Users Guide to FlightGear panel configuration
First Draft
Author: John Check <j4strngs@rockfish.net>
This document is an attempt to describe the configuration via
XML of FlightGear flight simulator's aircraft panel display.
The information was culled from the fgfs-devel@flightgear.org
mailing list. I'd like to say thanks to all the developers who
make FGFS happen and forgive me for any errors with regards to
who did what. I'd like to reguest that anybody who should be
mentioned give me a heads up so I can credit them properly.
Corrections and additions are encouraged.
History:
Older versions of FGFS had a hardcoded display of instruments.
This was a less than ideal state of affairs due to FGFS ability
to use different aircraft models. Being primarily developed on
UNIX type systems, a modular approach is taken towards the
aircraft modeling. To date, most alternatatives to the default
Cessna 172 aircraft are the product of research institutions
interested in the flight characteristics and not cosmetics.
The result of this was that one could fly the X-15 or a Boeing 747
but be limited to C172 instrumentation.
A rewrite of the panel display code was done around v0.7.5 by
developer David Megginson allowing for configuration of the panel
via XML to address this limitation.
The Basics:
David Megginson wrote:
> To get started, here's a basic, mostly-architectural outline:
>
> 1. All configuration files are XML-encoded property lists. The root
> element is always named <PropertyList>. None of the properties is
> mixed in with the main FlightGear properties (they're all separate
> lists).
>
> 2. There is a single, top-level configuration file for each panel.
> There is also a top-level configuration file for each instrument (I
> may also add configuration files for cropped textures, to enabled
> better reuse of common textures like needles and knobs).
>
> 3. A panel is composed of a background texture and zero or more
> instruments. The panel sets the position of each instrument and may
> also override the instrument's preferred size (the default panel does
> not do so, but if you want an altimeter covering a quarter of the
> screen, go for it!).
>
> 4. An instrument consists of a preferred width and height, one or more
> stacked layers, and zero or more actions. It is defined in a separate
> file.
>
> 5. A layer can be a texture (with alpha areas so that lower textures
> show through), text (static, generated, or both), or a switch between
> two other layers based on a boolean property. Each layer contains
> zero or more transformations.
>
> NOTE: There is one built-in layer -- for the mag compass ribbon --
> and all other layers are defined in the XML files. In the future,
> there may also be built-in layers for special things like a
> weather-radar display or a GPS (though the GPS could be handled with
> text properties).
>
> 6. A transformation is a rotation, an x-shift, or a y-shift.
> Transformations can be static (rotate 90 degrees) or they can be based
> on properties (rotate the number of degrees equal to the airspeed
> times something plus something else, etc.).
>
> 7. An action is a hotspot on an instrument where something will happen
> when the user clicks the left or centre mouse button. Actions are
> always tied to properties: they can toggle a boolean property, adjust
> the value of a numeric property, or swap the values of two properties.
>
> 8. You can find panel configuration files under $FG_ROOT/Panels/ and
> instrument configuration files under $FG_ROOT/Instruments/.
>
> 9. If there are *any* XML parsing errors, the panel will fail to load
> (them's the XML rules), so it's worth downloading a parser like Expat
> (http://www.jclark.com/xml/) so that you can check your XML.
> FlightGear will print the location of errors, but the messages are a
> little cryptic right now.
>
> 10. You can set the relative location of the top-level XML panel file
> (under $FG_ROOT) using the "/sim/panel" property. The default is
> $FG_ROOT/Panels/Default/default.xml.
To do:
Add some examples.
Integrate additonal questions and answers from the list.
