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, enabled, 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>
   <draggable>true</draggable>

   <text>
    <x>10</x>
    <y>50</y>
    <label>Hello, world</label>
    <color>
     <red>1.0</red>
     <green>0.0</green>
     <blue>0.0</blue>
    </color>
   </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.

 border - the border thickness, in pseudo-pixels.  The default is 2.

 color - a subgroup to specify the dialogs color:
  red   - specify the red color component of the color scheme.
  green - specify the green color component of the color scheme.
  blue  - specify the blue color component of the color scheme.
  alpha - specify the alpha color component of the color scheme.

 font - a subgroup to specify a specific font type
  name - the name of the font (excluding it's .txf extension)
  size - size of the font
  slant -  the slant of the font (in pseudo-pixels)

 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).

 keynum - the key code of a key that can be used to trigger the
   widget bindings via keyboard (e.g. <keynum>97</keynum> for
   the "a" key.

 key - like "keynum", but takes a character ("a", "A", "Shift-a",
   "Shift-A", "Ctrl-a", "%", etc.), or symbolic key name ("Tab",
   "Return" = "Enter", "Esc" = "Escape", "Space", "&amp;" = "and",
   "&lt;", "&gt;", "F1" -- "F12", "Left", "Up", "Right", "Down",
   "PageUp", "PageDn", "Home", "End", "Insert"). Note that you
   can't use "<", ">", and "&" directly.

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

 hide - if set to true, hides the whole widget that it is used
   in, along with its children. There's no empty space reserved
   for such widgets. The "hide" property can also be used to hide
   other XML groups from the layouter.

Objects may appear nested within the top-level dialog or a "group"
or a "frame" 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.

  draggable - false if the dialog is not draggable. The default is true.

  nasal - Nasal definition block
    open - Nasal script to be executed on dialog open
    close - Nasal script to be executed on dialog close

All Nasal code runs in a dialog namespace. Nasal bindings can
directly access variables and functions defined in an <open> block.
settimer() and setlistener() functions have to be removed manually
in the <close> block if they shouldn't remain active.


Example:

<PropertyList>

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

 <text>
  ...
 </text>

 <button>
  ...
 </button>

</PropertyList>


group and frame
---------------

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.

A frame is a visual representation of a group and has  a border and an
adjustable background color.

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>

  <text>
   <x>10</x>
   <y>200</y>
   <label>-9.9999</label> <!-- placeholder for width -->
   <format>%-0.4f m</format>
   <property>/foo/altitude</property>
  </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>



list
----

like "combo", but displays all values in a scrollable list box with
slider on the right side. Doesn't take bindings.



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>


textbox
-------

The text will be retrieved/buffered from/within a specified
property tree, like:

<textbox>
    <!-- position -->
    <x>100</x>
    <y>100</y>

    <!-- dimensions -->
    <width>200</width>
    <height>400</height>

    <property>/gui/path-to-text-node/contents</property>

    <slider>15</slider> <!--width for slider -->
    <wrap>false</wrap> <!-- don't wrap text; default: true -->

    <editable>true</editable> <!-- whether the puLargeInput is supposed to be editable -->
</textbox>


hrule/vrule
-----------

Draws a horizontal/vertical line that, by default, expands to full width/height.
Its thickness can be set with <pref-height>/<pref-width>.

  <hrule>
    <color>
      <red>1.0</red>
      <green>0.0</green>
      <blue>0.0</blue>
    </color>
    <pref-height>2</pref-height>
  </hrule>




GLOBAL SETTINGS ("THEMES")
--------------------------

FlightGear reads GUI style information from /sim/gui/, which is by default
loaded from file $FG_ROOT/gui/style.xml.  This file contains one <font> and
one <colors> group:


global font settings
--------------------

  <sim>
    <gui>
      <font>
        <name type="string">Helvetica.txf</name>
        <size type="float">15</size>
        <slant type="float">0</slant>
      </font>
    </gui>
  <sim>

<name> can either be the name of a built-in bitmap font (one of:
"FIXED_8x13", "FIXED_9x15", "TIMES_10", "TIMES_24", "HELVETICA_10",
"HELVETICA_12", "HELVETICA_14", "HELVETICA_18", "SANS_12B"), or the
name of a texture font in the $FG_FONT directory. $FG_FONT is by
default set to $FG_ROOT/Fonts/. Properties <size> and <slant> are
only applied to texture fonts, and otherwise ignored.


global color settings
---------------------

These define the color of the splash screen font, and the color of the
GUI elements. All colors are in /sim/gui/colors/ and follow the same
pattern:

  <sim>
    <gui>
      <colors>
        <!-- splash screen font color; ignores <alpha> value -->
        <splash>
          <red type="float">1.0</red>
          <green type="float">0.9</green>
          <blue type="float">0.0</blue>
        </splash>
      </colors>
    </gui>
  </sim>



As listed above, FlightGear implements several GUI elements:

(1)    "dialog"      "group"         "frame"       "hrule"      "vrule"
       "list"        "airport-list"  "input"       "text"       "checkbox"
       "radio"       "button"        "combo"       "slider"     "dial"
       "textbox"     "select"


The underlying plib library uses six colors for each GUI element.
These are:

(2)    "background"  "foreground"    "highlight"
       "label"       "legend"        "misc"


"button", for example, uses the first four colors from (2), while it
ignores "legend" and "misc" color. "text" only uses "label", and ignores
the rest. In some cases the use of colors isn't obvious and you have to
try or look up the plib sources to be sure. GUI colors can be defined
for each of the categories from (1) and (2), and for combinations of
them:

(3)    "button-legend"   "input-misc"    etc.


FlightGear has default colors for (2) built-in. Let's call them (0).
And this is how colors for individual GUI elements are determined,
if, for example, a button is to be drawn:

  For the button's background:
  a. read the hard-coded default "background" color from (0) as base
  b. merge the global "background" color from (2) in (if defined)
  c. merge a global color "button-background" from (3) in (if defined)
  d. merge a specific <color> from the dialog's XML file in (if defined)

  Repeat the four steps for the button's "foreground", "highlight",
  etc. color.




If you write a style file, you'll most likely start with the colors
from (2):

 <sim>
   <gui>
     <colors>
       <background>
         <red type="float">0.6</red>
         <green type="float">0.0</green>
         <blue type="float">0.0</blue>
         <alpha type="float">1.0</alpha>
       </background>

       <foreground>
       ...

This makes all dialogs dark red. But you don't, for example, want buttons
to be red, but yellow. So you define another color for buttons:

       <button>
         <red type="float">1.0</red>
         <green type="float">0.9</green>
         <blue type="float">0.0</blue>
         <alpha type="float">1.0</alpha>
       </button>
       ...

This sets all of a button's six colors (2) to some shades of red. plib
does this automatically. The lower and right border ("foreground") will
be darker, the upper and left border will be lighter ("highlight").
If you aren't happy with plib's choice, you can set each of the colors
explicitly. Let's say, we want the text on the button blue (3):

       <button-legend>
         <red type="float">0.3</red>
         <green type="float">0.3</green>
         <blue type="float">1.0</blue>
         <alpha type="float">1.0</alpha>
       </button-legend>
       ...

To set the cursor color from input fields, you'd define "input-misc",
etc.


You can change colors and font at runtime. Just open the property
browser, go to /sim/gui/colors and change whatever you like. The
new color will only take effect, though, if you re-init the GUI.
There's a menu entry for that, and you can define a key binding
for it:

  <key n="99">
    <name>c</name>
    <desc>Re-init GUI</desc>
    <binding>
      <command>reinit</command>
      <subsystem>gui</subsystem>
    </binding>
  </key>

Note that this will currently close all open dialogs!


__end__