path: root/XI2proto.txt

                            The X Input Extension
                                Version 2.0

                              Peter Hutterer
                         peter.hutterer@redhat.com
                               Red Hat, Inc.



1. Introduction

The X Input Extension version 2.0 (XI2) is the second major release of the X
Input Extension.

XI2 provides a number of enhancements over version 1.5, including:
- use of XGE and GenericEvents. GenericEvents are of flexible length with a
  minimum length of 32 bytes.
- explicit device hierarchy of master and slave devices. See Section 4.
- use of multiple independent master devices (Multi-Poiner X or MPX).
- the ability for devices to change capabilities at runtime.
- raw device events

XI2's intent is to replace both core input processing and prior versions of
the X Input Extension. Historically, the majority of applications employed the
core protocol requests and events to handle user input. The core protocol does
not provide information about which device generated the event. The X Input
Extension version up to 1.5 requires the differentiation between core and
extended devices. Extended devices may not be core devices and thus cannot be
used on applications employing the core protocol. XI2 addresses both of these
issues by enabling devices to be both extended and core devices and providing
device information in each event (with the exception of core events).

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2. Notations used in this document

Notation for requests:
┌───
    Name of request
        name of request field:       type of request field
        name of request field:       type of request field
        ▶
        name of reply field:         type of reply field
└───

Notation for events:
┌───
    Name of event
        name of field:               type of field
        name of field:               type of field
└───

Complex fields are specified in the following notation:
          name of field:                  COMPLEXFIELDTYPE
or, if multiple of these fields exist:
          name of field:                  LISTofCOMPLEXFIELDTYPE

COMPLEXFIELDTYPE:  { name of subfield:   type of subfield,
                    name of subfield:   type of subfield }

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3. Interoperability between version 1.x and 2.0

FIXME

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4. The Master/Slave device hierarchy

XI2 introduces a device hierarchy split up into so-called Master Devices (MD)
and Slave Devices (SD).

4.1 Master devices
An MD is a virtual device created and managed by the server. MDs may send core
events and XI events. However, an MD does not represent a physical device and
relies on SDs for event generation. MDs come in two forms: as master pointers
or as master keyboards. A master pointer is represented by a visible cursor on
the screen. A master keyboard is represented by a keyboard focus.

Each master pointer is paired with the respective master keyboard and vice
versa, and this pairing is constant for the lifetime of both input devices.
Clients can use this pairing behaviour to implement input paradigms that
require pointer and keyboard interation (e.g. SHIFT + Click).

4.2 Slave devices
An SD is usually a physical device configured in the server. SDs are not
represented by a cursor or keyboard focus and may be attached to a master
pointer or master keyboard. SDs can only be attached to any master of the same
type (e.g. a physical pointer device can be attached to any master pointer).

If an event is generated by an SD
- if the SD is attached to a master pointer, it changes the position and/or
  button state of the master pointer.
- if the SD is attached to a master keyboard, it sends events to this
  keyboard's focus window (if applicable) and/or changes the modifier state of
  this keyboard.
- if the SD is not attached to an MD ("floating"), it does not change 
  any master device. The SD has its own (invisible) sprite and its own focus.
  Both the sprite and the focus must be managed explicitly by the client
  program.

4.3 Event processing for attached slave devices

Whenever an SD changes its logical state,
- the event is delivered as an XI event to any interested clients. If the
  device is floating, event processing stops.
  Otherwise, if the device is attached,
- the master device changes its classes to reflect the SD's capabilities. All
  interested clients are notified of this device change.
- then, the event is delivered as an XI event from the MD to any interested
  clients. If the event has been delivered, event processing stops.
  Otherwise,
- the event is delivered as a core event to any interested clients.

Given that W is the event window, and P the parent window of W, event delivery
to P is only attempted if neither the XI event, nor the core event has been
delivered on W. Once an event has been delivered as either XI or core event,
event processing stops.

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5. Data types

BUTTONMASK
        A binary mask defined as (1 << button number).
        A SETofBUTTONMASK is a binary OR of zero or more BUTTONMASK.

DEVICE { DEVICEID, AllDevices, AllMasterDevices }
        A DEVICE specifies either a DEVICEID or AllDevices or
        AllMasterDevices.

DEVICEID { CARD16 }
        A DEVICEID is a numerical ID for a device currently available in the
        server. The server may re-use a device ID after a device's removal.
        The device IDs 0 and 1 are reserved.
        AllDevices ........ 0
        AllMasterDevices .. 1

DEVICEUSE { MasterPointer, MasterKeyboard, SlavePointer,
            SlaveKeyboard, FloatingSlave }
        A DEVICEUSE field specifies the current use of a device in the MD/SD
        device hierarchy. See Section 4 for more information.

EVENTMASK
        An EVENTMASK is a binary mask defined as (1 << event type).
        A SETofEVENTMASK is a binary OR of zero or more EVENTMASK.

FP1616
        Fixed point decimal in 16.16 format as one INT16 and one CARD16.
        The INT16 contains the integral part, the CARD32 the decimal fraction
        shifted by 16.

FP3232
        Fixed point decimal in 32.32 format as one INT32 and one CARD32.
        The INT32 contains the integral part, the CARD32 the decimal fraction
        shifted by 32.

VALUATORMASK
        A binary mask defined as (1 << valuator number).
        A SETofVALUATORMASK is a binary OR of zero or more VALUATORMASK.

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6. Errors

Errors are sent using core X error reports.

Device
        A value for a DEVICE argument does not specify a valid DEVICE.

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7. Requests:

The server does not guarantee that the length of a reply remains constant in
future revisions of XI2. A client must always retrieve the exact length of the
protocol reply from the connection, even if the reply is longer than defined
for the XI2 version supported by the client.
Additional bytes in a request may include data supported in later versions of
XI2. Clients should ignore this data.

7.1 Requests introduced in version 2.0

    ┌───
        XIQueryVersion
        major_version:          CARD16
        minor_version:          CARD16
        ▶
        major_version:          CARD16
        minor_version:          CARD16
    └───

    The client sends the highest supported version to the server and the
    server sends the highest version it supports, but no higher than the
    requested version. Major versions changes can introduce incompatibilities
    in existing functionality, minor version changes introduce only backward
    compatible changes.  It is the clients responsibility to ensure that the
    server supports a version which is compatible with its expectations.

    major_version
        Major XI2 version.
    minor_version
        Minor XI2 version.

    ┌───
        XIQueryDevice
        DEVICE                  deviceid
        ▶
        num_devices:            CARD16
        deviceinfo:             LISTofDEVICEINFO
    └───

    DEVICEINFO { deviceid:              DEVICEID
                 use:                   DEVICEUSE
                 attachment:            DEVICEID
                 enabled:               BOOL
                 num_classes:           CARD16
                 name_len:              CARD16
                 name:                  LISTofCHAR8
                 classes:               LISTofCLASS }

    CLASS { BUTTONCLASS KEYCLASS, AXISCLASS }

    BUTTONCLASS { type:                 ButtonClass
                  length:               CARD16
                  num_buttons:          CARD16
                  buttons:              LISTofATOM }

    KEYCLASS    { type:                 KeyClass
                  length:               CARD16
                  num_keys:             CARD16
                  keys:                 LISTofCARD32 }

    AXISCLASS   { type:                 AxisClass
                  length:               CARD16
                  axisnumber:           CARD16
                  axisname:             ATOM
                  min:                  FP3232
                  max:                  FP3232
                  resolution:           CARD32 }

    XIQueryDevices details information about the requested input devices.

    devices
        The device to list. If 'devices' is AllDevices, all enabled and
        disabled devices are listed. If 'devices' is AllMasterDevices, all
        enabled and disabled master devices are listed. If 'devices' is a
        valid DEVICE, only this DEVICE is listed and 'num_devices' is 1.
    num_devices
        The number of 'deviceinfos' returned.

    Each 'deviceinfo' is detailed as follows:
    deviceid
        The unique ID of the device. Device IDs may get re-used when a device
        is removed.
    use
        If the device is a master pointer, 'use' is MasterPointer.
        If the device is a master keyboard, 'use' is MasterKeyboard.
        If the device is a slave pointer, 'use' is SlavePointer.
        If the device is a slave keyboard, 'use' is SlaveKeyboard.
        If the device is a floating slave, 'use' is FloatingSlave.

    attachment
        If the device is a master pointer or a master keyboard, 'attachment'
        specifies the paired master keyboard, or the paired master pointer,
        respectively.  If the device is a non-floating slave device
        'attachment' specifies the master device this device is attached to.
        If the device is a floating slave, 'attachment' is undefined.

    enabled
        Zero if the device is disabled, non-zero otherwise.
    num_classes
        Number of 'classes' provided.
    name_len
        Length of the name in bytes.
    classes
        Details the available classes provided by the device in an undefined
        order.
    name
        The device's name, padded to a multiple of 4 bytes.

    For all classes, 'type' specifies the device class. Clients are required
    to ignore unknown device classes. The 'length' field specifies the length
    of the class in 4 byte units.
    The following classes may occur only once: ButtonClass, KeyClass

    ButtonClass:
    type
        Always ButtonClass.
    length
        Length in 4 byte units.
    num_buttons
        Number of buttons provided by the device.
    buttons
        List of Atoms specifying the type of each button. An atom of None
        specifies an unnamed button. Buttons are listed in the device-native
        order and potential button mappings are ignored.

    KeyClass:
    type
        Always KeyClass.
    length
        Length in 4 byte units.
    num_keys
        Number of keycodes provided by the device.
    keys
        List of keycodes provided.

    AxisClass:
    type
        Always AxisClass.
    length
        Length in 4 byte units.
    axisnumber
        Axis number of this axis. The axis number is in device-native
        order and potential axis mappings are ignored.
    axisname
        Atom specifying the axis name. An Atom of None specifies an unnamed
        axis.
    min
        Minimum value.
    max
        Minimum value.
    resolution
        Resolution in counts/meter.
    mode
        Relative or Absolute.

    An axis in Relative mode may specify 'min' and 'max' as a hint to the
    client. If no 'min' and 'max' information is available, both must be 0.

    ┌───
        XISelectEvents
            window:         Window
            num_masks:      CARD16
            masks:          LISTofEVENTMASK

    └───

    EVENTMASK { deviceid:          DEVICE,
                mask_len:          CARD16,
                mask:              SETofEVENTMASK

    window
        The window to select the events on.
    num_masks
        Number of items in mask.
    deviceid
        Numerical deviceid, or AllDevices, or AllMasterDevices.
    mask_len
        Length of mask in 4 byte units.
    mask
        Event mask. An event mask for an event type T is defined as (1 << T).

    XISelectEvents selects for XI2 events on 'window'.

    If 'num_masks' is 0, a BadValue error occurs.

    Each 'mask' sets the (and overwrites a previous) event mask for the DEVICE
    specified through 'deviceid'. The device 'AllDevices' or
    'AllMasterDevices' is treated as a separate device by server. A client's
    event mask is the union of 'AllDevices', 'AllMasterDevices' and the
    per-device event mask.
    The removal of device from the server unsets the event masks for the
    device. If an event mask is set for AllDevices or AllMasterDevices, the
    event mask is not cleared on device removal and affects all future
    devices.

    If 'mask_len' is 0, the event mask for the given device is cleared.

    ┌───
        XIQueryPointer
            window:         Window
            deviceid:       DEVICEID
            ▶
            root:           Window
            child:          Window
            root_x:         FP1616
            root_y:         FP1616
            win_x:          FP1616
            win_y:          FP1616
            same_screen:    BOOL
            mods:           MODIFIERINFO
            group:          GROUPINFO
            buttons_len:    CARD16
            buttons:        SETofBUTTONMASK
    └───

    Query a master pointer device for its current position.

    root
        The root window the pointer is logically on.
    child
        The child window of 'window' that contains the pointer or None.
    root_x
    root_y
        Pointer position relative to the root window's origin.
    win_x
    win_y
        Pointer position relative to 'window' or 0 if 'same_screen' is false.
    same_screen
        TRUE if 'window' is on the same screen as the pointer.
    mods
        XKB modifier state on the paired device.
    group
        XKB group state on the paired device.
    buttons_len
        The length of 'buttons' in 4 byte units.
    buttons
        Button state.

    ┌───
        XIWarpPointer
            src_win:         Window
            dst_win:         Window
            src_x:           FP1616
            src_y:           FP1616
            src_width:       INT16
            src_height:      INT16
            dst_x:           FP1616
            dst_y:           FP1616
            deviceid:        DEVICEID
    └───

    WarpPointer moves the pointer of 'deviceid' as if the user had moved
    the pointer. WarpPointer can only be called for MasterPointer and
    FloatingSlave devices.

    src_win
       If src_window is not None, the move only takes place if src_window
       contains the pointer and the pointer is contained in the specified
       rectangle of src_window.
    dst_win
       If dst_win is None, this request moves the pointer by offsets
       'dst_x'/'dst_y' relative to the current position of the pointer. If
        dst_window is a window, this request moves the pointer to
       'dst_x'/'dst_y' relative to dst_win's origin.
    src_x
    src_y
    src_width
    src_height
       Specifies the source window rectangle.
    dst_x
    dst_y
        The relative coordinates to move the pointer if 'dst_win' is None, or
        the absolute coordinates if 'dst_win' is a window.
    deviceid
        The device to warp.

    This request cannot be used to move the pointer outside the confine-to
    window of an active pointer grab. An attempt will only move the pointer as
    far as the closest edge of the confine-to window.

    This request will generate events just as if the user had instantaneously
    moved the pointer.

    ┌───
        XIChangeCursor
            win:             Window
            cursor:          Cursor
            deviceid:        DEVICEID
    └───

    Change a master pointer's cursor on the specified window.

    window
        The window.
    cursor
        The new cursor or None.
    deviceid
        The master pointer device.

    Whenever 'device' enters a window W, the cursor shape is selected in the
    following order:
    - if the current window has a device cursor C(d) defined for 'device',
      display this cursor C(d).
    - otherwise, if the current window has a cursor C(w) defined in the core
      protocol's window attributes, display cursor C(w).
    - repeat on parent window until a cursor has been found.

    ┌───
        XIChangeHierarchy
            num_changes:     CARD8
            changes:         LISTofHIERARCHYCHANGES
    └───

    HIERARCHYCHANGE { CREATEMASTER, REMOVEMASTER, ATTACHSLAVE, DETACHSLAVE }

    HIERARCHYCHANGETYPE { CreateMaster, RemoveMaster, AttachSlave, DetachSlave }

    CHANGEMODE { Float, Attach }

    CREATEMASTER { type:        HIERARCHYCHANGETYPE
                   length:      CARD16
                   name_len:    CARD16
                   send_core:   BOOL
                   enable:      BOOL
                   name:        LISTofCHAR8 }

    REMOVEMASTER { type:            HIERARCHYCHANGETYPE
                   length:          CARD16
                   deviceid:        DEVICEID
                   return_mode:     CHANGEMODE
                   return_pointer:  DEVICEID
                   return_keyboard: DEVICEID }

    ATTACHSLAVE   { type:        HIERARCHYCHANGETYPE
                    length:      CARD16
                    deviceid:    DEVICEID
                    master:      DEVICEID }

    DETACHSLAVE { type:       HIERARCHYCHANGETYPE
                  length:     CARD16
                  deviceid:   DEVICEID }

    XIChangeHierarchy allows a client to modify the MD/SD device
    hierarchy (see Section 4).

    num_changes
        The number of changes to apply to the current hierarchy.
    changes
        The list of changes.

    The server processes the changes one by one and applies changes
    immediately. If an error occurs, processing stops at the current change
    and returns the number of successfully applied changes in the error.

    CREATEMASTER creates a pair of master devices.
    type
        Always CreateMaster.
    length
        Length in 4 byte units.
    name_len
        Length of 'name' in bytes.
    send_core
        TRUE if the device should send core events.
    enable
        TRUE if the device is to be enabled immediately.
    name
        The name for the new master devices. The master pointer's name is
        automatically appended with " pointer", the master keyboard's name is
        automatically appended with " keyboard".

    REMOVEMASTER removes an existing master device.
    type
        Always RemoveMaster.
    length
        Length in 4 byte units.
    deviceid
        The device to remove.
    return_mode
        Return mode for attached slave devices.
        If 'return_mode' is Float, all slave devices are set to floating.
        If 'return_mode' is Attach, slave pointers are attached to
        'return_pointer' and slave keyboards are attached to
        'return_keyboard'.
    return_pointer
    return_keyboard
        The master pointer and master keyboard to attach slave devices to, if
        'return_mode' is Attach.

    Removing a master pointer removes the paired master keyboard and vice
    versa.

    ATTACHSLAVE attaches a slave device to a given master device.
    type
        Always ChangeAttachment.
    length
        Length in 4 byte units.
    deviceid
        Deviceid of the slave device.
    master
        The new master device to attach this slave device to.

    DETACHSLAVE detaches a slave device from its current master device.
    type
        Always ChangeAttachment.
    length
        Length in 4 byte units.
    deviceid
        Deviceid of the slave device.

    ┌───
        XISetClientPointer
            win:             Window
            deviceid:        DEVICEID
    └───

    Set the ClientPointer for the client owning 'win' to the given device.

    win
         Window or client ID.
    deviceid
         The master pointer or master keyboard that acts as ClientPointer.

    Some protocol requests are ambiguous and the server has to choose a device
    to provide data for a request or a reply. By default, the server will
    choose a client's ClientPointer device to provide the data, unless the
    client currently has a grab on another device.

    ┌───
        XIGetClientPointer
            win:             Window
            ▶
            set:             BOOL
            deviceid:        DEVICEID
    └───

    Query the ClientPointer for the client owning 'win'.

    win
        The window or client ID.
    set
        TRUE if the client has an explicitly set ClientPointer.
    deviceid
        The master pointer that acts as a ClientPointer if 'set' is TRUE.

    ┌───
        XISetFocus
            focus:           Window
            deviceid:        DEVICEID
            time:            Time
    └───

    Set the focus for the given device to the given window. Future key events
    from this device are sent to this window.
    This request generates FocusIn and FocusOut events.

    focus
        A viewable window or None.
    deviceid
        The device to modify the focus window for.
    time
        Specifies the time to change the focus or CurrentTime.

    If focus is None, key events from this device are discarded until a new
    focus window is set. If focus is a viewable window, key events from this
    device are sent to this window. If the window becomes unviewable, the
    window's first viewable ancestor automatically becomes the focus window
    and FocusIn and FocusOut events are sent as if a client had changed the
    focus window.
    This is equivalent to RevertToParent in the core XSetInputFocus window.

    This request has no effect if the specified time is earlier than the
    current last-focus-change time or is later than the current X server time.
    Otherwise, the last-focus-change time is set to the specified time.

    ┌───
        XIGetFocus
            deviceid:        DEVICEID
            ▶
            focus:           Window
    └───

    Return the current focus window for the given device.

    ┌───
        XIGrabDevice
            deviceid:        DEVICEID
            grab_window:     Window
            owner_events:    BOOL
            grab_mode:       { Synchronous, Asynchronous }
            paired_device_mode: { Synchronous, Asynchronous }
            time:            TIMESTAMP or CurrentTime
            cursor:          Cursor
            mask_len:        CARD16
            masks:           SETofEVENTMASK
            ▶
            status:          Success, AlreadyGrabbed, Frozen, InvalidTime, NotViewable
    └───

    This request actively grabs control of the specified input device. Further
    input events from this device are reported only to the grabbing client.
    This request overides any previous active grab by this client for this
    device.

    deviceid
        The device to grab.
    grab_window
        Events are reported relative to the grab window.
    owner_events
        Specifies whether event will be reported normally or relative to the
        grab window.
    grab_mode
        Specifies if this device will be frozen as a result of the grab.
    paired_device_mode
        Specifies if the master device paired with this device will be frozen
        as a result of the grab.
    time
        A valid server time or CurrentTime.
    cursor
        The cursor to display for the duration of the grab or None.
    mask_len
        Length of mask in 4 byte units.
    mask
        Event mask. An event mask for an event type T is defined as (1 << T).
    status
        Success or the reason why the grab could not be established.


    The masks parameter specifies which events the client wishes to receive
    while the device is grabbed.

    If owner-events is False, input events generated from this device are
    reported with respect to grab-window, and are only reported if selected by
    being included in the event-list.  If owner-events is True, then if a
    generated event would normally be reported to this client, it is reported
    normally, otherwise the event is reported with respect to the grab-window,
    and is only reported if selected by being included in the event-list. For
    either value of owner-events, unreported events are discarded.

    If grab-mode is Asynchronous, device event processing continues normally.
    If the device is currently frozen by this client, then processing of
    device events is resumed. If grab-mode is Synchronous, the state of the
    grabbed device (as seen by means of the protocol) appears to freeze,
    and no further device events are generated by the server until the
    grabbing client issues a releasing XIAllowEvents request or until the
    device grab is released. Actual device input events are not lost while the
    device is frozen; they are simply queued for later processing.

    If the device is a slave device, the paired-device-mode is ignored.
    Otherwise, if this device is a master device and paired-device-mode is
    Asynchronous, event processing is unaffected by activation of the grab. If
    this device is a master device and paired-device-mode is Synchronous, the
    state of the master device paired with this device (as seen by means of the
    protocol) appears to freeze, and no further events are generated by the
    server until the grabbing client issues a releasing XIAllowEvents request
    or until the device grab is released. Actual events are not lost while the
    devices are frozen; they are simply queued for later processing.

    If the cursor is not None and the device is a master pointer device, the
    cursor will be displayed until the device is ungrabbed.

    This request fails and returns:
    AlreadyGrabbed: If the device is actively grabbed by some other client.
    NotViewable: If grab-window is not viewable.
    InvalidTime: If the specified time is earlier than the last-grab-time for
                 the specified device or later than the current X server time.
                 Otherwise, the last-grab-time for the specified device is set
                 to the specified time and CurrentTime is replaced by the
                 current X server time.
    Frozen: If the device is frozen by an active grab of another client.

    To release a grab of a device, use XIUngrabDevice.

    ┌───
        XIUngrabDevice
            deviceid:        DEVICEID
            time:            TIMESTAMP or CurrentTime
    └───

    This request releases the device if this client has it actively grabbed
    (from either XIGrabDevice,  XIGrabDeviceKey or XIGrabDeviceButton) and
    releases any queued events. If any devices were frozen by the grab,
    XIUngrabDevice thaws them.

    deviceid
        The device to grab.
    time
        A valid server time or CurrentTime.

    The request has no effect if the specified time is earlier
    than the last-device-grab time or is later than the current server time.
    This request generates FocusIn and FocusOut events.
    An XIUngrabDevice is performed automatically if the event window for an
    active device grab becomes not viewable.

    ┌───
        XIAllowEvents:
            deviceid:        DEVICEID
            time:            TIMESTAMP or CurrentTime
            event_mode:      { AsyncDevice, SyncDevice,
                               AsyncPairedDevice, SyncPairedDevice,
                               ReplayDevice, AsyncPair, SyncPair }
    └───

    The XIAllowEvents request releases some queued events if the client
    has caused a device to freeze.

    deviceid
        The device to grab.
    time
        A valid server time or CurrentTime.
    event_mode
        Specifies whether a device is to be thawed and events are to be
        replayed.

    The request has no effect if the specified time is earlier than the
    last-grab time of the most recent active grab for the client, or if the
    specified time is later than the current X server time.

    The following describes the processing that occurs depending on what constant
    you pass to the event-mode argument:
    AsyncDevice:
        If the specified device is frozen by the client, event processing for that
        device continues as usual. If the device is frozen multiple times  by the
        client on behalf of multiple separate grabs, AsyncDevice thaws for
        all.
        AsyncDevice has no effect if the specified device is not frozen by the
        client, but the device need not be grabbed by the client.
    SyncDevice:
        If the specified device is frozen and actively grabbed by the client,
        event processing for that device continues normally until the next
        event is reported to the client. At this time, the specified device
        again appears to freeze. However, if the reported event causes the
        grab to be released, the specified device does not freeze.
        SyncDevice has no effect if the specified device is not frozen by the
        client or is not grabbed by the client.
     ReplayDevice:
        If the specified device is actively grabbed by the client and is frozen
        as the result of an event having been sent to the client (either from
        the activation of a XIGrabButton or from a previous XIAllowEvents with
        mode SyncDevice, but not from a Grab), the grab is released and
        that event is completely reprocessed.  This time, however, the request
        ignores any passive grabs at or above (towards the root) the
        grab-window of the grab just released.
        The request has no effect if the specified device is not grabbed by
        the client or if it is not frozen as the result of an event.
     AsyncPairedDevice
        If the paired master device is frozen by the client, event processing
        for it continues as usual. If the paired device is frozen multiple
        times by the client on behalf of multiple separate grabs,
        AsyncPairedDevice thaws for all.
        AsyncPairedDevice has no effect if the device is not frozen by the
        client, but those devices need not be grabbed by the client.
        AsyncPairedDevice has no effect if deviceid specifies a slave device.
     SyncPairedDevice
        If the paired master device is frozen by the client, event processing (for
        the paired master device) continues normally until the next button or key
        event is reported to the client for the grabbed device (button event for
        the grabbed device, key or motion event for the device), at which time
        the device again appears to freeze. However, if the reported event causes
        the grab to be released, then the device does not freeze.
        SyncPairedDevice has no effect if the specified device is not grabbed
        by the client or if it is no frozen as the result of an event.
        SyncPairedDevice has no effect if deviceid specifies a slave device.
     SyncPair
        If both the device and the paired master device are frozen by the
        client, event processing (for both devices) continues normally until
        the next XIButtonPress, XIButtonRelease, XIKeyPress, or XIKeyRelease
        event is reported to the client for a grabbed device (button event for
        a pointer, key event for a keyboard), at which time the devices again
        appear to freeze. However, if the reported event causes the grab to be
        released, then the devices do not freeze (but if the other device is
        still grabbed, then a subsequent event for it will still cause both
        devices to freeze).
        SyncPair has no effect unless both the device and the paired master
        device are frozen by the client. If the device or paired master device
        is frozen twice by the client on behalf of two separate grabs,
        SyncPair thaws for both (but a subsequent freeze for SyncPair will
        only freeze each device once).
        SyncPair has no effect if deviceid specifies a slave device.
     AsyncPair
        If the device and the paired master device are frozen by the client,
        event processing for both devices continues normally. If a device is
        frozen twice by the client on behalf of two separate grabs, AsyncBoth
        thaws for both. AsyncPair has no effect unless both the device and the
        paired master device frozen by the client.
        AsyncPair has no effect if deviceid specifies a slave device.

    ┌───
        XIPassiveGrabDevice
            deviceid:        DEVICEID
            detail:          CARD32
            grab_type:       { GrabtypeButton, GrabtypeKeysym }
            grab_window:     Window
            cursor:          Cursor
            owner_events:    Bool
            grab_mode:       { Synchronous, Asynchronous }
            paired_device_mode: { Synchronous, Asynchronous }
            num_modifiers:   INT16
            mask_len:        CARD16
            masks:           SETofEVENTMASK
            modifiers:       CARD32 or GrabAnyModifier
            ▶
            num_modifiers_return:    INT16
            modifiers_return:        GRABMODIFIERINFO
    └───

        GRABMODIFIERINFO {   status:    Access
                             modifiers: CARD32 }

        Establish an explicit passive grab for a button or keysym
        on the specified input device.

        cursor
            The cursor to display for the duration of the grab. If grab_type
            is not GrabtypeButton, this argument is ignored.
        deviceid
            The device to establish the passive grab on.
        detail
            The button number, or key symbol to grab for.
        grab_type
            The type of grab to establish.
        grab_window
            Events are reported relative to the grab window.
        grab_mode
            If grab-mode is Asynchronous, device event processing continues
            normally.  If the device is currently frozen by this client, then
            processing of device events is resumed. If grab-mode is
            Synchronous, the state of the grabbed device (as seen by means of
            the protocol) appears to freeze, and no further device events are
            generated by the server until the grabbing client issues a
            releasing XIAllowEvents request or until the device grab is
            released. Actual device input events are not lost while the device
            is frozen; they are simply queued for later processing.
        mask_len
            Length of mask in 4 byte units.
        mask
            Event mask. An event mask for an event type T is defined as (1 << T).
        modifiers
            XKB modifier state to activate this passive grab.
        num_modifiers
            Number of elements in modifiers.
        owner_events
            Specifies whether event will be reported normally or relative to the
            grab window.
        num_modifiers_return
            Number of elements in modifiers_return
        modifiers_return
            XKB modifier state that could not be grabbed.

        If owner-events is False, input events generated from this device are
        reported with respect to grab-window, and are only reported if
        selected by being included in the event-list.  If owner-events is
        True, then if a generated event would normally be reported to this
        client, it is reported normally, otherwise the event is reported
        with respect to the grab-window, and is only reported if selected
        by being included in the event-list. For either value of
        owner-events, unreported events are discarded.

        In the future, the device is actively grabbed if:
        - the device is not grabbed, and
        - the specified modifier keys are down, and
        - the grab_type is GrabtypeButton and the button specified in detail
          is logically pressed or the grab_type is GrabtypeKeysym and the
          keysym specified in detail is logically pressed, and
        - the grab_window contains the pointer, and
        - a passive grab on the same button/keysym + modifier
          combination does not exist on an ancestor of grab_window.

        A modifier of GrabAnyModifier is equivalent to issuing the request for
        all possible modifier combinations (including no modifiers). A client
        may request a grab for GrabAnyModifier and explicit modifier
        combinations in the same request.

        The grab is released when all buttons or keysyms are
        released, independent of the state of modifier keys. Note that the
        logical state of a device (as seen by means of the protocol) may lag
        the physical state if device event processing is frozen.
        This request overrides all previous passive grabs by the same client
        on the same button/key combinations on the same window.

        If some other client already has issued a XIPassiveGrabDevice request
        with the same button or keysym and modifier combination, the
        failed modifier combinations is returned in modifiers_return. If
        num_modifiers_return is zero, all passive grabs have been successful.

    ┌───
        XIPassiveUngrabDevice
            deviceid:        DEVICEID
            detail:          CARD32
            grab_type:       { ButtonGrab, KeycodeGrab, KeysymGrab }
            grab_window:     Window
            num_modifiers:   INT16
            modifiers:       MODIFIERINFO
    └───

        Release an explicit passive grab for a button or keysym on
        the specified input device.

        deviceid
            The device to establish the passive grab on.
        detail
            The button number or key symbol to ungrab.
        grab_type
            The type of grab to establish.
        grab_window
            Events are reported relative to the grab window.
        modifiers
            XKB modifier state to activate this passive grab.
        num_modifiers
            Number of elements in modifiers.

        This request has no effect if the matching button or keysym and
        modifier combination is not grabbed b this client.

    ┌───
        XIListProperties
            deviceid:        DEVICEID
            ▶
            num_properties:  INT16
            properties:      LISTofATOM
    └───

        List the properties associated with the given device.

        deviceid
            The device to list the properties for.
        num_atoms
            Number of atoms in the reply
        atoms
            All properties on the device.

    ┌───
        XIChangeProperty
            deviceid:        DEVICEID
            property:        ATOM
            type:            ATOM
            format:          { 8, 16, 32 }
            mode:            { Append, Prepend, Replace }
            num_items:       CARD32
            data:            LISTofINT8, or LISTofINT16, or LISTofINT32
    └───

        Change the given property on the given device.

        deviceid
            The device to change the property on.
        property
            The property to modify.
        type
            The property's type.
        mode
            One of Append, Prepend, or Replace
        num_items
            Number of items following this request.
        data
            Property data (nitems * format/8 bytes)

        The type is uninterpreted by the server. The format specifies whether
        the data should be viewed as a list of 8-bit, 16-bit, or 32-bit
        quantities so that the server can correctly byte-swap as necessary.

        If the mode is Replace, the previous propert y value is discarded.  If
        the mode is Prepend or Append, then the type and format must match the
        existing property value (or a Match error results). If the property is
        undefined, it is treated as defined with the correct type and format
        with zero-length data. For Prepend, the data is tacked on to the
        beginning of the existing data, and for Append, it is tacked on to the
        end of the existing data.

        The lifetime of a property is not tied to the storing client. Properties
        remain until explicitly deleted, until the device is removed, or
        until server reset.

        A property cannot be deleted by setting nitems to zero. To delete a
        property, use XIDeleteDeviceProperty.

        This request generates an XIPropertyEvent.

    ┌───
        XIDeleteProperty
            deviceid:        DEVICEID
            property:        ATOM
    └───

        Deletes the given property on the given device.

        deviceid
            The device to delete the property on.
        property
            The property to delete.

        If the property is deleted, an XIPropertyEvent is generated on the device.
        If the property does not exist, this request does nothing.

    ┌───
        XIGetProperty
            deviceid:        DEVICEID
            property:        ATOM
            type:            Atom or AnyPropertyType
            offset:          CARD32
            len:             CARD32
            delete:          BOOL
            ▶
            type:            Atom
            bytes_after:     CARD32
            num_items:       CARD32
            format:          { 8, 16, 32 }
            data:            LISTofINT8, or LISTofINT16, or LISTofINT32
    └───
        
        Get the data for the given property on the given device.

        deviceid
            The device to retrieve the property data from.
        property
            The property to retrieve the data from..
        type
            The property type to retrieve or AnyPropertyType
        offset
            The offset in 4-byte units.
        len
            Number of bytes to receive in 4-byte units.
        delete
            Delete the property after retrieving the data.
        bytes_after
            Number of unread bytes in the stored property
        num_items
            Number of items in data
        format
            8, 16, or 32
        data
            Property data (nitems * format/8 bytes)

        If the specified property does not exist for the specified device, then
        the return type is None, the format and bytes-after are zero, and the value is
        empty. The delete argument is ignored in this case. If the specified property
        exists but its type does not match the specified type, then the return
        type is the actual type of the property, the format is the actual format of the
        property (never zero), the bytes-after is the length of the property in bytes
        (even if the format is 16 or 32), and the value is empty. The delete
        argument is ignored in this case. If the specified property exists and
        either AnyPropertyType is specified or the specified type matches the actual
        type of the property, then the return type is the actual type of the property,
        the format is the actual format of the property
        (never zero), and the bytes-after and value are as follows, given:
                 N = actual length of the stored property in bytes
                    (even if the format is 16 or 32)
                 I = 4 * long-offset
                 T = N−I
                 L = MINIMUM(T, 4 * long-length)
                 A = N − (I + L)
        The returned value starts at byte index I in the property (indexing
        from 0), and its length in bytes is L. However, it is a Value error if
        offset is given such that L is negative. The value of bytes_after is A,
        giving the number of trailing unread bytes in the stored property. If
        delete is True and the bytes_after is zero, the property is also
        deleted from the device, and a XIPropertyNotify event is generated on
        the device.  
     

8. Events:

An event specifies its length in 4-byte units after the initial 32 bytes.
Future versions of the protocol may provide additional information
in the same event, thus increasing the event size. Clients are required to
always read the number of bytes specified by the event, not the size of the
event they may have been compiled against.


The following event types are available in XI2.

Version 2.0:
        HierarchyChanged
        DeviceChanged
        KeyPress
        KeyRelease
        ButtonPress
        ButtonRelease
        Motion
        RawEvent
        Enter
        Leave

All events have a set of common fields specified as EVENTHEADER.


EVENTHEADER { type:                       BYTE
              extension:                  BYTE
              sequenceNumber:             CARD16
              length:                     CARD32
              evtype:                     CARD16
              deviceid:                   DEVICEID
              time:                       Time }

    type
        Always GenericEvent.
    extension
        Always the X Input extension offset.
    sequenceNumber
        Sequence number of last request processed by the server.
    length
        Length in 4-byte units after the initial 32 bytes.
    evtype
        XI-specific event type.
    deviceid
        Numerical device id for a device.
    time
        Time in ms.


    ┌───
        HierarchyEvent:
            EVENTHEADER
            flags:                      SETofHIERARCHYMASK
            num_devices:                CARD16
            deviceinfo:                 LISTofHIERARCHYINFO
    └───


    HIERARCHYMASK { MasterAdded, MasterRemoved, SlaveAttached, SlaveDetached,
                    SlaveAdded, SlaveRemoved, DeviceEnabled, DeviceDisabled }

    HIERARCHYINFO { deviceid:           DEVICEID,
                    attachment:         DEVICEID,
                    type:               DEVICEUSE
                    enabled:            BOOL
                    flags:              SETofHIERARCHYMASK}

    flags
        Set of the changes that have occured, causing this event.
    num_devices
        The number of devices present in the hierarchy.
    devices
        The current hierarchy layout for each device.

    An XIHierarchyEvent is sent whenever the device hierarchy been
    changed. The 'flags' specify all types of hierarchy modifiations that have
    occured.
    For all devices, 'deviceinfo' details the hierarchy information after the
    modification of the hierarchy has occured. For each device specified with
    'deviceid':
    - if 'type' is MasterPointer or MasterKeyboard, 'attachment' decribes the
      pairing of this device.
    - if 'type' is SlavePointer or SlaveKeyboard, 'attachment' describes the
      master device this device is attached to.
    - if 'type' is FloatingSlave device, 'attachment' is undefined.

    enabled
         TRUE if the device is enabled and can send events. A disabled master
         device will not forward events from an attached, enabled slave
         device.

    Note: Multiple devices may be affected in one hierarchy change,
    'deviceid' in an XIHierarchyEvent is always the first affected
    device. Clients should ignore deviceid and instead use the 'devices' list.

    ┌───
        DeviceChangedEvent:
            EVENTHEADER
            reason:                CHANGEREASON
            source:                DEVICEID
            num_classes:           CARD16
            classes:               LISTofCLASS
    └───

    CHANGEREASON { SlaveSwitch, DeviceChange }

    A DeviceChangeEvent is sent whenever a device changes it's capabilities.
    This can happen either by a new slave device sending events through a
    master device, or by a physical device changing capabilities at runtime.

    reason
        The reason for generating this event.
        If 'reason' is SlaveSwitch, the slave device sending events through
        this device has changed and 'source' specifies the new slave device.
        A SlaveSwitch 'reason' can only occur on a master device.
        If 'reason' is DeviceChange, the device itself has changed through
        other means (e.g. a physical device change) and 'source' is
        undefined. A DeviceChange can only occur on a slave device.
    source
        The source of the new classes. Only defined in 'reason' is
        SlaveSwitch.
    num_classes
        Number of 'classes' provided.
    classes
        Details the available classes provided by the device.  The order the
        classes are provided in is undefined.

    For a detailed description of 'classes', see the XQueryInputDevice
    request.

    ┌───
        DeviceEvent:
            EVENTHEADER
            detail:                     CARD32
            root:                       Window
            event:                      Window
            child:                      Window
            root_x:                     FP1616
            root_y:                     FP1616
            event_x:                    FP1616
            event_y:                    FP1616
            buttons_len:                CARD16
            valuators_len:              CARD16
            sourceid:                   DEVICEID
            mods:                       MODIFIERINFO
            group:                      GROUPINFO
            buttons:                    SETofBUTTONMASK
            valuators:                  SETofVALUATORMASK
            axisvalues:                 LISTofFP3232
    └───

    BUTTONBIT { (1 << Button1), (1 << Button2), ... , (1 << ButtonN) }
    VALUATORBIT { (1 << 1), ( 1 << 2), ... ( 1 << n) }

    MODIFIERINFO  { base_mods:           CARD32,
                    latched_mods:        CARD32,
                    locked_mods:         CARD32}
    GROUPINFO     { base_group:          CARD8,
                    latched_group:       CARD8,
                    locked_group:        CARD8 }

    An XIDeviceEvent is generated whenever the logical state of a device
    changes in response to a button press, a button release, a motion, a key
    press or a key release.

    detail
        The button number or key code, or 0.
    root
    event
    child
        The root window, event window or subwindow, respectively. See core
        protocol specification for more detail.
    root_x
    root_y
        The position of the pointer in screen coordinates (16.16 fixed point).
    event_x
    event_y
        The position of the pointer in screen coordinates relative to the
        event window (16.16 fixed point).

    buttons_len
        The length of 'buttons' in 4 byte units.
    valuators_len
        The length of 'valuators' in 4 byte units.
    sourceid
        The source device that originally generated the event.
    mods
        XKB modifier state before the event occured.
    group
        XKB group state before the event.
    buttons
        Button state before the event.
    valuators
        Bitmask of valuators provided in 'axisvalues'.
    axisvalues
        Valuator data in device-native resolution.

    Modifier state in 'mods' is detailed as follows:
    base_mods
        XKB base modifier state.
    latched_mods
        XKB latched modifier state.
    locked_mods
        XKB locked modifier state.

    Group state in 'group' is detailed as follows:
    base_group
        XKB base group state.
    latched_group
        XKB latched group state.
    locked_group
        XKB locked group state.

    ┌───
        RawEvent
            EVENTHEADER
            eventtype:                 RAWTYPE
            detail:                    CARD32
            valuators_len:             CARD16
            valuators:                 SETofVALUATORMASK
            axisvalues:                LISTofFP3232
            axisvalues_raw:            LISTofFP3232
    └───

    RAWTYPE { Motion, KeyPress, KeyRelease, ButtonPress, ButtonRelease }

    A RawDevice event provides the information provided by the driver to the
    client. RawDevice events are only generated for slave devices and provide
    both the raw data as supplied by the driver and transformed data as used
    in the server. Transformations include, but are not limited to, axis
    clipping and acceleration.
    Transformed valuator data may be equivalent to raw data. In this case,
    both raw and transformed valuator data is provided.
    RawEvents are sent exclusively to all root windows or to the client
    that grabbed the device only.

    eventtype
        The type of event that occured on the device.
    detail
        The button number or keycode.
    valuators_len
        The length of 'valuators' in 4 byte units.
    valuators
        Bitmask of valuators provided in 'axisvalues' and 'axisvalues_raw'.
    axisvalues
        Valuator data in device-native resolution.
    axisvalues_raw
        Untransformed valuator data in device-native resolution.

    ┌───
        Enter or Leave or FocusIn or FocusOut
            EVENTHEADER
            root:               Window
            event:              Window
            child:              Window
            sourceid:           DEVICEID
            root_x:             FP1616
            root_y:             FP1616
            event_x             FP1616
            event_y:            FP1616
            mode:               NOTIFYMODE
            detail:             NOTIFYDETAIL
            same_screen:        BOOL
            focus:              BOOL
            mods:               MODIFIERINFO
            group:              GROUPINFO
            buttons_len:        CARD16
            buttons:            SETofBUTTONMASK
    └───

    NOTIFYMODE { Normal, Grab, Ungrab }
    NOTIFYDETAIL { Ancestor, Virtual, Inferior, Nonlinear, NonlinearVirtual,
                   Pointer, PointerRoot, None }

    Enter or Leave events are sent whenever a device's pointer enters or
    leaves a window.
    FocusIn or FocusOut events are sent whenever a device's focus is set to or
    away from a window.
    The enter/leave and focus in/out model is described in the core protocol
    specification, Section 11. (EnterNotify, LeaveNotify events).

    For enter and leave events, the modifier and group state is the state of
    the paired master device if the device is a master device, or the state of
    the attached master keyboard if the device is an attached slave device, or
    zero if the device is a floating slave device.

    For focus in and out events, the button state is the state of the paired
    master device if the device is a master device, or the state of the
    attached master keyboard if the device is an attached slave device, or
    zero if the device is a floating slave device.

    root
    event
    child
        The root window, event window, and child window, respectively. See the
        core protocol specification for more detail.
    sourceid
        The device that caused the pointer to move.
    root_x
    root_y
        The pointer coordinates relative to the root window.
    event_x
    event_y
        The pointer coordinates relative to the event window.
    mode
        Normal pointer motion events have mode Normal. Pseudo-motion events
        when a grab activates have mode Grab, and pseudo-motion events when a
        grab deactivates have mode Ungrab.
    detail
        Specifies the relation of the event window to the window the pointer
        entered or left. See the core protocol spec for details.
    same_screen
        TRUE if the event window is on the same screen as the pointer's root
        window.
    focus
        If the event window is the focus window or an inferior of the focus
        window, then focus is True. Otherwise, focus is False. This field is
        unspecified for focus in/out events.
    mods
        XKB modifier state before the event occured.
    group
        XKB group state before the event.
    buttons_len
        The length of 'buttons' in 4 byte units.
    buttons
        Button state before the event.

    ┌───
        XIPropertyEvent
            EVENTHEADER
            property:           ATOM
            what:               { PropertyCreated, PropertyDeleted, PropertyModified }
    └───

    XIPropertyEvents are sent whenever a device property is created, deleted or
    modified by a client.

    property
        The property that has been created, deleted, or modified
    what
        Specifies what has been changed.
     

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