Howto:Nasal in scenery object XML files: Difference between revisions

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(This is not implemented yet in FlightGear!)
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{{Stub}}
{{Nasal Navigation}}
[[FlightGear]] supports '''embedding [[Nasal]] scripts into scenery object XML files'''. This can be used for "intelligent" objects, such as special lighting features, specific lighthouse signals, and animated hangar doors. In other words, things that couldn't be done with [[Howto:Animate models|animations]] alone.


{{WIP}}
In the example below, the code in the <syntaxhighlight lang="xml" inline><load></syntaxhighlight> tag is run as soon as the tile loader decides to load the model. Using a {{func link|maketimer()}}, it prints a message every 5 seconds. When the object is removed from the memory, the code within the <syntaxhighlight lang="xml" inline><unload></syntaxhighlight> tag is executed. The timer is stopped and a message is printed. The code in the <syntaxhighlight lang="xml" inline><unload></syntaxhighlight> tag may also do things like [[Nasal library#removelistener.28.29|removing listeners]].


'''This feature is not implemented in FlightGear yet. It might get after the upcoming release. Till then, this does not work.'''
{{warning| In dialogs you have to use <open> and <close> instead of <load> and <unload>}}


(As of 05/2009, this is work in progress and entirely based on [http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg01757.html]).
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>


<strike>There's now support for embedding Nasal code (scripts) into object XML files.</strike>
<PropertyList>


This can be used for 'intelligent' objects -- such as for example special lighting features, specific lighthouse signals, things that couldn't be done with animations alone.  
<path>helipad.ac</path>
<nasal>
  <load><![CDATA[
    print("Hello, I'm the helipad!");
    var timer = maketimer(5, func(){
        print("I'm still here!");
    });
    timer.start();
  ]]></load>


The code is run as soon as the tile loader decided to load the model. It can use listeners and timers and so run as long as it wishes. If the object is removed from memory, then a variable is changed in the object's namespace, so that the code can stop itself. An optional destructor part can be used for further cleanup (remove listeners etc.)
  <unload><![CDATA[
    timer.stop();
    print("Bye, bye!")
  ]]></unload>
</nasal>


It is using two properies <load> and <unload>.
</PropertyList>
Example:
</syntaxhighlight>


<?xml version="1.0"?>
{{note|The object has to be present at sim startup. If you place an object with the UFO, the XML code will be executed, but not the Nasal code.}}
<PropertyList>
        <path>helipad.ac</path>
        <nasal>
                <load>
                        loaded = 1;
                        print("Hello, I'm the helipad!");
                        var f = func {
                                if (!loaded) { return }
                                print("I'm still there!");
                                settimer(f, 5);
                        }
                        f();
                </load>
                <unload>
                        loaded = 0;
                        print("Bye, bye!")
                </unload>
        </nasal>
        <animation>
                <type>noshadow</type>
                <object-name>helipad</object-name>
        </animation>
</PropertyList>


[[Category:Howto|Nasal in scenery object XML files]]
{{note|It is best practice to put Nasal code in a [[XML#Data|CDATA section]]. This prevents problems with the Nasal code containing {{wikipedia|List of XML and HTML character entity references#Predefined entities in XML|predefined XML entities}}.
[[Category:Nasal|Nasal in scenery object XML files]]
<syntaxhighlight lang="xml">
[[Category:Scenery enhancement|Nasal in scenery object XML files]]
<nasal>
  <load><![CDATA[
    # ...
    # your nasal code here
    # ...
  ]]></load>
<nasal>
</syntaxhighlight>
}}
 
[[Category:Nasal howto]]
[[Category:Scenery enhancement]]

Latest revision as of 14:51, 24 April 2020

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Nasal internals
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FlightGear supports embedding Nasal scripts into scenery object XML files. This can be used for "intelligent" objects, such as special lighting features, specific lighthouse signals, and animated hangar doors. In other words, things that couldn't be done with animations alone.

In the example below, the code in the <load> tag is run as soon as the tile loader decides to load the model. Using a maketimer() , it prints a message every 5 seconds. When the object is removed from the memory, the code within the <unload> tag is executed. The timer is stopped and a message is printed. The code in the <unload> tag may also do things like removing listeners.

Warning  In dialogs you have to use <open> and <close> instead of <load> and <unload> 
<?xml version="1.0" encoding="UTF-8"?>

<PropertyList>

<path>helipad.ac</path>
<nasal>
  <load><![CDATA[
    print("Hello, I'm the helipad!");
    var timer = maketimer(5, func(){
        print("I'm still here!");
    });
    timer.start();
  ]]></load>

  <unload><![CDATA[
    timer.stop();
    print("Bye, bye!")
  ]]></unload>
</nasal>

</PropertyList>
Note  The object has to be present at sim startup. If you place an object with the UFO, the XML code will be executed, but not the Nasal code.
Note  It is best practice to put Nasal code in a CDATA section. This prevents problems with the Nasal code containing predefined XML entities This is a link to a Wikipedia article. 
<nasal>
  <load><![CDATA[
    # ...
    # your nasal code here
    # ...
   ]]></load>
<nasal>
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