ActionScript: Язык программирования для Flash и AIR

Object oriented programming language created for the Flash multimedia platform

ActionScript is an object oriented programming language originally developed by Macromedia Inc. (later acquired by Adobe). It is influenced by HyperTalk, the scripting language for HyperCard. It is now an implementation of ECMAScript (meaning it is a superset of the syntax and semantics of the language more widely known as JavaScript), though it originally arose as a sibling, both being influenced by HyperTalk. ActionScript code is usually converted to byte code format by a compiler. ActionScript is used primarily for the development of websites and software targeting the Adobe Flash platform, originally finding use on web pages in the form of embedded SWF files. ActionScript 3 is also used with the Adobe AIR system for the development of desktop and mobile applications. The language itself is open source in that its specification is offered free of charge and both an open source compiler (as part of Apache Flex) and open source virtual machine (Tamarin) are available. ActionScript was also used with Scaleform GFx for the development of three dimensional video game user interfaces and heads up displays.

ActionScript was initially designed for controlling simple two dimensional vector animations made in Adobe Flash (formerly Macromedia Flash). Initially focused on animation, early versions of Flash content offered few interactivity features, thus had very limited scripting ability. Later versions added functionality allowing for the creation of web based games and rich web applications with streaming media (such as video and audio). Today, ActionScript is suitable for desktop and mobile development through Adobe AIR; it is used in some database applications and in basic robotics as in Make Controller Kit. Flash MX 2004 introduced ActionScript 2.0, a scripting language more suited to the development of Flash applications. Saving time is often possible by scripting something rather than animating it, which usually also enables a higher level of flexibility when editing. Since the arrival of the Flash Player 9 alpha (in 2006), a newer version of ActionScript has been released, ActionScript 3.0. This version of the language is intended to be compiled and run on a version of the Tamarin virtual machine, formerly ActionScript Virtual Machine 2, that was also fully rewritten (dubbed AVM2). Because of this, code written in ActionScript 3.0 is generally targeted for Flash Player 9 and higher, and will not work in prior versions. At the same time, ActionScript 3.0 executes up to 10 times faster than legacy ActionScript code due to the just in time compiler enhancements. Flash libraries can be used with the XML abilities of the browser to render rich content in the browser. This technology is known as Asynchronous Flash and XML, much like AJAX. Adobe offers its Flex product line to meet the demand for rich web applications built on the Flash runtime, with behaviors and programming done in ActionScript. ActionScript 3.0 forms the foundation of the Flex 2 application programming interface (API).

ActionScript started as an object oriented programming language for Macromedia's Flash authoring tool, later developed by Adobe Systems as Adobe Flash. The first three versions of the Flash authoring tool provided limited interactivity features. Early Flash developers could attach a simple command, called an "action", to a button or a frame. The set of actions was basic navigation controls, with commands such as "play", "stop", "getURL", and "gotoAndPlay". With the release of Flash 4 in 1999, this simple set of actions became a small scripting language. New capabilities introduced for Flash 4 included variables, expressions, operators, if statements, and loops. Although referred to internally as "ActionScript", the Flash 4 user manual and marketing documents continued to use the term "actions" to describe this set of commands.

Flash Player 2: The first version with scripting support, its actions included gotoAndPlay, gotoAndStop, nextFrame and nextScene for timeline control. Flash Player 3: Expanded basic scripting support, it has the ability to load external SWFs (loadMovie). Flash Player 4: The first player with a full scripting implementation (called Actions), the scripting was a Flash based syntax and contained support for loops, conditionals, variables, and other basic language constructs. Flash Player 5: Included in the first version of ActionScript, it used prototype based programming based on ECMAScript, and allowed full procedural programming and object oriented programming. Design based development. Flash Player 6 added an event handling model, accessibility controls, and support for switch. The first version with support for the Action Message Format (AMF) and Real Time Messaging Protocol (RTMP) allowed for on demand audio/video streaming. Flash Player 7: Additions to it include Cascading Style Sheets (CSS) styling for text and support for ActionScript 2.0, a programming language based on the ECMAScript 4 Netscape Proposal. with class based inheritance. However, ActionScript 2.0 can cross compile to ActionScript 1.0 bytecode, so that it can run in Flash Player 6. Flash Player 8 further extended ActionScript 1/ActionScript 2 by adding new class libraries with APIs for controlling bitmap data at run time, file uploads, and live filters for blur and dropshadow. Flash Player 9 (initially called 8.5) added ActionScript 3.0 with the advent of a new virtual machine, called ActionScript Virtual Machine 2 (AVM2), which coexists with the previous AVM1 needed to support legacy content. Performance increases were a major objective for this release of the player, including a new just in time (JIT) compiler. Support for binary sockets, ECMAScript for XML (E4X) XML parsing, full screen mode, and regular expressions were added. This is the first release of the player to be titled Adobe Flash Player. Flash Player 10 (initially called Astro): Added basic 3D manipulation, such as rotating on the X, Y, and Z axis, a 3D drawing API, and texture mapping. Ability to create custom filters using Adobe Pixel Bender. Several visual processing tasks are now offloaded to the GPU which gives a noticeable decrease to rendering time for each frame, resulting in higher frame rates, especially with H.264 video. There is a new sound API which allows for custom creation of audio in flash, something that has never been possible before. Furthermore, Flash Player 10 supports Peer to Peer (P2P) communication with Real Time Media Flow Protocol (RTMFP). Flash Player 11: The major addition in this version are the Stage3D based advanced (graphic card accelerated) 3D capabilities for Windows Desktop, Mac Desktop, iOS, Android, and other major platforms. Significant compatibility improvements have been added for the iOS platform, and other non desktop platforms. Other features include H.264 encoding for cameras, Native JSON support, Cubic Bézier Curves, a secure random number generator, LZMA compression for swf files, workers to offload some code execution to other processor threads, graphics card accelerated camera feed rendering, memory intrinsics and performance analysis, and the ActionScript Compiler 2.0, as well as some other minor additions. Flash Player 11.2: released in March 2012, focused on adding features that are key for the gaming and video markets. Some of the features in the release include the following: Mouse lock support. Right and middle mouse click support. Context menu disabling. Hardware accelerated graphics/Stage 3D support for Apple iOS and Android via Adobe AIR. Support for more hardware accelerated video cards (from January 2008) in order to expand availability of hardware accelerated content. New Throttle event API (dispatches event when Flash Player throttles, pauses, or resumes content). Multithreaded video decoding pipeline on PCs, which improves overall performance of video on all desktop platforms. Notification of use of premium features in the debug players; content runs unrestricted in the release players. Flash Player 11.3: released in June 2012, focused on enabling features and functionality key for the gaming market, as well as addressing popular feature requests from developers. Some of the features in this release include the following: Keyboard input support in full screen mode. Improved audio support for working with low latency audio. Ability to progressively stream textures for Stage 3D content. Protected mode for Flash Player in Firefox. Frame label events. Support for compressing BitmapData to JPEG and PNG formats. Support for Mac OS X App Store application sandboxing requirements. Text streaming support for Stage 3D. Expanded information about GPU driver details. Bitmap draw with quality API (new). Release outside mouse event API. Flash Player silent update support for Mac OS. Stylus support for Android 4.0 devices (Adobe AIR). USB debugging for iOS (Adobe AIR). iOS simulator support (Adobe AIR). Flash Player 11.4: Released in August 2012, it focused on enabling features and functionality that are key for the gaming market, as well as addressing popular feature requests from developers. Some of the features in this release include ActionScript workers (enables concurrent ActionScript execution on separate threads), support for advanced profiling, LZMA compression support for ByteArray, support for hardware accelerated video cards for Stage 3D expanded to 2006, improved ActionScript performance when targeting Apple iOS, performance index API to inform about performance capabilities of current environment, support for compressed textures with alpha support, support for StageVideo. attachCamera API, and support for push notifications for iOS (Adobe AIR). Flash Player 11.5: Released in November 2012, it focused on performance improvement and stability. Some of the features in this release include shared ByteArray support for ActionScript workers, debug stack trace in release builds of Flash Player, and various bug fixes. Flash Player 11.6: Released in March 2013, it focuses on performance improvements, security enhancements, and stability. Some of the features in this release include ability to query graphics vector data at runtime, full screen permission dialog user interface improvements, ability to load SWFs at runtime when deploying as an AIR application in AOT mode on iOS, finer grained control over supported display resolution on iOS devices when deploying as an AIR application, HiDPI support for Flash Professional, and ActionScript 3 access to fast memory operations/intrinsics. Flash Player 11.7: Released in June 2013, code named "Geary", this release focuses on premium video, gaming, security, and stability. Some of the features planned for this release Android captive runtime debugging, support for the OUYA controller, remote hosting of SWF files on iOS, and preventing backup of shared objects on iOS for better iCloud support. Flash Player 11.8: Adobe was planning to release this version in the early part of the second half of 2013, code named "Harrison" This release focused on premium video, gaming, security, and stability. Some of the features in this release would have included recursive stop API on MovieClips and GamePad support on desktop browsers and Android

With the release of Flash 5 in September 2000, the "actions" from Flash 4 were enhanced once more and named "ActionScript" for the first time. This was the first version of ActionScript with influences from JavaScript and the ECMA 262 (Third Edition) standard, supporting the said standard's object model and many of its core data types. Local variables may be declared with the statement, and user defined functions with parameter passing and return values can also be created. Notably, ActionScript could now also be typed with a text editor rather than being assembled by choosing actions from drop down lists and dialog box controls. With the next release of its authoring tool, Flash MX, and its corresponding player, Flash Player 6, the language remained essentially unchanged; there were only minor changes, such as the addition of the statement and the "strict equality" operator, which brought it closer to being ECMA 262 compliant. Two important features of ActionScript that distinguish it from later versions are its loose type system and its reliance on prototype based inheritance. Loose typing refers to the ability of a variable to hold any type of data. This allows for rapid script development and is particularly well suited for small scale scripting projects. Prototype based inheritance is the ActionScript 1.0 mechanism for code reuse and object oriented programming. Instead of a keyword that defines common characteristics of a class, ActionScript 1.0 uses a special object that serves as a "prototype" for a class of objects. All common characteristics of a class are defined in the class's prototype object and every instance of that class contains a link to that prototype object.

The next major revision of the language, ActionScript 2.0, was introduced in September 2003 with the release of Flash MX 2004 and its corresponding player, Flash Player 7. In response to user demand for a language better equipped for larger and more complex applications, ActionScript 2.0 featured compile time type checking and class based syntax, such as the keywords and (While this allowed for a more structured object oriented programming approach, the code would still be compiled to ActionScript 1.0 bytecode, allowing it to be used on the preceding Flash Player 6 as well. In other words, the class based inheritance syntax was a layer on top of the existing prototype based system.) With ActionScript 2.0, developers could constrain variables to a specific type by adding a type annotation so that type mismatch errors could be found at compile time. ActionScript 2.0 also introduced class based inheritance syntax so that developers could create classes and interfaces, much as they would in class based languages such as Java and C++. This version conformed partially to the ECMAScript Fourth Edition draft specification.

Flash Lite 1.0: Flash Lite is the Flash technology specifically developed for mobile phones and consumer electronics devices. Supports Flash 4 ActionScript. Flash Lite 1.1: Flash 4 ActionScript support and additional device APIs added. Flash Lite 2.0 and 2.1: Added support for Flash 7 ActionScript 2.0 and some additional fscommand2 API. Flash Lite 3: Added support for Flash 8 ActionScript 2.0 and also FLV video playback. Flash Lite 4: Added support for Flash 10 ActionScript 3.0 as a browser plugin and also hardware graphics acceleration.

Adobe AIR supports ActionScript, in addition to some extended contents, such as the Stage3D engine Adobe has developed. The number of APIs (Application programming interfaces) available to ActionScript 3.0 has also risen dramatically.

ActionScript code is free form and thus may be created with whichever amount or style of whitespace that the author desires. The basic syntax is derived from ECMAScript.

Like most bytecode file formats, Flash SWF files can be decompiled into their source code and assets (similarly to how Microsoft NET files can be decompiled). Some decompilers are capable of nearly full reconstruction of the original source file, down to the actual code that was used during creation (although results vary on a case by case basis). In opposition to the decompilers, ActionScript obfuscators have been introduced, which transform code into a form that breaks decompiler output while preserving the functionality and structure of the program. Higher quality obfuscators implement lexical transformations such as identifier renaming, control flow transformation, and data abstraction transformation which collectively make it harder for decompilers to generate output likely to be useful to a human. Less robust obfuscators insert traps for decompilers. Such obfuscators either cause the decompiler software to crash unexpectedly or to generate unintelligible source code.