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Added Docs directory and start populating it. Added Files: README.Joystick README.xmlpanel
2001-07-02 21:58:43 +00:00
Users Guide to FlightGear panel configuration
Version 0.7.7.1, June 23 2001
Author: John Check <j4strngs@rockfish.net>
This document describes the configuration of
FlightGear flight simulator's aircraft panel display via XML.
The information was culled from the fgfs-devel@flightgear.org
mailing list and my experiences making alternate panels.
Corrections and additions are encouraged.
Some History:
------------
Older versions of FGFS had a hard coded 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
simulation. To date, most alternatives 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. Some major changes and additions
were made during the course of version 0.7.7 necessitating a rewrite
and expansion of this document.
About The Property Manager:
--------------------------
While intimate knowledge of the property manager is unnecessary to create
aircraft panels, some familiarity with the concept is required.
FlightGear provides a hierarchical representation of all aspects of
the state of the running simulation that is known as the property tree.
Some properties, such as velocities, are read only. Others such as the frequencies
to which the navcom radios are tuned or the position of control surfaces
can be set by various means.
FlightGear can optionally provide an interface to these properties for external
applications such as Atlas, the moving map program, or even lowly telnet via
a network socket. Data can even be routed to a serial port and connected to
say, a GPS receiver.
Aside from its usefulness in a flight training context, being able to manipulate
the property tree on a running copy of FG allows for switching components on the fly,
a positive boon for panel authors.
To see the property tree start FG with the following command line:
fgfs --props=socket,bi,5,localhost,5500,tcp
Then use telnet to connect to localhost on port 5500. You can browse the
tree as you would a filesystem.
XML and the Property Manager:
----------------------------
Panel instruments interface with the property tree to get/set values as
appropriate. Properties for which FG doesn't yet provide a value can be
created by simply making them up. Values can be adjusted using the telnet
interface allowing for creation and testing of instruments while code to
drive them is being developed.
If fact, the XML configuration system allows a user to combine
components such as flight data model, aircraft exterior model,
heads up display, and of course control panel. Furthermore,
such a preconfigured aircraft.xml can be included into a scenario
with specific flight conditions. These can be manually specified or
a FG session can be saved and/or edited and reloaded later. Options specified
in these files can be overridden on the command line. For example:
--prop:/sim/panel/path=Aircraft/c172/Panels/c172-panel.xml
passed as an option, would override a panel specified elsewhere.
Property tree options all have the same format, specify the node
and supply it a value.
The order of precedence for options is thus:
Source Location Format
------ -------- ------
command line
.fgfsrc Users home directory. command line options
system.fgfsrc $FG_ROOT "" ""
preferences.xml $FG_ROOT XML property list
Loading Panels on the fly:
-------------------------
When editing a panel configuration, pressing Shift +F3 will reload the
panel. If your changes don't seem to be taking effect, check the console output.
It will report the success or failure of the panel reload*. Editing textures requires
restarting FGFS so the new textures can be loaded. Panels can be switched on the fly
by setting the /sim/panel/path property value and reloading.
Regarding Window Geometry:
-------------------------
For the sake of simplicity the FGFS window is always considered to be 1024x768
so all x/y values for instrument placement should relative to these dimensions.
Since FG uses OpenGL 0,0 represents the lower left hand corner of the
screen. Panels may have a virtual size larger than 1024x768. Vertical scrolling is accomplished
with Shift+F5/F6. Horizontal scrolling is via Shift+F7/F8. An offset should be supplied
to set the default visible area. It is possible to place items to overlap the 3D viewport.
Panel Architecture:
-------------------
All of the panel configuration files are XML-encoded* property lists.
The root element of each file is always named <PropertyList>. Tags are
almost always found in pairs, with the closing tag having a slash prefixing
the tag name, i.e </PropertyList>. The exception is the tag representing an aliased
property. In this case a slash is prepended to the closing angle bracket.
(see section Aliasing)
The top level panel configuration file is composed of a <name>, a <background>
texture and zero or more <instruments>.
[ Paths are relative to $FG_ROOT ( the installed location of FGFS data files ). ]
[ Absolute paths may be used. Comments are bracketed with <!-- -->. ]
Example Top Level Panel Config:
----------------------------------------
<PropertyList>
<name>Example Panel</name>
<background>Aircraft/c172/Panels/Textures/panel-bg.rgb</background>
<w>1024</w> <!-- virtual width -->
<h>768</h> <!-- virtual height -->
<y-offset>-305</y-offset> <!-- hides the bottom part -->
<view-height>172</view-height> <!-- amount of overlap between 2D panel and 3D viewport -->
<instruments>
<instrument include="../Instruments/clock.xml">
<name>Chronometer</name> <!-- currently optional but strongly recommended -->
<x>150</x> <!-- required horizontal placement -->
<y>645</y> <!-- required vertical placement -->
<w>72</w> <!-- optional width specification -->
<h>72</h> <!-- optional height specification -->
</instrument>
</instruments>
</PropertyList>
Indexed Properties
------------------
The property manager assigns incremental indices to repeated
properties with the same parent node, so that
<PropertyList>
<x>1</x>
<x>2</x>
<x>3</x>
</PropertyList>
shows up as
/x[0] = 1
/x[1] = 2
/x[2] = 3
In fact, the panel I/O code insists that every instrument have the XML element
name "instrument", every layer have the name "layer", every text chunk have the
name "chunk", every action have the name "action", and every transformation
have the name "transformation" -- this makes the XML more regular (so
that it can be created in a DTD-driven tool) and also allows us to
include other kinds of information (such as doc strings) in the lists
without causing confusion.
Inclusion:
----------
Inclusion means that a node can include another property list as if it
were a part of the current file.
To clarify how inclusion works, consider the following examples:
If bar.xml contains
<PropertyList>
<a>1</a>
<b>
<c>2</c>
</b>
</PropertyList>
then the declaration
<foo include="../bar.xml">
</foo>
is exactly equivalent to
<foo>
<a>1</a>
<b>
<c>2</c>
</b>
</foo>
However, it is also possible to selectively override properties in the
included file. For example, if the declaration were
<foo include="../bar.xml">
<a>3</a>
</foo>
then the property manager would see
<foo>
<a>3</a>
<b>
<c>2</c>
</b>
</foo>
with the original 'a' property's value replaced with 3.
Inclusion allows property files to be broken up and reused
arbitrarily -- for example, there might be separate texture cropping
property lists for commonly-used textures or layers, to avoid
repeating the information in each instrument file.
Aliasing
--------
Properties can alias other properties, similar to a symbolic link
in Unix. When the target property changes value, the new value will
show up in the aliased property as well. For example,
<PropertyList>
<foo>3</foo>
<bar alias="/foo"/>
</PropertyList>
will look the same to the application as
<PropertyList>
<foo>3</foo>
<bar>3</bar>
</PropertyList>
except that when foo changes value, bar will change too.
*IMPORTANT*
-----------
The combination of inclusions and aliases is very powerful, because it
allows for parameterized property files. However, you must keep in
mind that when an instrument is included by reference, its root is
*not* the root of the property tree, therefore aliases must be relative.
The relative location of the alias' root in the property hierarchy depends
on whether the alias is used in a layer, a switch or an action.
In lieu of snappy mnemonic, please use the following table.
when alias
is used in go up
--------- -----
layer 5 ( ../../../../../params/foo )
switch 3 ( ../../../params/foo )
action 3 ( ../../../params/foo )
As an example of inclusion and aliasing, consider the XML file
for the NAVCOM radio, which includes a parameter subtree at the start,
like this:
<PropertyList>
<params>
<comm-freq-prop>/radios/comm1/frequencies/selected</comm-freq-prop>
<nav-freq-prop>/radios/nav1/frequencies/selected</nav-freq-prop>
</params>
...
<chunk>
<type>number-value</type>
<property alias="../../../../../params/nav-freq-prop"/>
</chunk>
...
</PropertyList>
The same instrument file is used for navcomm1 and navcomm2 simply by
overriding the parameters at inclusion in the top level panel property list.
<instrument include="../Instruments/navcomm.xml">
<name>NAVCOM 1 radio</name>
<params>
<comm-freq-prop>/radios/comm1/frequencies/selected</comm-freq-prop>
<nav-freq-prop>/radios/nav1/frequencies/selected</nav-freq-prop>
</params>
.....
</instrument>
<instrument include="../Instruments/navcomm.xml">
<name>NAVCOM 2 radio</name>
<params>
<comm-freq-prop>/radios/comm2/frequencies/selected</comm-freq-prop>
<nav-freq-prop>/radios/nav2/frequencies/selected</nav-freq-prop>
</params>
.....
</instrument>
Instrument Architecture:
-----------------------
Instruments are defined in separate configuration files. An instrument
consists of a base width and height, one or more stacked layers,
and zero or more actions. Base dimensions are specified as follows:
<PropertyList> <!-- remember, all xml files start like this -->
<name>Airspeed Indicator</name> <!-- names are good -->
<w-base>128</w-base> <!-- required width spec-->
<h-base>128</h-base> <!-- required height spec-->
<layers> <!-- begins layers section -->
Height and width can be overriden in the top level panel.xml by
specifying <w> and <h>. Transformations are caculated against the base size
regardless of the display size. This ensures that instruments remain calibrated.
Textures:
--------
FG uses red/green/blue/alpha .rgba files for textures. Dimensions for
texture files should be power of 2 with a maximum 8:1 aspect ratio.
The lowest common denominator for maximum texture size is 256 pixels.
This is due to the limitations of certain video accelerators, most notably
those with 3Dfx chipset such as the Voodoo2.
Instrument Layers**:
-------------------
The simplest layer is a <texture>. These can be combined in <switch> layers
<texture>
A texture layer looks like this:
<layer> <!-- creates a layer -->
<name>face</name>
<texture> <!-- defines it as a texture layer -->
<path>Aircraft/c172/Instruments/Textures/faces-2.rgb</path>
<x1>0</x1> <!-- lower boundary for texture cropping-->
<y1>0.51</y1> <!-- left boundary for texture cropping-->
<x2>0.49</x2> <!-- upper boundary for texture cropping-->
<y2>1.0</y2> <!-- right boundary for texture cropping-->
</texture> <!-- closing texure tag -->
</layer> <!-- closing layer tag -->
The texture cropping specification is represented as a decimal. There is a table
at the end of this document for converting from pixel coordinates to percentages.
This particular layer, being a gauge face has no transformations applied to it.
Layers with that aren't static *must* include <w> and <h> parameters to be visible.
<type> May be either text or switch..
<type>switch</type>
A switch layer is composed of two or more nested layers and will display
one of the nested layers based on a boolean property. For a simple example
of a switch see $FG_ROOT/Aircraft/c172/Instruments/brake.xml.
<layer>
<name>Brake light</name>
<type>switch</type> <!-- define layer as a switch -->
<property>/controls/brakes</property> <!-- tie it to a property -->
<layer1> <!-- layer for true state -->
<name>on</name> <!-- label to make life easy -->
<texture> <!-- layer1 of switch is a texture layer -->
<path>Aircraft/c172/Instruments/Textures/brake.rgb</path>
<x1>0.25</x1>
<y1>0.0</y1>
<x2>0.5</x2>
<y2>0.095</y2>
</texture>
<w>64</w> <!-- required width - layer isn't static -->
<h>24</h> <!-- required height - layer isn't static -->
</layer1> <!-- close layer1 of switch -->
<layer2> <!-- layer for false state -->
<name>off</name>
<texture>
<path>Aircraft/c172/Instruments/Textures/brake.rgb</path>
<x1>0.0</x1>
<y1>0.0</y1>
<x2>0.25</x2>
<y2>0.095</y2>
</texture>
<w>64</w>
<h>24</h>
</layer2>
</layer>
Switches can have more than 2 states. This requires nesting one switch inside another.
One could make, for example, a 3 color LED by nesting switch layers.
<type>text</type>
A text layer may be static, as in a label, generated from a property or a combination of both.
This example is a switch that contains both static and dynamic text:
<layer1> <!-- switch layer -->
<name>display</name>
<type>text</type> <!-- type == text -->
<point-size>12</point-size> <!-- font size -->
<color> <!-- specify rgb values to color text -->
<red>1.0</red>
<green>0.5</green>
<blue>0.0</blue>
</color> <!-- close color section -->
<chunks> <!-- sections of text are referred to as chunks -->
<chunk> <!-- first chunk of text -->
<type>number-value</type> <!-- value defines it as dynamic -->
<property>/radios/nav1/dme/distance</property> <!-- ties it to a property -->
<scale>0.00053995680</scale> <!-- convert between statute and nautical miles? -->
<format>%5.1f</format> <!-- define format -->
</chunk>
</chunks>
</layer1>
<layer2> <!-- switch layer -->
<name>display</name>
<type>text</type> <!-- type == text -->
<point-size>10</point-size> <!-- font size -->
<color> <!-- specify rgb values to color text -->
<red>1.0</red>
<green>0.5</green>
<blue>0.0</blue>
</color> <!-- close color section -->
<chunks> <!-- sections of text are referred to as chunks -->
<chunk> <!-- first chunk of text -->
<type>literal</type> <!-- static text -->
<text>---.--</text> <!-- fixed value -->
</chunk>
</chunks>
</layer2>
Transformations:
---------------
A transformation is a rotation, an x-shift, or a y-shift. Transformations
can be static or they can be based on properties. Static rotations are
useful for flipping textures horizontally or vertically. Transformations
based on properties are useful for driving instrument needles. I.E. rotate the
number of degrees equal to the airspeed. X and y shifts are relative to the
center of the instrument. Each specified transformation type takes an <offset>.
Offsets are relative to the center of the instrument. A shift without an offset
has no effect. For example, let's say we have a texure that is a circle. If we
use this texture in two layers, one defined as having a size of 128x128 and
the second layer is defined as 64x64 and neither is supplied a shift and offset
the net result appears as 2 concentric circles.
About Transformations and Needle Placement:
------------------------------------------
When describing placement of instrument needles, a transformation offset must
be applied to shift the needles fulcrum or else the needle will rotate around it's
middle. The offset will be of <type> x-shift or y-shift depending on the orientation of
the needle section in the cropped texture.
This example comes from the altimeter.xml
<layer>
<name>long needle (hundreds)</name> <!-- the altimeter has more than one needle -->
<texture>
<path>Aircraft/c172/Instruments/Textures/misc-1.rgb</path>
<x1>0.8</x1>
<y1>0.78125</y1>
<x2>0.8375</x2>
<y2>1.0</y2>
</texture>
<w>8</w>
<h>56</h>
<transformations> <!-- begin defining transformations -->
<transformation> <!-- start definition of transformation that drives the needle -->
<type>rotation</type>
<property>/steam/altitude</property> <!-- bind it to a property -->
<max>100000.0</max> <!-- upper limit of instrument -->
<scale>0.36</scale> <!-- once around == 1000 ft -->
</transformation> <!-- close this transformation -->
<transformation> <!-- this one shifts the fulcrum of the needle -->
<type>y-shift</type> <!-- y-shift relative to needle -->
<offset>24.0</offset> <!-- amount of shift -->
</transformation>
</transformations>
</layer>
This needles has its origin in the center of the instrument. If the needles fulcrum was
towards the edge of the instrument, the transformations to place the pivot point must
precede those which drive the needle,
Interpolation
-------------
Non linear transformations are now possible via the use of interpolation tables.
<transformation>
...
<interpolation>
<entry>
<ind>0.0</ind> <!-- raw value -->
<dep>0.0</dep> <!-- displayed value -->
</entry>
<entry>
<ind>10.0</ind>
<dep>100.0</dep>
</entry>
<entry>
<ind>20.0</ind>
<dep>-5.0</dep>
</entry>
<entry>
<ind>30.0</ind>
<dep>1000.0</dep>
</entry>
</interpolation>
</transformation>
Of course, interpolation tables are useful for non-linear stuff, as in
the above example, but I kind-of like the idea of using them for
pretty much everything, including non-trivial linear movement -- many
instrument markings aren't evenly spaced, and the interpolation tables
are much nicer than the older min/max/scale/offset stuff and should
allow for a more realistic panel without adding a full equation parser
to the property manager.
If you want to try this out, look at the airspeed.xml file in the base
package, and uncomment the interpolation table in it for a
very funky, non-linear and totally unreliable airspeed indicator.
Actions:
-------
An action is a hotspot on an instrument where something will happen
when the user clicks the left or center 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.
The x/y placement for actions specifies the origin of the lower left corner.
In the following example the first action sets up a hotspot 32 pixels wide
and 16 pixels high. It lower left corner is placed 96 pixels (relative to the
defined base size of the instrument) to the right of the center of the
instrument. It is also 32 pixels below the centerline of the instrument.
The actual knob texture over which the action is superimposed is 32x32.
Omitted here is a second action, bound to the same property, with a positive
increment value. This second action is placed to cover the other half of the
knob. The result is that clicking on the left half of the knob texture decreases
the value and clicking the right half increases the value. Also omitted here
is a second pair of actions with the same coordinates but a larger increment
value. This second pair is bound to a different mouse button. The net result
is that we have both fine and coarse adjustments in the same hotspot, each
bound to a different mouse button.
These examples come from the radio stack:
<actions> <!-- open the actions section -->
<action> <!- first action -->
<name>small nav frequency decrease</name>
<type>adjust</type>
<button>0</button> <!-- bind it to a mouse button -->
<x>96</x> <!-- placement relative to instrument center -->
<y>-32</y>
<w>16</w> <!-- size of hotspot -->
<h>32</h>
<property>/radios/nav1/frequencies/standby</property> <!-- bind to a property -->
<increment>-0.05</increment> <!-- amount of adjustment per mouse click -->
<min>108.0</min> <!-- lower range -->
<max>117.95</max> <!-- upper range -->
<wrap>1</wrap> <!-- boolean value -- value wraps around when it hits bounds -->
</action>
<action>
<name>swap nav frequencies</name>
<type>swap</type> <!-- define type of action -->
<button>0</button>
<x>48</x>
<y>-32</y>
<w>32</w>
<h>32</h>
<property1>/radios/nav1/frequencies/selected</property1> <!-- properties to toggle between -->
<property2>/radios/nav1/frequencies/standby</property2>
</action>
<action>
<name>ident volume on/off</name>
<type>adjust</type>
<button>1</button>
<x>40</x>
<y>-24</y>
<w>16</w>
<h>16</h>
<property>/radios/nav1/ident</property> <!-- this property is for Morse code identification of nav beacons -->
<increment>1.0</increment> <!-- the increment equals the max value so this toggles on/off -->
<min>0</min>
<max>1</max>
<wrap>1</wrap> <!-- a shortcut to avoid having separate actions for on/off -->
</action>
</actions>
More About Textures:
-------------------
As previously stated, the usual size instrument texture files in FGFS are 256x256
pixels, red/green/blue/alpha format. However the mechanism for specifying
texture cropping coordinates is decimal in nature. When calling a section
of a texture file the 0,0 lower left convention is used.
There is a pair of x/y coordinates defining which section of the texture
to use.
The following table can be used to calculate texture cropping specifications.
# of divisions | width in pixels | decimal specification
per axis
1 = 256 pixels 1
2 = 128 pixels, 0.5
4 = 64 pixels, 0.25
8 = 32 pixels, 0.125
16 = 16 pixels, 0.0625
32 = 8 pixels, 0.03125
64 = 4 pixels, 0.015625
128 = 2 pixels, 0.0078125
A common procedure for generating gauge faces is to use a
vector graphics package such as xfig, exporting the result as a
postscript file. 3D modeling tools may also be used and I prefer them
for pretty items such as levers, switches, bezels and so forth.
Ideally, the size of the item in the final render
should be of proportions that fit into the recommended pixel widths.
The resulting files can be imported into a graphics manipulation
package such as GIMP, et al for final processing.
How do I get my panels/instruments into the base package?
-------------------------------------------------------
Cash bribes always help ;) Seriously though, there are two main considerations.
Firstly, original artwork is a major plus since you as the creator can dictate the terms
of distribution. All Artwork must have a license compatible with the GPL.
Artwork of unverifiable origin is not acceptable.
Secondly, texture sizes must meet the lowest common denominator of 256e2 pixels.
Artwork from third parties may be acceptable if it meets these criteria.
* If there are *any* XML parsing errors, the panel will fail to load,
so it's worth downloading a parser like Expat (http://www.jclark.com/xml/)
for checking your XML. FlightGear will print the location of errors, but
the messages are a little cryptic right now.
** 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).
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