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Multi-touch
and UPDD Revision
1.4 – 7th Apr 2010 www.touch-base.com\documentation\general |
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There has been a
resurgence of interest in the concept of multi-touch devices since the
demonstration by Jeff Han of his conceptual multi-touch interface in 2006 and
more recently the successful launch of the Apple iPhone and iPod Touch and
the most recent and highly publicised Windows 7 launch, all with multi-touch
capabilities. Multi touch devices have
been around for a long time and an overview of legacy system and the
background of multi touch development by Bill Buxton is available at http://www.billbuxton.com/multitouchOverview.html. Wikipedia’s entry is http://en.wikipedia.org/wiki/Multi-touch. As of version 4.1.4 our
UPDD has support for multi touch enabled devices and supports up to 16 styli
and this documentation covers in detail UPDD multi-touch implementation. For those customers contacting us for our advice on implementing multi-touch devices or applications
this document also addresses general multi-touch considerations and therefore
it is hoped will also answer general multi-touch queries. Multi-touch utilisation
needs to consider four main components, the touch hardware, driver, operating
system driver interface and applications: Hardware considerations
Until recently, touch
devices only processed
one touch point (co-ordinate data) at a time due to limitations of the input
technology. However, some technologies allow for multi-touch sensing and
increasingly touch hardware is now available that is able to detect multiple
touches and report a separate data streams per stylus. Before multi-touch can be
utilised it is imperative that the touch hardware is delivering touch data
streams for each stylus in use and in a manner that is recognised by the
driver, such as UPDD or HID. Multi-touch cannot be achieved with software
only solutions and therefore cannot be achieved with tradition touch hardware
generating a single stylus data stream. With traditional touch
hardware, if you place two or more stylus on the touch screen the device will
only output a single data stream representing the mean average position of all
touch points. Data packet considerations One of the most important
features of a multi-touch device is the unique identification of individual
stylus. The device must uniquely identify each packet of data sent to
the host with a stylus number representing the input stream. The means of
identification is a matter for the hardware manufacture, but consideration
must be given to the end application. For example an application that is
looking at relative positioning of styli, perhaps to look at gestures such as
“squeezing” need only identify a number of stylus inputs, the correspondence
of a stylus to a particular physical input is perhaps unimportant. Another
example is an application that takes different actions depending on the
stylus, such as a whiteboard program that has several pens to represent
different colours or users will also need to be able to associate a
particular stylus with a stylus number in the data packet. The input
technology in use will influence the means by which styli are reported to the
host. Not all input technologies will be able to uniquely
identify individual styli. In line with our standard
recommendations for touch packets we suggest stylus identification be by
means of a positive real binary encoded number in each packet. i.e. if 2 bits
are used for stylus information then 00 = S1, 01=2, 10=3 and 11=4 UPDD implements a
flexible packet parser so can recognise a number of different formats. The
driver can also pre-process received multi touch data packets so if systems
are sending data in a manner not immediately catered for by the UPDD data
packet parser the received data can be reformatted into a structure more
readily handled by the parser. For operating systems
that implement an HID (Human Interface Device) driver with multi touch
extensions, such as Windows 7, then any HID MT compatible device can take
full advantage of the MT functions available via the HID interface. Touch gestures Whilst it is possible for
a controller to calculate and report only gestures this is not a recommended
approach as this limits the flexibility available to drivers or application
software to extend and improve the gesture capabilities of the device. In most cases it is better to deliver the
stylus co-ordinate information and let the driver interface determine the
gesture which is fed to the OS and applications as appropriate. Driver operation
A driver receives the
touch data stream from the hardware interface (USB, Serial etc) and makes
that data available for use by the operating system mouse port (pointer)
interface or application programs. In the case of most touch
drivers that work in standard desktop environments, the incoming co-ordinate
data stream is processed to extract the co-ordinate data which is then scaled
(based on calibration data) and passed to the mouse port interface of the
operating system so that the system cursor is positioned under the point of
touch. In addition to the cursor movement mouse clicks are emulated, either at
the point of touch or lift-off, thus the touch screen functions as a pointer
device by effectively emulating a mouse device. Although this usage
reduces the touch screen function to that of a mouse it has the benefit of
interacting with both the desktop manager and the system applications that
have been developed to be controlled via a point and click device (normally a
mouse or touch pad on a notebook) and therefore they also function with the touch
device. Our driver also makes
touch data information available to system applications via the driver’s
Application Programming Interface (API). An application can register to
receive data when certain events occur on the pointer device. One such event
is the processing of a touch co-ordinate and the application code can receive
the data directly and handle the data independent from the ‘mouse emulation’
interface. A UPDD API call also exists to enable /
disable the system mouse port interface as required. In a multi-touch
environment the driver makes available the multi-touch stylus information to
calling applications. In future
versions of UPDD the driver could also derive gesture information and pass
this to calling applications and optionally feed the gesture information to
any future operating systems, or OS extensions, which can process multi-touch
gestures. Operating system mouse
pointer interface
Touch co-ordinate data received by the driver is either delivered to
the operating system to be processed by the underlying system pointer
interface or passed directly to applications that have registered to receive
co-ordinate data. In operating systems
designed for only 1 touch interface, such as XP, In the case of When processing
multi-touch input UPDD considers stylus zero to be the primary stylus and associates
this to the pointer interface in single touch environments. Delivery of touch
co-ordinate data to the OS can be disabled as
required via a UPDD API function call. Applications
Ultimately it is the
individual applications that will utilise multi-touch input and as such will
need an interface with the touch hardware. In multi-touch aware operating
systems, such as Windows 7, applications can be written to receive both touch
and gesture information via the appropriate interface and act accordingly.
Where there is not a OS MT interface or where an application does not want to
be restricted to one specific OS then direct access to the multi-touch data,
such as via the touch driver’s API or other interface method, is desirable.
Once the touch data is received it is used to perform the multi-touch gesture
as required, such as shrink or enlarge a photo or resize a browser etc. To this end it is
important that applications can interface with the driver to receive the
touch data and it is also important that the application can identify
individual stylus, either by individual stylus identification or code to
identify the stylus based on received data. With UPDD, input from all styli are
processed and made available to client programs via the API callback
mechanism. This extensible mechanism allows the device to be used for any
purpose, such as concurrent drawing, touch typing, or gesture recognition. We will add support for specific
multi-touch hardware as it is made available. Stylus recognition Identification of a
stylus is a function of the hardware; some input technologies, e.g. magnetic
or infra-red pen devices might be able to associate a given physical stylus
with a stylus number. Others might recognise the first touch as stylus 0,
second as stylus 1, etc. Applications utilising the multi-touch features of
UPDD should consider the details of the stylus recognition implementation of
the hardware when choosing a suitable multi-touch input device. API example This simple example
illustrates the use of a UPDD callback function to print co-ordinate and
stylus information. The XY coordinates and touch events (touch / release)
reported via the UPDD callback interface are identified as being for a given
stylus with the new hStylus member. HTBDEVICE hd =
TBApiGetRelativeDevice(0); TBApiRegisterDataCallback(hd,0,_ReadDataTypeXY,CBFunc);
void TBAPI CBFunc(unsigned
long context, _PointerData* data) {
printf("device %d generated x=%d y=%d for stylus:
%d\n",(int)data->pd.device,(int)data->pd.xy->rawx,(int)data->pd.xy->rawy,
(int)data->pd.hStylus); } Some applications might
require that the default UPDD mouse processing be disabled. UPDD API function
call TBApiMousePortInterfaceEnable() can be used for this purpose. UPDD test program with multi-touch
The driver’s test program has been updated to handle
multi-touch input. A simple, full
screen, video demonstration of the test program in use with a multi-touch
device is available here. Over time we will write example
applications to receive multi-touch data and act accordingly and make the
source code available for general reference. UPDD supported or under development
multi-touch hardware
This section will be
updated as we add support for additional multi-touch devices:
ContactFor further information or technical assistance please email the technical support team at technical@touch-base.com |
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