of a shell surface. If the wl_surface already has another role, it raises a protocol error. Only one shell surface can be associated with a given surface. An interface that may be implemented by a wl_surface, for implementations that provide a desktop-style user interface. It provides requests to treat surfaces like toplevel, fullscreen or popup windows, move, resize or maximize them, associate metadata like title and class, etc. On the server side the object is automatically destroyed when the related wl_surface is destroyed. On the client side, wl_shell_surface_destroy() must be called before destroying the wl_surface object. A client must respond to a ping event with a pong request or the client may be deemed unresponsive. Start a pointer-driven move of the surface. This request must be used in response to a button press event. The server may ignore move requests depending on the state of the surface (e.g. fullscreen or maximized). These values are used to indicate which edge of a surface is being dragged in a resize operation. The server may use this information to adapt its behavior, e.g. choose an appropriate cursor image. Start a pointer-driven resizing of the surface. This request must be used in response to a button press event. The server may ignore resize requests depending on the state of the surface (e.g. fullscreen or maximized). Map the surface as a toplevel surface. A toplevel surface is not fullscreen, maximized or transient. These flags specify details of the expected behaviour of transient surfaces. Used in the set_transient request. Map the surface relative to an existing surface. The x and y arguments specify the location of the upper left corner of the surface relative to the upper left corner of the parent surface, in surface-local coordinates. The flags argument controls details of the transient behaviour. Hints to indicate to the compositor how to deal with a conflict between the dimensions of the surface and the dimensions of the output. The compositor is free to ignore this parameter. Map the surface as a fullscreen surface. If an output parameter is given then the surface will be made fullscreen on that output. If the client does not specify the output then the compositor will apply its policy - usually choosing the output on which the surface has the biggest surface area. The client may specify a method to resolve a size conflict between the output size and the surface size - this is provided through the method parameter. The framerate parameter is used only when the method is set to "driver", to indicate the preferred framerate. A value of 0 indicates that the client does not care about framerate. The framerate is specified in mHz, that is framerate of 60000 is 60Hz. A method of "scale" or "driver" implies a scaling operation of the surface, either via a direct scaling operation or a change of the output mode. This will override any kind of output scaling, so that mapping a surface with a buffer size equal to the mode can fill the screen independent of buffer_scale. A method of "fill" means we don't scale up the buffer, however any output scale is applied. This means that you may run into an edge case where the application maps a buffer with the same size of the output mode but buffer_scale 1 (thus making a surface larger than the output). In this case it is allowed to downscale the results to fit the screen. The compositor must reply to this request with a configure event with the dimensions for the output on which the surface will be made fullscreen. Map the surface as a popup. A popup surface is a transient surface with an added pointer grab. An existing implicit grab will be changed to owner-events mode, and the popup grab will continue after the implicit grab ends (i.e. releasing the mouse button does not cause the popup to be unmapped). The popup grab continues until the window is destroyed or a mouse button is pressed in any other client's window. A click in any of the client's surfaces is reported as normal, however, clicks in other clients' surfaces will be discarded and trigger the callback. The x and y arguments specify the location of the upper left corner of the surface relative to the upper left corner of the parent surface, in surface-local coordinates. Map the surface as a maximized surface. If an output parameter is given then the surface will be maximized on that output. If the client does not specify the output then the compositor will apply its policy - usually choosing the output on which the surface has the biggest surface area. The compositor will reply with a configure event telling the expected new surface size. The operation is completed on the next buffer attach to this surface. A maximized surface typically fills the entire output it is bound to, except for desktop elements such as panels. This is the main difference between a maximized shell surface and a fullscreen shell surface. The details depend on the compositor implementation. Set a short title for the surface. This string may be used to identify the surface in a task bar, window list, or other user interface elements provided by the compositor. The string must be encoded in UTF-8. Set a class for the surface. The surface class identifies the general class of applications to which the surface belongs. A common convention is to use the file name (or the full path if it is a non-standard location) of the application's .desktop file as the class. Ping a client to check if it is receiving events and sending requests. A client is expected to reply with a pong request. The configure event asks the client to resize its surface. The size is a hint, in the sense that the client is free to ignore it if it doesn't resize, pick a smaller size (to satisfy aspect ratio or resize in steps of NxM pixels). The edges parameter provides a hint about how the surface was resized. The client may use this information to decide how to adjust its content to the new size (e.g. a scrolling area might adjust its content position to leave the viewable content unmoved). The client is free to dismiss all but the last configure event it received. The width and height arguments specify the size of the window in surface-local coordinates. The popup_done event is sent out when a popup grab is broken, that is, when the user clicks a surface that doesn't belong to the client owning the popup surface. A surface is a rectangular area that is displayed on the screen. It has a location, size and pixel contents. The size of a surface (and relative positions on it) is described in surface-local coordinates, which may differ from the buffer coordinates of the pixel content, in case a buffer_transform or a buffer_scale is used. A surface without a "role" is fairly useless: a compositor does not know where, when or how to present it. The role is the purpose of a wl_surface. Examples of roles are a cursor for a pointer (as set by wl_pointer.set_cursor), a drag icon (wl_data_device.start_drag), a sub-surface (wl_subcompositor.get_subsurface), and a window as defined by a shell protocol (e.g. wl_shell.get_shell_surface). A surface can have only one role at a time. Initially a wl_surface does not have a role. Once a wl_surface is given a role, it is set permanently for the whole lifetime of the wl_surface object. Giving the current role again is allowed, unless explicitly forbidden by the relevant interface specification. Surface roles are given by requests in other interfaces such as wl_pointer.set_cursor. The request should explicitly mention that this request gives a role to a wl_surface. Often, this request also creates a new protocol object that represents the role and adds additional functionality to wl_surface. When a client wants to destroy a wl_surface, they must destroy this 'role object' before the wl_surface. Destroying the role object does not remove the role from the wl_surface, but it may stop the wl_surface from "playing the role". For instance, if a wl_subsurface object is destroyed, the wl_surface it was created for will be unmapped and forget its position and z-order. It is allowed to create a wl_subsurface for the same wl_surface again, but it is not allowed to use the wl_surface as a cursor (cursor is a different role than sub-surface, and role switching is not allowed). These errors can be emitted in response to wl_surface requests. Deletes the surface and invalidates its object ID. Set a buffer as the content of this surface. The new size of the surface is calculated based on the buffer size transformed by the inverse buffer_transform and the inverse buffer_scale. This means that the supplied buffer must be an integer multiple of the buffer_scale. The x and y arguments specify the location of the new pending buffer's upper left corner, relative to the current buffer's upper left corner, in surface-local coordinates. In other words, the x and y, combined with the new surface size define in which directions the surface's size changes. Surface contents are double-buffered state, see wl_surface.commit. The initial surface contents are void; there is no content. wl_surface.attach assigns the given wl_buffer as the pending wl_buffer. wl_surface.commit makes the pending wl_buffer the new surface contents, and the size of the surface becomes the size calculated from the wl_buffer, as described above. After commit, there is no pending buffer until the next attach. Committing a pending wl_buffer allows the compositor to read the pixels in the wl_buffer. The compositor may access the pixels at any time after the wl_surface.commit request. When the compositor will not access the pixels anymore, it will send the wl_buffer.release event. Only after receiving wl_buffer.release, the client may reuse the wl_buffer. A wl_buffer that has been attached and then replaced by another attach instead of committed will not receive a release event, and is not used by the compositor. Destroying the wl_buffer after wl_buffer.release does not change the surface contents. However, if the client destroys the wl_buffer before receiving the wl_buffer.release event, the surface contents become undefined immediately. If wl_surface.attach is sent with a NULL wl_buffer, the following wl_surface.commit will remove the surface content. This request is used to describe the regions where the pending buffer is different from the current surface contents, and where the surface therefore needs to be repainted. The compositor ignores the parts of the damage that fall outside of the surface. Damage is double-buffered state, see wl_surface.commit. The damage rectangle is specified in surface-local coordinates, where x and y specify the upper left corner of the damage rectangle. The initial value for pending damage is empty: no damage. wl_surface.damage adds pending damage: the new pending damage is the union of old pending damage and the given rectangle. wl_surface.commit assigns pending damage as the current damage, and clears pending damage. The server will clear the current damage as it repaints the surface. Alternatively, damage can be posted with wl_surface.damage_buffer which uses buffer coordinates instead of surface coordinates, and is probably the preferred and intuitive way of doing this. Request a notification when it is a good time to start drawing a new frame, by creating a frame callback. This is useful for throttling redrawing operations, and driving animations. When a client is animating on a wl_surface, it can use the 'frame' request to get notified when it is a good time to draw and commit the next frame of animation. If the client commits an update earlier than that, it is likely that some updates will not make it to the display, and the client is wasting resources by drawing too often. The frame request will take effect on the next wl_surface.commit. The notification will only be posted for one frame unless requested again. For a wl_surface, the notifications are posted in the order the frame requests were committed. The server must send the notifications so that a client will not send excessive updates, while still allowing the highest possible update rate for clients that wait for the reply before drawing again. The server should give some time for the client to draw and commit after sending the frame callback events to let it hit the next output refresh. A server should avoid signaling the frame callbacks if the surface is not visible in any way, e.g. the surface is off-screen, or completely obscured by other opaque surfaces. The object returned by this request will be destroyed by the compositor after the callback is fired and as such the client must not attempt to use it after that point. The callback_data passed in the callback is the current time, in milliseconds, with an undefined base. This request sets the region of the surface that contains opaque content. The opaque region is an optimization hint for the compositor that lets it optimize the redrawing of content behind opaque regions. Setting an opaque region is not required for correct behaviour, but marking transparent content as opaque will result in repaint artifacts. The opaque region is specified in surface-local coordinates. The compositor ignores the parts of the opaque region that fall outside of the surface. Opaque region is double-buffered state, see wl_surface.commit. wl_surface.set_opaque_region changes the pending opaque region. wl_surface.commit copies the pending region to the current region. Otherwise, the pending and current regions are never changed. The initial value for an opaque region is empty. Setting the pending opaque region has copy semantics, and the wl_region object can be destroyed immediately. A NULL wl_region causes the pending opaque region to be set to empty. This request sets the region of the surface that can receive pointer and touch events. Input events happening outside of this region will try the next surface in the server surface stack. The compositor ignores the parts of the input region that fall outside of the surface. The input region is specified in surface-local coordinates. Input region is double-buffered state, see wl_surface.commit. wl_surface.set_input_region changes the pending input region. wl_surface.commit copies the pending region to the current region. Otherwise the pending and current regions are never changed, except cursor and icon surfaces are special cases, see wl_pointer.set_cursor and wl_data_device.start_drag. The initial value for an input region is infinite. That means the whole surface will accept input. Setting the pending input region has copy semantics, and the wl_region object can be destroyed immediately. A NULL wl_region causes the input region to be set to infinite. Surface state (input, opaque, and damage regions, attached buffers, etc.) is double-buffered. Protocol requests modify the pending state, as opposed to the current state in use by the compositor. A commit request atomically applies all pending state, replacing the current state. After commit, the new pending state is as documented for each related request. On commit, a pending wl_buffer is applied first, and all other state second. This means that all coordinates in double-buffered state are relative to the new wl_buffer coming into use, except for wl_surface.attach itself. If there is no pending wl_buffer, the coordinates are relative to the current surface contents. All requests that need a commit to become effective are documented to affect double-buffered state. Other interfaces may add further double-buffered surface state. This is emitted whenever a surface's creation, movement, or resizing results in some part of it being within the scanout region of an output. Note that a surface may be overlapping with zero or more outputs. This is emitted whenever a surface's creation, movement, or resizing results in it no longer having any part of it within the scanout region of an output. This request sets an optional transformation on how the compositor interprets the contents of the buffer attached to the surface. The accepted values for the transform parameter are the values for wl_output.transform. Buffer transform is double-buffered state, see wl_surface.commit. A newly created surface has its buffer transformation set to normal. wl_surface.set_buffer_transform changes the pending buffer transformation. wl_surface.commit copies the pending buffer transformation to the current one. Otherwise, the pending and current values are never changed. The purpose of this request is to allow clients to render content according to the output transform, thus permitting the compositor to use certain optimizations even if the display is rotated. Using hardware overlays and scanning out a client buffer for fullscreen surfaces are examples of such optimizations. Those optimizations are highly dependent on the compositor implementation, so the use of this request should be considered on a case-by-case basis. Note that if the transform value includes 90 or 270 degree rotation, the width of the buffer will become the surface height and the height of the buffer will become the surface width. If transform is not one of the values from the wl_output.transform enum the invalid_transform protocol error is raised. This request sets an optional scaling factor on how the compositor interprets the contents of the buffer attached to the window. Buffer scale is double-buffered state, see wl_surface.commit. A newly created surface has its buffer scale set to 1. wl_surface.set_buffer_scale changes the pending buffer scale. wl_surface.commit copies the pending buffer scale to the current one. Otherwise, the pending and current values are never changed. The purpose of this request is to allow clients to supply higher resolution buffer data for use on high resolution outputs. It is intended that you pick the same buffer scale as the scale of the output that the surface is displayed on. This means the compositor can avoid scaling when rendering the surface on that output. Note that if the scale is larger than 1, then you have to attach a buffer that is larger (by a factor of scale in each dimension) than the desired surface size. If scale is not positive the invalid_scale protocol error is raised. This request is used to describe the regions where the pending buffer is different from the current surface contents, and where the surface therefore needs to be repainted. The compositor ignores the parts of the damage that fall outside of the surface. Damage is double-buffered state, see wl_surface.commit. The damage rectangle is specified in buffer coordinates, where x and y specify the upper left corner of the damage rectangle. The initial value for pending damage is empty: no damage. wl_surface.damage_buffer adds pending damage: the new pending damage is the union of old pending damage and the given rectangle. wl_surface.commit assigns pending damage as the current damage, and clears pending damage. The server will clear the current damage as it repaints the surface. This request differs from wl_surface.damage in only one way - it takes damage in buffer coordinates instead of surface-local coordinates. While this generally is more intuitive than surface coordinates, it is especially desirable when using wp_viewport or when a drawing library (like EGL) is unaware of buffer scale and buffer transform. Note: Because buffer transformation changes and damage requests may be interleaved in the protocol stream, it is impossible to determine the actual mapping between surface and buffer damage until wl_surface.commit time. Therefore, compositors wishing to take both kinds of damage into account will have to accumulate damage from the two requests separately and only transform from one to the other after receiving the wl_surface.commit. A seat is a group of keyboards, pointer and touch devices. This object is published as a global during start up, or when such a device is hot plugged. A seat typically has a pointer and maintains a keyboard focus and a pointer focus. This is a bitmask of capabilities this seat has; if a member is set, then it is present on the seat. This is emitted whenever a seat gains or loses the pointer, keyboard or touch capabilities. The argument is a capability enum containing the complete set of capabilities this seat has. When the pointer capability is added, a client may create a wl_pointer object using the wl_seat.get_pointer request. This object will receive pointer events until the capability is removed in the future. When the pointer capability is removed, a client should destroy the wl_pointer objects associated with the seat where the capability was removed, using the wl_pointer.release request. No further pointer events will be received on these objects. In some compositors, if a seat regains the pointer capability and a client has a previously obtained wl_pointer object of version 4 or less, that object may start sending pointer events again. This behavior is considered a misinterpretation of the intended behavior and must not be relied upon by the client. wl_pointer objects of version 5 or later must not send events if created before the most recent event notifying the client of an added pointer capability. The above behavior also applies to wl_keyboard and wl_touch with the keyboard and touch capabilities, respectively. The ID provided will be initialized to the wl_pointer interface for this seat. This request only takes effect if the seat has the pointer capability, or has had the pointer capability in the past. It is a protocol violation to issue this request on a seat that has never had the pointer capability. The ID provided will be initialized to the wl_keyboard interface for this seat. This request only takes effect if the seat has the keyboard capability, or has had the keyboard capability in the past. It is a protocol violation to issue this request on a seat that has never had the keyboard capability. The ID provided will be initialized to the wl_touch interface for this seat. This request only takes effect if the seat has the touch capability, or has had the touch capability in the past. It is a protocol violation to issue this request on a seat that has never had the touch capability. In a multiseat configuration this can be used by the client to help identify which physical devices the seat represents. Based on the seat configuration used by the compositor. Using this request a client can tell the server that it is not going to use the seat object anymore. The wl_pointer interface represents one or more input devices, such as mice, which control the pointer location and pointer_focus of a seat. The wl_pointer interface generates motion, enter and leave events for the surfaces that the pointer is located over, and button and axis events for button presses, button releases and scrolling. Set the pointer surface, i.e., the surface that contains the pointer image (cursor). This request gives the surface the role of a cursor. If the surface already has another role, it raises a protocol error. The cursor actually changes only if the pointer focus for this device is one of the requesting client's surfaces or the surface parameter is the current pointer surface. If there was a previous surface set with this request it is replaced. If surface is NULL, the pointer image is hidden. The parameters hotspot_x and hotspot_y define the position of the pointer surface relative to the pointer location. Its top-left corner is always at (x, y) - (hotspot_x, hotspot_y), where (x, y) are the coordinates of the pointer location, in surface-local coordinates. On surface.attach requests to the pointer surface, hotspot_x and hotspot_y are decremented by the x and y parameters passed to the request. Attach must be confirmed by wl_surface.commit as usual. The hotspot can also be updated by passing the currently set pointer surface to this request with new values for hotspot_x and hotspot_y. The current and pending input regions of the wl_surface are cleared, and wl_surface.set_input_region is ignored until the wl_surface is no longer used as the cursor. When the use as a cursor ends, the current and pending input regions become undefined, and the wl_surface is unmapped. Notification that this seat's pointer is focused on a certain surface. When a seat's focus enters a surface, the pointer image is undefined and a client should respond to this event by setting an appropriate pointer image with the set_cursor request. Notification that this seat's pointer is no longer focused on a certain surface. The leave notification is sent before the enter notification for the new focus. Notification of pointer location change. The arguments surface_x and surface_y are the location relative to the focused surface. Describes the physical state of a button that produced the button event. Mouse button click and release notifications. The location of the click is given by the last motion or enter event. The time argument is a timestamp with millisecond granularity, with an undefined base. The button is a button code as defined in the Linux kernel's linux/input-event-codes.h header file, e.g. BTN_LEFT. Any 16-bit button code value is reserved for future additions to the kernel's event code list. All other button codes above 0xFFFF are currently undefined but may be used in future versions of this protocol. Describes the axis types of scroll events. Scroll and other axis notifications. For scroll events (vertical and horizontal scroll axes), the value parameter is the length of a vector along the specified axis in a coordinate space identical to those of motion events, representing a relative movement along the specified axis. For devices that support movements non-parallel to axes multiple axis events will be emitted. When applicable, for example for touch pads, the server can choose to emit scroll events where the motion vector is equivalent to a motion event vector. When applicable, a client can transform its content relative to the scroll distance. Using this request a client can tell the server that it is not going to use the pointer object anymore. This request destroys the pointer proxy object, so clients must not call wl_pointer_destroy() after using this request. Indicates the end of a set of events that logically belong together. A client is expected to accumulate the data in all events within the frame before proceeding. All wl_pointer events before a wl_pointer.frame event belong logically together. For example, in a diagonal scroll motion the compositor will send an optional wl_pointer.axis_source event, two wl_pointer.axis events (horizontal and vertical) and finally a wl_pointer.frame event. The client may use this information to calculate a diagonal vector for scrolling. When multiple wl_pointer.axis events occur within the same frame, the motion vector is the combined motion of all events. When a wl_pointer.axis and a wl_pointer.axis_stop event occur within the same frame, this indicates that axis movement in one axis has stopped but continues in the other axis. When multiple wl_pointer.axis_stop events occur within the same frame, this indicates that these axes stopped in the same instance. A wl_pointer.frame event is sent for every logical event group, even if the group only contains a single wl_pointer event. Specifically, a client may get a sequence: motion, frame, button, frame, axis, frame, axis_stop, frame. The wl_pointer.enter and wl_pointer.leave events are logical events generated by the compositor and not the hardware. These events are also grouped by a wl_pointer.frame. When a pointer moves from one surface to another, a compositor should group the wl_pointer.leave event within the same wl_pointer.frame. However, a client must not rely on wl_pointer.leave and wl_pointer.enter being in the same wl_pointer.frame. Compositor-specific policies may require the wl_pointer.leave and wl_pointer.enter event being split across multiple wl_pointer.frame groups. Describes the source types for axis events. This indicates to the client how an axis event was physically generated; a client may adjust the user interface accordingly. For example, scroll events from a "finger" source may be in a smooth coordinate space with kinetic scrolling whereas a "wheel" source may be in discrete steps of a number of lines. The "continuous" axis source is a device generating events in a continuous coordinate space, but using something other than a finger. One example for this source is button-based scrolling where the vertical motion of a device is converted to scroll events while a button is held down. The "wheel tilt" axis source indicates that the actual device is a wheel but the scroll event is not caused by a rotation but a (usually sideways) tilt of the wheel. Source information for scroll and other axes. This event does not occur on its own. It is sent before a wl_pointer.frame event and carries the source information for all events within that frame. The source specifies how this event was generated. If the source is wl_pointer.axis_source.finger, a wl_pointer.axis_stop event will be sent when the user lifts the finger off the device. If the source is wl_pointer.axis_source.wheel, wl_pointer.axis_source.wheel_tilt or wl_pointer.axis_source.continuous, a wl_pointer.axis_stop event may or may not be sent. Whether a compositor sends an axis_stop event for these sources is hardware-specific and implementation-dependent; clients must not rely on receiving an axis_stop event for these scroll sources and should treat scroll sequences from these scroll sources as unterminated by default. This event is optional. If the source is unknown for a particular axis event sequence, no event is sent. Only one wl_pointer.axis_source event is permitted per frame. The order of wl_pointer.axis_discrete and wl_pointer.axis_source is not guaranteed. Stop notification for scroll and other axes. For some wl_pointer.axis_source types, a wl_pointer.axis_stop event is sent to notify a client that the axis sequence has terminated. This enables the client to implement kinetic scrolling. See the wl_pointer.axis_source documentation for information on when this event may be generated. Any wl_pointer.axis events with the same axis_source after this event should be considered as the start of a new axis motion. The timestamp is to be interpreted identical to the timestamp in the wl_pointer.axis event. The timestamp value may be the same as a preceding wl_pointer.axis event. Discrete step information for scroll and other axes. This event carries the axis value of the wl_pointer.axis event in discrete steps (e.g. mouse wheel clicks). This event does not occur on its own, it is coupled with a wl_pointer.axis event that represents this axis value on a continuous scale. The protocol guarantees that each axis_discrete event is always followed by exactly one axis event with the same axis number within the same wl_pointer.frame. Note that the protocol allows for other events to occur between the axis_discrete and its coupled axis event, including other axis_discrete or axis events. This event is optional; continuous scrolling devices like two-finger scrolling on touchpads do not have discrete steps and do not generate this event. The discrete value carries the directional information. e.g. a value of -2 is two steps towards the negative direction of this axis. The axis number is identical to the axis number in the associated axis event. The order of wl_pointer.axis_discrete and wl_pointer.axis_source is not guaranteed. The wl_keyboard interface represents one or more keyboards associated with a seat. This specifies the format of the keymap provided to the client with the wl_keyboard.keymap event. This event provides a file descriptor to the client which can be memory-mapped to provide a keyboard mapping description. Notification that this seat's keyboard focus is on a certain surface. Notification that this seat's keyboard focus is no longer on a certain surface. The leave notification is sent before the enter notification for the new focus. Describes the physical state of a key that produced the key event. A key was pressed or released. The time argument is a timestamp with millisecond granularity, with an undefined base. Notifies clients that the modifier and/or group state has changed, and it should update its local state. Informs the client about the keyboard's repeat rate and delay. This event is sent as soon as the wl_keyboard object has been created, and is guaranteed to be received by the client before any key press event. Negative values for either rate or delay are illegal. A rate of zero will disable any repeating (regardless of the value of delay). This event can be sent later on as well with a new value if necessary, so clients should continue listening for the event past the creation of wl_keyboard. The wl_touch interface represents a touchscreen associated with a seat. Touch interactions can consist of one or more contacts. For each contact, a series of events is generated, starting with a down event, followed by zero or more motion events, and ending with an up event. Events relating to the same contact point can be identified by the ID of the sequence. A new touch point has appeared on the surface. This touch point is assigned a unique ID. Future events from this touch point reference this ID. The ID ceases to be valid after a touch up event and may be reused in the future. The touch point has disappeared. No further events will be sent for this touch point and the touch point's ID is released and may be reused in a future touch down event. A touch point has changed coordinates. Indicates the end of a set of events that logically belong together. A client is expected to accumulate the data in all events within the frame before proceeding. A wl_touch.frame terminates at least one event but otherwise no guarantee is provided about the set of events within a frame. A client must assume that any state not updated in a frame is unchanged from the previously known state. Sent if the compositor decides the touch stream is a global gesture. 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 reuse the touch point ID. Sent when a touchpoint has changed its shape. This event does not occur on its own. It is sent before a wl_touch.frame event and carries the new shape information for any previously reported, or new touch points of that frame. Other events describing the touch point such as wl_touch.down, wl_touch.motion or wl_touch.orientation may be sent within the same wl_touch.frame. A client should treat these events as a single logical touch point update. The order of wl_touch.shape, wl_touch.orientation and wl_touch.motion is not guaranteed. A wl_touch.down event is guaranteed to occur before the first wl_touch.shape event for this touch ID but both events may occur within the same wl_touch.frame. A touchpoint shape is approximated by an ellipse through the major and minor axis length. The major axis length describes the longer diameter of the ellipse, while the minor axis length describes the shorter diameter. Major and minor are orthogonal and both are specified in surface-local coordinates. The center of the ellipse is always at the touchpoint location as reported by wl_touch.down or wl_touch.move. This event is only sent by the compositor if the touch device supports shape reports. The client has to make reasonable assumptions about the shape if it did not receive this event. Sent when a touchpoint has changed its orientation. This event does not occur on its own. It is sent before a wl_touch.frame event and carries the new shape information for any previously reported, or new touch points of that frame. Other events describing the touch point such as wl_touch.down, wl_touch.motion or wl_touch.shape may be sent within the same wl_touch.frame. A client should treat these events as a single logical touch point update. The order of wl_touch.shape, wl_touch.orientation and wl_touch.motion is not guaranteed. A wl_touch.down event is guaranteed to occur before the first wl_touch.orientation event for this touch ID but both events may occur within the same wl_touch.frame. The orientation describes the clockwise angle of a touchpoint's major axis to the positive surface y-axis and is normalized to the -180 to +180 degree range. The granularity of orientation depends on the touch device, some devices only support binary rotation values between 0 and 90 degrees. This event is only sent by the compositor if the touch device supports orientation reports. An output describes part of the compositor geometry. The compositor works in the 'compositor coordinate system' and an output corresponds to a rectangular area in that space that is actually visible. This typically corresponds to a monitor that displays part of the compositor space. This object is published as global during start up, or when a monitor is hotplugged. This enumeration describes how the physical pixels on an output are laid out. This describes the transform that a compositor will apply to a surface to compensate for the rotation or mirroring of an output device. The flipped values correspond to an initial flip around a vertical axis followed by rotation. The purpose is mainly to allow clients to render accordingly and tell the compositor, so that for fullscreen surfaces, the compositor will still be able to scan out directly from client surfaces. The geometry event describes geometric properties of the output. The event is sent when binding to the output object and whenever any of the properties change. These flags describe properties of an output mode. They are used in the flags bitfield of the mode event. The mode event describes an available mode for the output. The event is sent when binding to the output object and there will always be one mode, the current mode. The event is sent again if an output changes mode, for the mode that is now current. In other words, the current mode is always the last mode that was received with the current flag set. The size of a mode is given in physical hardware units of the output device. This is not necessarily the same as the output size in the global compositor space. For instance, the output may be scaled, as described in wl_output.scale, or transformed, as described in wl_output.transform. This event is sent after all other properties have been sent after binding to the output object and after any other property changes done after that. This allows changes to the output properties to be seen as atomic, even if they happen via multiple events. This event contains scaling geometry information that is not in the geometry event. It may be sent after binding the output object or if the output scale changes later. If it is not sent, the client should assume a scale of 1. A scale larger than 1 means that the compositor will automatically scale surface buffers by this amount when rendering. This is used for very high resolution displays where applications rendering at the native resolution would be too small to be legible. It is intended that scaling aware clients track the current output of a surface, and if it is on a scaled output it should use wl_surface.set_buffer_scale with the scale of the output. That way the compositor can avoid scaling the surface, and the client can supply a higher detail image. Using this request a client can tell the server that it is not going to use the output object anymore. A region object describes an area. Region objects are used to describe the opaque and input regions of a surface. Destroy the region. This will invalidate the object ID. Add the specified rectangle to the region. Subtract the specified rectangle from the region. The global interface exposing sub-surface compositing capabilities. A wl_surface, that has sub-surfaces associated, is called the parent surface. Sub-surfaces can be arbitrarily nested and create a tree of sub-surfaces. The root surface in a tree of sub-surfaces is the main surface. The main surface cannot be a sub-surface, because sub-surfaces must always have a parent. A main surface with its sub-surfaces forms a (compound) window. For window management purposes, this set of wl_surface objects is to be considered as a single window, and it should also behave as such. The aim of sub-surfaces is to offload some of the compositing work within a window from clients to the compositor. A prime example is a video player with decorations and video in separate wl_surface objects. This should allow the compositor to pass YUV video buffer processing to dedicated overlay hardware when possible. Informs the server that the client will not be using this protocol object anymore. This does not affect any other objects, wl_subsurface objects included. Create a sub-surface interface for the given surface, and associate it with the given parent surface. This turns a plain wl_surface into a sub-surface. The to-be sub-surface must not already have another role, and it must not have an existing wl_subsurface object. Otherwise a protocol error is raised. An additional interface to a wl_surface object, which has been made a sub-surface. A sub-surface has one parent surface. A sub-surface's size and position are not limited to that of the parent. Particularly, a sub-surface is not automatically clipped to its parent's area. A sub-surface becomes mapped, when a non-NULL wl_buffer is applied and the parent surface is mapped. The order of which one happens first is irrelevant. A sub-surface is hidden if the parent becomes hidden, or if a NULL wl_buffer is applied. These rules apply recursively through the tree of surfaces. The behaviour of a wl_surface.commit request on a sub-surface depends on the sub-surface's mode. The possible modes are synchronized and desynchronized, see methods wl_subsurface.set_sync and wl_subsurface.set_desync. Synchronized mode caches the wl_surface state to be applied when the parent's state gets applied, and desynchronized mode applies the pending wl_surface state directly. A sub-surface is initially in the synchronized mode. Sub-surfaces have also other kind of state, which is managed by wl_subsurface requests, as opposed to wl_surface requests. This state includes the sub-surface position relative to the parent surface (wl_subsurface.set_position), and the stacking order of the parent and its sub-surfaces (wl_subsurface.place_above and .place_below). This state is applied when the parent surface's wl_surface state is applied, regardless of the sub-surface's mode. As the exception, set_sync and set_desync are effective immediately. The main surface can be thought to be always in desynchronized mode, since it does not have a parent in the sub-surfaces sense. Even if a sub-surface is in desynchronized mode, it will behave as in synchronized mode, if its parent surface behaves as in synchronized mode. This rule is applied recursively throughout the tree of surfaces. This means, that one can set a sub-surface into synchronized mode, and then assume that all its child and grand-child sub-surfaces are synchronized, too, without explicitly setting them. If the wl_surface associated with the wl_subsurface is destroyed, the wl_subsurface object becomes inert. Note, that destroying either object takes effect immediately. If you need to synchronize the removal of a sub-surface to the parent surface update, unmap the sub-surface first by attaching a NULL wl_buffer, update parent, and then destroy the sub-surface. If the parent wl_surface object is destroyed, the sub-surface is unmapped. The sub-surface interface is removed from the wl_surface object that was turned into a sub-surface with a wl_subcompositor.get_subsurface request. The wl_surface's association to the parent is deleted, and the wl_surface loses its role as a sub-surface. The wl_surface is unmapped. This schedules a sub-surface position change. The sub-surface will be moved so that its origin (top left corner pixel) will be at the location x, y of the parent surface coordinate system. The coordinates are not restricted to the parent surface area. Negative values are allowed. The scheduled coordinates will take effect whenever the state of the parent surface is applied. When this happens depends on whether the parent surface is in synchronized mode or not. See wl_subsurface.set_sync and wl_subsurface.set_desync for details. If more than one set_position request is invoked by the client before the commit of the parent surface, the position of a new request always replaces the scheduled position from any previous request. The initial position is 0, 0. This sub-surface is taken from the stack, and put back just above the reference surface, changing the z-order of the sub-surfaces. The reference surface must be one of the sibling surfaces, or the parent surface. Using any other surface, including this sub-surface, will cause a protocol error. The z-order is double-buffered. Requests are handled in order and applied immediately to a pending state. The final pending state is copied to the active state the next time the state of the parent surface is applied. When this happens depends on whether the parent surface is in synchronized mode or not. See wl_subsurface.set_sync and wl_subsurface.set_desync for details. A new sub-surface is initially added as the top-most in the stack of its siblings and parent. The sub-surface is placed just below the reference surface. See wl_subsurface.place_above. Change the commit behaviour of the sub-surface to synchronized mode, also described as the parent dependent mode. In synchronized mode, wl_surface.commit on a sub-surface will accumulate the committed state in a cache, but the state will not be applied and hence will not change the compositor output. The cached state is applied to the sub-surface immediately after the parent surface's state is applied. This ensures atomic updates of the parent and all its synchronized sub-surfaces. Applying the cached state will invalidate the cache, so further parent surface commits do not (re-)apply old state. See wl_subsurface for the recursive effect of this mode. Change the commit behaviour of the sub-surface to desynchronized mode, also described as independent or freely running mode. In desynchronized mode, wl_surface.commit on a sub-surface will apply the pending state directly, without caching, as happens normally with a wl_surface. Calling wl_surface.commit on the parent surface has no effect on the sub-surface's wl_surface state. This mode allows a sub-surface to be updated on its own. If cached state exists when wl_surface.commit is called in desynchronized mode, the pending state is added to the cached state, and applied as a whole. This invalidates the cache. Note: even if a sub-surface is set to desynchronized, a parent sub-surface may override it to behave as synchronized. For details, see wl_subsurface. If a surface's parent surface behaves as desynchronized, then the cached state is applied on set_desync.