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- Calibrating Touchscreen

If you ever tried to set up a touchscreen device in linux, you might have noticed that it is either working out of the box (besides some calibration) or is very tedious, especially when it is not supported by the kernel.

## Introduction

This article assumes that your touchscreen device is supported by the kernel (e.g. by the usbtouchscreen module). That means there exists a `/dev/input/event*` node for your device. Check out

    $ less /proc/bus/input/devices

to see if your device is listed or try

    # cat /dev/input/event? # replace ? with the event numbers

for every of your event nodes while touching the display. If you found the corresponding node, it is likely that you will be able to get the device working.

## Available X11 drivers

There are a lot of touchscreen input drivers for X11 out there. The most common ones are in the extra repository:

- xf86-input-evdev (likely the default driver if you plug in your touchscreen and it "just works")
- xf86-input-libinput; see also libinput
- xf86-input-elographics

Less common drivers, not contained in the repository, are:

- xf86-input-magictouch
- xf86-input-mutouch
- xf86-input-plpevtch
- xf86-input-palmax

Proprietary drivers exist for some devices (e.g.: xf86-input-egalaxAUR), but it is recommended to try the open source drivers first.

Depending on your touchscreen device choose an appropriate driver. Again, evdev is likely to be the default if your touchscreen "just works."

## Two-fingers scrolling

The two-fingers scrolling has to be implemented on the application side (see this link). For Firefox, see Firefox/Tweaks#Enable touchscreen gestures.

There is a hack to emulates this scrolling behavior for every application in #Touchegg, but the X server still handles it as text selection (at least with Plasma).

## evdev drivers

### Calibration

Install xinput_calibratorAUR (AUR). Then, run xinput_calibrator and follow the instructions.

## Using a touchscreen in a multi-head setup

To use multiple displays (some of which are touchscreens), you need to tell Xorg the mapping between the touch surface and the screen. This can be achieved with xinput as follows.

Take for example the setup of having a wacom tablet and an external monitor; `xrandr` shows both displays:

    $ xrandr

    Screen 0: minimum 320 x 200, current 2944 x 1080, maximum 8192 x 8192
    LVDS1 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
       1024x768       60.0*+
       800x600        60.3     56.2
       640x480        59.9
    VGA1 connected 1920x1080+1024+0 (normal left inverted right x axis y axis) 477mm x 268mm
       1920x1080      60.0*+
       1600x1200      60.0
       1680x1050      60.0
       1680x945       60.0

You see we have two displays here. LVDS1 and VGA1. LVDS1 is the display internal to the tablet, and VGA1 is the external monitor. We wish to map our stylus input to LVDS1. So we have to find the ID of the stylus input:

    $ xinput --list

    ⎡ Virtual core pointer                    	id=2	[master pointer  (3)]
    ⎜   ↳ Virtual core XTEST pointer              	id=4	[slave  pointer  (2)]
    ⎜   ↳ QUANTA OpticalTouchScreen               	id=9	[slave  pointer  (2)]
    ⎜   ↳ TPPS/2 IBM TrackPoint                   	id=11	[slave  pointer  (2)]
    ⎜   ↳ Serial Wacom Tablet WACf004 stylus      	id=13	[slave  pointer  (2)]
    ⎜   ↳ Serial Wacom Tablet WACf004 eraser      	id=14	[slave  pointer  (2)]
    ⎣ Virtual core keyboard                   	id=3	[master keyboard (2)]
        ↳ Virtual core XTEST keyboard             	id=5	[slave  keyboard (3)]
        ↳ Power Button                            	id=6	[slave  keyboard (3)]
        ↳ Video Bus                               	id=7	[slave  keyboard (3)]
        ↳ Sleep Button                            	id=8	[slave  keyboard (3)]
        ↳ AT Translated Set 2 keyboard            	id=10	[slave  keyboard (3)]
        ↳ ThinkPad Extra Buttons                  	id=12	[slave  keyboard (3)]

We see that we have two stylus inputs. We now need to simply map our inputs to our output like so:

    $ xinput --map-to-output 'Serial Wacom Tablet WACf004 stylus' LVDS1
    $ xinput --map-to-output 'Serial Wacom Tablet WACf004 eraser' LVDS1

You can automate this by putting these commands in your `~/.xinitrc` or similar. The mapping will be lost if the touchscreen is disconnected and re-connected, for example, when switching monitors via a KVM. In that case it is better to use a udev rule. The Calibrating Touchscreen page has an example udev rule for the case when a transformation matrix has been calculated manually and needs to be applied automatically.

### Using xrandr-watch-git to automate map-to-output

There are xrandr events we can capture from a script. Install xrandr-watch-gitAUR, create a script `~/.xrandr-changed` with execution permission to perform map-to-output, for example:

    ~/.xrandr-changed

    #!/bin/sh
    xinput --map-to-output "Wacom HID 4861 Finger touch" "eDP1"

and start, test and enable the systemd/User service `xrandr-watcher.service`.

### Wayland/Weston

Wayland does not currently have a known method to lock touching to a specific display in any environment other than sway (or wlroots-based supported compositors). There are tools such as weston-touch-calibrator, but Gnome Wayland uses Xwayland leaving the calibrator unable to locate any touchscreen.

Wayland/Xwayland also masks the xinput list and funnels them down to generic xwayland devices such as "xwayland-pointer","xwayland-relative-pointer","xwayland-touch-pointer", etc. The Wayland method of "Xinput" is "Libinput", but does not have all the same functionality. The current known method to use touchscreens in a multi-head setup is to force Gnome or KDE to use X11. libinput currently assumes the touchscreen(s) covers all available monitors.

See Sway#Touch display mapping for settings in sway.

## Touchegg

Touchegg is a multitouch gesture program, only compatible with X, that runs as a user in the background, recognizes gestures, and translates them to more conventional events such as mouse wheel movements, so that you can for example use two fingers to scroll. But it also interferes with applications or window managers which already do their own gesture recognition. If you have both a touchpad and a touchscreen, and if the touchpad driver (such as synaptics or libinput) has been configured not to recognize gestures itself, but to pass through the multi-touch events, then Touchegg will recognize gestures on both: this cannot be configured. In fact it does a better job of recognizing gestures than either the synaptics or libinput touchpad drivers; but on the touchscreen, it is generally better for applications to respond to touch in their own unique ways. Some Qt and GTK applications do that, but they will not be able to if you have Touchegg "eating" the touch events. So, Touchegg is useful when you are running mainly legacy applications which do not make their own use of touch events.

The two-fingers scrolling has been disabled in the recent rewrite of touchegg 2.0. To enable it, install xdotool and see this closed issue.

Categories:

- Input devices
- Displays