System Interfaces


As discussed in the driver introduction the driver is responsible for interfacing with the pointer device hardware (touch screens, pens, digitizers etc) to receive incoming co-ordinate data.p

Thereafter, this data can, if required, be posted by the driver into the operating system in various ways to control the system pointer or interface with the underlying input subsystem to interact with any native touch features built into the OS. Applications can also register to receive co-ordinate data via the driver's API and implement their own system interface as required, as is the case with our own UPDD Gestures application under MacOS.

Given that client applications can also be used to interface with the system pointer or input subsystem then to aid synchronization between these applications and the core driver interfaces a device setting, active_touch_interface (A_T_I), is used to indicate what interface is currently enabled. The setting is passive, in that it does not in itself invoke the described functionality, but is used to indicate the interface in use, against which tests can be performed by any components that implement a system interface.

If this setting is not defined or the setting is blank then the driver will select an appropriate default interface for the operating system as follows:

OS Default system interface 
 Windows Virtual HID interface (if it is present and the Windows 'tablet' component also exists) otherwise the single mouse interface.
XP - No Virtual HID or tablet components will exist.
For WES7 note that only WS7P contains the table component. WS7E and WS7C do not appear to contain the tablet component.
All other Windows editions should have both the Virtual HID and tablet components present.
The tablet component is deemed to exist if the registry entry HKLM\SYSTEM\\CurrentControlSet\services\TabletInputService branch exists
 Linux Uinput single touch events  
 MacOS Simple touch client interface is used (unless gestures module is loaded in which case gestures has its own interface)


  1. Most UPDD Mac installers install the driver plus gestures so it is likely that the gesture extension is actually in control of posting the touch data. Gestures is not bound by this setting. Only the driver references this setting should gesture not be in control of posting the touch data, either because its mode of operation does not post data or it has been stopped.
  2. If you switch interfaces there is a possibility that calibration may be lost, especially if switching in a complex multi-monitor system in Linux whereby the internal kernel video mapping using uinput could be different when switching to X or vise-visa.

UPDD components implement a number of system interfaces:

A_T_I Value Component OS  Description 
 tbupddsu  Driver  Windows  A basic single touch, mouse type, kernel interface for Windows XP and higher
 upddvh  VirtualHID  Windows  A multi touch Virtual HID interface for Windows systems running Pen Services (native touch support) 
 w32_events  Driver  Windows  An experimental method to post touch data directly into an application bypassing the OS mouse and touch processing
 simpletouch  Driver  Mac  A basic single touch client interface that works only when a user is logged in (HID library)
 simpletouch_cg  Driver   Mac  A basic single touch client interface that works only when a user is logged in (core graphics library) 
 xtouch  Driver  Linux  Linux xtest interface
 uinput  Driver  Linux  Linux event system interface - requires the uinput component to be discovered
 N/A  Gestures  Mac  The UPDD Gestures utility

If a third party component wishes to control this interface, or if the current interface is to be disabled, then the setting should be changed to a custom name or set to a dummy value. Specifying the name here hands control to the custom interface. Such an interface implementation should also check the value of this field and only deliver touches into the system if this value matches the custom name, as described here.

Note: simpletouch_cg was implemented to utilise a different interface as implemented in the MacOS gesture software such that the driver and gestures use the same method to control the system cursor and generate clicks. There is concern that the interface used in the simpletouch interface uses an old API that may be deprecated in future releases of MacOS.

Example usage

If under Windows you wanted to disable the Virtual HID interface and revert to single touch mouse interface then set the setting to tbupddsu.  The driver will only post to this interface irrespective of the presence of the Virtual HID interface.
i.e. upddutils set active_touch_interface tbupddsu

If a 3rd party UPDD client application wanted to process incoming data and post the data to a specific application only, to satisfy the native touch event api only within that application, then set this setting to a non standard value and data will no longer be posted via one of the standard interfaces.

If you utilised the UPDD TUIO server interface to post touches into TUIO client applications and only wanted TUIO client applications to work with touch then set this setting to a non standard value and data will no longer be posted via one of the standardinterfaces.