# Indicators

Although the core X implementation supports up to 32 LEDs on an input device, it does not provide any linkage between the state of the LEDs and the logical state of the input device. For example, most keyboards have a CapsLock LED, but X does not provide a mechanism to make the LED automatically follow the logical state of the CapsLock key.

Furthermore, the core X implementation does not provide clients with the ability to determine what bits in the led_mask field of the XKeyboardState map to the particular LEDs on the keyboard. For example, X does not provide a method for a client to determine what bit to set in the led_mask field to turn on the Scroll Lock LED or whether the keyboard even has a Scroll Lock LED.

Xkb provides indicator names and programmable indicators to help solve these problems. Using Xkb, clients can determine the names of the various indicators, determine and control the way that the individual indicators should be updated to reflect keyboard changes, and determine which of the 32 keyboard indicators reported by the protocol are actually present on the keyboard. Clients may also request immediate notification of changes to the state of any subset of the keyboard indicators, which makes it straightforward to provide an on-screen "virtual" LED panel. This chapter describes Xkb indicators and the functions used for manipulating them.

## Indicator Names

Xkb provides the capability of symbolically naming indicators. Xkb itself doesn’t use these symbolic names for anything; they are there only to help make the keyboard description comprehensible to humans. To set the names of specific indicators, use XkbSetNames as discussed in Chapter 18. Then set the map using XkbSetMap (see section 14.3) or XkbSetNamedIndicator (below). To retrieve indicator names, use XkbGetNames (Chapter 18).

## Indicator Data Structures

Use the indicator description record, XkbIndicatorRec , and its indicator map, XkbIndicatorMapRec , to inquire about and control most indicator properties and behaviors.

### XkbIndicatorRec

The description for all the Xkb indicators is held in the indicators field of the complete keyboard description (see Chapter 6), which is defined as follows:

    #define      XkbNumIndicators      32

    typedef struct {
          unsigned long                   phys_indicators;        /* LEDs existence */
          XkbIndicatorMapRec              maps[XkbNumIndicators]; /* indicator maps */
    } XkbIndicatorRec,*XkbIndicatorPtr;

This structure contains the phys_indicators field, which relates some information about the correspondence between indicators and physical LEDs on the keyboard, and an array of indicator maps , one map per indicator.

The phys_indicators field indicates which indicators are bound to physical LEDs on the keyboard; if a bit is set in phys_indicators , then the associated indicator has a physical LED associated with it. This field is necessary because some indicators may not have corresponding physical LEDs on the keyboard. For example, most keyboards have an LED for indicating the state of CapsLock , but most keyboards do not have an LED that indicates the current group. Because phys_indicators describes a physical characteristic of the keyboard, you cannot directly change it under program control. However, if a client program loads a completely new keyboard description via XkbGetKeyboardByName , or if a new keyboard is attached and the X implementation notices, phys_indicators changes if the indicators for the new keyboard are different.

### XkbIndicatorMapRec

Each indicator has its own set of attributes that specify whether clients can explicitly set its state and whether it tracks the keyboard state. The attributes of each indicator are held in the maps array, which is an array of XkbIndicatorRec structures:

    typedef struct {
          unsigned char    flags;         /* how the indicator can be changed */
          unsigned char    which_groups;  /* match criteria for groups */
          unsigned char    groups;        /* which keyboard groups the indicator watches */
          unsigned char    which_mods;    /* match criteria for modifiers */
          XkbModsRec       mods;          /* which modifiers the indicator watches */
          unsigned int     ctrls;         /* which controls the indicator watches */
    } XkbIndicatorMapRec, *XkbIndicatorMapPtr;

This indicator map specifies for each indicator:

- The conditions under which the keyboard modifier state affects the indicator

- The conditions under which the keyboard group state affects the indicator

- The conditions under which the state of the boolean controls affects the indicator

- The effect (if any) of attempts to explicitly change the state of the indicator using the functions XkbSetControls or XChangeKeyboardControl

For more information on the effects of explicit changes to indicators and the relationship to the indicator map, see section 8.4.1.

#### XkbIndicatorMapRec flags field

The flags field specifies the conditions under which the indicator can be changed and the effects of changing the indicator. The valid values for flags and their effects are shown in Table 8.1.

##### XkbIndicatorMapRec flags Field

Value |  | Effect
--- | --- | ---
XkbIM_NoExplicit | (1L<<7) | Client applications cannot change the state of the indicator.
XkbIM_NoAutomatic | (1L<<6) | Xkb does not automatically change the value of the indicator based upon a change in the keyboard state, regardless of the values for the other fields of the indicator map.
XkbIM_LEDDrivesKB | (1L<<5) | A client application changing the state of the indicator causes the state of the keyboard to change.

Note that if XkbIM_NoAutomatic is not set, by default the indicator follows the keyboard state.

If XkbIM_LEDDrivesKB is set and XkbIM_NoExplicit is not, and if you call a function which updates the server’s image of the indicator map (such as XkbSetIndicatorMap or XkbSetNamedIndicator ), Xkb changes the keyboard state and controls to reflect the other fields of the indicator map, as described in the remainder of this section. If you attempt to explicitly change the value of an indicator for which XkbIM_LEDDrivesKB is absent or for which XkbIM_NoExplicit is present, keyboard state or controls are unaffected.

For example, a keyboard designer may want to make the CapsLock LED controllable only by the server, but allow the Scroll Lock LED to be controlled by client applications. To do so, the keyboard designer could set the XkbIM_NoExplicit flag for the CapsLock LED, but not set it for the Scroll Lock LED. Or the keyboard designer may wish to allow the CapsLock LED to be controlled by both the server and client applications and also have the server to automatically change the CapsLock modifier state whenever a client application changes the CapsLock LED. To do so, the keyboard designer would not set the XkbIM_NoExplicit flag, but would instead set the XkbIM_LEDDrivesKB flag.

The remaining fields in the indicator map specify the conditions under which Xkb automatically turns an indicator on or off (only if XkbIM_NoAutomatic is not set). If these conditions match the keyboard state, Xkb turns the indicator on. If the conditions do not match, Xkb turns the indicator off.

#### XkbIndicatorMapRec which_groups and groups fields

The which_groups and the groups fields of an indicator map determine how the keyboard group state affects the corresponding indicator. The which_groups field controls the interpretation of groups and may contain any one of the following values:

    #define XkbIM_UseNone             0
    #define XkbIM_UseBase             (1L << 0)
    #define XkbIM_UseLatched          (1L << 1)
    #define XkbIM_UseLocked           (1L << 2)
    #define XkbIM_UseEffective        (1L << 3)
    #define XkbIM_UseAnyGroup         XkbIM_UseLatched | XkbIM_UseLocked |
                                      XkbIM_UseEffective

The groups field specifies what keyboard groups an indicator watches and is the bitwise inclusive OR of the following valid values:

    #define XkbGroup1Mask            (1<<0)
    #define XkbGroup2Mask            (1<<1)
    #define XkbGroup3Mask            (1<<2)
    #define XkbGroup4Mask            (1<<3)
    #define XkbAnyGroupMask          (1<<7)
    #define XkbAllGroupsMask         (0xf)

If XkbIM_NoAutomatic is not set (the keyboard drives the indicator), the effect of which_groups and groups is shown in Table 8.2.

##### XkbIndicatorMapRec which_groups and groups, Keyboard Drives Indicator

which_groups | Effect
--- | ---
XkbIM_UseNone | The groups field and the current keyboard group state are ignored.
XkbIM_UseBase | If groups is nonzero, the indicator is lit whenever the base keyboard group is nonzero. If groups is zero, the indicator is lit whenever the base keyboard group is zero.
XkbIM_UseLatched | If groups is nonzero, the indicator is lit whenever the latched keyboard group is nonzero. If groups is zero, the indicator is lit whenever the latched keyboard group is zero.
XkbIM_UseLocked | The groups field is interpreted as a mask. The indicator is lit when the current locked keyboard group matches one of the bits that are set in groups.
XkbIM_UseEffective | The groups field is interpreted as a mask. The indicator is lit when the current effective keyboard group matches one of the bits that are set in groups .

The effect of which_groups and groups when you change an indicator for which XkbIM_LEDDrivesKB is set (the indicator drives the keyboard) is shown in Table 8.3. The "New State" column refers to the new state to which you set the indicator.

##### XkbIndicatorMapRec which_groups and groups, Indicator Drives Keyboard

which_groups | New State | Effect on Keyboard Group State
--- | --- | ---
XkbIM_UseNone | On or Off | No effect
XkbIM_UseBase | On or Off | No effect
XkbIM_UseLatched | On | The groups field is treated as a group mask. The keyboard group latch is changed to the lowest numbered group specified in groups ; if groups is empty, the keyboard group latch is changed to zero.
XkbIM_UseLatched | Off | The groups field is treated as a group mask. If the indicator is explicitly extinguished, keyboard group latch is changed to the lowest numbered group not specified in groups ; if groups is zero, the keyboard group latch is set to the index of the highest legal keyboard group.
XkbIM_UseLocked or XkbIM_UseEffective | On | If the groups mask is empty, group is not changed; otherwise, the locked keyboard group is changed to the lowest numbered group specified in groups.
XkbIM_UseLocked or XkbIM_UseEffective | Off | Locked keyboard group is changed to the lowest numbered group that is not specified in the groups mask, or to Group1 if the groups mask contains all keyboard groups.

#### XkbIndicatorMapRec which_mods and mods fields

The mods field specifies what modifiers an indicator watches. The mods field is an Xkb modifier definition, XkbModsRec , as described in section 7.2, which can specify both real and virtual modifiers. The mods field takes effect even if some or all of the virtual indicators specified in mods are unbound. To specify the mods field, in general, assign the modifiers of interest to mods.real_mods and the virtual modifiers of interest to mods.vmods . You can disregard the mods.mask field unless your application needs to interpret the indicator map directly (that is, to simulate automatic indicator behavior on its own). Relatively few applications need to do so, but if you find it necessary, you can either read the indicator map back from the server after you update it (the server automatically updates the mask field whenever any of the real or virtual modifiers are changed in the modifier definition) or you can use XkbVirtualModsToReal to determine the proper contents for the mask field, assuming that the XkbDescRec contains the virtual modifier definitions.

which_mods specifies what criteria Xkb uses to determine a match with the corresponding mods field by specifying one or more components of the Xkb keyboard state. If XkbIM_NoAutomatic is not set (the keyboard drives the indicator), the indicator is lit whenever any of the modifiers specified in the mask field of the mods modifier definition are also set in any of the current keyboard state components specified by which_mods . Remember that the mask field is comprised of all of the real modifiers specified in the definition plus any real modifiers that are bound to the virtual modifiers specified in the definition. (See Chapter 5 for more information on the keyboard state and Chapter 7 for more information on virtual modifiers.) Use a bitwise inclusive OR of the following values to compose a value for which_mods:

    #define XkbIM_UseNone             0
    #define XkbIM_UseBase             (1L << 0)
    #define XkbIM_UseLatched          (1L << 1)
    #define XkbIM_UseLocked           (1L << 2)
    #define XkbIM_UseEffective        (1L << 3)
    #define XkbIM_UseCompat           (1L << 4)
    #define XkbIM_UseAnyMods          XkbIM_UseBase | XkbIM_UseLatched |
                                      XkbIM_UseLocked | XkbIM_UseEffective |
                                      XkbIM_UseCompat

If XkbIM_NoAutomatic is not set (the keyboard drives the indicator), the effect of which_mods and mods is shown in Table 8.4

##### XkbIndicatorMapRec which_mods and mods, Keyboard Drives Indicator

which_mods | Effect on Keyboard Modifiers
--- | ---
XkbIM_UseNone | The mods field and the current keyboard modifier state are ignored.
XkbIM_UseBase | The indicator is lit when any of the modifiers specified in the mask field of mods are on in the keyboard base state. If both mods.real_mods and mods.vmods are zero, the indicator is lit when the base keyboard state contains no modifiers.
XkbIM_UseLatched | The indicator is lit when any of the modifiers specified in the mask field of mods are latched. If both mods.real_mods and mods.vmods are zero, the indicator is lit when none of the modifier keys are latched.
XkbIM_UseLocked | The indicator is lit when any of the modifiers specified in the mask field of mods are locked. If both mods.real_mods and mods.vmods are zero, the indicator is lit when none of the modifier keys are locked.
XkbIM_UseEffective | The indicator is lit when any of the modifiers specified in the mask field of mods are in the effective keyboard state. If both mods.real_mods and mods.vmods are zero, the indicator is lit when the effective keyboard state contains no modifiers.
XkbIM_UseCompat | The indicator is lit when any of the modifiers specified in the mask field of mods are in the keyboard compatibility state. If both mods.real_mods and mods.vmods are zero, the indicator is lit when the keyboard compatibility state contains no modifiers.

The effect on the keyboard modifiers of which_mods and mods when you change an indicator for which XkbIM_LEDDrivesKB is set (the indicator drives the keyboard) is shown in Table 8.5. The "New State" column refers to the new state to which you set the indicator.

##### XkbIndicatorMapRec which_mods and mods, Indicator Drives Keyboard

which_mods | New State | Effect on Keyboard Modifiers
--- | --- | ---
XkbIM_UseNone or XkbIM_UseBase | On or Off | No Effect
XkbIM_UseLatched | On | Any modifiers specified in the mask field of mods are added to the latched modifiers.
XkbIM_UseLatched | Off | Any modifiers specified in the mask field of mods are removed from the latched modifiers.
XkbIM_UseLocked, XkbIM_UseCompat, or XkbIM_UseEffective | On | Any modifiers specified in the mask field of mods are added to the locked modifiers.
XkbIM_UseLocked | Off | Any modifiers specified in the mask field of mods are removed from the locked modifiers.
XkbIM_UseCompat or XkbIM_UseEffective | Off | Any modifiers specified in the mask field of mods are removed from both the locked and latched modifiers.

#### XkbIndicatorMapRec ctrls field

The ctrls field specifies what controls (see Chapter 10) the indicator watches and is composed using the bitwise inclusive OR of the following values:

    #define XkbRepeatKeysMask           (1L << 0)
    #define XkbSlowKeysMask             (1L << 1)
    #define XkbBounceKeysMask           (1L << 2)
    #define XkbStickyKeysMask           (1L << 3)
    #define XkbMouseKeysMask            (1L << 4)
    #define XkbMouseKeysAccelMask       (1L << 5)
    #define XkbAccessXKeysMask          (1L << 6)
    #define XkbAccessXTimeoutMask       (1L << 7)
    #define XkbAccessXFeedbackMask      (1L << 8)
    #define XkbAudibleBellMask          (1L << 9)
    #define XkbOverlay1Mask             (1L << 10)
    #define XkbOverlay2Mask             (1L << 11)
    #define XkbAllBooleanCtrlsMask      (0x00001FFF)

Xkb lights the indicator whenever any of the boolean controls specified in ctrls is enabled.

## Getting Information About Indicators

Xkb allows applications to obtain information about indicators using two different methods. The first method, which is similar to the core X implementation, uses a mask to specify the indicators. The second method, which is more suitable for applications concerned with interoperability, uses indicator names. The correspondence between the indicator name and the bit position in masks is as follows: one of the parameters returned from XkbGetNamedIndicators is an index that is the bit position to use in any function call that requires a mask of indicator bits, as well as the indicator’s index into the XkbIndicatorRec array of indicator maps.

### Getting Indicator State

Because the state of the indicators is relatively volatile, the keyboard description does not hold the current state of the indicators. To obtain the current state of the keyboard indicators, use XkbGetIndicatorState.

Status XkbGetIndicatorState ( display , device_spec , state_return )
Display * display ; /* connection to the X server */
unsigned int device_spec ; /* device ID, or XkbUseCoreKbd */
unsigned int * state_return ; /* backfilled with a mask of the indicator state */

XkbGetIndicatorState queries the display for the state of the indicators on the device specified by the device_spec . For each indicator that is "turned on" on the device, the associated bit is set in state_return . If a compatible version of the Xkb extension is not available in the server, XkbGetIndicatorState returns a BadMatch error. Otherwise, it sends the request to the X server, places the state of the indicators into state_return, and returns Success . Thus the value reported by XkbGetIndicatorState is identical to the value reported by the core protocol.

### Getting Indicator Information by Index

To get the map for one or more indicators, using a mask to specify the indicators, use XkbGetIndicatorMap.

Status XkbGetIndicatorMap ( dpy , which , desc )
Display * dpy ; /* connection to the X server */
unsigned int which ; /* mask of indicators for which maps should be returned */
XkbDescPtr desc ; /* keyboard description to be updated */

XkbGetIndicatorMap obtains the maps from the server for only those indicators specified by the which mask and copies the values into the keyboard description specified by desc . If the indicators field of the desc parameter is NULL , XkbGetIndicatorMap allocates and initializes it.

XkbGetIndicatorMap can generate BadAlloc , BadLength , BadMatch , and BadImplementation errors.

To free the indicator maps, use XkbFreeIndicatorMaps (see section 8.6).

### Getting Indicator Information by Name

Xkb also allows applications to refer to indicators by name. Use XkbGetNames to get the indicator names (see Chapter 18). Using names eliminates the need for hard-coding bitmask values for particular keyboards. For example, instead of using vendor-specific constants such as WSKBLed_ScrollLock mask on Digital workstations or XLED_SCROLL_LOCK on Sun workstations, you can instead use XkbGetNamedIndicator to look up information on the indicator named "Scroll Lock."

Use XkbGetNamedIndicator to look up the indicator map and other information for an indicator by name.

Bool XkbGetNamedIndicator ( dpy , dev_spec , name , ndx_rtrn , state_rtrn , map_rtrn , real_rtrn )
Display * dpy ; /* connection to the X server */
unsigned int device_spec ; /* keyboard device ID, or XkbUseCoreKbd */
Atom name ; /* name of the indicator to be retrieved */
int * ndx_rtrn ; /* backfilled with the index of the retrieved indicator */
Bool * state_rtrn ; /* backfilled with the current state of the retrieved indicator */
XkbIndicatorMapPtr map_rtrn ; /* backfilled with the mapping for the retrieved indicator */
Bool * real_rtrn ; /* backfilled with True if the named indicator is real (physical) */

If the device specified by device_spec has an indicator named name , XkbGetNamedIndicator returns True and populates the rest of the parameters with information about the indicator. Otherwise, XkbGetNamedIndicator returns False .

The ndx_rtrn field returns the zero-based index of the named indicator. This index is the bit position to use in any function call that requires a mask of indicator bits, as well as the indicator’s index into the XkbIndicatorRec array of indicator maps. state_rtrn returns the current state of the named indicator ( True = on, False = off). map_rtrn returns the indicator map for the named indicator. In addition, if the indicator is mapped to a physical LED, the real_rtrn parameter is set to True .

Each of the " _rtrn " arguments is optional; you can pass NULL for any unneeded " _rtrn " arguments.

XkbGetNamedIndicator can generate BadAtom and BadImplementation errors.

## Changing Indicator Maps and State

Just as you can get the indicator map using a mask or using an indicator name, so you can change it using a mask or a name.

You cannot change the phys_indicators field of the indicators structure. The only way to change the phys_indicators field is to change the keyboard map.

There are two ways to make changes to indicator maps and state: either change a local copy of the indicator maps and use XkbSetIndicatorMap or XkbSetNamedIndicator , or, to reduce network traffic, use an XkbIndicatorChangesRec structure and use XkbChangeIndicators.

### Effects of Explicit Changes on Indicators

This section discusses the effects of explicitly changing indicators depending upon different settings in the indicator map. See Tables 8.3 and Table 8.5 for information on the effects of the indicator map fields when explicit changes are made.

If XkbIM_LEDDrivesKB is set and XkbIM_NoExplicit is not, and if you call a function that updates the server’s image of the indicator map (such as XkbSetIndicatorMap or XkbSetNamedIndicator ), Xkb changes the keyboard state and controls to reflect the other fields of the indicator map. If you attempt to explicitly change the value of an indicator for which XkbIM_LEDDrivesKB is absent or for which XkbIM_NoExplicit is present, keyboard state or controls are unaffected.

If neither XkbIM_NoAutomatic nor XkbIM_NoExplicit is set in an indicator map, Xkb honors any request to change the state of the indicator, but the new state might be immediately superseded by automatic changes to the indicator state if the keyboard state or controls change.

The effects of changing an indicator that drives the keyboard are cumulative; it is possible for a single change to affect keyboard group, modifiers, and controls simultaneously.

If you change an indicator for which both the XkbIM_LEDDrivesKB and XkbIM_NoAutomatic flags are specified, Xkb applies the keyboard changes specified in the other indicator map fields and changes the indicator to reflect the state that was explicitly requested. The indicator remains in the new state until it is explicitly changed again.

If the XkbIM_NoAutomatic flag is not set and XkbIM_LEDDrivesKB is set, Xkb applies the changes specified in the other indicator map fields and sets the state of the indicator to the values specified by the indicator map. Note that it is possible in this case for the indicator to end up in a different state than the one that was explicitly requested. For example, Xkb does not extinguish an indicator with which_mods of XkbIM_UseBase and mods of Shift if, at the time Xkb processes the request to extinguish the indicator, one of the Shift keys is physically depressed.

If you explicitly light an indicator for which XkbIM_LEDDrivesKB is set, Xkb enables all of the boolean controls specified in the ctrls field of its indicator map. Explicitly extinguishing such an indicator causes Xkb to disable all of the boolean controls specified in ctrls .

### Changing Indicator Maps by Index

To update the maps for one or more indicators, first modify a local copy of the keyboard description, then use XkbSetIndicatorMap to download the changes to the server:

Bool XkbSetIndicatorMap ( dpy , which , desc )
Display * dpy ; /* connection to the X server */
unsigned int which ; /* mask of indicators to change */
XkbDescPtr desc ; /* keyboard description from which the maps are taken */

For each bit set in the which parameter, XkbSetIndicatorMap sends the corresponding indicator map from the desc parameter to the server.

### Changing Indicator Maps by Name

XkbSetNamedIndicator can do several related things:

- Name an indicator if it is not already named

- Toggle the state of the indicator

- Set the indicator to a specified state

- Set the indicator map for the indicator

Bool XkbSetNamedIndicator ( dpy , device_spec , name , change_state, state , create_new , map )
Display * dpy ; /* connection to the X server */
unsigned int device_spec ; /* device ID, or XkbUseCoreKbd */
Atom name ; /* name of the indicator to change */
Bool change_state ; /* whether to change the indicator state or not */
Bool state ; /* desired new state for the indicator */
Bool create_new ; /* whether a new indicator with the specified name should be created when necessary */
XkbIndicatorMapPtr map ; /* new map for the indicator */

If a compatible version of the Xkb extension is not available in the server, XkbSetNamedIndicator returns False . Otherwise, it sends a request to the X server to change the indicator specified by name and returns True.

If change_state is True , and the optional parameter, state , is not NULL , XkbSetNamedIndicator tells the server to change the state of the named indicator to the value specified by state.

If an indicator with the name specified by name does not already exist, the create_new parameter tells the server whether it should create a new named indicator. If create_new is True , the server finds the first indicator that doesn’t have a name and gives it the name specified by name.

If the optional parameter, map , is not NULL , XkbSetNamedIndicator tells the server to change the indicator’s map to the values specified in map.

XkbSetNamedIndicator can generate BadAtom and BadImplementation errors. In addition, it can also generate XkbIndicatorStateNotify (see section 8.5), XkbIndicatorMapNotify , and XkbNamesNotify events (see section 18.5).

### The XkbIndicatorChangesRec Structure

The XkbIndicatorChangesRec identifies small modifications to the indicator map. Use it with the function XkbChangeIndicators to reduce the amount of traffic sent to the server.

    typedef struct _XkbIndicatorChanges {
          unsigned int             state_changes;
          unsigned int             map_changes;
    }
    XkbIndicatorChangesRec,*XkbIndicatorChangesPtr;

The state_changes field is a mask that specifies the indicators that have changed state, and map_changes is a mask that specifies the indicators whose maps have changed.

To change indicator maps or state without passing the entire keyboard description, use XkbChangeIndicators .

Bool XkbChangeIndicators ( dpy, xkb, changes, state )
Display * dpy ; /* connection to the X server */
XkbDescPtr xkb ; /* keyboard description from which names are to be
taken. */
XkbIndicatorChangesPtr changes ; /* indicators to be updated on the server */
unsigned int state ; /* new state of indicators listed in
changes -> state_changes */

XkbChangeIndicators copies any maps specified by changes from the keyboard description, xkb , to the server specified by dpy . If any bits are set in the state_changes field of changes , XkbChangeIndicators also sets the state of those indicators to the values specified in the state mask. A 1 bit in state turns the corresponding indicator on, a 0 bit turns it off.

XkbChangeIndicator s can generate BadAtom and BadImplementation errors. In addition, it can also generate XkbIndicatorStateNotify and XkbIndicatorMapNotify events (see section 8.5).

## Tracking Changes to Indicator State or Map

Whenever an indicator changes state, the server sends XkbIndicatorStateNotify events to all interested clients. Similarly, whenever an indicator’s map changes, the server sends XkbIndicatorMapNotify events to all interested clients.

To receive XkbIndicatorStateNotify events, use XkbSelectEvents (see section 4.3) with both the bits_to_change and values_for_bits parameters containing XkbIndicatorStateNotifyMask . To receive XkbIndicatorMapNotify events, use XkbSelectEvents with XkbIndicatorMapNotifyMask .

To receive events for only specific indicators, use XkbSelectEventDetails . Set the event_type parameter to XkbIndicatorStateNotify or XkbIndicatorMapNotify , and set both the bits_to_change and values_for_bits detail parameters to a mask where each bit specifies one indicator, turning on those bits that specify the indicators for which you want to receive events.

Both types of indicator events use the same structure:

    typedef struct _XkbIndicatorNotify {
          int            type;        /* Xkb extension base event code */
          unsigned long  serial;      /* X server serial number for event */
          Bool           send_event;  /*  True => synthetically generated */
          Display *      display;     /* server connection where event generated */
          Time           time;        /* server time when event generated */
          int            xkb_type;    /* specifies state or map notify */
          int            device;      /* Xkb device ID, will not be  XkbUseCoreKbd */
          unsigned int   changed;     /* mask of indicators with new state or map */
          unsigned int   state;       /* current state of all indicators */
    } XkbIndicatorNotifyEvent;

xkb_type is either XkbIndicatorStateNotify or XkbIndicatorMapNotify , depending on whether the event is a kbIndicatorStateNotify event or kbIndicatorMapNotify event.

The changed parameter is a mask that is the bitwise inclusive OR of the indicators that have changed. If the event is of type XkbIndicatorMapNotify , changed reports the maps that changed. If the event is of type XkbIndicatorStateNotify , changed reports the indicators that have changed state. state is a mask that specifies the current state of all indicators, whether they have changed or not, for both XkbIndicatorStateNotify and IndicatorMapNotify events.

When your client application receives either a XkbIndicatorStateNotify event or XkbIndicatorMapNotify event, you can note the changes in a changes structure by calling XkbNoteIndicatorChanges.

void XkbNoteIndicatorChanges ( old , new , wanted )
XkbIndicatorChangesPtr old ; /* XkbIndicatorChanges structure to be updated */
XkbIndicatorNotifyEvent * new ; /* event from which changes are to be copied */
unsigned int wanted ; /* which changes are to be noted */

The wanted parameter is the bitwise inclusive OR of XkbIndicatorMapMask and XkbIndicatorStateMask . XkbNoteIndicatorChanges copies any changes reported in new and specified in wanted into the changes record specified by old.

To update a local copy of the keyboard description with the actual values, pass the results of one or more calls to XkbNoteIndicatorChanges to XkbGetIndicatorChanges:

Status XkbGetIndicatorChanges ( dpy , xkb , changes , state )
Display * dpy ; /* connection to the X server */
XkbDescPtr xkb ; /* keyboard description to hold the new values */
XkbIndicatorChangesPtr changes ; /* indicator maps/state to be obtained from the server */
unsigned int * state ; /* backfilled with the state of the indicators */

XkbGetIndicatorChanges examines the changes parameter, pulls over the necessary information from the server, and copies the results into the xkb keyboard description. If any bits are set in the state_changes field of changes , XkbGetIndicatorChanges also places the state of those indicators in state . If the indicators field of xkb is NULL , XkbGetIndicatorChanges allocates and initializes it. To free the indicators field, use XkbFreeIndicators (see section 8.6).

XkbGetIndicatorChanges can generate BadAlloc , BadImplementation, and BadMatch errors.

## Allocating and Freeing Indicator Maps

Most applications do not need to directly allocate the indicators member of the keyboard description record (the keyboard description record is described in Chapter 6). If the need arises, however, use XkbAllocIndicatorMaps.

Status XkbAllocIndicatorMaps ( xkb )
XkbDescPtr xkb ; /* keyboard description structure */

The xkb parameter must point to a valid keyboard description. If it doesn’t, XkbAllocIndicatorMaps returns a BadMatch error. Otherwise, XkbAllocIndicatorMaps allocates and initializes the indicators member of the keyboard description record and returns Success . If XkbAllocIndicatorMaps was unable to allocate the indicators record, it reports a Bad Alloc error.

To free memory used by the indicators member of an XkbDescRec structure, use XkbFreeIndicatorMaps.

void XkbFreeIndicatorMaps ( xkb )
XkbDescPtr xkb ; /* keyboard description structure */

If the indicators member of the keyboard description record pointed to by xkb is not NULL , XkbFreeIndicatorMaps frees the memory associated with the indicators member of xkb.