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Appendix D - CTKERN Function Reference CARROLL TOUCH
D-32 Touch System Programmer’s Guide
The absolute pixel value is derived by taking a percentage of either the
scaled or raw touch coordinate range, depending on whether scaling is
enabled.
Figure D-1 pictures an example of a spatial filter box set to 25%. Note
that this is a much larger value than is usually used - this value is usually
less than 10%.
Figure D-1. Temporal Filter Spatial Box Size
This approach ensures that the spatial filter box size remains constant
for a given monitor. However, if a touch application that uses the
temporal filter is run on several monitors of differing sizes, the absolute
size of the spatial filter box will vary and may need to be adjusted.
The Temporal Filter Time is specified in milliseconds. The valid range
for this parameter is between 0 ms and 2000 ms, and the default is 500
ms. The actual filter time that is used, however, is restricted to multiples
of 55 ms. The actual formula used is as follows:
absolute time = Trunc (specified filter time / 55) * 55
For example, if you specify a time of 50, the time value used is actually
set to 0. If you specified a value of 100, the time value is 55. If you
specified a value of 500, the time value is 495. The filter time resolution
is 55 ms, which means that the actual amount of time that is required to
trigger a touch may vary from the actual filter time by +/- 55 ms.
box size
+