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I connected yesterday a Raspberry Pi 3 Model B at a 3M touch Systems touchscreen. For installing I followed this tutorial that I found here: Inverted GPIO Touchscreen (Using 99-calibration.conf)

What I did was:

  • git clone https://github.com/swkim01/waveshare-dtoverlays.git
  • sudo cp waveshare-dtoverlays/waveshare35a-overlay.dtb /boot/overlays/
  • sudo nano /boot/config.txt
  • I added there: dtoverlay=waveshare35a:rotate=270,swapxy=1
  • I ran xinput-calibration
  • I added the values resulted from calibration into /X11/xorg.conf.d/99-calibration.conf and the following transformation matrix: 0 1 0 -1 0 1 0 0 1

The 99-calibration file looks like this: 

Section "InputClass"
Identifier  "calibration"
MatchProduct    "3M 3M USB Touchscreen - EX II"
Option  "MinX"  "57679"
Option  "MaxX"  "7631"
Option  "MinY"  "8256"
Option  "MaxY"  "55187"
Option "TransformationMatrix" "0 1 0 -1 0 1 0 0 1"
EndSection

The problem is that the x axis is inverted. The SwapX or InvertX doesn't work. Also when I installed the raspberry pi the first time x and y axes were swaped. What should I do? Can You give me a Transformation Matrix that works both for x and y and doesn't swap them?

Galescu Raul
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1 Answers1

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Assuming you're using Raspbian stretch, touchscreens are now handled by libinput instead of evdev, and settings in 99-calibration.conf (mostly) no longer apply. A workaround is to download evdev and make touchscreens use evdev again instead of libinput - so 99-calibration.conf will once again be useful. However, the better fix is to set the proper coordinate transformation matrix by an xinput command.

I found the procedures outlined in https://gist.github.com/KurtJacobson/37288a0300a9c1b3e859c8dcff403300 to be very helpful. Since Raspbian is based on Debian, the procedure applies. It includes a link to an interactive tool to visualize changes in the transformation matrix. I simply used trial and error to adjust a transformation matrix to get perfect tracking on the touchscreen I was using.

But before you start, edit your 99-calibration.config file to delete or disable the transformation matrix. For some reason, the matrix in 99-calibration.config IS read.

Once you've fine-tuned your transformation matrix, you'll need to save it in ~/.xsessionrc, so it will be applied every time the system reboots. Here's mine as an example.

#!/bin/bash
# Set coordinate transformation matrix for Pi-RAQ touch display
# (rotate left; adjust for accurate pointer tracking)
xinput set-prop 'TSC-50 DMC' 'Coordinate Transformation Matrix' 0 1.05 -0.025 -1.6 0 1.3 0 0 1
Mark Bersalona
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