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

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Howto:Nasal in scenery object XML files (view source)

Revision as of 09:03, 7 April 2016

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[[FlightGear]] supports '''embedding [[Nasal]] code (scripts) into object XML files'''. This can be used for 'intelligent' objects -- such as for example special lighting features, specific lighthouse signals, animated hangar doors. In other words, things that couldn't be done with [[Howto:Animate models|animations]] alone.  
{{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.  


The code is run as soon as the tile loader decides 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.)
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]].


It is using two properies <load> and <unload>.
<syntaxhighlight lang="xml">
<?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>


<syntaxhighlight lang="xml">
  <unload><![CDATA[
<?xml version="1.0"?>
    timer.stop();
<PropertyList>
    print("Bye, bye!")
        <path>helipad.ac</path>
  ]]></unload>
        <nasal>
</nasal>
                <load>
 
                        loaded = 1;
</PropertyList>
                        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>
</PropertyList>
</syntaxhighlight>
</syntaxhighlight>


Advice for testing: the object has to be present at sim startup. If you place an object with the UFO the xml-code gets executed, but not the Nasal code.
{{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.}}


To avoid problems with particular characters like &lt; and &gt;, consider [[XML#Data|using a CDATA block]]:
{{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}}.
<syntaxhighlight lang="xml">
<syntaxhighlight lang="xml">
<nasal>
<nasal>
<load>
  <load><![CDATA[
  <![CDATA[
    # ...
    # ...
    # your nasal code here
    # your nasal code here
    # ...
    # ...
   ]]></load>
   ]]>
</load>
<nasal>
<nasal>
</syntaxhighlight>
</syntaxhighlight>
}}


[[Category:Nasal howto]]
[[Category:Nasal howto]]
[[Category:Scenery enhancement]]
[[Category:Scenery enhancement]]
Retrieved from "https://wiki.flightgear.org/Special:MobileDiff/96740"

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