calibrate touchscreen

[Peter Hutterer]

On Wed, Oct 19, 2016 at 03:52:56PM +0200, Jens Harms wrote:
> Hi. I try to calibrate  a resisitive Touchscreen.
> The touchscreen is a bit rotatated (3-5 degree), therefore i can not use
> xinput_calibrator. I try to understand how the the evdev driver works.
> 
> Do i need to set "Evdev Axis Calibration" and "Coordinate Transformation
> Matrix" ? Or is it sufficent to set the CTM alone?

don't use the axis calibration, use the matrix only.

> How are Touch coordinates calculated? Which transformations are applied to
> the raw data?

the matrix is a basic transformation matrix, so you can use your normal
rotational elements, etc. The values are normalized to [0, 1] where 1
represents "total width" or "total height".

https://wiki.archlinux.org/index.php/Calibrating_Touchscreen
https://wiki.ubuntu.com/X/InputCoordinateTransformation

Cheers,
   Peter