Tag Archives: AIR

Fast AS3 Signals with SignalsLite

I was playing around and ended up writing a lite Signals class (ok, 3 classes). The set works like a basic AS3 Signal, minus most of the extra functionality of AS3 Signals (run-time dispatching argument type checking as one example). The goal was to create a very fast Signal dispatcher, with very little overhead, and to dispatch with absolutely no heap allocation (check, check and check) – targeted mostly for mobile (AIR). Regular AS3 Signals does well, but it seemed to have a lot of extra stuff that I don’t need – and this was a fun kind of exercise anyway.

Some quick numbers from the performance-test with 1,000,000 iterations on a Core 2 Duo 2.6GHz (in milliseconds):

Func call time: 15
Runnable call time: 5
Event (1 listener) time: 863
Signal (1 listener) time: 260
SignalLite (1 listener) time: 232
RunnableSignal (1 listener) time: 56

Func call (10 listeners) time: 190
Runnable call (10 listeners) time: 399
Event (10 listeners) time: 2757
Signal (10 listeners) time: 741
SignalLite (10 listeners) time: 725
RunnableSignal (10 listeners) time: 221

The bold line is a vanilla SignalLite, and the line above Robert Penner’s AS3 Signals. They are pretty close, but SignalsLite takes a modest edge. But let’s look at the same test on iOS (iPhone 4S) with 100,000 iterations:

Func call time: 171
Runnable call time: 26
Event (1 listener) time: 3723
Signal (1 listener) time: 789
SignalLite (1 listener) time: 481
RunnableSignal (1 listener) time: 117

Func call (10 listeners) time: 2004
Runnable call (10 listeners) time: 1892
Event (10 listeners) time: 9217
Signal (10 listeners) time: 4030
SignalLite (10 listeners) time: 2074
RunnableSignal (10 listeners) time: 498

On iPhone you can see that SignalLite is almost twice as fast as AS3 Signals – a more substantial difference than on desktop. I’m not sure why that is, maybe the AOT compiler can optimize something about SignalLite better – IDK, but it sure is fast!

Then there’s that last line in each group – RunnableSignal. Now your talking speed. That one also solves a particular problem with function callback systems that they all seem to have – there is no compile time function signature checking. You have to wait until the thing runs, and then find out you are taking the wrong number of arguments, or the wrong type, etc. But, solving one problem (compile time type checking), solves the other (speed), and that brings us to SignalTyped which RunnableSignal in the test above extends (I’ll probably rename at some point).

SignalTyped is beginnings of a fast executing type safe implementation of AS3 Signals. The idea is, you extend 2 classes – SignalTyped and SlotLite. SignalTyped is effectively an abstract class – you must extend it and implement the dispatch method, and the constructor (at least for now, I’m looking for better ways to handle this). It takes a bit of boilerplate to implement this in a class that would expose signals. This example is based on the performance test from Jackson Dunstan’s CallbackTest which I borrowed (I hope that’s ok!):

// Interface for your class that might have listeners for the SignalTyped.
// Make one of these per listener type.
interface IRunnable {
	function run(): void;
} 

// Custom Slot has a specific property for the Runnable class.
class RunnableSlot extends SlotLite
{
	public function RunnableSlot( runnable:IRunnable ) {
		this.runnable = runnable;
	}
	public var runnable:IRunnable = new EmptyRunnable;
}

// An empty IRunnable class for first node.
class EmptyRunnable implements IRunnable {
	public function run():void {};
}

// You need one of these per dispatch type.
class RunnableSignal extends SignalTyped
{
	// last and first must be set to the typed Slot.
	public function RunnableSignal() {
		last = first = new RunnableSlot;
	} 

	// implement the dispatch method to call the runnable prop directly
	// It's easy to have it take and dispatch any type you want - with compile time type checking!
	public function dispatchRunnable():void
	{
		var node:RunnableSlot = first as RunnableSlot;
		while ( node = (node.next as RunnableSlot) ) {
			node.runnable.run(); // FAST!
		}
	}
}

That’s all necessary for the implementation requirements – a lot of boilerplate, I admit. Then you expose that in a class that might use it all:

class MyDisplayObject
{
	// could probably make this a getter..
	public var signaled:RunnableSignal = new RunnableSignal;
}

Now for the consumer to use this, it’s just a bit more boilerplate than a normal signal:

class MyConsumerOfSignalLite implements IRunnable // boilerplate point 1
{
	public function MyConsumerOfSignalLite()
	{
		var dspObj:MyDisplayObject = new MyDisplayObject();
		// add the signal (boilerplate point 2 - normal)
		dspObj.signaled.addSlot( this );
	} 
    
	// boilerplate 3 - normal, but more strict - naming is specific - FAST!
	public function run(): void {
		// do whatever when signals
	}
}
// boilerplates 2 and 3 are normal for any signal, except the strictness of #3

What’s cool about this is you get compile time type checking for your method signature, and the performance improvement that comes with skipping those checks at runtime.

I’m also thinking about a slightly different signal API that would be more like the Robot Legs’ contract system – think signals by contract – I’m working on it. Since we would be implementing a defined interface per signal type, we could boil the add methods and signal nodes down to one method to add all the listeners of a single object – one add method per dispatching class, instead of one per signal on the dispatching class. This could lead to a reduction in boilerplate. We’d filter by interface type instead of using multiple signal.add nodes and methods. So – improved runtime performance, reduction in (usage) boilerplate (if not implementation) and compile time type checking. I love it!

Note – I tested none of the example in this post, and the code in github is all very early stage stuff. The performance-test class works though – give it a try!

Oh, here’s the github repo:
https://github.com/CaptainN/SignalsLite

Flash and AIR, Nothing But Opportunity

Preface: I wrote this one of the last few times the Flash is dead thing made the media rounds, because it seems as though many participants in the discussion are simply missing the bigger picture, that the market for rich interactive work is splitting between app store apps (native applications), and desktop browser-based apps (websites), and that those divisions are deep enough to require different development mindsets. The post is overly long – I don’t have an editor – but I figured I’d post it in its current draft state, since this keeps coming up, and so I don’t have to noodle with it anymore. :-P So here it is. (Instant update: Lee Brimelow has said similar things in fewer words on his blog Update 2: Thibault Imbert chimes in. Update 3: Mike Chambers rolls the narrative. Now back to making awesome!).

In the technology business, if you aren’t looking ahead, you are being left behind. There is fundamental shift occurring in the content technology space, where Flash and HTML live their happy lives. This shift has mostly been explained using old terms, like “apps” and “HTML5 vs. Flash” – these explanations miss the point. They all describe how things were yesterday and are today, but miss how they will be tomorrow. The browser has been and is today, the primary means of application and content delivery. A new set of opportunities for delivering content are changing all that. The Split puts the traditional desktop browser market on one side, and app stores on new platforms, with new hardware, and new interface paradigms on the other.

App stores should be more broadly called content stores, because the line between apps and other kinds of content is pretty thin. Market specific content stores have been around for a while already on the desktop. Game shops like Steam and Direct2Drive already make up the lion’s share of the PC games market, and iTunes was already a form of an app store, before apps where apps.

The companies behind every platform are adopting apps stores, including all major operating systems on traditional PCs, including OSX, and soon Windows. Open source trail blazers like Ubuntu have actually had something like app stores for a long while now. Additionally, more and more types of content are being pulled into them, from apps, to music and movies, to Magazines and local newspapers. The models for monetization are so much clearer, and the tools to take advantage of the various models are already built, and for the consumer, very convenient. App stores are the new reality.

To really understand why this is happening, and what it means for those of us who make a living in the weeds, we need to understand where we are, and how we got here.

The PC Era

In the early days of personal computing, “applications” (or “programs”) were the hot action. You needed something to do with your new beige personal computer (PC), so you bought (or borrowed) software or other types of content on diskettes, and later CD-ROM (oh the magic) and installed that software to run on your PC or Mac. It was an offline process, but it was the only realistic way to go. Even if you had access to the internet, you weren’t going to download megabytes of data over your cutting edge 14.4KB fax/modem connection. Traditional forms of acquisition ruled in those days. You had to take yourself to the store, and buy a box or a publication or whatever else, to obtain content – probably paying with cash.

When the internet hit mainstream in the 90s, and data speeds increased, the transition from “applications” delivered through boxed diskettes, to continuously updated “websites” began. The internet had some advantages over boxed content. The biggest was that accessing a web site through the internet was exceedingly convenient for consumers. Far more convenient than traveling to the store and buying a box with a CD of clip art on it. For content producers there is also a sense of limitless shelf space compared with traditional retail outlets, so they were quick to try to carve out advantage there. Search engines and content indexing services like Google and Yahoo! made a killing on both ends by providing a way for content producers to get their content in front of users.

Broadband completed the transition. At the dawn of the new millennium and “the internet,” became the primary means of content and application delivery (aside from a few important smaller markets like games and productivity apps). The browser was the primary means of application and content delivery, and for good reason. The content is easy to access from multiple platforms, and is super convenient. All you need is an internet connection, and a browser.

A Flash of brilliance

At around the same time, Microsoft mostly won “the browser wars” with Internet Explorer 6, and basically stopped forward movement in their browser, and for many years, the internet – the commerce in the browser era’s “website” based economy was able to mature. The stagnant development of the dominant browser platform created a challenging environment, one in which it’s easy to see why Flash was able to thrive.

Flash brought many improvements over the browser, through constant performance and scriptability advancements, as well as significant additional features the browsers in the aggregate simply couldn’t match – video being an important notable feature. Additionally, Flash provided consistency across browsers and operating systems, and comparably great performance, when measured against HTML and JavaScript. A browser-based app simply couldn’t (still can’t) match it. Flash in the browser became the go to platform for serious interactive work on the internet. You just couldn’t get similar levels of awesome out of IE6 and the rest of the browsers of the time.

All good things

The split started to happen in 2006. On the PC, which really means in the PC browser, Adobe was getting more serious about the application space in the browser by releasing the first version of Flash with AVM2 (and s 3.0), a much more stable foundation than Actionscript 2.0 had been, along with an update to its application framework, Flex that took advantage of the improvements to Actionscript 3.0. This helped move trends in Flash’s direction, as seemingly every great site was build using the plugin technology. IE7 had come out that same year, but it only added to developers’ pain in the short-term, and it still wasn’t the robust interoperable platform that browser ecosystem needed to compete in the applications space. So in that space, movement continued toward Flash.

This could be considered the golden age for Flash. Flash ruled the content space during that time, in everything from banner ads, to browser-based games, to anything dealing with charts, and data (so-called RIAs), to just about all the video delivery on the internet.

Browsers didn’t come without problems. They have been slow to innovate, incompatible with one another – universally slow, buggy and crashy – and often full of horrible security holes (especially IE – the dominant player). They were mired in standards battles, forks, company and social politics (open source/EU fines) – but mostly, the leader – Microsoft with IE6, just held everything up. On top of all that, it was difficult for content producers, like traditional newspapers, to find revenue sources other than ad systems. The market was set for change.

That’s about when Apple fired the first warning shots across the bows of the PC browser fleet, by releasing the first iPhone, which could browse the internet, but didn’t run Flash. A brand new platform – software and hardware, with a brand new interface paradigm – touch, instead of mouse and keyboard. This would be a platform built from the lessons of the browser era, and it provided a wide open space for Apple to do what it does best. They rapidly iterated on their ecosystem, and came up with the overwhelmingly successful App Store, a system that seemingly everyone wanted in to. This was a system that came with multiple obvious revenue systems built right in – app sales, technology cross-licensing, advertising, etc. – all things that could be done in the browser space, but the app store made exceedingly convenient, to both producers and consumers. Apple catered to that demand masterfully, and over time expanded opportunities to include, in-app purchases, magazine publishing platforms, and subscriptions services, among others.

In the same way the internet – the modern PC era – had provided enough advantages over the previous content delivery systems to overshadow any of its shortcomings, the App Store model would provide enough promise to overshadow its possible shortcomings measured against its predecessor. App stores proved so compelling, and so big a threat to the existing browser-based models, it almost immediately ended a cozy relationship between Apple and Google, who ruled the browser era, as the gatekeeper to content, and the owner of essentially all advertising on the web. Google moved quickly to duplicate the app system  for Android, and the other platform makers – WebOS, and Microsoft Windows Phone 7 Series – have been playing catch-up ever since. Eventually, Apple brought the app store system to the desktop in OSX Lion, and even Microsoft is picking it up in their Windows 8 Metro interface for full app store coverage in the traditional PC markets.

The rapidly evolving iPhone (later iOS) platform created new ways to think about a lot things. The most important new things were app and content delivery, and revenue sources through new monetization strategies. The Apple App Store changed everything.

The end of an era

When Apple released the iPad in April, 2010, Steve Jobs announced the “end of the PC era.” With the release of the iPad Apple did nothing less than complete and publish the rule book rewrite they began with the iPhone. More than anyone else, the folks at Apple seemed to understand that there is a divide between the “PC era” – which is really the “PC browser era” – and the new app store era. They understood that these two are on two different trajectories, and the app store era will supersede the browser. From now on, for better or for worse, applications would exist in App Stores, and websites would just be websites.

In the same month Apple announced the iPad, Steve Jobs followed up with a special letter in his open letter titled “Thoughts on Flash”, which highlighted some of the negatives of the browser-based “PC era,” where Flash was settling in as the dominant platform. The letter also exploited a division between the Flash crowd and the standards and open source crowds. And he directly addressed the “full web,” – Adobe’s tone-deaf name for “the PC era”. In that direct critique Jobs highlighted the disadvantages of the new app store model, by putting the “full web” flash apps in the “free” – or unprofitable box, and painting the technology with the old brush. Even the main part of the label “PC” is an old term, from a time that came before the modern browser era.

That letter was truly a brilliant piece of market positioning magic, but it was ultimately unnecessary, and Apple has since backed off. The app store model provides a marvelous promise without the need to degenerate the old browser based economy. Content makers, all of whom struggled to find revenue from websites, now have multiple new revenue streams to explore, through app sales, and licensing, and other kinds of content transactions within apps.

During the PC Era, browsers dominated users’ mind share, and time on the PC, native applications were still the clear leaders in performance, access to hardware, and close integration with the underlying OS platform. Despite that advantage, native apps were hamstrung by seemingly insurmountable inconvenience – the boxed distribution model – an inconvenience that most online distribution stores of the time simply duplicated (download, unzip setup, run setup, store setup file somewhere in case you lose your hard drive, etc.).

App stores solve these native application distribution problems by providing a central hub for content, simple e-commerce (no more credit card into the random unverified website), and can be integrated with the legacy system – the website.

My head hurts.

So what does this all mean for us, the front line Flash developers? It means opportunity. There are now three platforms to develop for!

Yeah, that’s right – three.

The transition to app stores on the desktop will take a while to roll out, and old habbits die hard, and Flash will stick around in that space for .. well, as long as that space exists. There are still a chunk of 98%+ of the user out there on the internet, still accessing the web through their existing PCs. That won’t change overnight. Even initiatives like Microsoft’s plugin blockade with Windows 8 and Metro mode take effect, they will come hand in hand with app stores, so there’s a workaround.

But let’s get real for a second, the Flash Player – in the browser – sits at the core of entire new lucrative markets on the PC, in the browser. Take browser era social gaming and Zynga – a game company, with a quirky social media, micro-transaction game library, integrated with Facebook’s social platform, is more profitable than top traditional PC game companies like E.A. Flash in the browser is having a grand time. Stage3d was just released, Unreal Engine was shown running on it at MAX. Flash is still tops for the best kinds of awesome on the internet.

Second, you have all the HTML5 opportunity – not directly relevant for Flash devs (yet), but for those of us that have had their hands in both worlds this whole time, this is exciting! HTML, JavaScript and CSS are finally getting to the point where you can build really awesome stuff with it. And, for app store monetization to work, discovery is key. Searchable HTML (and HTML5) will dominate for that. App stores are easy to search and easy to link into – from a website. Websites aren’t going anywhere – in every way, the app store model can’t work without the browser based internet.

And finally, the new kid on the block, the app store. For Flash devs, that means AIR – which is essentially Flash for app stores. If you have Flash (or even HTML) skills to burn, you can almost, just recompile your Flash app for AIR. Adobe has built this amazing tool – the best kept secret they didn’t mean to keep (don’t get me started on their PR). The sky is the start with AIR for Mobile, never mind the limit (Apollo indeed). The best part is, once you build for one app store with AIR, you can build for basically all of them, with very little additional effort.

Have a look at Machinarium. A traditionally packaged standalone desktop app, made with Flash, and distributed in a box through traditional outlets (and the specialty PC app stores, like Steam) with an online demo that runs in the desktop browser in Flash Player. Now republished for the Apple App Store with AIR and some optimizations, to run on iPad as a native app.

So where are we? Flash is alive and kicking – thriving even – despite the clueless ramblings of know-nothing media pundits and their bandwagon seeking behavior. You don’t need to listen to them, just get out there, and make cool apps/websites/games/whatever else with the same technology you’ve always used. These are exciting times.

 

Performance Benchmarks with AIR 2.7 for iOS

I’ve been working on this Benchmark based on Iain Lobb’s BunnyMark. Being a bit confused sometimes about what things speed things up or slow things down, I didn’t want to guess anymore, so I grabbed Iain’s code base (cause I’m lazy, and didn’t want to start from scratch), and added some tests for things I suspect are slowing things down (or speeding things up). I think this will also help shed some light on why some folks see a huge gain in AIR 2.7 CPU mode, while others do not.

Some caveats – this only tests instances of flash.display.Bitmap on the display list, at the size they are, moving the way they move. It’s on my list to add Blitting (I have some initial work on that done, thanks to Iain, but I need to add the rotation, and alpha settings to it), and I’d like to add a vector test, and maybe some extra sized Bitmaps (I’ve heard that makes a difference).

Enough! Here are some results – quality had no effect on GPU mode, so I included only one line:

Note: some are reporting they see a difference in GPU mode, but I still don’t. Update: It appears some users are confusing “Mobile Performance Tester” with BunnyMark, which explains the discrepancy. BunnyMark is not currently in any App Store, which is one key distinguishing feature. ;-)

BunnyMark Results – 500 Bunnies
Alpha
Rotation
CaB
CaBM
iPhone 3GS – GPU
FPS 24 18 17 22 13 13 19 1 19
iPhone 3GS – CPU
FPS-L 28 21 19 9 19 5 7 5 5
FPS-M 28 21 19 4 18 3 7 5 3
FPS-H 28 21 19 3 18 2 7 5 2
FPS-B 28 21 19 3 18 2 7 5 2
iPhone 4 (Retina) – GPU
FPS 25 21 20 25 13 13 16 0.5 16
iPhone 4 (Retina) – CPU
FPS-L 32 23 20 10 21 6 8 6 7
FPS-M 32 23 20 5 20 3 8 6 3
FPS-H 32 23 19 4 20 2 8 6 2
FPS-B 32 23 19 4 20 2 8 6 2

Notes about the Benchmark:

  • In general, the CPU mode seems pretty consistent with the way you’d expect things to work on the desktop – the same optimizations you’d apply for the browser plugin, you’d also apply to mobile for CPU mode.
  • Rotation in this benchmark is not continuous – the Bunny graphics are only rotated at the edge of the stage, which is why cacheAsBitmap works to speed those up. If they were constantly updated, it would likely be much more expensive on CPU mode (probably more like rotation without CaB).
  • Alpha is continuous – the alpha value of each Bunny is based on the y position and is updated every frame. I would like to add a mode similar to the rotation, so see what effect CaB has on alpha transparent objects that don’t constantly change.
  • iPhone 4 and 3GS numbers aren’t directly comparable for practical purposes. The Bitmaps on the screen on 3GS take up much more real estate, since the 3GS screen res has 1/4 as many pixels as the iPhone 4. In a normal app, we’d probably resize things to look comparable between the two devices. I’ll try to add a mode that makes this more comparable (because I suspect we’ll find that 3GS can keep up with iPhone 4 with similar looking content).
  • Touching the screen seems to cost about 4 fps across the board.
  • I think there may be an issue with returning to rotation = 0 costing some performance in GPU mode. Still have to test that.
  • I’m definitely getting some variance on default speeds – basically, before any settings are messed with on some runs I get the faster numbers (the baseline numbers in the tables above). Other times it runs at default settings a couple of FPS slower (on start, or after resetting the switches). With any of the settings, everything is consistent across multiple runs.

 

It’d be nice to have more benchmarks for more devices, but I only have the above devices available. This should run just fine on Android, Blackberry Playbook, and iPads. If anyone wants to contribute a set of benchmarks, hit the comments. Here is the source. One of these days I’ll make another post, and try to draw some conclusions, maybe wrap the bullet points into a narrative, and edit some of this, but the tables are there, and the source code, and that’s the important stuff.

In the midst of playing with this benchmark, I found (or was pointed at) some great resources. Here are some of them:

Here is the Benchmark to see it in action:

What is a “Native” App?

I was recently asked my opinion on what makes a “native” app, and this was my response:

It depends on how you split that hair.

I think it depends on what platform level (hardware, OS, etc.) the particular user of the word native thinks that word applies to. It seems many use the word to refer to the actual bytecode and whether it matches the hardware (the CPU) – but in those cases I often see the term native used with the CPU architecture in the description – such as native ARM, or not native x86. iOS apps compiled with AIR 2.6 I’d say are compiled to native ARM bytecode.

There are other ways to parse it though – for example, it was pointed out to me that AIR for iOS apps are compiled from ABC bytecode into ARM bytecode to avoid the JIT (and Apple’s restrictions on the use of JIT), but that code still uses the virtual machine – the garbage collector, sandbox and whatnot. This gets right up to the edge of my understanding of virtual machines. But, if the use of a VM precludes an app from being called native then could .NET be native on Windows, or Dalvik apps on Android? In the case of .NET, there is even a JIT (pretty sure on that one, but not entirely so).

Then there’s the issue of targeted API (and ABI) – if an app is compiled to run on Windows, but is running in a VM on Linux, it’s probably not native (even though it’s CPU architecture probably matches), but if it runs in WINE on Linux, is that native?

Speaking of the Linux crowd – they parse their platforms even more granularity – Gnome apps, running on KDE are not native to some people, simply because they use a different GUI toolkit, though something running in an interpreted language like Python are native if they use the “native” GUI toolkit. Games are not subject to this line of reasoning – if it runs on Linux in OpenGL (without WINE) then it’s native.

I even remember reading some opinions in various places that programs not written in C are not native to Linux, and programs not written in C++ are not native to Windows – despite those programs using all the same APIs, ABIs, and not running a in VM.

So what is my opinion? As it relates to my current favorite target platform, I wouldn’t call an AIR app native – especially since it requires a 3rd party runtime to be installed separately (like on Android or desktops), and doesn’t have access to the native GUI toolkits and widgets and other OS APIs. That’s not a hard and fast opinion though, my definition of native is pretty malleable, and likely to change over time (or over the course of writing this response). I think I’d have a hard time selling the idea that a Java or AIR app is native to a client – on Android mostly because of the separate runtime requirement – and on all platforms, because of the lack of access to OS level APIs. It would feel disingenuous to call an AIR app a native app.

AIR for iOS comes closest to being reasonably called a native app – it is compiled as a complete standalone package, and runs pretty close to the metal (being compiled to ARM code) – and most importantly doesn’t require a third party runtime to be installed separately. If AIR for iOS apps had access to the native (underlying OS platform) GUI toolkit and other APIs, I would be more comfortable calling it native, though probably still wouldn’t.

Probably the best definition of “native” I could come up (which you still won’t get anywhere close to universal agreement on) is an app that comes out of using the platform maker’s tools to develop apps for the platform – XCode + Objective-C (and other supported languages) for OSX and iOS, Visual Studio for Windows and Windows Phone, Android SDK for Android – even using Adobe’s tools to make an AIR app makes it a “native” AIR app – where using HaXe may not count as native.

Generally though, as much as I could, I would try not to discuss whether or not an app development tool like AIR is native at all – especially since that term is so subjective. A project needs a particular problem solved, and if I can do that with AIR (on iOS that means it doesn’t require iOS GUI elements and conventions, or other features of iOS), then that’s what I’d recommend.

Update: AIR 3.0 closes this gap, and makes the “Native App” comparison easier because of two features; 1. Captive runtime – no more separate runtime requirement means it’s a standalone app. 2. Native Extensions – now an app has access to all the native functionality of the underlying platform. I’m comfortable calling an AIR app a Native App with AIR 3.0.

Flash iPhone Game at Silky 60FPS on 3GS

Well, it’s only a tech demo at the moment. I’ve been playing with this Breakout like game for a while, trying to learn the ins and outs of Flash mobile development – particularly as it relates to performance. I now have the unBrix demo running at close to 60FPS (59.1) – smooth as silk.

This won’t run at 60FPS on Android Flash Player plugin in the browser (or Firefox on Mac!) – this post is about the iPhone build – but here’s the web version to look at anyway.

Here is a blurry video of the thing running as a native iPhone app on a 3GS (I smoothed out the choppy splash transition in a later build by setting the BG element with cacheAsBitmapMatrix):

The most important thing was to make sure GPU acceleration was working, and to learn what things will impact performance in that area.

It turns out, there are some important differences with how GPU accelerated Flash woks compared with the traditional software renderer. In the software Flash renderer keeping your display list shallow, and sparse (using addChild/removeChild a lot) or avoiding the display list completely (by writing to BitmapData – as the Flixel game engine does) is a key optimization for performance. This is how the exploding bunny video demo is done, and why it’s so fast.

My current theory is that on GPU accelerated content (even on desktop) the reverse is true. You want to avoid CPU/system RAM to GPU/video RAM updates as much as possible – which means avoiding BitmapData updates which cause the player to upload a new texture to the GPU VRAM with every update. Because I don’t have access to the internals of the Flash Player architecture, I can’t be sure, but I think the bottle neck comes from clogging up the lanes between the CPU and GPU, and all stressing all three areas of the rendering pipeline (CPU, GPU and the bus) as they juggle around objects in memory. The key observation this conclusion is based on is the large performance impact addChild and removeChild has on the framerate. So I relentlessly avoid that in my iPhone Flash development – I precache everything, and don’t mess with the display list. This is also one reason why filters (which operate on a BitmapData representation of the DisplayObject you apply them to) are not recommended on mobile content.

Anyway, hopefully I can turn this into a full app for iPhone in a reasonable timeframe. :-)