ofxLua

<p align="center"> <img src="https://raw.github.com/danomatika/ofxLua/master/res/logo.png"/> </p>

A Lua instance addon

Copyright (c) Dan Wilcox 2011-2023

BSD Simplified License.

For information on usage and redistribution, and for a DISCLAIMER OF ALL WARRANTIES, see the file, "LICENSE.txt," in this distribution.

See <https://github.com/danomatika/ofxLua> and the Openframeworks Forum post for documentation

_If you want to use Lua + openFrameworks without building your own app, check out loaf: danomatika.com/code/loaf._

This project has been supported by the CMU Frank-Ratchey STUDIO for Creative Inquiry, the DU Emergent Digital Practices Program, and my time at the ZKM | Hertz-Lab.

Description

ofxLua is an openFrameworks addon for running a Lua embedded scripting interpreter within an openFrameworks application. Using the SWIG (Simple Wrapper and Interface Generator) tool, C++ functions and classes can be bound to the Lua api allowing them to be called within a Lua script. This is useful in separating the upper level logic from the lower level application and is utilized in numerous video games and applications.

In addition, ofxLua provides bindings for the openFrameworks API.

Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics. Lua is dynamically typed, runs by interpreting bytecode for a register-based virtual machine, and has automatic memory management with incremental garbage collection, making it ideal for configuration, scripting, and rapid prototyping.

SWIG is a software development tool that connects programs written in C and C++ with a variety of high-level programming languages. It is used to generate the C++ bindings which wrap the openFrameworks API for Lua.

(Optional) LuaJIT is a Just-In-Time Compiler (JIT) for the Lua programming language. It implements the Lua API but is optimized for performance over the standard Lua distribution. It is recommended to use LuaJIT when speed is a concern and it is enabled on embedded Linux in addon_config.mk for this reason.

openFrameworks is a cross platform open source toolkit for creative coding in C++.

Why not Javascript?

Those coming from a Javascript background may ask "Why Lua? Why not Javascript? I like Javascript!"

Lua has a long history of use as a embedded scripting language and, as such, is both smaller & much easier to embed on pretty much every platform. The compiled language adds less than 500kb to your app binary versus many Mbs for Javascript or Python. Speed-wise, the base Lua interpreter is oftentimes faster than either language due to it's simplicity and using LuaJIT may add a speed increase of many orders of magnitude. As an embedded language, Lua makes it relatively easy to bind C/C++ functions & objects to it's scripting environment.

For these reasons, Lua has been used for game development for many years:

World of Warcraft scripting LuaCraft = Minecraft + Lua love2d game engine

Those coming from an embedded computing or game development background are probably familiar with Lua while those coming from design and/or web development are used to Javascript. In many ways, both languages share a number of similarities and the rest is due to simple syntax or design differences. When it comes down to it, no one language or environment is better than another, they just have different focuses and design backgrounds. Do not dismiss Lua because you are unfamiliar with it as not every nail needs the same hammer.

Lua is not scary, trust me :)

See:

About Lua Lua wikipedia page) Programming in Lua Learning Lua from JS

Build Requirements

To use ofxLua, first you need to download and install openFrameworks. The examples are developed against the latest release version of openFrameworks on <http://openframeworks.cc/download>.

OF github repository

Currently, ofxLua is being developed on macOS and has been tested on macOS, iOS, & Linux. Android should work but has not been tested extensively.

Installation and Build

Place ofxLua within a folder in the apps folder of the OF directory tree:

openframeworks/addons/ofxLua

The easiest way to do this is via cloning with git:

cd openframeworks/addons/ git clone git://github.com/danomatika/ofxLua.git

You'll need to checkout the swig-openframeworks submodule as well using:

cd ofxLua git submodule init git submodule update

Which version to use?

The master branch of ofxLua will work with the current stable version of openFrameworks and can be considered relatively stable.

Previous versions are tagged using Semantic Versioning with the updates to newer versions of openFrameworks and Lua noted in the changelog, CHANGES.txt. You can select the tag in the Github "Current Branch" menu or clone and check it out using git.

If you want to use ofxLua with a previous version of openFrameworks, find the tag corresponding to your OF version by looking at the changelog or releases. Note that the ofxLua tag and OF version do not match.

For example,

git clone git://github.com/danomatika/ofxLua.git cd ofxLua git checkout 1.3.0

will checkout a version that's compatible with OF 0.11.0.

Dependencies

For embedded Linux (arm, Raspberry Pi, etc), LuaJIT is used for better performance. Make sure you have the luajit-5.1 development package installed.

Visual Studio

If you run into compilation issues in Visual Studio (ie. "unresolved external symbol" errors with "\_lua_\" library functions), you may need to tell the VS to build the Lua library using the C compiler instead of the C++ compiler:

In the Solution Explorer:

1. Select the Lua C files in addons/ofxLua/libs/lua, e.g. lapi.c + lauxlib.c ... 2. Right click -> choose Properties 3. Select C/C++ -> Advanced from left tree 4. Change Compile As -> Compile as C Code (/TC)

If there is an alternate solution to this issue in the addons_config.mk, please let us know!

Android Studio

_Contributed by Zach Lee_

In Android Studio, the addon_config.mk exclude flags may not have an effect when using the OF ProjectGenerator app, and the following platform-specific bindings folders may need to be manually removed from the AS project:

ofxLua/src/bindings/desktop ofxLua/src/bindings/linuxarm

Next, to make Android Studio read the C flags from the addon_config.mk file, add the following code below cppFlags.addAll(addonCppFlags(abi, ofRoot())) in build.gradle file:

~~~ CFlags.addAll(addonCppFlags(abi, ofRoot())) ~~~

After the fix, the ofxLua project should hopefully build and run on an Android device.

Running the Example Projects

The example projects are located in the luaExample & luaExampleIOS folders.

Project files for the examples are not included so you will need to generate the project files for your operating system and development environment using the OF ProjectGenerator which is included with the openFrameworks distribution.

To (re)generate project files for an existing project:

Click the "Import" button in the ProjectGenerator Navigate to the project's parent folder ie. "ofxLua", select the base folder for the example project ie. "luaExample", and click the Open button Click the "Update" button

If everything went Ok, you should now be able to open the generated project and build/run the example.

macOS

Open the Xcode project, select the "luaExample Debug" scheme, and hit "Run".

Linux

Open the Code::Blocks .cbp and hit F9 to build. Optionally, you can build the example with the Makefile.

To build and run it on the terminal:

make make run

How to Create a New ofxLua Project

ProjectGenerator

Simply select ofxLua from the available addons in the ProjectGenerator before generating a new project.

Manual Method

To develop your own project based on ofxLua, simply copy an example project and rename it. You probably want to put it in your apps folder, for example, after copying:

openFrameworks/addons/ofxLua/example/ => openFrameworks/apps/myApps/example/

It must be 3 levels down in the openframeworks folder structure.

Then after renaming:

openFrameworks/apps/myApps/myLuaProject/

On Mac, rename the project in Xcode (do not rename the .xcodeproj file in Finder!): Long click on the project name in the project tree.

Adding ofxLua to an Existing Project

ProjectGenerator

Select ofxLua and other addons used by your project from the available addons in the ProjectGenerator, select the parent folder of your project, and set the exact name of the existing project in the text box. This will overwrite the existing project files with new ones that now include ofxLua.

Note: you will lose any custom settings you've added manually to your project.

Manual Method

If you want to add ofxLua to another project, you need to make sure you add the following src files:

openFrameworks/addons/ofxLua/src/ofxLua.h openFrameworks/addons/ofxLua/src/ofxLua.cpp openFrameworks/addons/ofxLua/src/ofxLuaFileWriter.h openFrameworks/addons/ofxLua/src/ofxLuaFileWriter.cpp

and optionally

openFrameworks/addons/ofxLua/src/bindings/ofBindings.h openFrameworks/addons/ofxLua/src/bindings/YOURPLATFORM/ofBindings.cpp openFrameworks/addons/ofxLua/src/bindings/glmBindings.h

You also need to add the Lua library files in the libs directory:

openFrameworks/addons/ofxLua/libs/lua

For Xcode:

Right-click and create a new group "ofxLua" Drag ofxLua/src into "ofxLua" Drag ofxLua/libs into "ofxLua" Remove bindings files that do not match your platform aka remove src/bindings/desktop for iOS

On older macOS versions (pre 10.8), a header file which is included with the OS contains some macros which conflict with several lua macros. They can be renamed by setting this CFLAG:

-D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES=0

OF API Bindings

SWIG generated bindings for the OF API can be found in src/bindings. Currently it covers most of the api while leaving out base classes. More specific documentation may come at a future date, but for now check the example scripts on usage.

Basic documentation:

There is a main "of" module and functions, classes, constants, & enums are renamed: function: ofBackground -> of.background class: ofColor -> of.Color constant: OF_LOG_VERBOSE -> of.LOG_VERBOSE enum: ofShader::POSITION_ATTRIBUTE -> of.Shader.POSITION_ATTRIBUTE begin & end: these are lua keywords, so functions with this name are renamed in the following classes: _ofFbo_: beginFbo() & endFbo() _ofCamera_: beginCamera() & endCamera() _ofMaterial_: beginMaterial() & endMaterial() _ofShader_: beginShader() & endShader()

Base classes, deprecations, variable arguments (...), ofThread, ofPtr, ofMutex, & ofScopedLock are ignored for now.

Functions that return a std::vector return a wrapped std::vector in Lua. As with Lua tables, indexes start at 1.

glm

As of OF 0.10.0, there is also a "glm" module for the glm types and math functions. Note that the OF math types cannot be implicitly cast to glm types in Lua as they are in C++, so you need to use special conversion functions:

-- error! local v = of.Vec2f(100, 100) of.drawRectangle(v, 20, 20) -- needs a glm::vec2 -- convert of.drawRectangle(v:vec2(), 20, 20) -- ofVec2f -> glm::vec2 -- or use the ofVec2f attributes directly of.drawRectangle(v.x, v.y, 20, 20)

It looks as those ofVec\, ofMatrix\, and ofQuaternion may be deprecated in the future, so it's probably best to transition to using glm::vec\, glm::mat\, and glm::quat over time:

-- using glm::vec2 local v = glm.vec2(100, 100) of.drawRectangle(v, 20, 20)

See swig/README.txt for details.

Math & String

The basic string and math functions are provided by built-in Lua libraries:

math string

Other standard Lua libraries are: table, io, and os.

Comparing Key Values

OF uses integers for the key event values so comparisons can be made using character literals in C++:

if(key == 'f') { ofToggleFullscreen(); } else if(key == OF_KEY_UP) { ofLog() << "up pressed"; }

Lua does not have character literals so 'f' is treated as a string. In order to do the same comparison, convert 'f' to a number using the string library string.byte function:

if key == string.byte("f") then of.toggleFullscreen() elseif key == of.KEY_UP then print("up pressed") end

Working with Class Instances

Calling class member functions requires using a : character -> image:draw(20, 100, 100, 100)

Calling class member variables requires using a . character -> print(image.width)

Mixing up : and . is probably the most common pitfall when coming from C++ to Lua:

-- create instance of a class image = of.Image() -- this will cause an error image.load("helloworld.jpg") -- using . to call member function

-- this will work image:load("helloworld.jpg") -- use a : instead

-- access class instance properties with a . print("Image size: "..image.width.."x"..image.height)

Details

To see the detailed differences with the OF C++ API run the following:

find swig -type f -name ".i" -exec grep DIFF {} \; To see work to be done on the bindings run:

find swig -type f -name ".i" -exec grep TODO {} \;

Classes

Simple Lua class support is provided by the class() function from the Lua Users wiki:

-- class declaration MyClass = class() -- constructor & attributes function MyClass:__init(x, y) self.x = x self.y = y self.radius = 4 end

-- class function function MyClass:draw() of.drawEllipse(self.x, self.y, self.radius, self.radius) end

-- create instance & access attribute myclass = MyClass(10, 10) myclass.x = 100

-- calling a class function, note use of : for instance function instead of . myclass:draw()

This implementation allows for inheritance and usage is as follows:

-- inherit first class and add an attribute OtherClass = class(MyClass) function OtherClass:__init(x, y, z) MyClass.__init(self, x, y) -- call super constructor self.z = z end -- create instance of derived class & access attributes otherclass = OtherClass(10, 10, 5) otherclass.x = 100 otherclass.z = 100

-- calling a class function, note use of : for instance function instead of . otherclass:draw()

Checking Types

Lua comes with the built-in type() function which returns a string denoting the argument's type: "nil", "number", "string", "function", "table", "userdata", etc. Calling type() on a wrapped object will return a "userdata" string, ie. type(of.Mesh()), as it is basically an object pointer to something Lua doesn't know about but is handled by the language bindings.

For more detailed type info for objects wrapped by SWIG, use the special swig_type() function which is not native to Lua, but added by SWIG:

local mesh = of.Mesh() print(type(mesh)) print(swig_type(mesh))

will print the following:

~~~ userdata ofMesh_< ofDefaultVertexType,ofDefaultNormalType,ofDefaultColorType,ofDefaultTexCoordType > |ofMesh ~~~

Making Your Own Bindings

SWIG Interface

Create a SWIG interface file (\.i) with includes headers for the functions and classes which you want to bind. You then run SWIG with this file to generate the \.cpp wrapper.

It could be as simple as the following:.

MyCode.h, your custom code:

#pragma once

include "ofMain.h"

float myFunction(float aNumber) { return aNumber+1; } class MyCoolClass { public: MyCoolClass() { myFloat = 0; myInt = 0; aString = "hello world"; } MyCoolClass(float aNumber) { myFloat = aNumber; myInt = (int) aNumber; aString = "foo bar"; } // member function void doSomething() { ofLog() << "did something: " << aString; } // getter/setter void setInt(int newInt) {myInt = newInt;} int getInt() {return myInt;} // member variable, read/write string aString;

protected:

// some protected member variables, won't be wrapped float myFloat; int myInt; };

MyBindings.i, your custom SWIG interface file:

%module my %{ // include any needed headers here

include "MyCode.h"

%} // include support for some common C++ STL types you might be using, // see http://swig.org/Doc3.0/Library.html#Library_stl_cpp_library %include <stl.i> %include <std_string.i> %include <std_vector.i> %include <std_map.i>

// if you're using "string" instead of "std::string" (like the openFrameworks source code), // you'll need this so swig will know that a "string" can be considered a "std::string" typedef std::string string;

// include custom code you want to be wrapped, // note the '%' instead of '#' as '%include' is a SWIG // command to wrap code in the given header %include "MyCode.h"

That's it, SWIG will handle the rest! Of course this is a simple example but there are lots more options for specific bindings settings such as generating properties from getters & setters, etc.

Generate .cpp Wrapper

Now call SWIG to generate your .cpp wrapper:

swig -c++ -lua -fcompact -fvirtual -I../../../libs/openFrameworks MyBindings.i _Make sure to add search paths to headers used by your code (aka the "-I" line in the command above)._

If all went well, SWIG will have generated the MyBindings_wrap.cxx C++ file. Put this into your project's source directory and build it with your project.

Opening Your Lua Library

You will need to open your new Lua library provided by the SWIG-generated .cpp file in order to use it in your lua state.

SWIG creates a "luaopen" C function using your module name which, in this case, will be "luaopen_my". This function needs to be defined in C++ in order to be used, so add it to the top of the .cpp file where you initialize your ofxLua object:

// declare the module bindings extern "C" { int luaopen_my(lua_State* L); }

Then call this function after initing ofxLua:

lua.init(true); luaopen_my(lua); // open bindings

Using Your Lua Library

If everything is working, you should be able to call your bindings in Lua using your new "my" module: aNumber = my.myFunction(3.45) -- class coolClass = my.MyCoolClass() -- constructor