Ksp reference Manual

0
and 
1
: the active cursor can only be changed manually, by setting this control parameter. Inactive cursors
don't receive any clicks.
Mouse Mode = 
2
: it is set automatically based on the last clicked cursor. Setting it manually from within the 
ui_control
callback
of the XY pad can result in unexpected results, but using it in other callbacks is fully encouraged and makes
sense in many scenarios. The value is -1 when not clicking on any cursor.
The index can only be an even number (with the exception of the -1 value) that matches the index of the X axis of the cursor
in the main array representing the XY control, e.g. the first cursor has an index of 0, the second one has an index of 2, etc
$CONTROL_PAR_CURSOR_PICTURE
Sets the cursor image. Each cursor can have its own image set using the 
set_control_par_str_arr()
command.
Using 
$CONTROL_PAR_PICTURE 
with the XY pad will set the background image of the control.
The cursor images can have up to 6 frames, corresponding to the following states. Frame selection is automatic as with but-
tons/switches.
1: Inactive
2: Active
3: Inactive pressed
4: Active pressed
5: Inactive mouse over
6: Active mouse over
$HIDE_PART_CURSOR