Ardour Lua Bindings

This documentation is far from complete may be inaccurate and subject to change.

Overview

The top-level entry point are and . Most other Classes are used indirectly starting with a Session function. e.g. Session:get_routes().

A few classes are dedicated to certain script types, e.g. Lua DSP processors have exclusive access to and . Action Hooks Scripts to etc.

Detailed documentation (parameter names, method description) is not yet available. Please stay tuned.

Short introduction to Ardour classes

Ardour's structure is object oriented. The main object is the Session. A Session contains Audio Tracks, Midi Tracks and Busses. Audio and Midi tracks are derived from a more general "Track" Object, which in turn is derived from a "Route" (aka Bus). (We say "An Audio Track is-a Track is-a Route"). Tracks contain specifics. For Example a track has-a diskstream (for file i/o).

Operations are performed on objects. One gets a reference to an object and then calls a method. e.g obj = Session:route_by_name("Audio") obj:set_name("Guitar").

Lua automatically follows C++ class inheritance. e.g one can directly call all SessionObject and Route methods on Track object. However lua does not automatically promote objects. A Route object which just happens to be a Track needs to be explicily cast to a Track. Methods for casts are provided with each class. Note that the cast may fail and return a nil reference.

Likewise multiple inheritance is a non-trivial issue in lua. To avoid performance penalties involved with lookups, explicit casts are required in this case. One example is which is-a StatefulDestructible which inhertis from both Stateful and Destructible.

Object lifetimes are managed by the Session. Most Objects cannot be directly created, but one asks the Session to create or destroy them. This is mainly due to realtime constrains: you cannot simply remove a track that is currently processing audio. There are various factory methods for object creation or removal.

Pass by Reference

Since lua functions are closures, C++ methods that pass arguments by reference cannot be used as-is. All parameters passed to a C++ method which uses references are returned as Lua Table. If the C++ method also returns a value it is prefixed. Two parameters are returned: the value and a Lua Table holding the parameters.

C++

void set_ref (int& var, long& val)
{
	printf ("%d %ld\n", var, val);
	var = 5;
	val = 7;
}

Lua

local var = 0;
ref = set_ref (var, 2);
-- output from C++ printf()
0 2
-- var is still 0 here
print (ref[1], ref[2])
5 7

int set_ref2 (int &var, std::string unused)
{
	var = 5;
	return 3;
}

rv, ref = set_ref2 (0, "hello");
print (rv, ref[1], ref[2])
3 5 hello

Pointer Classes

Libardour makes extensive use of reference counted boost::shared_ptr to manage lifetimes. The Lua bindings provide a complete abstration of this. There are no pointers in lua. For example a is a pointer in C++, but lua functions operate on it like it was a class instance.

shared_ptr are reference counted. Once assigned to a lua variable, the C++ object will be kept and remains valid. It is good practice to assign references to lua local variables or reset the variable to nil to drop the ref.

All pointer classes have a isnil () method. This is for two cases: Construction may fail. e.g. .newplugin() may not be able to find the given plugin and hence cannot create an object.

The second case if for boost::weak_ptr. As opposed to boost::shared_ptr weak-pointers are not reference counted. The object may vanish at any time. If lua code calls a method on a nil object, the interpreter will raise an exception and the script will not continue. This is not unlike a = nil a:test() which results in en error "attempt to index a nil value".

From the lua side of things there is no distinction between weak and shared pointers. They behave identically. Below they're inidicated in orange and have an arrow to indicate the pointer type. Pointer Classes cannot be created in lua scripts. It always requires a call to C++ to create the Object and obtain a reference to it.

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∅ '.htmlentities ($ns).'

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ℕ '.ctorname($ns).'

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⋯ '.htmlentities ($ns).'

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↠ '. htmlentities ($ns).'

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∁ '.htmlentities ($ns).'

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is-a: '.$isa.'

'.NL; } echo '

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This class object is only used indirectly as return-value and function-parameter. It provides no methods by itself.

'.NL; } else { echo ''.NL; echo $tbl; echo '

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Inherited from '.$pns.'

'.NL; echo ''.NL; echo $tbl; echo '

'.NL; } } } #################### # Enum and Constants echo '

Enum/Constants

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∈ '.ctorname ($ns).'

'.NL; echo '

'.ctorname ($c['lua']).'

'.NL; } ###################### # Index of all classes echo '

Class Index

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'.typelink($ns).'

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