Specifications

Appendix D - CTKERN Function Reference CARROLL TOUCH
D-28 Touch System Programmer’s Guide
SetScalingMode (8)
Description
This function sets the scaling mode, which determines how the touch
coordinates reported by CTKERN are scaled.
Call with
AL = 8 (function number).
BL = Scaling mode.
00 = Scaling disabled.
01 = Fixed scaling. This is the default.
02 = Automatic scaling.
Notes
If scaling is disabled (00), the calibrated touch coordinates are not
scaled before being passed on to the application program.
If scaling is fixed (01), the calibrated touch coordinates are scaled using
0, 0 for the upper left x and y scaling parameters and (Xres - 1, Yres -
1) from the calibration parameters of the default calibration entry for
the lower right x and y scaling parameters before being passed on to the
application program. If no calibration entry is marked as the default, the
first calibration entry (calibration table index 0) is used.
If scaling is automatic (02), the calibrated touch coordinates are scaled
using 0, 0 for the upper left x and y scaling parameters and (Xres - 1,
Yres - 1) from the calibration parameters for the currently selected
BIOS video mode for the lower right x and y scaling parameters before
being passed on to the application program. The driver determines the
video mode by intercepting calls to BIOS mode 10H function 0
(SetVideoMode). If an entry in the table of calibration parameters that
corresponds to that video mode exists, the Xres, Yres values of those
calibration parameters are used. If no such entry exists, the Xres, Yres
values of the default calibration parameters are used. If no calibration
entry is marked as the default, the first calibration entry (calibration
table index 0) is used.
At the time that the scaling mode is set to automatic, CTKERN does a
GetVideoMode BIOS call, and looks in the calibration table for an entry
that matches the currently selected video mode. If a matching entry is
found, it is used. If there is no matching entry, the default entry is used.
CTKERN then hooks the BIOS Video Interrupt (Int 10H). If the scaling
mode is subsequently changed to other than automatic, the BIOS Video
Interrupt is unhooked.