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C library for filtering touchscreen events

tslib consists of the library libts and tools that help you calibrate and use it in your environment.

contact

If you have problems, questions, ideas or suggestions, please contact us by writing an email to tslib@lists.infradead.org, which is our mailing list.

website

Visit the tslib website for an overview of the project.

table of contents

setup and configure tslib

install tslib

tslib runs on various hardware architectures and operating systems, including GNU/Linux, FreeBSD or Android/Linux. See building tslib for details. Apart from building the latest tarball release, running ./configure, make and make install, tslib is available from distributors like Arch Linux / Arch Linux ARM, Buildroot, Debian / Ubuntu, Fedora or OpenSUSE and their package management.

configure tslib

This is just an example /etc/ts.conf file. Touch samples flow from top to bottom. Each line specifies one module and it's parameters. Modules are processed in order. Use one module_raw on top, that accesses your device, followed by any combination of filter modules.

module_raw input
module median depth=3
module dejitter delta=100
module linear

see the section below for available filters and their parameters. On Linux, your first commented-in line should always be module_raw input which offers one optional parameter: grab_events=1 if you want it to execute EVIOCGRAB on the device.

With this configuration file, we end up with the following data flow through the library:

driver --> raw read --> median  --> dejitter --> linear --> application (using ts_read_mt())
           module       module      module       module

calibrate the touch screen

Calibration is done by the linear plugin, which uses it's own config file /etc/pointercal. Don't edit this file manually. It is created by the ts_calibrate program:

# ts_calibrate

The calibration procedure simply requires you to touch the cross on screen, where is appears, as accurate as possible.

ts_calibrate

test the filtered input behaviour

You may quickly test the touch behaviour that results from the configured filters, using ts_test_mt:

# ts_test_mt

ts_test_mt

On the bottom left of the screen, you see the available concurrent touch contacts supported, and whether it's because the driver says so, or ts_test_mt was started with the -j commandline option to overwrite it.

environment variables (optional)

You may override defaults. In most cases you won't need to do so though:

TSLIB_TSDEVICE          Touchscreen device file name.
                        Default:                automatic detection (on Linux)

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. (not needed when using --with-sdl2)
                        Default:                /dev/tty

TSLIB_FBDEVICE          Framebuffer device.
                        Default:                /dev/fb0

use the filtered result in your system (X.org method)

If you're using X.org graphical X server, things should be very easy. Install tslib and xf86-input-tslib, reboot, and you should instantly have your ts.conf filters running, without configuring anything else yourself.

use the filtered result in your system (ts_uinput method)

TL;DR: Run tools/ts_uinput_start.sh during startup and use /dev/input/ts_uinput as your evdev input device.

tslib tries to automatically find your touchscreen device in /dev/input/event* on Linux. Now make ts_uinput use it, instead of your graphical environment directly:

# ts_uinput -d -v

-d makes the program return and run as a daemon in the background. -v makes it print the new /dev/input/eventX device node before returning.

Now make your graphical environment use that new input device, using evdev drivers.

  • For Qt5 for example you'd probably set something like this:

    QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS=/dev/input/eventX:rotate=0

  • For X11 you'd probably edit your xorg.conf Section "InputDevice" for your touchscreen to have

    Option "Device" "/dev/input/eventX"

Please consult your input system's documentation on how to use a specific evdev input device.

Let's recap the data flow here:

driver --> raw read --> filter(s) ... --> ts_uinput --> libevdev read  --> GUI app/toolkit
           module       module(s) ...     daemon        e.g. in libinput

symlink /dev/input/ts_uinput to the new event file

/dev/input/event numbers are not persistent. In order to know in advance, what enumerated input device file is created by ts_uinput, you can use a symlink:

  • use the included tools/ts_uinput_start.sh script that starts ts_uinput -d -v and creates the symlink called /dev/input/ts_uinput for you, or

  • if you're using systemd, create the following udev rule, for example /etc/udev/rules.d/98-touchscreen.rules:

    SUBSYSTEM=="input", KERNEL=="event[0-9]*", ATTRS{name}=="ts_uinput", SYMLINK+="input/ts_uinput"
    

running as systemd service (optional)

in case you have to use non-default paths, create a file containing the environment for tslib, like /etc/ts.env

  TSLIB_CALIBFILE=/etc/pointercal
  TSLIB_CONFFILE=/etc/ts.conf
  TSLIB_PLUGINDIR=/usr/lib/ts

and create a systemd service file, like /usr/lib/systemd/system/ts_uinput.service

  [Unit]
  Description=touchscreen input
  Wants=dev-input-ts_raw.device
  After=dev-input-ts_raw.device

  [Service]
  Type=oneshot
  EnvironmentFile=/etc/ts.env
  ExecStart=/bin/sh -c 'exec /usr/bin/ts_uinput &> /var/log/ts_uinput.log'

  [Install]
  WantedBy=multi-user.target

and

  #systemctl enable ts_uinput

will enable it permanently.

other operating systems

There is no tool that we know of that reads tslib samples and uses the Windows touch injection API, for example (yet).

filter modules

module: linear

Linear scaling - calibration - 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. It's the only module that reads a configuration file.

Parameters (usually not needed):

  • rot

    overwrite the rotation to apply. clockwise: rot=1, upside down: rot=2, couter-clockwise: rot=3. Default: screen-rotation during ts_calibrate calibration.

  • 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. Default: 0

  • pressure_mul

    factor to multiply the pressure value with. Default: 1.

  • pressure_div

    value to divide the pressure value by. Default: 1.

Example: module linear rot=0

module: invert

Invert values in X and/or Y direction around the given value. There are no default values. If specified, a value has to be set. If one axis is not specified, it's simply untouched.

Parameters:

  • x0

    X-axis (horizontal) value around which to invert.

  • y0

    Y-axis (vertical) value around which to invert.

Example: module invert y0=640 (Y-axis inverted for 640 screen height, X-axis untouched)

module: median

The median filter reduces noise in the samples' coordinate values. It is able to filter undesired single large jumps in the signal. For some theory, see Wikipedia

Parameters:

  • depth

    Number of samples to apply the median filter to. Default: 3.

Example: module median depth=5

module: pthres

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.

Parameters:

  • pmin

    Minimum pressure value for a sample to be valid. Default: 1.

  • pmax

    Maximum pressure value for a sample to be valid. Default: (INT_MAX).

Example: module pthres pmin=10

module: iir

Infinite impulse response filter. This is a smoothing filter to remove low-level noise. There is a trade-off between noise removal (smoothing) and responsiveness. The parameters N and D specify the level of smoothing in the form of a fraction (N/D).

Wikipedia has some theory.

Parameters:

  • N

    numerator of the smoothing fraction. Default: 0.

  • D

    denominator of the smoothing fraction. Default: 1.

Example: module iir N=6 D=10

module: dejitter

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 theory.

Parameters:

  • 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. Default: 100.

Example: module dejitter delta=100

module: debounce

Simple debounce mechanism that drops input events for the specified time after a touch gesture stopped. Wikipedia has more theory.

Parameters:

  • drop_threshold

    drop events up to this number of milliseconds after the last release event. Default: 0.

Example: module debounce drop_threshold=40

module: skip

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. Default: 1.

  • ntail

    Number of events to drop before release. Default: 1.

Example: module skip nhead=2 ntail=1

module: lowpass

Simple lowpass exponential averaging filtering module.

Parameters:

  • factor

    floating point value between 0 and 1; for example 0.2 for more smoothing or 0.8 for less. Default: 0.4.

  • threshold

    x or y minimum distance between two samples to start applying the filter. Default: 2.

Example: module lowpass factor=0.5 threshold=1

module: variance

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).

There is no multitouch support for this filter (yet). ts_read_mt() will limit your input to one slot when this filter is used. Try using the median filter instead.

Parameters:

  • 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.


The following example setup

       |--------|       |-----|      |--------------|
x ---> | median | ----> | IIR | ---> |              | ---> x'
       |--------|    -> |-----|      |    screen    |
                    |                |  transform   |
                    |                | (calibrate)  |
       |--------|   |   |-----|      |              |
y ---> | median | ----> | IIR | ---> |              | ---> y'
       |--------|   |-> |-----|      |--------------|
                    |
                    |
             |----------|
p ---------> | debounce | -------------------------------> p'
             |----------|

would be achieved by the following ts.conf:

module_raw input
module debounce drop_threshold=40
module median depth=5
module iir N=6 D=10
module linear

while you are free to play with the parameter values.

screen rotation

The graphical tools support rotating the screen, see ts_calibrate --help or the man pages for the details. ts_calibrate will (in the background) ignore screen rotation but will save the current rotation state in the "calibration file" TSLIB_CALIBFILE. The linear filter module will pick that up and apply the given rotation. It can be overwritten by using the rot module parameter: module linear rot=0 (if your toolkit or higher level application does rotation).


the libts library

the libts API

The API is documented in our man pages in the doc directory. Check out our tests directory for examples how to use it.

tslib_version()
ts_libversion()
ts_open()
ts_config()
ts_setup()
ts_close()
ts_reconfig()
ts_option()
ts_fd()
ts_load_module()
ts_read()
ts_read_raw()
ts_read_mt()
ts_read_raw_mt()
int (*ts_error_fn)(const char *fmt, va_list ap)
int (*ts_open_restricted)(const char *path, int flags, void *user_data)
void (*ts_close_restricted)(int fd, void *user_data)
ts_get_eventpath()
ts_print_ascii_logo()
ts_conf_get()
ts_conf_set()

using libts

To use the library from C or C++, include the following preprocessor directive in your source files:

#include <tslib.h>

To link with with library, specify -lts as an argument to the linker.

compiling using autoconf and pkg-config

On UNIX systems you can use pkg-config to automatically select the appropriate compiler and linker switches for libts. The PKG_CHECK_MODULES m4 macro may be used to automatically set the appropriate Makefile variables:

PKG_CHECK_MODULES([TSLIB], [tslib >= 1.10],,
  AC_MSG_ERROR([libts 1.10 or newer not found.])
)

If you want to support tslib < 1.2, while still support multitouch and all recent versions of tslib, you'd do something like this:

#include <tslib.h>

#ifndef TSLIB_VERSION_MT
        /* ts_read() as before (due to old tslib) */
#else
        /* new ts_setup() and ret = ts_read_mt() */
        if (ret == -ENOSYS)
                /* ts_read() as before (due to user config) */
#endif

This is a complete example program, similar to ts_print_mt.c:

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/time.h>
#include <unistd.h>
#include <errno.h>

#include <tslib.h>

#define SLOTS 5
#define SAMPLES 1

int main(int argc, char **argv)
{
    struct tsdev *ts;
    char *tsdevice = NULL;
    struct ts_sample_mt **samp_mt = NULL;
    int ret, i, j;

    ts = ts_setup(tsdevice, 0);
    if (!ts) {
            perror("ts_setup");
            return -1;
    }

    samp_mt = malloc(SAMPLES * sizeof(struct ts_sample_mt *));
    if (!samp_mt) {
            ts_close(ts);
            return -ENOMEM;
    }
    for (i = 0; i < SAMPLES; i++) {
            samp_mt[i] = calloc(SLOTS, sizeof(struct ts_sample_mt));
            if (!samp_mt[i]) {
                    free(samp_mt);
                    ts_close(ts);
                    return -ENOMEM;
            }
    }

    while (1) {
            ret = ts_read_mt(ts, samp_mt, SLOTS, SAMPLES);
            if (ret < 0) {
                    perror("ts_read_mt");
                    ts_close(ts);
                    exit(1);
            }

            for (j = 0; j < ret; j++) {
            	for (i = 0; i < SLOTS; i++) {
		#ifdef TSLIB_MT_VALID
			if (!(samp_mt[j][i].valid & TSLIB_MT_VALID))
				continue;
		#else
			if (samp_mt[j][i].valid < 1)
				continue;
		#endif

			printf("%ld.%06ld: (slot %d) %6d %6d %6d\n",
			       samp_mt[j][i].tv.tv_sec,
			       samp_mt[j][i].tv.tv_usec,
			       samp_mt[j][i].slot,
			       samp_mt[j][i].x,
			       samp_mt[j][i].y,
			       samp_mt[j][i].pressure);
                    }
            }
    }

    ts_close(ts);
}

If you know how many slots your device can handle, you could avoid malloc:

struct ts_sample_mt TouchScreenSamples[SAMPLES][SLOTS];

struct ts_sample_mt (*pTouchScreenSamples)[SLOTS] = TouchScreenSamples;
struct ts_sample_mt *ts_samp[SAMPLES];
for (i = 0; i < SAMPLES; i++)
        ts_samp[i] = pTouchScreenSamples[i];

and call ts_read_mt() like so

ts_read_mt(ts, ts_samp, SLOTS, SAMPLES);

ABI - Application Binary Interface

Wikipedia has background information.

libts Soname versions

Usually, and every time until now, libts does not break the ABI and your application can continue using libts after upgrading. Specifically this is indicated by the libts library version's major number, which should always stay the same. According to our versioning scheme, the major number is incremented only if we break backwards compatibility. The second or third minor version will increase with releases. In the following example

libts.so -> libts.so.0.7.0
libts.so.0 -> libts.so.0.7.0
libts.so.0.7.0

use libts.so for using tslib unconditionally and libts.so.0 to make sure your current application never breaks.

If a release includes changes like added features, the second number is incremented and the third is set to zero. If a release includes mostly just bugfixes, only the third number is incremented.

tslib package version

A tslib tarball version number doesn't tell you anything about it's backwards compatibility.

dependencies

  • libc (with libdl only when building dynamically linked)
  • libsdl2-dev (only when using --with-sdl2 for SDL2 graphical applications)

related libraries

libts users

This lists the programs for the every day use of tslib, facing the outside world. For testing purposes there are tools like ts_test_mt too.

shipped as part of tslib

  • ts_calibrate - graphical calibration tool. Configures the linear filter module.
  • ts_uinput - userspace evdev driver for the tslib-filtered samples.

third party applications

  • xf86-input-tslib - direct tslib input driver for X11
  • qtslib - direct Qt5 tslib input plugin
  • enlightenment - A Window Manager (direct support in framebuffer mode, X11 via xf86-input-tslib)
  • DirectFB - Graphics library on top of framebuffer

tslib module API

struct tslib_module_info
struct tslib_vars
struct tslib_ops
tslib_parse_vars(struct tslib_module_info *,const struct tslib_vars *, int, const char *);

tslib modules (filter or driver/raw module) in the plugins directory need to implement mod_init(). If the module takes parameters, it has to declare a const struct tslib_vars and pass that, it's lengths and the params string that is passed to mod_init to tslib_parse_vars() during mod_init().

Furthermore a const struct tslib_ops has to be declared, with it's members pointing to the module's implementation of module-operations like read_mt that get called in the chain of filters.

Symbols in Versions

Name Introduced
TSLIB_VERSION_MT 1.10
TSLIB_VERSION_OPEN_RESTRICTED 1.13
TSLIB_VERSION_EVENTPATH 1.15
TSLIB_VERSION_VERSION 1.16
TSLIB_MT_VALID 1.13
TSLIB_MT_VALID_TOOL 1.13
tslib_version 1.16
ts_print_ascii_logo 1.16
ts_libversion 1.10
ts_close 1.0
ts_config 1.0
ts_reconfig 1.3
ts_setup 1.4
ts_error_fn 1.0
ts_open_restricted 1.13
ts_close_restricted 1.13
ts_fd 1.0
ts_load_module 1.0
ts_open 1.0
ts_option 1.1
ts_read 1.0
ts_read_mt 1.3
ts_read_raw 1.0
ts_read_raw_mt 1.3
tslib_parse_vars 1.0
ts_get_eventpath 1.15
ts_conf_get 1.18
ts_conf_set 1.18

building tslib

shared vs. static builds

libts can be built to fit your needs. Use the configure script to enable only the modules you need. By default, libts is built as a shared library, with each module being a shared library object itself. You can, however, configure tslib to build libts statically linked, and the needed modules compiled inside of libts. Here's an example for this:

./configure --enable-static --disable-shared --enable-input=static --enable-linear=static --enable-iir=static

This should result in a libts.a of roughly 50 kilobytes, ready for using calibration (linear filter) and the infinite impulse response filter in ts.conf.

CMake

Alternatively you can use CMake to build the project. To create an build in the project tree:

mkdir build && cd build
cmake ../
cmake --build .
cmake -P cmake_install.cmake

By default the core tslib is built as a shared library. In order to build it as static, add -DBUILD_SHARED_LIBS=OFF to the configure line.

Also the plugins are by default built as shared. Add -Dstatic-<module>=ON to the configuration step to build plugin statically into the core tslib. To disable and enable modules, use flags: -Denable-<module>=ON/OFF.

Using tslib in client apps

The following is a minimal example how to use tslib built with CMake in your client app. Adding tslib::tslib as a link target will add required dependencies and include directories generated build files.

cmake_minimum_required(VERSION 3.10)
project(tslib_client)
find_package(tslib 1.16)
add_executable(tslib_client main.c)
target_link_libraries(tslib_client PUBLIC tslib::tslib)

portable ts_calibrate and ts_test_mt using SDL2

In case you cannot draw to the framebuffer directly, there is an experimental implentation of the necessary graphical tools using SDL2. They are more portable but require more resources to run. To use them, make sure you have SDL2 and the development headers installed and use ./configure --with-sdl2.

portability

tslib is cross-platform; you should be able to build it on a large variety of operating systems.

libts and filter plugins (module)

This is the hardware independent core part: libts and all filter modules as shared libraries, build on the following operating systems and probably more.

  • GNU / Linux
  • Android / Linux
  • FreeBSD
  • GNU / Hurd
  • Haiku
  • Windows
  • Mac OS X

input plugins (module_raw)

This makes the thing usable in the real world because it accesses your device. See hardware support for the currently possible configuration for your platform.

The libts default configuration currently has the following input modules disabled:

  • cy8mrln-palmpre
  • dmc_dus3000
  • galax
  • arctic2
  • corgi
  • collie
  • dmc
  • h3600
  • mk712
  • ucb1x00
  • tatung

Please note that this list may grow over time. If you rely on a particular input plugin, you should enable it explicitely. On Linux you should only need input though.

  • GNU / Linux - all (most importantly input)
    • ./configure
  • Android / Linux - all (most importantly input)
    • ./configure
  • FreeBSD - almost all (most importantly input)
    • ./configure --disable-waveshare
  • GNU / Hurd - some, see hardware support
    • ./configure --disable-input --disable-waveshare
  • Haiku - some, see hardware support
    • ./configure --disable-input --disable-touchkit --disable-waveshare
  • Windows - no tslib module for the Windows touchscreen API (yet)
    • ./configure --with-sdl2 --disable-input --disable-touchkit --disable-waveshare

Writing your own plugin is quite easy, in case an existing one doesn't fit.

test programs and tools

  • GNU / Linux - all
  • Android / Linux - all (?)
  • FreeBSD - all (?)
  • GNU / Hurd - ts_print_mt, ts_print, ts_print_raw, ts_finddev
  • Haiku - ts_print_mt, ts_print, ts_print_raw, ts_finddev
  • Windows - ts_print.exe, ts_print_raw.exe ts_print_mt.exe ts_test_mt.exe ts_calibrate.exe

download binaries?

For GNU/Linux all architectures are very well covered, thanks to Debian or Arch Linux or others.

If you're lucky, you'll find some unofficial testing builds for Windows or other platforms here.

Please help porting missing programs!

touchscreen hardware support

TL;DR: On Linux, use module_raw input

For mostly historical reasons, tslib includes device specific module_raw userspace drivers. The ts.conf man page has details on the available module_raw drivers; not all of them are listed in the default etc/ts.conf config file. Those are to be considered workarounds and may get disabled in the default configuration in the future. If you use one of those, please ./configure --enable-... it explicitely.

It is strongly recommended to have a real device driver for your system and use a generic access module_raw of tslib. For Linux (evdev) this is called input. There is an equivalent experimental module that needs libevdev installed: module_raw input_evdev.