Bindings
Bindings define what happens when a user:
- Clicks an object in the scenery or in an aircraft.
- Presses a key/button on the keyboard or joystick.
- Clicks a menu item
- Interacts with a dialog
You can assign multiple bindings to one object, button or key. Bindings may contain conditions to make them conditionally executed. Each binding must specify a command node with its particular type, see below.
This article gives a small overview of frequently used bindings. Please refer to $FG_ROOT/Docs/README.commands for additional information and a complete list of available bindings.
All given codes are examples, found on various places in the FlightGear package.
Commands
Below are a number of useful commands. See for the complete list, see flightgear/src/Main/fg_commands.cxx (line 1425).
To learn more about adding your own custom fgcommands to the source code, see Howto:Add new fgcommands to FlightGear
dialog-close
Closes the active dialog.
<binding>
<command>dialog-close</command>
</binding>
dialog-show
Shows a dialog, which should be present in $FG_ROOT/gui/dialogs. Starting with FlightGear 2.7, dialog files located in <aircraft directory>/gui/dialogs are also loaded. This should be used for dialogs specific to a certain aircraft.
<binding>
<command>dialog-show</command>
<dialog-name>location-in-air</dialog-name>
</binding>
- dialog-name: the name of the dialog, as designated in its .xml file.
nasal
Nasal is frequently used for complicated systems, because it can execute virtually any function and allows running previously-defined Nasal functions.
<binding>
<command>nasal</command>
<script>b777.afds.input(0,1);</script>
</binding>
The cmdarg
function is often useful in these situations to extract offset values passed to the binding. It returns the specific <binding> node, which contains a <setting> node at runtime if used in a joystick axis that represents the value of that axis.
In joysticks and keyboard keys the script is run in a specific namespace; please refer to the documentation for what the namespace is.
property-adjust
Increases or decreases a property's value with a given step. Maximum and minimum values are optional.
<binding>
<command>property-adjust</command>
<property>/autopilot/settings/heading-bug-deg</property>
<step>1</step> <!-- will add 1 to /autopilot/settings/heading-bug-deg whenever this binding is called -->
<min>000</min> <!-- the property will never be allowed to go below 0 -->
<max>360</max> <!-- ...or above 360 -->
<wrap>true</wrap> <!-- when we hit 361, wrap back to 0 and vice-versa -->
</binding>
property-assign
One of the most important commands. It sets a property to a predefined value.
<binding>
<command>property-assign</command>
<property>/autopilot/settings/target-speed-kt</property>
<value>0</value>
</binding>
property-cycle
Cycles between a list of values and assigns one to a property. The value-list can vary in length. If the current value is "value1", it will change to "value2"; if it is "value2", it will change to "value3", and so on, wrapping around the end. If the current value is not in the list, it will jump to the first one.
<binding>
<command>property-cycle</command>
<property>/autopilot/autobrake/setting</property>
<value type="string">ARM</value>
<value type="string">DISARM</value>
<value type="string">OFF</value>
</binding>
As of May 2013, the command supports additional behaviours to simplify use with the new knob and slider animations. The wrapping behaviour can be disabled by setting <wrap>0</wrap>, and the command uses the 'offset' argument to select a direction of movement. This means a property-cycle bound to a multi-position knob will function as expected for movement in both directions.
property-interpolate
Interpolates to a value with a given rate of change (per second).
<binding>
<command>property-interpolate</command>
<property>/controls/flight/aileron-trim</property>
<value type="double">0</value>
<rate>0.5</rate><!-- 2 seconds to 0 from 1 or -1 -->
</binding>
Instead of using <rate>, one could use
<binding>
<command>property-interpolate</command>
<property>/controls/flight/aileron-trim</property>
<value type="double">0</value>
<time>2</time><!-- 2 seconds to 0 from 1, 0.5, -1 etc. -->
</binding>
You can also interpolate to a value given by a property.
<binding>
<command>property-interpolate</command>
<property>/controls/flight/aileron-trim</property>
<property>/controls/flight/default-aileron-trim</property><!-- the value to interpolate to, is 0 -->
<rate>0.5</rate><!-- 2 seconds to 0 from 1 or -1 -->
</binding>
property-multiply
Multiply the value of a property by a given factor.
<binding>
<command>property-multiply</command>
<property>/controls/flight/aileron</property>
<factor>0.5</factor>
<min>-1</min>
<max>1</max>
<mask>all</mask>
<wrap>true</wrap>
</binding>
- factor: the amount to multiply by.
- min: minimum value.
- max: maximum value.
- mask:
- integer: mutiply only left of the decimal point.
- decimal: multiply only the right of the decimal point.
- all: multiply the entire value.
- wrap: true if the value should be wrapped if it passes min/max. It is required to set both min and max in that case.
property-randomize
Assigns a random value (between min and max) to a property.
<binding>
<command>property-randomize</command>
<property>/orientation/pitch-deg</property>
<min>0</min>
<max>360</max>
</binding>
property-scale
Set the value of a property based on an axis, often used in joystick configuration files.
<binding>
<command>property-scale</command>
<property>/controls/flight/aileron</property>
<offset>0.001</offset>
<factor>-1</factor>
<power>3</power>
</binding>
- offset: the offset to shift by, before applying the factor.
- factor: the factor to multiply by (use negative to reverse).
- squared: if true will square the resulting value (same as power=2).
- power: the resulting value will be taken to the power of this integer value (overrides squared).
Remember: ((property+offset)*factor)^power=result
property-swap
Swaps the values of two properties, useful for radio panels.
<binding>
<command>property-swap</command>
<property>/instrumentation/comm/frequencies/selected-mhz</property>
<property>/instrumentation/comm/frequencies/standby-mhz</property>
</binding>
property-toggle
Toggles the value of a property on each click, between true (1) and false (0).
<binding>
<command>property-toggle</command>
<property>/controls/gear/gear-down</property>
</binding>
Or - if defined - it toggles between two custom values.
<binding>
<command>property-toggle</command>
<property>/controls/gear/gear-down</property>
<value>2</value>
<value>3</value>
</binding>
request-metar
fgcommand("request-metar", props.Node.new({"path": "/foo/mymetar", "station": "LOWI"})); If you pass an existing path, the station ID will be updated, and if you pass the same station ID as before, no additional request is made. As usual for metar-properties, there's a time-to-live and valid flags you can check, and the metar refreshes automatically every 900 seconds. You can also write to the station ID directly to change station, update the time-to-live, and wait for the valid signal. There's also an unregister command ('clear-metar') to cancel the binding into the property tree.[1]— James Turner
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- ↑ James Turner (Sun, 23 Sep 2012 08:56:48 -0700). [Flightgear-devel] Requesting arbitrary metar.