[Flightgear-devel] [DRAFT] generic input devices and hotplug support

[Torsten D. <To...@t3...>]

Hi,

I am currently playing with the input subsystem. This was triggered because I 
have two devices that currently do not work with FlightGear, neither Linux nor 
Windows.

1. A set of rudder pedals that does not get recognized as a joystick from 
joydev, because it reports it's axes as RX,RY and Z and the lack of an X-Axis 
stops joydev from using it as a joystick.

2. A 3dconnexion (http://www.3dconnexion.com/) SpaceNavigator 3D-Mouse which 
is basically a 6-axes/2buttons/1LED device.

Both devices are HID devices and are handled by the Linux input/event driver. 
For example, the SpaceNavigator shows up in /proc/bus/input/devices as

I: Bus=0003 Vendor=046d Product=c626 Version=0110
N: Name="3Dconnexion SpaceNavigator"
P: Phys=usb-0000:00:1d.1-1/input0
S: Sysfs=/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0/input/input9
U: Uniq=
H: Handlers=event9
B: EV=20017
B: KEY=3 0 0 0 0
B: REL=3f
B: MSC=10
B: LED=100

My idea is to extend the FGInput class so it can use the devices presented 
thru the event interface. While at it, I'd also like to add hotplug support 
for devices, plugged in or out while FlightGear runs.

What I have so far locally is a system that can use the input devices. Events 
and devices are configured with xml config files like this, similiar to 
joystick config files (just one event shown here for better readability):

<PropertyList>
 <name>3Dconnexion SpaceNavigator</name>
 <event>
   <name>rel-y-translate</name>
   <binding>
    <command>property-adjust</command>
     <property>sim/current-view/field-of-view</property>
     <factor type="double">0.01</factor>
     <min type="double">10.0</min>
     <max type="double">80.0</max>
     <wrap type="bool">false</wrap>
   </binding>
 </event>
</PropertyList>

See it in action here:
http://www.youtube.com/watch?v=b8Me8d9UZLA
The black knob can be twisted around and shifted along the x/y/z axes. These 
movements are translated into events which adjust the current-view direction 
and the field of view. The cool blue LED-light is controlled by FlightGear 
and indicates gear-down (YES! It's bidirectional communication).

Adding/removing of devices is reported by HAL and DBUS on Linux and 
DirectInput on Win. I don't know how Macs deal with that, but I am certain 
there is a way for the macs, too.

While I really like the new functionality and I see many advantages from 
moving into this direction, there are also some disadvantage and I'd like to 
open the discussion before I commit anything.

Advantages:
- Adding additional and generic support for a wide variety of devices
- Named events, no more axis numbers and confusion between Linux/Win/Mac
- Bidirectional communication (switch on/off LED's, probably force feedback 
etc.)
- Might obsolete one plib dependency

Disadvantages:
- Introduces platform dependency, individual implementations needed for 
Linux/Win/Mac
- Adds new library dependency (dbus/hal on linux DirectInput on Win, ??? on 
Mac)

What do you think? Are the new features worth introducing new dependencies and 
platform dependent modules?

Torsten

P.S.: The GIMP also uses these techniques. Go to the "settings" dialog and 
select "Input Devices".