Scripting Flash apps: scanning the input file

Here we go. I know that probably I should have started this new topic talking about the grammar of the language we are going to implement, but as long as I see grammar strictly related to parsing, I’ve preferred to talk about scanning first.

We will go back to the grammar the next time, when talking about how to parse an input file.

I wrote about scanning (or lexing if you prefer) a while ago, when blogging about expression evalution in ActionScript. Scanning an input file is quite always the same (although some languages might require unusual features), and what I wrote about expressions works also for a general language.

The goal of the scanning process is to group some characters together, skipping the ones that have no meaning for the language like spaces. Each group of characters is usually called token. So a Scanner converts a textual input into a stream of tokens, each one rappresenting a possible valid word for our language. While scanning you don’t take care about the meaning of what you are grouping or about the fact that a sequence of tokens is meaningful. This is a task for the Parser as we will see.

When talking about expressions, I showed a manual implementation for a Lexer. Now I want to take a different approach and show you a possible implementation for a simple dynamic scanner. This scanner will be based on regular expressions: each regular expression will rappresent a given token, and we will be able to assign callbacks to the scanner that will be executed each time a given token is extracted from the input.
Writing a general and reusable scanner is usually a good practice. A common approach is to use some scanner generators, that are usually regular expression based too but are able to generate the code for a scanner at compile time. Our approach is different (and generates slower scanners) because regular expressions are evaluated at runtime; but it is fine for a test project.

You can download the source code for the regular expression based lexer (RegexLexer) here, as long as a simple usage example. Let’s see this example together so we can briefly discuss it (

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Scripting Flash apps: design the language

Finally I had a bit of time to go back to the discussion I started about a month ago: scripting your flash applications. I spent a bit of time thinking which is the best approach to start discussing this kind of topic; it is not as easy as it seems because the risk is to fall into a too complex discussion that a lot of people won’t benefit from.

So I decided to start with a simple example that is somehow related to what I’m doing in these months; more examples will come and I’ll analyze different aspects of scripting trying always to keep the discussion as simple as possible even if this may bring me to do avoid some hard to discuss approaches or optimizations.

Our first scripting language will be an extremely simple language that will be used to manipulate images (like Pixel Bender does). Obviously the goal is not to write something that can be compared with Pixel Bender, but at least we would like to provide an implementation that will lead to scripts as fast as native code (at least we hope so :P).

The first step is to design the language, and to do that we need to do the step zero that is to define the goals we want to achive with the first implementation:

  • The language must be extremely simple to design and implement (it is a didactic stuff indeed!);
  • The language must be as simple as possible to learn and use: we won’t be an alternative to Pixel Bender (because we can’t … yet ;P)
  • The language must be quick to compile and execute.
  • A script must accept some parmeters to control its behaviour.
  • We must support comments!

Now that we decided which are the goals, let’s start definign some limitation or features we must include to quickly reach a solution:

  • The first implementation of the language will support a sigle data type: Numbers. We will move further adding more data types later – I don’t want to focus on type checking yet.
  • We will add support for basic expression operators, basic control flow. No support for functions yet.
  • The language will provide some useful operators or builtin functions to manage common operations like packing/unpacking color components and peform some mathematical operations.
  • Arguments to a script will be only Numbers at first.
  • A script will be defined as a simple sequence of arguments followed by a function definition. This function will be applied sequentially to every pixel of one or more source images.
  • We will provide to implementations for the language: a simple (and slow) interpreter at first, then we will generate native SWF code to speedup the performances.

Even if briefly, it is quite important to define the goals of our language and then the features, because a lack of design (even if extremely simple and poor as the current one :P) may lead to unexpected issues during implementation.

Now that we defined those basic pointers, let’s see how the language will look like:
// Simple crossfade filter
// The crossfade intensity
argument intensity;
* A quick explanation of the used builtins:
* - in( id, x, y ): gets the ARGB color at x and y of the image identified by id (there can be more than one image as input);
* - out( id, x, y, color ): sets the ARGB color at x and y for the output image identified by id;
* - argb( a, r, b, b ): build an ARGB color from its components (clamping and rounding the values as required);
evaluatePixel( x, y )
// this kind of assignment is similar to the python unpack assignment
// but extracts the 4 components (ARGB) from a color.
a1, r1, g1, b1 = in( 0, x, y );
a2, r2, g2, b2 = in( 1, x, y );
out( 0, x, y, argb(
( 1 - intensity ) * a1 + intensity * a2,
( 1 - intensity ) * r1 + intensity * r2,
( 1 - intensity ) * g1 + intensity * g2,
( 1 - intensity ) * b1 + intensity * b2 ));

As a side not, I must say that the language may change during implementation because of unexpected limitations we will find during development.

Next week we will move forward start implementing the language. Stay tuned!

AMFPHP recent updates

Well, after a long time without any news it seems now we’re close to different updates about AMFPHP.

As you probably know Wade Arnold took the place of Patrick some time ago as project leader but no real big changes were committed since then.
But after the partnership between Zend and Adobe things started to change and amfphp started to move forward to the Zend Framework… and in fact many developers were afraid about the real future of amfphp.
Bt, as Wade said, the amfphp core will remain separated from the framework implementation ( a framework which I will never use however ), in order to have a shared core and 2 different branches for the implementation. ( a new release was promised before Adobe MAX )
However I’m afraid too about what could happen expecially when 2 major software houses “promote” an opensource project.
Probably I’m too sceptical, but I believe that in the future more and more things will be only supported in the zend_amf and not in the standalone amfphp project.

Scripting your Flash applications …

As someone of you may know, I really like studying programming languages and sometimes implement for fun (or for work) simple scripting languages that help me out during development.

The fight between scripting and programming languages will probably never end. Well, it is not really a fight but more an infinite race where the first position is exchanged continuosly between the two participants.
We need flexibility first, and so we add to our complex applications a way to support scripting to be able to easilly perform changes without the need to run the long time taking compilation process a low level language might take; then, the more the scripts became complex, the more we need an increase in performances, and so we rapidly move to compiled plugin egines; plugins offer a bit of flexibility and usually a good speed. Then we grant other users the permission to write plugins and so we need a sandbox to run the plugins in and to be sure every single line of code that is executed doesn’t harm our application. And so we revert back to scripting … and so on.
The race will never end but the technologies will continue to increase in speed and sometimes in complexity.

All the introduction is to say that its not the point to choose if scripting is useful or not for Flash applications, but to say that someone might need it for reasons we cannot think about right now, and someone else might not need it because they are fine with recompiling everything from scratch at each single small change.

I don’t think there are some many Flash applications that support scripting. I built myself a few of them for my company but they are for a particular purpose and probably the same motivations that made me decide to implement a scripting language are hard to find for other kind of applications.

As far as I know, the most of the applications that need to be flexible use a plugin system (more or less complicated – as Aviary for instance and Hobnox) and are fine with it because – we must say that – ActionScript is itself a scripting language and a SWF file is nothing more than a bunch of instructions (more or less) generated by compiled ActionScript.

But sometimes security comes into account, and it is hard (even if possible) to limit the funcionalities used by a plugin if this plugin is created by a 3rd party developer.

And so it comes into account scripting. With scripting we have full control over what a developer can do an how he can do that. We can limit it, provide builtin functionalities … But everything costs something, and building a fast/flexible/powerful/useful scripting languages is not that easy as it might seem.

This is why I decided to spend a bit of time in explaining the basics to implement a scripting language in actionscript to be able to script our applications. I’ll walk through all the passes – from lexing to bytecode generation and maybe a quick look into Virtual Machines – with the aim to provide someone (maybe in the far future) a bunch of documents to use as reference to build their own scripting language.

I’ll try to give an in depth look, but as far as the argument is quite complicated and full of facets, you may not find here the right solution for you. Nor the fastest or the most flexible. But it is better then nothing so if you are interested in that keep reading the blog 🙂

Win a 3D Flash Gallery!

This is a great opportunity for all the readers! Thanks for flashloaded we’re giving 3 free licenses of 3D Wall Pro ($199/each).

To win the prize is very simple, just leave a comment to this post with at least “I want the license” text besides any other comment and after 12 days we will select randomly 3 winners! ( remember to leave your email in the comment )

What is 3D Wall?

The 3D Wall is a papervision powered component to isplays images on an engaging interactive 3D wall. This PRO version can also display FLV videos and SWF’s and more..

Some of the key features of the 3D Wall are:

  • Flat or curved wall
  • Customizable animations
  • Glow and reflections
  • Double sided thumbnails
  • Complete customizable properties (rows, columns, preloader…)
  • Complete interaction (keyboard or mouse)
  • Use of external xml configuration file
  • A Flash component inspector
  • Images, flv and swfs
  • Customizable video controls
  • Youtube, flickr images
  • Watermarks

Here’s a couple of screenshots:

See more screenshots at the 3D Wall page

REMEMBER: Winners will be selected randomly from commenters 10 days later (31 October 2008) and will be contacted directly via email.

Contest is over!

Today (1st November 2008) the contest is over! After running this mysql query to find out 3 random commenters:
SELECT * FROM mt_comment WHERE comment_entry_id = 268 order by RAND() LIMIT 3
we got the three winners who are: (5170) moon, (5135) Pieter and (5176) tm!

Java 6 Update 10 breaks Flex compiler!

I just want to share this problem I found so maybe someone can save some time..

Today while surfing the net I received a notification of an update of my Java installation to the Update 10 in order to see correctly the contents of that site.. bla bla bla..

Sometime later I switched to Flex and at the first execution of my ant script for compiling a flex project I suddenly received this beautiful error:
[exec] Error: java/security/MessageDigest
[exec] java.lang.NoClassDefFoundError: java/security/MessageDigest
[exec] at Source)
[exec] at$100(Unknown Source)
[exec] at$ Source)
[exec] at Method)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at Source)
[exec] at flex.util.SerializedTemplateFactory.load(
[exec] at flex2.compiler.util.VelocityManager.getTemplate(
[exec] at flex2.compiler.util.VelocityManager.getTemplate(
[exec] at flex2.compiler.util.VelocityManager.getTemplate(
[exec] at flex2.compiler.as3.genext.GenerativeSecondPassEvaluator.generateSupportCode(
[exec] at flex2.compiler.as3.genext.GenerativeSecondPassEvaluator.modifySyntaxTree(
[exec] at flex2.compiler.as3.binding.BindableSecondPassEvaluator.evaluate(
[exec] at macromedia.asc.parser.ClassDefinitionNode.evaluate(
[exec] at
[exec] at macromedia.asc.parser.StatementListNode.evaluate(
[exec] at
[exec] at macromedia.asc.parser.ProgramNode.evaluate(
[exec] at flex2.compiler.as3.genext.GenerativeExtension.parse2(
[exec] at flex2.compiler.as3.Compiler.parse2(
[exec] at flex2.compiler.API.parse2(
[exec] at flex2.compiler.API.parse2(
[exec] at flex2.compiler.API.batch2(
[exec] at flex2.compiler.API.batch(
[exec] at flex2.compiler.API.compile(
[exec] at flex2.compiler.API.compile(
[exec] at
[exec] at

so I tried also to compile another project before go crazy, but I got this another java funny error, which was more or less unreadable as the previous one!

Fortunately I remembered the update I did of Java! And in fact after remove that update everything worked again!