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Slide 1: Inside Flash MX 2004 March 2004 Gary Grossman, Director of Engineering, Flash
Slide 2: The Essence of Flash What is the essence of Flash? That is, what are the key values that led to the product’s extraordinary success? Flash is freedom of design rich interactivity compact, ubiquitous player Flash is the only product that brings design and development together
Slide 3: What’s in a SWF file? SWF is tag-based file format What is a tag? Uniform data block for easy parsing  Perform basic operations in Flash Player  “Machine code” of Flash Player     What are typical tags? stagDefineShape  stagPlaceObject  stagShowFrame   SWF file format is documented at http://www.macromedia.com/software/flash/open/licensing/fileformat/  Best illustrated by a simple example...
Slide 4: Motion Tween SWF simple shape tweened to move from left, to right, to left again in loop
Slide 5: Deconstructing Motion Tween SWF         shapes and sprites are characters each character has a unique ID (#1, #2) shape #1 is defined sprite #2 (movie clip) is defined using the shape initial place tag creates instance of sprite each timeline frame is delimited by show frame subsequent place tags move the existing instance main timeline automatically loops when end of SWF tag stream is reached
Slide 6: Flash execution model      Flash Player starts at beginning of SWF and executes tags one after the other, like reading a tape Entire SWF resides in memory, but playback can start when only one frame is loaded, so SWF’s can stream Player tries to display graphics on Frame 1 even when not completely loaded; results in some quirks When a showFrame tag is hit, the frame is displayed to the user Rewinding on a long Timeline can be slow, because entire SWF must be re-parsed from beginning to the desired point
Slide 7: Motion Tween: A touch of ActionScript Added stop() action: animation will stop after one iteration How does it look in the SWF?
Slide 8: ActionScript in the SWF file      some tags contain action records action records contain stream of action bytecodes Flash compiles ActionScript source code into stream of action bytecodes action bytecodes can represent simple actions (stop), up to sophisticated scripts FLASM is a tool that can disassemble the bytecodes in a SWF http://flasm.sourceforge.net
Slide 9: ActionScript execution model   Frame actions, on/onClipEvent, callbacks and listeners are all queued up and executed before frame is displayed Flash Player is not multi-threaded    Typically runs in same thread as browser, via system timer callback Scripts must exit nicely, thus 15 seconds warning if they don’t One reason we don’t have “updateStage” like Director
Slide 10: Do frames ever get skipped? Frame rate is not guaranteed  Frames are dropped only when using streaming sound, to maintain sync   All ActionScript is executed, even on dropped frames
Slide 11: Interval timers Does setInterval guarantee millisecond accuracy?     No. There is a system timer used for all timeline execution. The same timer is used for all setIntervals. Accuracy is typically to 10X frame rate and no more In future, setInterval may be more accurate onEnterFrame may give smoother results
Slide 12: Unicode  Software and Web are becoming global commodities Growing number of companies deliver products in many languages  Example: Flash MX 2004 available in 11 languages   SWF file format has been Unicode (UTF-8) since Flash Player 6 Flash MX 2004 authoring tool is now fully Unicode   Create multilingual content without switching system languages
Slide 13: Font Chaining      Over 1.1 million Unicode characters Font chaining is means of avoiding gibberish characters If a needed glyph is not in the selected font, another font is found which has it Operating system determines which font is used for chained glyphs Eliminates need for language-specific device fonts  Can use _sans, _serif, _typewriter instead
Slide 14: System.useCodePage Means of working with data in non-Unicode encodings (EUC-KR) Must be set on Frame 1 and not changed later. Behavior is undefined if you alter it later! All client/server communication will be conducted in system code page: XML  XMLSocket  LoadVars  loadVariables      Internally, everything is still converted to Unicode.
Slide 15: Alias Text      A key advantage of Flash over HTML has always been ability to use any fonts you desire, and embed them in the SWF Flash text looks blurry at small point sizes due to lack of hint information Solution has been to use device fonts for small text Alias Text feature makes small text crisp & readable Backwards compatible: Flash Player 7 not required! Example: Lucida Sans Unicode, 10 point text, zoomed 400%
Slide 16: ActionScript optimizations: Register allocation      ActionScript interpreter is called “AVM”, ActionScript VM AVM is stack machine and also has registers 4 initial registers were added in Flash 5 but not used heavily by compiler until Flash MX 2004 Flash MX 2004 uses registers to get massive performance boost for ActionScript code Flash Player 6 r65 and Flash Player 7 support up to 256 registers to further boost performance
Slide 17: Flash Player 6 register allocation Only 4 registers in AVM for Flash Player 6 r:0, r:1, r:2, r:3  r:0 reserved for compiler use  So, 3 registers available for local variables     Compiler determines 3 most popular variables and allocates to registers If you open a Flash MX FLA file in FMX 2004 and export... It will run faster!  Even if “Optimize for r65” is not checked 
Slide 18: Optimizing for Flash Player 6 r65   New checkbox in Publish Settings... What’s with it? Flash Player r65      Player release code named “Firefox” Added “defineFunction2” opcode, making large performance boost possible w/ 256 registers Need Flash MX 2004 to export SWF’s that leverage Flash Player 6 r65 Higher penetration than Flash Player 7 (for now) Use new Flash Player Detection feature to check for minor version r65
Slide 19: Performance gains in Flash Player 7   New performance features like register allocation Flash Player 7 has been fine-tuned for performance throughout  Performance work done by Flash Player team “raises all boats” ... even existing content that hasn’t been reexported now runs faster!  For supercharged performance, target your Flash movie to Flash Player 7!
Slide 20: Local variables  Use local variables (var)     Good programming practice Compiler can optimize local variables to registers Significant performance benefits In following example, every variable and parameter can be optimized into a register function factorial(x:Number):Number { var sum:Number = 1; for (var i:Number=2; i<=x; i++) { sum *= i; } return sum; }
Slide 21: Variable names It used to improve performance to use shorter variable names  Still true for timeline variables and object members  Not true for local variables allocated to registers     Best practice: Use variable names that are reasonable but not overly verbose Name of variable doesn’t even go in SWF Also, harder to decompile your SWF
Slide 22: The Dot or Slash Notation Debate Dot notation (Flash 5 and later): results.obj.value Slash notation (Flash 4): results/obj:value Some Flashcoders discovered that slash notation is sometimes faster than dot notation Not necessarily true now, because slash notation cannot take advantage of register allocation Slash notation had to be taken out of AS2 to support strong typing     
Slide 23: Common sub-expression elimination The following code contains common sub-expressions: for (var i=0; i<srcItems.length; i++) { destItems[i].name = srcItems[i].name; destItems[i].value = srcItems[i].value; destItems[i].id = srcItems[i].id; destItems[i].data = srcItems[i].data; } The code runs faster if we factor out the CSE’s: for (var i=0; i<srcItems.length; i++) { var destItem = destItems[i]; var srcItem = srcItems[i]; destItem.name = srcItem.name; destItem.value = srcItem.value; destItem.id = srcItem.id; destItem.data = srcItem.data; } Many compilers can factor out CSE’s automatically. ActionScript can’t do this yet, so factoring CSE’s yourself will provide performance benefits. Expect to see many compiler optimizations in the future.
Slide 24: ActionScript 2.0  Real OOP much better for managing complexity Cleaner, easier to read code  Greater maintainability      Demo: Puzzle, TipCalculator examples AS2 compiles down to AS1, so it is backwards compatible to Flash Player 6 In future, compiler will optimize for language model One can go crazy and “overengineer” with too many classes. One must strike the right balance.
Slide 25: Benefits of Typed Variables  Consider the following AS1 code: var myXML = new XML(); myXML.loadd("menu.xml");   The compiler will not detect any error. In AS2, you can specify variable type: var myXML:XML = new XML(); myXML.loadd("menu.xml");  The compiler will detect that "loadd" is not a method of XML, saving you debugging time.
Slide 26: Pitfalls of Typed Variables  This code uses a common AS1 pattern: class Menu { public function initXML() { var myXML:XML = new XML(); myXML.owner = this; myXML.onLoad = function () { this.owner.callback(); } myXML.load("menu.xml"); } public function callback() { ... } }  The compiler will give error on "owner“ because owner is not a member of XML. How to solve? 
Slide 27: Pitfalls of Typed Variables: Solution  One solution is to leverage variable scoping rules class Menu { public function initXML() { var myXML:XML = new XML(); var owner = this; myXML.onLoad = function () { owner.callback(); } myXML.load("menu.xml"); } public function callback() { ... } }  Local variable "owner" is visible to function defined within a function
Slide 28: V2 components    Built in AS2 for use in AS2 Macromedia HALO look and feel Advanced features for Rich Internet Application development        For small use cases, updated V1 components available as extension on Flash support center: http:// www.macromedia.com/cfusion/exchange/index.cfm?view =sn111&extID=1009423 Focus Manager Depth Manager Popup Manager CSS styles Accessibility Integrated with Data Binding
Slide 29: V2 Components: Event Model    Listener/broadcaster pattern More flexible, scalable, and object-oriented than V1 callback function approach Centralize event handling code in AS2 classes
Slide 30: Pitfalls of V2 Event Model  This code has two common errors class Menu extends mx.screens.Form { var myButton:mx.controls.Button; function Menu() { myButton.addEventListener(“click”, onButtonClicked); } public function onButtonClicked() { ... } } Constructor is too early to add event listeners... wait until onLoad  Due to behavior of ActionScript function references, onButtonClicked will be executed in myButton’s context, which is not desired behavior. 
Slide 31: Pitfalls of V2 Event Model: Solution   Many different strategies exist for event handling One approach is EventProxy, posted on Mike Chambers’s blog http://www.markme.com/mesh/archives/004286.cfm class Menu extends mx.screens.Form { var myButton:mx.controls.Button; public function onLoad() { myButton.addEventListener(“click”, new EventProxy(this, onButtonClicked)); } public function onButtonClicked() { ... } }
Slide 32: Integrating Flash into production environment   The new JSAPI in Flash MX 2004 offers lots of possibilities for automating Flash Example: Command-line compilation with FlashCommand by Mike Chambers http://www.markme.com/mesh/archives/003656.cfm  FlashCommand can be used to create an automated build system for a team developing with Flash
Slide 33: Code Security    Many people want to know: How can I prevent people from decompiling my SWF? As the SWF specification is open, it is not possible to prevent decompilers like ASV. Suggestions: Obfuscation by register allocation will help a little.  All client/server communication should require proper authentication on the server side  Push sensitive logic that could be harmfully spoofed up to the server side; Flash should be “presentation tier” only.   Macromedia is aware of this issue and is looking for solutions.
Slide 34: Dynamic Generation of SWF  Demo
Slide 35: Questions?