genode/repos/os/src/app/global_keys_handler

The "global-key-handler" component transforms a stream of nitpicker input
events to state reports. The states and the ways of how the user input affects
the states is configurable. Examples for such states are the system-global
capslock and numlock states, or the nitpicker X-ray mode activated by a global
secure-attention key. The configuration looks as follows:

! <config>
!   <bool name="xray" initial="no"/>
! 
!   <press   name="KEY_F1" bool="xray" change="on"/>
!   <release name="KEY_F1" bool="xray" change="off"/>
!   <press   name="KEY_F2" bool="xray" change="toggle"/>
! 
!   <report name="xray" delay_ms="125">
!     <hovered domain="panel"/>
!     <bool name="xray"/>
!   </report>
! </config>

A '<bool>' node declares a boolean state variable with the given name and its
initial value (default is "no"). There may by any number of such variables.

The '<press>' and '<release>' nodes define how key events affect the state
variables. Each of those nodes refers to a specific state variable via the
'bool' attribute, and the operation as the 'change' attribute. Possible
'change' attribute values are "on", "off", and "toggle".

The '<report>' node defines a state-dependent report with the name as
specified in the 'name' attribute. The report-generation rate can be
artificially limited by the 'delay_ms' attribute. If specified, the report is
not issued immediately on a state change but after the specified amount of
milliseconds. The '<report>' node contains a number of conditions. Whenever
one of those conditions is true, a report of the following form is generated:

! <xray enabled="yes"/>

Otherwise, the report's 'enabled' attribute has the value "no". Possible
conditions are '<bool>' and '<hovered>'. The '<bool>' condition is true if the
named boolean state variable has the value true. The '<hovered>' condition is
true if the currently hovered nitpicker client belongs to the domain as
specified in the 'domain' attribute. The latter information is obtained from a
ROM module named "hover", which correponds to nitpicker's hover reports.

To use the global-keys-handler in practice, one needs to configure the
nitpicker GUI server such that the press/release events of the global keys of
interest are routed to the global-keys-handler. This can be achieved by
nitpicker's '<global-key>' configuration nodes. For example:

! <global-key name="KEY_F1" label="global_keys_handler -> input" />
! <global-key name="KEY_F2" label="global_keys_handler -> input" />