FlightGear GUI Mini-HOWTO

David Megginson
Started: 2003-01-20
Last revised: 2003-01-20


FlightGear creates its drop-down menubar and dialog boxes from XML
configuration files under $FG_ROOT/gui.  This document gives a quick
explanation of how to create or modify the menubar and dialogs.  The
toolkit for the FlightGear GUI is PUI, which is part of plib.

All of the XML files use the standard FlightGear PropertyList format.


MENUBAR
-------

FlightGear reads the configuration for its menubar from
$FG_ROOT/gui/menubar.xml.  The file consists of a series of top-level
elements named "menu", each of which defines on of the drop-down
menus, from left to right.  Each menu contains a series of items,
representing the actual items a user can select from the menu, and
each item has a series of bindings that FlightGear will activate when
the user selects the item.

Here's a simplified grammar:

  [menubar] : menu*

  menu : label, item*

  item : label, binding*

The bindings are standard FlightGear bindings, the same as the ones
used for the keyboard, mouse, joysticks, and the instrument panel.
Any commands allowed in those bindings are allowed here as well.

Here's an example of a simple menubar with a "File" drop-down menu and
a single "Quit" item:

  <PropertyList>

   <menu>
    <label>File</label>
 
    <item>
     <label>Quit</label>
     <binding>
      <command>exit</command>
     </binding>
    </item>

  </PropertyList>

PUI menus do not allow advanced features like submenus or checkmarks.
The most common command to include in a menu item binding is the
'dialog-show' command, which will open a user-defined dialog box as
described in the next section.


DIALOGS
-------

The configuration files for XML dialogs use a nested structure to set
up dialog boxes.  The top-level always describes a dialog box, and the
lower levels describe the groups and widgets that make it up.  Here is
a simple, "hello world" dialog:

  <PropertyList>

   <name>hello</name>

   <width>150</width>
   <height>100</height>
   <modal>false</modal>

   <text>
    <x>10</x>
    <y>50</y>
    <label>Hello, world</label>
   </text>

   <button>
    <x>40</x>
    <y>10</y>
    <legend>Close</legend>
    <binding>
     <command>dialog-close</command>
    </binding>
   </button>

  </PropertyList>

The dialog contains two sub-objects: a text field and a button.  The
button contains one binding, which closes the active dialog when the
user clicks on the button.

Coordinates are pseudo-pixels.  The screen is always assumed to be
1024x768, no matter what the actual resolution is.  The origin is the
bottom left corner of the screen (or parent dialog or group); x goes
from left to right, and y goes from bottom to top.

All objects, including the top-level dialog, accept the following
properties, though they will ignore any that are not relevant:

 x - the X position of the bottom left corner of the object, in
   pseudo-pixels.  The default is to center the dialog.

 y - the Y position of the bottom left corner of the object, in
   pseudo-pixels.  The default is to center the dialog.

 width - the width of the object, in pseudo-pixels.  The default is
   the width of the parent container.

 height - the height of the object, in pseudo-pixels.  The default is
   the width of the parent container.

 legend - the text legend to display in the object.

 label - the text label to display near the object.

 property - the name of the FlightGear property whose value will
   be displayed in the object (and possibly modified through it).

 binding - a FlightGear command binding that will be fired when the
   user activates this object (more than one allowed).

 default - true if this is the default object for when the user
   presses the [RETURN] key.

Objects may appear nested within the top-level dialog or a "group"
object.  Here are all the object types allowed, with their special
properties:


dialog
------

The top-level dialog box; the name does not actually appear in the
file, since the root element is named PropertyList.

  name - (REQUIRED) the unique name of the dialog for use with the
    "dialog-show" command.

  modal - true if the dialog is modal (it blocks the rest of the
    program), false otherwise.  The default is false.

Example:

<PropertyList>

 <name>sample</name>
 <width>500</width>
 <height>210</height>
 <modal>false</modal>

 <text>
  ...
 </text>

 <button>
  ...
 </button>

</PropertyList>


group
-----

A group of subobjects.  This object does not draw anything on the
screen, but all of its children specify their coordinates relative to
the group; using groups makes it easy to move parts of a dialog
around.

Example:

  <group>
   <x>0</x>
   <y>50</y>

   <text>
    ...
   </text>

   <input>
    ...
   </input>

   <button>
    ...
   </button>

  </group>


input
-----

A simple editable text field.

Example:

  <input>
   <x>10</x>
   <y>60</y>
   <width>200</width>
   <height>25</height>
   <label>sea-level temperature (degC)</label>
   <property>/environment/temperature-sea-level-degc</property>
  </input>


text
----

A non-editable text label.

Example:

  <text>
   <x>10</x>
   <y>200</y>
   <label>Heading</label>
  </text>


checkbox
--------

A checkbox, useful for linking to boolean properties.

Example:

  <checkbox>
   <x>150</x>
   <y>200</y>
   <width>12</width>
   <height>12</height>
   <property>/autopilot/locks/heading</property>
  </checkbox>



button
------

A push button, useful for firing command bindings.

  one-shot - true if the button should pop up again after it is
    pushed, false otherwise.  The default is true.

  <button>
   <x>0</x>
   <y>0</y>
   <legend>OK</legend>
   <binding>
    <command>dialog-apply</command>
   </binding>
   <binding>
    <command>dialog-close</command>
   </binding>
   <default>true</default>
  </button>



combo
-----

A pop-up list of selections.

  value - one of the selections available for the combo.  There may be
  any number of "value" fields.

Example:

  <combo>
   <x>10</x>
   <y>50</y>
   <width>200</width>
   <height>25</height>
   <property>/environment/clouds/layer[0]/type</property>
   <value>clear</value>
   <value>mostly-sunny</value>
   <value>mostly-cloudy</value>
   <value>overcast</value>
   <value>cirrus</value>
  </combo>



select
------

A scrollable list of selections.

  selection - a path in the property tree which holds the selectable items.

Example:

  <select>
   <x>10</x>
   <y>50</y>
   <width>200</width>
   <height>25</height>
   <property>/sim/aircraft</property>
   <selection>/sim/aircraft-types</selection>
  </select>



slider
------

A horizontal or vertical slider for setting a value.

  vertical - true if the slider should be vertical, false if it should
    be horizontal.  The default is false.

  min - the minimum value for the slider.  The default is 0.0.

  max - the maximum value for the slider.  The default is 1.0.

Example:

  <slider>
   <x>10</x>
   <y>50</y>
   <width>200</width>
   <property>/environment/visibility-m</property>
   <min>5</min>
   <max>50000</max>
  </slider>


dial
----

A circular dial for choosing a direction.

  wrap - true if the dial should wrap around, false otherwise.  The
    default is true.

  min - the minimum value for the dial.  The default is 0.0.

  max - the maximum value for the dial.  The default is 1.0.

Example:

  <dial>
   <x>10</x>
   <y>50</y>
   <width>20</width>
   <property>/environment/wind-from-direction-deg</property>
   <min>0</min>
   <max>360</max>
  </dial>


__end__