654 lines
26 KiB
Text
654 lines
26 KiB
Text
Users Guide to FlightGear panel configuration
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Version 0.7.7, May 16 2001
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Author: John Check <j4strngs@rockfish.net>
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This document is an attempt to describe the configuration of
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FlightGear flight simulator's aircraft panel display via XML. The
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information was culled from the fgfs-devel@flightgear.org mailing list
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and my experiences making alternate panels. Corrections and additions
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are encouraged.
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Some History:
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------------
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Older versions of FGFS had a hard coded display of instruments. This
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was a less than ideal state of affairs due to FGFS ability to use
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different aircraft models. Being primarily developed on UNIX type
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systems, a modular approach is taken towards the simulation. To date,
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most alternatives to the default Cessna 172 aircraft are the product
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of research institutions interested in the flight characteristics and
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not cosmetics. The result of this was that one could fly the X-15 or
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a Boeing 747 but be limited to C172 instrumentation.
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A rewrite of the panel display code was done around v0.7.5 by
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developer David Megginson allowing for configuration of the panel via
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XML to address this limitation. Some major changes and additions were
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made during the course of version 0.7.7 necessitating a rewrite and
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expansion of this document.
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About The Property Manager:
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--------------------------
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While not absolutely necessary in order to create aircraft panels,
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some familiarity with the property manager is beneficial....
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FlightGear provides a hierarchical representation of all aspects of
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the state of the running simulation that is known as the property
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tree. Some properties, such as velocities are read only. Others such
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as the frequencies to which the navcom radios are tuned or the
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position of control surfaces can be set by various means. FlightGear
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can optionally provide an interface to these properties for external
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applications such as Atlas, the moving map program, or even lowly
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telnet, via a network socket. Data can even be placed on a serial port
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and connected to, say a GPS receiver. Aside from its usefulness in a
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flight training context, being able to manipulate the property tree on
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a running copy of FG allows for switching components on the fly, a
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positive boon for panel authors. To see the property tree start FG
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with the following command line:
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fgfs --props=socket,bi,5,localhost,5500,tcp
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Then use telnet to connect to localhost on port 5500. You can browse
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the tree as you would a filesystem.
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XML and the Property Manager:
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----------------------------
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Panel instruments interface with the property tree to get/set values
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as appropriate. Properties for which FG doesn't yet provide a value
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can be created by simply making them up. Values can be adjusted using
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the telnet interface allowing for creation and testing of instruments
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while code to drive them is being developed.
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If fact, the XML configuration system allows a user to combine
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components such as flight data model, aircraft exterior model, heads
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up display, and of course control panel. Furthermore, such a
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preconfigured aircraft.xml can be included into a scenario with
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specific flight conditions. These can be manually specified or a FG
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session can be saved and/or edited and reloaded later. Options
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specified in these files can be overridden on the command line. For
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example:
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--prop:/sim/panel/path=Aircraft/c172/Panels/c172-panel.xml
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passed as an option, would override a panel specified elsewhere.
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Property tree options all have the same format, specify the node and
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supply it a value.
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The order of precedence for options is thus:
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Source Location Format
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------ -------- ------
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command line
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.fgfsrc Users home directory. command line options
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system.fgfsrc $FG_ROOT "" ""
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preferences.xml $FG_ROOT XML property list
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Loading Panels on the fly:
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-------------------------
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When editing a panel configuration, pressing Shift +F3 will reload the
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panel. If your changes don't seem to be taking effect, check the
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console output. It will report the success or failure of the panel
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reload*. Editing textures requires restarting FGFS so the new textures
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can be loaded. Panels can be switched on the fly by setting the
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/sim/panel/path property value and reloading.
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Regarding Window Geometry:
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-------------------------
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For the sake of simplicity the FGFS window is always considered to be
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1024x768 so all x/y values for instrument placement should relative to
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these dimensions. Since FG uses OpenGL 0,0 represents the lower left
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hand corner of the screen. Panels may have a virtual size larger than
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1024x768. Vertical scrolling is accomplished with
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Shift+F5/F6. Horizontal scrolling is via Shift+F7/F8. An offset should
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be supplied to set the default visible area. It is possible to place
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items to overlap the 3D viewport.
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Panel Architecture:
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-------------------
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All of the panel configuration files are XML-encoded* property lists.
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The root element of each file is always named <PropertyList>. Tags are
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almost always found in pairs, with the closing tag having a slash
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prefixing the tag name, i.e </PropertyList>. The exception is the tag
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representing an aliased property. In this case a slash is prepended to
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the closing angle bracket. (see section Aliasing)
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The top level panel configuration file is composed of a <name>, a
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<background> texture and zero or more <instruments>.Earlier versions
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required instruments to have a unique name and a path specification
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pointing to the instruments configuration file.
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[ Paths are relative to $FG_ROOT (the installed location of FGFS data files.) ]
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[ Absolute paths may be used.Comments are bracketed with <!-- -->. ]
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Old style instrument call in top level panel.xml:
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------------------------------------------------
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<clock> <!-- required "unique_name" -->
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<path>Aircraft/c172/Instruments/clock.xml</path>
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<x>110</x> <!-- required horizontal placement -->
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<y>320</y> <!-- required vertical placement -->
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<w>72</w> <!-- optional width specification -->
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<h>72</h> <!-- optional height specification -->
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</clock>
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The difference between the old and new styles, while subtle, is rather
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drastic. The old and new methods are indeed incompatible. I cover the
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old style only to acknowledge the incompatibility. This section will
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be removed after the next official FGFS release.
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New Style Example Top Level Panel Config:
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----------------------------------------
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<PropertyList>
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<name>Example Panel</name>
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<background>Aircraft/c172/Panels/Textures/panel-bg.rgb</background>
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<w>1024</w> <!-- virtual width -->
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<h>768</h> <!-- virtual height -->
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<y-offset>-305</y-offset> <!-- hides the bottom part -->
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<view-height>172</view-height> <!-- amount of overlap between 2D panel and 3D viewport -->
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<instruments> <!-- from here down is where old and new styles break compatibility -->
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<instrument include="../Instruments/clock.xml">
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<name>Chronometer</name> <!-- currently optional but strongly recommended -->
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<x>150</x> <!-- required horizontal placement -->
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<y>645</y> <!-- required vertical placement -->
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<w>72</w> <!-- optional width specification -->
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<h>72</h> <!-- optional height specification -->
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</instrument>
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</instruments>
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</PropertyList>
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Indexed Properties
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------------------
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This is a lot to do with the compatibility break so lets get it out of
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the way. The property manager now assigns incremental indices to
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repeated properties with the same parent node, so that
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<PropertyList>
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<x>1</x>
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<x>2</x>
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<x>3</x>
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</PropertyList>
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shows up as
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/x[0] = 1
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/x[1] = 2
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/x[2] = 3
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This means that property files no longer need to make up a separate
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name for each item in a list of instruments, layers, actions,
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transformations, or text chunks. In fact, the new panel I/O code now
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insists that every instrument have the XML element name "instrument",
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every layer have the name "layer", every text chunk have the name
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"chunk", every action have the name "action", and every transformation
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have the name "transformation" -- this makes the XML more regular (so
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that it can be created in a DTD-driven tool) and also allows us to
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include other kinds of information (such as doc strings) in the lists
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without causing confusion.
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Inclusion:
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----------
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The property manager now supports file inclusion and aliasing.
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Inclusion means that a node can include another property file as if it
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were a part of the current file. To clarify how inclusion works,
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consider the following examples:
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If bar.xml contains
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<PropertyList>
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<a>1</a>
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<b>
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<c>2</c>
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</b>
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</PropertyList>
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then the declaration
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<foo include="../bar.xml">
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</foo>
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is exactly equivalent to
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<foo>
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<a>1</a>
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<b>
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<c>2</c>
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</b>
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</foo>
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However, it is also possible to selectively override properties in the
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included file. For example, if the declaration were
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<foo include="../bar.xml">
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<a>3</a>
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</foo>
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then the property manager would see
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<foo>
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<a>3</a>
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<b>
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<c>2</c>
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</b>
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</foo>
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with the original 'a' property's value replaced with 3.
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This new inclusion feature allows property files to be broken up and
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reused arbitrarily -- for example, there might be separate cropping
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property lists for commonly-used textures or layers, to avoid
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repeating the information in each instrument file.
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Aliasing
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--------
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Properties can now alias other properties, similar to a symbolic link
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in Unix. When the target property changes value, the new value will
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show up in the aliased property as well. For example,
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<PropertyList>
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<foo>3</foo>
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<bar alias="/foo"/>
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</PropertyList>
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will look the same to the application as
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<PropertyList>
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<foo>3</foo>
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<bar>3</bar>
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</PropertyList>
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except that when foo changes value, bar will change too.
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The combination of inclusions and aliases is very powerful, because it
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allows for parameterized property files. For example, the XML file for
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the NAVCOM radio can include a parameter subtree at the start, like
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this:
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<PropertyList>
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<params>
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<comm-freq-prop>/radios/comm1/frequencies/selected</comm-freq-prop>
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<nav-freq-prop>/radios/nav1/frequencies/selected</comm-freq-prop>
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</params>
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...
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<chunk>
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<type>number-value</type>
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<property alias="/params/nav-freq-prop"/>
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</chunk>
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...
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</PropertyList>
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Now, the same instrument file can be used for navcomm1 and navcomm2,
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for example, simply by overriding the parameters at inclusion:
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<instrument include="../Instruments/navcomm.xml">
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<params>
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<comm-freq-prop>/radios/comm1/frequencies/selected</comm-freq-prop>
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<nav-freq-prop>/radios/nav1/frequencies/selected</comm-freq-prop>
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</params>
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</instrument>
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<instrument include="../Instruments/navcomm.xml">
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<params>
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<comm-freq-prop>/radios/comm2/frequencies/selected</comm-freq-prop>
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<nav-freq-prop>/radios/nav2/frequencies/selected</comm-freq-prop>
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</params>
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</instrument>
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Instrument Architecture:
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-----------------------
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Instruments are defined in separate configuration files. An instrument
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consists of a base width and height, one or more stacked layers, and
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zero or more actions. Base dimensions are specified as follows:
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<PropertyList> <!-- remember, all xml files start like this -->
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<name>Airspeed Indicator</name> <!-- names are good -->
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<w-base>128</w-base> <!-- required width spec-->
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<h-base>128</h-base> <!-- required height spec-->
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<layers> <!-- begins layers section -->
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Height and width can be overriden in the top level panel.xml by
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specifying <w> and <h>. Transformations are caculated against the base
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size regardless of the display size. This ensures that instruments
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remain calibrated
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Textures:
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--------
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FG uses red/green/blue/alpha .rgba files for textures. Dimensions for
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texture files should be power of 2 with a maximum 8:1 aspect ratio.
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The lowest common denominator for maximum texture size is 256 pixels.
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This is due to the limitations of certain video accelerators, most
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notably those with 3Dfx chipset such as the Voodoo2.
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Instrument Layers**:
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-------------------
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The simplest layer is a <texture>. These can be combined in <switch> layers
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<texture>
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A texture layer looks like this:
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<layer> <!-- creates a layer -->
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<name>face</name>
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<texture> <!-- defines it as a texture layer -->
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<path>Aircraft/c172/Instruments/Textures/faces-2.rgb</path>
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<x1>0</x1> <!-- lower boundary for texture cropping-->
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<y1>0.51</y1> <!-- left boundary for texture cropping-->
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<x2>0.49</x2> <!-- upper boundary for texture cropping-->
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<y2>1.0</y2> <!-- right boundary for texture cropping-->
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</texture> <!-- closing texure tag -->
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</layer> <!-- closing layer tag -->
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The texture cropping specification is represented as a decimal. There
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is a table at the end of this document for converting from pixel
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coordinates to percentages.
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This particular layer, being a gauge face has no transformations
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applied to it. Layers with that aren't static *must* include <w> and
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<h> parameters to be visible.
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<type> May be either text or switch..
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<type>switch</type>
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A switch layer is composed of two or more nested layers and will
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display one of the nested layers based on a boolean property. For a
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simple example of a switch see
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$FG_ROOT/Aircraft/c172/Instruments/brake.xml.
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<layer>
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<name>Brake light</name>
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<type>switch</type> <!-- define layer as a switch -->
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<property>/controls/brakes</property> <!-- tie it to a property -->
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<layer1> <!-- layer for true state -->
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<name>on</name> <!-- label to make life easy -->
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<texture> <!-- layer1 of switch is a texture layer -->
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<path>Aircraft/c172/Instruments/Textures/brake.rgb</path>
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<x1>0.25</x1>
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<y1>0.0</y1>
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<x2>0.5</x2>
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<y2>0.095</y2>
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</texture>
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<w>64</w> <!-- required width - layer isn't static -->
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<h>24</h> <!-- required height - layer isn't static -->
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</layer1> <!-- close layer1 of switch -->
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<layer2> <!-- layer for false state -->
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<name>off</name>
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<texture>
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<path>Aircraft/c172/Instruments/Textures/brake.rgb</path>
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<x1>0.0</x1>
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<y1>0.0</y1>
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<x2>0.25</x2>
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<y2>0.095</y2>
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</texture>
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<w>64</w>
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<h>24</h>
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</layer2>
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</layer>
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Switches can have more than 2 states. This requires nesting one switch
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inside another. One could make, for example, a 3 color LED by nesting
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switch layers.
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<type>text</type>
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A text layer may be static, as in a label, generated from a property
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or a combination of both. This example is a switch that contains both
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static and dynamic text:
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<layer1> <!-- switch layer -->
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<name>display</name>
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<type>text</type> <!-- type == text -->
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<point-size>12</point-size> <!-- font size -->
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<color> <!-- specify rgb values to color text -->
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<red>1.0</red>
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<green>0.5</green>
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<blue>0.0</blue>
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</color> <!-- close color section -->
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<chunks> <!-- sections of text are referred to as chunks -->
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<chunk> <!-- first chunk of text -->
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<type>number-value</type> <!-- value defines it as dynamic -->
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<property>/radios/nav1/dme/distance</property> <!-- ties it to a property -->
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<scale>0.00053995680</scale> <!-- convert between statute and nautical miles? -->
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<format>%5.1f</format> <!-- define format -->
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</chunk>
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</chunks>
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</layer1>
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<layer2> <!-- switch layer -->
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<name>display</name>
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<type>text</type> <!-- type == text -->
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<point-size>10</point-size> <!-- font size -->
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<color> <!-- specify rgb values to color text -->
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<red>1.0</red>
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<green>0.5</green>
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<blue>0.0</blue>
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</color> <!-- close color section -->
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<chunks> <!-- sections of text are referred to as chunks -->
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<chunk> <!-- first chunk of text -->
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<type>literal</type> <!-- static text -->
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<text>---.--</text> <!-- fixed value -->
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</chunk>
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</chunks>
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</layer2>
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Transformations:
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---------------
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A transformation is a rotation, an x-shift, or a
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y-shift. Transformations can be static or they can be based on
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properties. Static rotations are useful for flipping textures
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horizontally or vertically. Transformations based on properties are
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useful for driving instrument needles. I.E. rotate the number of
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degrees equal to the airspeed. X and y shifts are relative to the
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center of the instrument. Each specified transformation type takes an
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<offset>. Offsets are relative to the center of the instrument. A
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shift without an offset has no effect. For example, let's say we have
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a texure that is a circle. If we use this texture in two layers, one
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defined as having a size of 128x128 and the second layer is defined as
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64x64 and neither is supplied a shift and offset the net result
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appears as 2 concentric circles.
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About Transformations and Needle Placement:
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------------------------------------------
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When describing placement of instrument needles, a transformation
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offset must be applied to shift the needles fulcrum or else the needle
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will rotate around it's middle. The offset will be of <type> x-shift
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or y-shift depending on the orientation of the needle section in the
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cropped texture.
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This example comes from the altimeter.xml
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<layer>
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<name>long needle (hundreds)</name> <!-- the altimeter has more than one needle -->
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<texture>
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<path>Aircraft/c172/Instruments/Textures/misc-1.rgb</path>
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<x1>0.8</x1>
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<y1>0.78125</y1>
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<x2>0.8375</x2>
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<y2>1.0</y2>
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</texture>
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<w>8</w>
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<h>56</h>
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<transformations> <!-- begin defining transformations -->
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<transformation> <!-- start definition of transformation that drives the needle -->
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<type>rotation</type>
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<property>/steam/altitude</property> <!-- bind it to a property -->
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<max>100000.0</max> <!-- upper limit of instrument -->
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<scale>0.36</scale> <!-- once around == 1000 ft -->
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</transformation> <!-- close this transformation -->
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<transformation> <!-- this one shifts the fulcrum of the needle -->
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<type>y-shift</type> <!-- y-shift relative to needle -->
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<offset>24.0</offset> <!-- amount of shift -->
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</transformation>
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</transformations>
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</layer>
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This needles has its origin in the center of the instrument. If the
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needles fulcrum was towards the edge of the instrument, the
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transformations to place the pivot point must precede those which
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drive the needle,
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Interpolation
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-------------
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Non linear transformations are now possible via the use of
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interpolation tables.
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<transformation>
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...
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<interpolation>
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<entry>
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<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).
|
|
|