Absolute devices

The elo directory contains an example of a touchscreen protocol module.

Absolute devices (e.g. touchscreens) need to be calibrated. They typically generate "raw" coordinates that must be translated into actual screen coordinates. The screen coordinates they're translated into depend on the screen resolution.

The device/protocol layer module receives raw coordinates from the touchscreen device, formats a packet_abs structure, and passes it up to the absolute filter.

The absolute filter module takes care of translating raw coordinates into screen coordinates. To do this, the module tries to locate and read in a calibration file on startup via:

1. Command-line option to the absolute filter (-f filename)
2. ABSF environment variable
3. /etc/system/config/calib.hostname