Touchscreen access library
Apart from directly building it, tslib is currently maintained by the following distributors:
For tarballs ./configure && make && make install
applies, see the
INSTALL
file for more details. For the sources run ./autogen.sh
first.
Extract tslib's tarball into <base>/external/
of your
Android sources and build the components you need
like make libts
, make ts/plugins/input
, make ts_uinput
, ...,
see LOCAL_MODULE in Android.mk.
Refer to Android's documentation for the details.
The idea of tslib is to have a core library that provides standardised services, and a set of plugins to manage the conversion and filtering of touchscreen input data as needed.
The plugins for a particular touchscreen are loaded automatically by the library under the control of a static configuration file, ts.conf. ts.conf gives the library basic configuration information. Each line specifies one module, and the parameters for that module. The modules are loaded in order, with the first one processing the touchscreen data first. For example:
module_raw input
module median depth=3
module dejitter delta=100
module linear
These parameters are described below.
With this configuration file, we end up with the following data flow through the library:
raw read --> median --> dejitter --> linear --> application
module module module module
You can re-order these modules as you wish, add more modules, or remove them
all together. When you call ts_read()
or run ts_uinput -d
and read from
the new input device, see below,
the values you read are values that
have passed through the chain of filters and scaling conversions. Another
call is provided, ts_read_raw()
which bypasses all the modules and reads the
raw data directly from the device.
There are a couple of programs in the tslib/tests
directory which give example
usages. They are by no means exhaustive, nor probably even good examples.
They are basically the programs used to test this library.
Years ago (or in part still for resistive touch screens) a use case for tslib to enable using the device would look like
- use a hardware specific
module_raw
plugin (single touch only) - mainly use the
linear
filter plugin (andts_calibrate
) - use
ts_read()
(in the form of a plugin for Qt, X11, ...)
While being fully backwards compatible, nowadays, for capacitive touch screens a use case to optimize the touch experience or work around hardware or driver bugs would be
- use the
module_raw input
plugin for Linux drivers (and have multi touch) - use a combination of other filter plugins to optimize the touch experience
- have the
ts_uinput -d
daemon running and use it's input device in your environment
Instead of using tslib's API calls, you can use tslib/tools/ts_uinput
which
creates (via uinput) a new standard input event device you can use in your
environment. The new device provides the filtered and calibrated values and
should work with single- and multitouch devices. ts_uinput_start.sh
starts
ts_uinput
as a daemon and creates a link named /dev/input/ts_uinput
for
convenience.
Similar to the mentioned ts_read()
, ts_read_mt()
reads one struct ts_sample_mt
per slot (number of possible contacts) and desired number of samples. You have
to provide slots*nr of them to hold the resulting values, see the multitouch
programs in tslib/tests
for examples; there is, of course, ts_read_raw_mt()
too.
ts_read_mt()
aims to be a drop-in replacement for ts_read()
, so you can use
it for any single touch device too, providing space for one slot.
TSLIB_TSDEVICE TS device file name.
Default (inputapi): /dev/input/ts
/dev/input/touchscreen
/dev/input/event0
Default (non inputapi): /dev/touchscreen/ucb1x00
TSLIB_CALIBFILE Calibration file.
Default: ${sysconfdir}/pointercal
TSLIB_CONFFILE Config file.
Default: ${sysconfdir}/ts.conf
TSLIB_PLUGINDIR Plugin directory.
Default: ${datadir}/plugins
TSLIB_CONSOLEDEVICE Console device.
Default: /dev/tty
TSLIB_FBDEVICE Framebuffer device.
Default: /dev/fb0
Variance filter. Tries to do it's best in order to filter out random noise coming from touchscreen ADC's. This is achieved by limiting the sample movement speed to some value (e.g. the pen is not supposed to move quicker than some threshold).
This is a 'greedy' filter, e.g. it gives less samples on output than receives on input. It can cause problems on capacitive touchscreens that already apply such a filter.
There is no multitouch support for this filter (yet). ts_read_mt()
will
only read one slot, when this filter is used. You can try using the median
filter instead.
-
delta
Set the squared distance in touchscreen units between previous and current pen position (e.g. (X2-X1)^2 + (Y2-Y1)^2). This defines the criteria for determining whenever two samples are 'near' or 'far' to each other.
Now if the distance between previous and current sample is 'far', the sample is marked as 'potential noise'. This doesn't mean yet that it will be discarded; if the next reading will be close to it, this will be considered just a regular 'quick motion' event, and it will sneak to the next layer. Also, if the sample after the 'potential noise' is 'far' from both previously discussed samples, this is also considered a 'quick motion' event and the sample sneaks into the output stream.
Removes jitter on the X and Y co-ordinates. This is achieved by applying a weighted smoothing filter. The latest samples have most weight; earlier samples have less weight. This allows to achieve 1:1 input->output rate. See Wikipedia for some general theory.
-
delta
Squared distance between two samples ((X2-X1)^2 + (Y2-Y1)^2) that defines the 'quick motion' threshold. If the pen moves quick, it is not feasible to smooth pen motion, besides quick motion is not precise anyway; so if quick motion is detected the module just discards the backlog and simply copies input to output.
Linear scaling module, primerily used for conversion of touch screen
co-ordinates to screen co-ordinates. It applies the corrections as recorded
and saved by the ts_calibrate
tool.
-
xyswap
interchange the X and Y co-ordinates -- no longer used or needed if the linear calibration utility
ts_calibrate
is used. -
pressure_offset
offset applied to the pressure value
-
pressure_mul
factor to multiply the pressure value with
-
pressure_div
value to divide the pressure value by
Pressure threshold filter. Given a release is always pressure 0 and a press is always >= 1, this discards samples below / above the specified pressure threshold.
-
pmin
Minimum pressure value for a sample to be valid.
-
pmax
Maximum pressure value for a sample to be valid.
Simple debounce mechanism that drops input events for the specified time after a touch gesture stopped. Wikipedia has more theory.
-
drop_threshold
drop events up to this number of milliseconds after the last release event.
Skip nhead samples after press and ntail samples before release. This should help if for the device the first or last samples are unreliable.
Parameters:
-
nhead
Number of events to drop after pressure
-
ntail
Number of events to drop before release
Similar to what the variance filter does, the median filter suppresses spikes in the gesture. For some theory, see Wikipedia
Parameters:
-
depth
Number of samples to apply the median filter to
For those creating tslib modules, it is important to note a couple things with regard to handling of the ability for a user to request more than one ts event at a time. The first thing to note is that the lower layers may send up less events than the user requested, because some events may be filtered out by intermediate layers. Next, your module should send up just as many events as the user requested in nr. If your module is one that consumes events, such as variance, then you loop on the read from the lower layers, and only send the events up when
- you have the number of events requested by the user, or
- one of the events from the lower layers was a pen release.