Lua Alchemy v0.1a Released

The first release of Lua Alchemy has been released; the library SWC, demo, and code can be downloaded from here:
http://code.google.com/p/lua-alchemy/

Since my preview post (which is now running the same demo code) we have

• Added many Lua scripting samples.
• Fixed some memory leaks.
• Cleaned up function callbacks created in Lua which would typically be used for event listeners.
  

Below is a preview of the release:

Note that the demo above requires Flash Player 10 (required by Alchemy and my use of the local file system to allow opening/saving files). It is also hosted here where it can take up a full browser screen and is much easier to read.

The next version will include syntax sugar so instead of calling as3.call(var, "function", param) you could call var.function(param) and similar calls to make calling ActionScript code look the same as calling Lua code.

LuaAlchemy Project v.1a Preview

Since my last post my experiment to make Lua a runtime scripting language in Flash using Alchemy has become a full open source project located here:
http://code.google.com/p/lua-alchemy/

I even have a partner named Alexander Gladysh whom I met on the Lua boards.

We are approaching a V.1a release of the project. Using LuaAlchemy you can now create any ActionScript class available at runtime, get/set properties, call functions, and set event listeners (actually you can return a Lua function to use as an ActionScript function). The Lua to ActionScript interface is a little raw right now but we plan on adding some Lua sugar to make accessing ActionScript objects, classes, and namespaces in Lua look and feel like using Lua objects.

Below is a preview of the release:

Note that the demo above requires Flash Player 10 (required by Alchemy and my use of the local file system to allow opening/saving files). It is also hosted here where it can take up a full browser screen and is much easier to read.

Along the way to this release we have encountered a few problems which I will discuss. The first problem was speed. Although the Alchemy V.4a compiled code was fast enough for our purposes, it was about 30 times slower running a life simulator written in Lua than natively compiled Lua. The release of Alchemy V.5a has made life run 4 times faster so progress is being made (v.4a had some debug code compiled in that slowed things down).

The second problem has been gluegen. Gluegen is a tool to help you create wrappers around C code that takes a mix of C and ActionScript code to generate C and ActionScript wrappers. Unfortunately this seems to interfear with CLibInit.setSprite() which we wanted to use to provide a sprite that Lua could use for stdin, stdout, and stderr. Glugen created code creates and inits CLibInit as static members and you seemingly need to call setSprite() before init(). We worked around that problem by providing an output TextArea in the demo below, but we plan on writing the wrapper ourselves and not using gluegen at all.

The third problem is related to garbage collection in Flash and Lua. To make Lua functions usable as an ActionScript function we call AS3_Function() to create an ActionScript function that calls a C callback function passing in some contextual data. This data includes some Lua references in a malloced structure and we would like to know when it isn't needed anymore so it can be released. We haven't figured out any way for Alchemy to tell us when the object is no longer needed. A future version will do some cleanup when the lua_state is closed.

Overall our experience has been a positive one and Alchemy is still in Alpha.

Lua ActionScript Alchemy

At Adobe MAX 2008 San Francisco, Alchemy was released. Alchemy was once known as FlaCC or Cassava and is a C/C++ to ActionScript compiler.

Alchemy works by translating C/C++ code to ActionScript through a LLVM compiler which instead of producing machine or bytecode produces ActionScript. The translated C/C++ code uses a big ActionScript ByteArray as the C/C++ heap and stack. The performance of alchemy is slow if you martial data from C/C++ code to ActionScript or back but faster (supposedly up to 10 times faster) than ActionScript code you write yourself for data intensive actions where everything operates in the C/C++ memory space - speed improvements over AS code are also due to LLVM doing code optimization which is missing from the normal AS compiler.

After downloading and setting up Alchemy, I started trying to port over a few C/C++ libraries. The following libraries have given me some trouble mainly with needing to adjust makefiles or the ./configure script: Angband, Nethack, guile, Python, Ruby, ARToolkitPlus, SDL, and Squeak. I haven't given up on them but I wasn't in the mood to do battle with Makefiles; I wanted to learn Alchemy.

My success came with compiling the scripting language Lua 5.1.4 and embedding it into a Flex application. The following proof of concept can run a Lua script which returns one or more values and are shown in the Lua Stack Panel. Lua can make the following calls into Flex:

• getTextAreaProperty(property_name) - Returns the given property of the text area in the lower left hand corner.
  
• setTextAreaProperty(property_name, value) - Sets the given property on the text area in the lower left hand corner (must accept string values).
  
• callTextAreaFunction(function_name[, param1, ..., paramN]) - Calls a function on the text area in the lower left hand corner (must accept string values).
  
• average(value1, ..., valueN) - Returns the average and sum of the given values.
  

Note that the demo above requires Flash Player 10 (required by Alchemy and my use of the local file system to allow opening/saving files). It is also hosted here.

Should I continue working on this library, I'd want to allow Lua to create and call functions on any arbitrary ActionScript class. Alchemy is still in beta and does have its own problems - not everything builds easily and while pure Alchemy code can be faster than ActionScript, marshaling from ActionScript to C/C++ code and back can slow things down - for example life.lua takes 4 seconds with the standard compile of Lua and 13 minutes! with the Alchemy build. Still it works quite well for my purposes of embedding a runtime scripting language into my Flex applications.

For more information check out the following blog posts:

• http://www.automatastudios.com/2008/11/21/understanding-adobe-alchemy
• http://docs.google.com/View?docid=dg7w6sqr_8fbhvz6d6
• http://techblog.floorplanner.com/2008/11/23/alchemy-first-looks
• http://www.theregister.co.uk/2008/12/02/adobe_alchemy/

Edit: Created a google code project to share efforts in using Alchemy to embed Lua in ActionScript. Uploaded the proof of concept:

• http://code.google.com/p/lua-alchemy
• http://code.google.com/p/lua-alchemy/downloads/list