Home#include <lua/touch.lh>
- cal = touchhandle:calibration()
- cal = touchhandle:calibration(cal)
- cal = touchhandle:calibration("clear")
SYNOPSIS
DESCRIPTION
Query or set the calibration for the touch screen. The table cal contains the fields:
| xoffs | X-offset |
| xscale | X scaling factor |
| xyscale | Y correction scaling factor |
| xmax | X display resolution |
| yoffs | Y-offset |
| yscale | Y scaling factor |
| yxscale | X correction scaling factor |
| ymax | Y display resolution |
| penthr | Pen pressure threshold |
| fingerthr | Finger pressure threshold |
| flags | Flags indicating screen orientation |
The following piece of code shows how the calibration data is used. Assume raw_x and raw_y contain the raw data from the hardware, while screen_x and screen_y will receive the calculated result.
if (cal.flags & TOUCHCAL_SWAPPED) then
local tmp = raw_x
raw_x = raw_y
raw_y = tmp
end
screen_x = ((raw_x * cal.xscale) >> 16) + ((raw_y * cal.xyscale) >> 16) - cal.xoffs
screen_y = ((raw_y * cal.yscale) >> 16) + ((raw_x * cal.yxscale) >> 16) - cal.yoffs
if (cal.flags & TOUCHCAL_XMIRROR) then screen_x = cal.xmax - screen_x end
if (cal.flags & TOUCHCAL_YMIRROR) then screen_y = cal.ymax - screen_y end
if (screen_x < 0) then screen_x = 0 end
if (screen_x >= cal.xmax) then screen_x = cal.xmax - 1 end
if (screen_y < 0) then screen_y = 0 end
if (screen_y >= cal.ymax) then screen_y = cal.ymax - 1 end
A touch event will indicate an event if the raw pressure value is greater than cal.penthr. In addition, it will report a finger event if the pressure is greater that cal.fingerthr. Note that the finger pressure threshold is always larger than the pen threshold.
The third form tch:calibration("clear") will clear the current calibration data. For touch screens that need a calibration to work, this immediately prompts the user to calibrate. Touch screens with a hard-wired calibration (e.g. Infrared) revert to their default.
RETURN VALUE
Returns a table containing the calibration values.