xinput calibration and options

Question

I'm on a lenovo thinkpad x220t running a fresh installation of fedora 22. Everything works fine, except when I connect the tablet to a projector, due to change of resolution the pen is not calibrated anymore. I've tried xinput_calibrator to adjust it, but since it "auto-detect"s misclicks I can't really get it to work. I tried to turn it off using the option --misclick 0, but that also didn't work. The option --precalib doesn't get me anywhere.

I think the best way to work this out for me is to set in manually in xinput, but I can't find the options in the xinput manual. So, here is my question:

Questions: In the xinput, I want to use the option --set-int-prop device property format value. The name of the device for me is "Wacom ISDv4 E6 Pen stylus".

1. What shall I use as property for x_min, x_max etc.?
2. What shall be the format? I know the available formats are 8, 16, and 32, but which one shall I choose and what do they mean?
3. Is there anywhere I can read more about these options?

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Alternatively, is there a better way of dealing with this calibration? The xinput_calibrator manual says I probably have one of the following problems:

1. you are bad at clicking on crosses, use a stylus or increase the --misclick threshold
2. your device is not properly supported by the kernel, it interprets the clicks wrong
3. your screen has a non-linear deformation, 4-point calibration can not help you

well, I'm sure 1 is not the case. It cannot be 2, because it works fine in the original resolution. And it probably isn't 3 since I can really see that it is a linear deformation as the pen gets to the edge of the monitor (not screen) the pointer is on the edge of the screen and in the center they match! I believe all I need is to tell xinput to scale everything by a constant factor, which I don't know how.

Any help would be really appreciated.

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UPDATE: The instruction here exactly tells me how to "scale" and "shift" the screen, but it seems like I can't get the numbers right. Here are some of my outputs:

for xrandr I get several lines, and among them there are:

1366x768      60.02 +
...
1024x768      60.00*
...

The top one (the one with +) is the highest my monitor supports, and in that resolution I get pen to work properly. The bottom one (the one with *) is my current resolution. The numbers that the link suggest to use are:

 c0 = touch_area_width / total_width
 c2 = touch_area_height / total_height
 c1 = touch_area_x_offset / total_width
 c3 = touch_area_y_offset / total_height

c2 = 1 and c3 = 0 for me, since I don't have any problem with width. for c0 and c3 I'm using this numbers: touch_area_width = 1366 total_width = 1024 touch_area_x_offset = -171

I'm getting 171 from (1366 - 1024) / 2.

This translation "almost" works. Does anyone know which of this parameters I'm using wrong, and how do I find its exact value?

Answer 1

I found this wiki post from ArchLinux and it does exactly what I need to do, except the numbers are a little off. This thread got too messy, I'm answering it, but there's still one last but that I need to work out (see below).

To follow the discussion on this last bit see this post.

Here is what I've done:

From xrandr I get:

Screen 0: minimum 8 x 8, current 1024 x 768, maximum 32767 x 32767
LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 277mm x 156mm
   1366x768      60.02 +
   1280x720      60.00  
   1024x768      60.00* 
   1024x576      60.00  
   ...

The one with + is maximum resolution my monitor supports and the one with * is the current resolution. So, I conclude

total_width = 1024
touch_area_width = 1366
touch_area_x_offset = (1024 - 1366) /2 = -171

This is probably what I'm doing wrong, because at the end I don't get exactly what I need, but almost there.

Then I look at the output of xinput list

⎡ Virtual core pointer                        id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                  id=4    [slave  pointer  (2)]
⎜   ↳ Logitech M325                               id=9    [slave  pointer  (2)]
⎜   ↳ Wacom ISDv4 E6 Pen stylus                   id=10    [slave  pointer  (2)]
⎜   ↳ Wacom ISDv4 E6 Finger                       id=11    [slave  pointer  (2)]
⎜   ↳ SynPS/2 Synaptics TouchPad                  id=13    [slave  pointer  (2)]
⎜   ↳ TPPS/2 IBM TrackPoint                       id=14    [slave  pointer  (2)]
⎜   ↳ Wacom ISDv4 E6 Pen eraser                   id=16    [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=12    [slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                      id=15    [slave  keyboard (3)]

The lines 4,5, and 8 are the ones that I need, so the DEVICE NAMEs for me will be "Wacom ISDv4 E6 Pen stylus", "Wacom ISDv4 E6 Finger", and "Wacom ISDv4 E6 Pen eraser".

xinput list-props "device name" | grep Matrix should list the current Coordinate Transformation Matrix. The default is the identity matrix which is listed by rows:

Coordinate Transformation Matrix (138): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000

The transformation matrix is The matrix is

[ c0 0  c1 ]
[ 0  c2 c3 ]
[ 0  0  1  ]

The tutorial says to calculate the matrix as follows: (the numbers on the right are the ones that I calculated for my case)

c0 = touch_area_width / total_width = 1366/1024 = 1.333984375
c2 = touch_area_height / total_height = 768/768 = 1
c1 = touch_area_x_offset / total_width = -171/768 = -0.22265625
c3 = touch_area_y_offset / total_height = 0/768 = 0

The reason c2=1 and c3=0 for me is that in my situation the height is fine, so I only need to scale and shift the width.

All I need to do now is to represent my matrix as an array of rows, that is:

c0 0 c1 0 c2 c3 0 0 1

and that for me becomes:

1.333984375 0 -0.22265625 0 1 0 0 0 1

Then the following command should do the translation for me:

xinput set-prop "DEVICE NAME" --type=float "Coordinate Transformation Matrix" 1.333984375 0 -0.22265625 0 1 0 0 0 1

That almost gets me where I want to be except it's still a little off. So, I did a little bit of trial and error to get the following numbers 1.345 0 -0.17 0 1 0 0 0 1

So, here is my question

How to find the exact values for the transformation matrix? I need to work with different resolutions and I can't repeat the trial and error process for all of them!

Answer 2

I think your calculation of c1 is wrong. Instead of -171/768, you should have -171/1024 = -0.167, which matches what you found experimentally.