As can be seen in do_property_scale()'s definition in
flightgear/src/Main/fg_commands.cxx, property-scale rightfully uses a
default factor of 1.0. However, if a joystick axis' property-scale
binding has no 'factor' node defined, and one opens the joystick
configuration dialog, then PropertyScaleAxis.parse() creates an empty
'factor' node that implicitely gets a value of 0. This method is called
by joystick.readConfig() when the joystick-config dialog is opened. This
has the effect of rendering the corresponding joystick axis inoperant.
How to reproduce the bug:
- take a joystick such as the SAITEK CYBORG 3D USB, with its default
binding file from
fgdata/Input/Joysticks/Saitek/Cyborg-Gold-3d-USB.xml (this file uses
property-scale for the aileron, with no explicitely defined factor);
- start FlightGear; move the joystick left or right while looking at
the plane wings -> the ailerons move, it works fine;
- now, open the joystick-config dialog and do the same test -> the
ailerons don't move anymore and the 'Aileron' value at the bottom of
the dialog stays at 0 (0.0 or -0.0...). Just opening the dialog to
test the joystick has "corrupted" its setup! This is very confusing
for users.
This fix corrects the problem by avoiding the apparently unneeded
creation of an empty 'factor' node when there is none inside the
<binding>. An alternative would be to create a 'factor' node with value
1.0. In any case, if someone later expands the joystick-config dialog to
allow modification of property-scale's factor, he should make sure to
use a default value of 1.0!
