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Nasal for C++ programmers: Difference between revisions
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Nasal itself has a standard library of general purpose functions, in addition it supports dozens of FG-specific extension functions to do various FG-related things, for example to interact with other subsystems (e.g. AI traffic, weather, FDM, GUI etc). In other words, while you'll find lots of standard library functions, there are many FG/simulation-specific functions available in FlightGear/Nasal. | Nasal itself has a standard library of general purpose functions, in addition it supports dozens of FG-specific extension functions to do various FG-related things, for example to interact with other subsystems (e.g. AI traffic, weather, FDM, GUI etc). In other words, while you'll find lots of standard library functions, there are many FG/simulation-specific functions available in FlightGear/Nasal. | ||
An increasing number of subsystems in FlightGear no longer have direct scripting bindings via extension functions, but instead work by replicating their APIs on top of the property tree - so that these systems can be mostly controlled just by setting/getting properties - the autopilot system, AI Traffic and the canvas are some more recent examples of this. | An increasing number of subsystems in FlightGear no longer have direct scripting bindings via extension functions, but instead work by replicating their APIs on top of the property tree - so that these systems can be mostly controlled just by setting/getting properties - the autopilot system, AI Traffic and the canvas are some more recent examples of this. To add new bindings to Nasal, the cppbind framework in Nasal should be used (the Canvas system and NasalPositioned being the implementation reference here for the time being). | ||
One of the oldest mechanism to run custom code are so called "fgcommands", which is just a fancy word for "FlightGear commands" that work purely via the property tree - i.e. they accept parameters solely as properties, and they may also only return values via the property tree. So these know nothing about Nasal or Nasal's data structures - which makes them pretty flexible and powerful, because they can also be used in non-scripting contexts, such as in XML files/bindings - from Nasal space, these can still be easily invoked via the fgcommand() API. | |||
Also, there are extension functions available which allow callbacks to be registered in the form of property listeners (which get invoked whenever a property is updated/written to) or via timers (that may expire and trigger a callback that gets called after expiration). | Also, there are extension functions available which allow callbacks to be registered in the form of property listeners (which get invoked whenever a property is updated/written to) or via timers (that may expire and trigger a callback that gets called after expiration). | ||