To calibrate a touch screen a number of crosses are displayed on the desktop that are touched as they appear. For cosmetic reasons only these crosses are normally shown on a white background that covers the full screen.
There are 2 scenarios whereby the crosses may be displaced, leading to offset calibration. We have catered for two known issues as follows:
Desktop Geometry
The driver can determine the geometry from the screen metrics or that which is available.
Two global setting are used, defining 'screen' or 'available':
calibration.force_geometry
segmentation.force_geometry
The first controls placement of the screen and the second placement of the segment within the screen, 1x1 is treated as a single segment for consistency of processing.
| calibration.force_geometry |
By default UPDD uses the available geometry to determine the placement of the calibration window (the screen geometry minus menu bar and similar areas).
This setting allows the non-default option screen to be used.
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| segmentation.force_geometry |
This setting allows for a different option to be used for the placement of a segment within a window. If set calibration.force_geometry is used for the window geometry and this value for the segment positioning.
In builds < 6.0.655 this had to be set explicitly
In builds >= 655 if this is not set the value of calibration.force_geometry is used for window and segment placement.
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If calibration placement are offset try the screen option using the command 'upddutils nodevice set calibration.force_geometry screen'
Full screen issues
Full screen is not always possible to achieve in Linux and we are aware that full screen mode via the Windows Manager can be a bit inconsistent under X and there appears to be no sure fire way to implement a foolproof solution.
When requesting full screen via the Windows Manager with some Linux distributions, virtualized environments or certain visual effect settings the method used by our graphical calibration program to force full screen can give unpredictable results.
In cases where the calibration background fails to display in full screen we offset the calibration crosses so that calibration is unaffected.
To date we have seen this with VMWare tilizedation, Linux distribution Maemo and main stream distributions with certain visual effects enabled.
On systems where the full screen issue occurs you may be able to reconfigure the system to allow full screen or utilise a basic 2 point corner calibration program, as described below.
Configure the system to allow full screen
For example, if a window manager is preventing full screen mode try running without the window manager active. (This has been necessary on systems using the TWM window manager)
Where visual effects are preventing full screen, temporarily disable the effect. We have had reports that on some Ubuntu systems the calibration screen is windowed (having a title bar) instead of taking up the entire desktop. This is due to the desktop effects interfering with the window manager. If this effect is experienced, then follow these instructions to temporarily disable desktop effects for the duration of the calibration.
| Open the “Appearance” application as shown below |
Navigate to the “Visual Effects” tab |
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If “Normal” or “Extra” is selected then select “None” and now try calibrating the touchscreen
When calibration is complete, select the visual effect that was in use before and click “Close”
Here the auto-launcher is preventing the calibration screen covering the left-most side of the screen. This can be hidden to allow for calibration.
Full screen not possible
In cases where full screen is not possible leading to incorrect calibration you can achieve accurate calibration as follows:
- Set 4 point calibration with 0% margin and when asked to touch the calibration point just touch in the corner of the touch screen.
- Utilise the basic 2 point corner calibration as described here.