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Howto:Extend Nasal: Difference between revisions
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some more examples, untested/uncompiled at the moment
m (even more Nasal docs) |
m (some more examples, untested/uncompiled at the moment) |
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The simplest way to do this is to look at the existing functions in [http://cvs.flightgear.org/viewvc/source/src/Scripting/ $FG_SRC/Scripting]/NasalSys.cxx (src/Scripting/NasalSys.cxx). | The simplest way to do this is to look at the existing functions in [http://cvs.flightgear.org/viewvc/source/src/Scripting/ $FG_SRC/Scripting]/NasalSys.cxx (src/Scripting/NasalSys.cxx). | ||
There is a static table of function pointers referencing extension functions: | There is a static table of function pointers referencing extension functions, along with their corresponding names in Nasal: | ||
// Table of extension functions. Terminate with zeros. | // Table of extension functions. Terminate with zeros. | ||
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{ 0, 0 } | { 0, 0 } | ||
}; | }; | ||
You will need to add your new extension function to this list of static functions, preferably following the existing naming convention (i.e. "f_" prefix). | |||
= Extension Function Signature = | = Extension Function Signature = | ||
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} | } | ||
If you don't have anything else to return, you can just return naNil(). | So, this is basically the boilerplate that you'll need to use in order to expose a new function. | ||
If you don't have anything else to return, you can just return naNil(), so that the function looks like this: | |||
static naRef f_cool (naContext c, naRef me, int argc, naRef* args) | |||
{ | |||
return naNil(); | |||
} | |||
In order to make this function known to the Nasal interpreter, you'll want to extend the previously mentioned list of Nasal extension functions, to read: | |||
// .... | |||
{ "airportinfo", f_airportinfo }, | |||
{ "cool", f_cool }, //this is where we add our new function | |||
{ 0, 0 } | |||
}; | |||
Once you have made these modifications, you can simply invoke your new function, of course it will not yet do anything useful, though. | |||
So, in order to make it slightly more interesting, we are going to change the return statement to return something else, instead of nil: | |||
static naRef f_cool (naContext c, naRef me, int argc, naRef* args) | |||
{ | |||
const char* cool="cool"; | |||
naRef retval; | |||
naStr_fromdata(retval, cool, strlen(cool) ); | |||
return retval; | |||
} | |||
So, after rebuilding the FlightGear binary, whenever you call the new "cool" API function, it will always return a "cool" string. | |||
= Argument Processing = | = Argument Processing = | ||