Posts Tagged actionscript

Lightspark’s news

Lightspark pro­gresses are never been so good. The last achieve­ment was to cor­rectly load, exe­cute and par­tially ren­der the YouTube player. As you may have seen YouTube has recently switched to Flash 10 and Action­Script 3.0 to serve some HD con­tent, while keep­ing the old AS2 based player for lower qual­ity videos. The old player is sup­ported by Gnash but, until now, there where no open source alter­na­tives to play newer, high def­i­n­i­tion con­tent. As Lightspark AS3 engine matures, that gap is almost closed. Stay tuned, as I’m plan­ning to release a new tech­nol­ogy demo very soon.

UPDATE: Demo tar­ball released on source­forge

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Extreme FLEXibility

Although there has been no offi­cial news about Lightspark for sev­eral months, i’ve been doing a great deal of work under the hood. As my bach­e­lor the­sis, I’ve mostly com­pleted and throughly tested my LLVM based Action­script 3 .0 JIT engine and, dur­ing the last days, I’ve been work­ing on pol­ish­ing a bit the Vir­tual Machine. I’m proudly announc­ing that, in some days, a new tech­ni­cal demo of Lightspark will be released, but this time we’re not talk­ing about basic exam­ples. Lightspark is now mature enough to run a sim­ple appli­ca­tion based on Flex.

Flex is a rich open source frame­work writ­ten in Action­script and devel­oped mainly by Adobe. Even if right now the test appli­ca­tion fea­tures only a progress bar and a square, there is a lot of stuff being done by the frame­work under the hood.

If the frame­work works it means that the engine is now sta­ble enough to move from a pre-alpha to an alpha sta­tus. The design is also now sat­is­fy­ing enough for me to allow other peo­ple to join the project and work on on sub­sys­tems with­out know­ing the inter­nal details of every­thing. As an added bonus pre­lim­i­nary sup­port for the Win­dows plat­form will be included in the release.

The screen­shot above is the result of the exe­cu­tion of my test appli­ca­tion, for curi­ous peo­ple the flash file is gen­er­ated using the mxmlc com­piler, from the fol­low­ing source file

<?xml version="1.0" encoding="utf-8"?>
horizontalAlign="center" verticalAlign="middle">
<mx:VBox x="0" y="0" width="201" height="200" backgroundColor="0x0080C0" alpha="0.8"/>

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Lightspark second technical demo announcement


I’m cur­rently fin­ish­ing some last cleanups and enhance­ments before releas­ing a sec­ond tech­ni­cal demo of the Lightspark Project. Much time is passed from the first demo, and the project is grow­ing healty. This release aims at ren­der­ing the fol­low­ing movie, selected from adobe demo. The results may not be very impres­sive. But many things are going on under the hood.

The most inter­est­ing fea­ture in this release are:

  • GLSL based ren­der­ing of fill styles (eg. gradients)
  • LLVM based Action­Script exe­cu­tion. Code is com­piled just in time
  • A few tricks are also played to decrease the stack traf­fic tipi­cal of stack machines.
  • First, although sim­ple, fram­er­ate timing
  • Frame­work to han­dle Action­Script asyn­chro­nous events. Cur­rently only the enter­Frame event works, as the input sub­sys­tem is not yet in place. But stay tuned, as I’ve some nice plan about that.

The code will be released in a cou­ple of more days, or at least I hope so :-)

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ActionScript meets LLVM: part I

One of the major chal­lenges in the design of lightspark is the Action­Script exe­cu­tion engine. Most of the more recent flash con­tent is almost com­pletely build out of the Action­Script tech­nol­ogy, which with ver­sion 3.0 matured enough to become a foun­da­tional block of the cur­rent, and prob­a­bly future web. The same tech­nol­ogy is going to become also wide­spread offline if the Adobe AIR plat­form suc­ceedes as a cross plat­form appli­ca­tion framework.

But what is Action­Script? Basi­cally it is an almost ECMAscript com­pla­iant lan­guage; the spec­i­fi­ca­tion cov­ers the lan­guage itself, a huge library of com­po­nents and the byte­code for­mat that is used to deliver code to the clients, usu­ally as part of a SWF (flash) file.

The byte­code mod­els a stack-machine as most of the argu­ments are passed on the stack and not as operands in the code. This oper­a­tional descrip­tion — although quite dense — requires a lot of stack traf­fic, even for sim­ple com­pu­ta­tions. It should be noted that mod­ern x86/amd64 proces­sors employ spe­cific stack trac­ing units to opti­mize out such traf­fic, but this is highly archi­tec­ture depen­dent and not guaranteed.

LLVM (which stands fot Low-Level Vir­tual Machine) is on the other hand based on an Inter­me­di­ate Lan­guage in SSA form. This means that each sym­bol can be assigned only one time. This form is extremely use­ful when doing opti­miza­tion over the code. LLVM offers a nice inter­face for a bunch of fea­ture, most notably sophis­ti­cated opti­miza­tion of the code and Just-In-Time com­pi­la­tion to native assemply.

The chal­lenge is: how to exploit llvm power to build a fast Action­Script engine.

The answer is, as usual, a mat­ter of com­pro­mises. Quite a lot of com­mon usage pat­terns of the stack-machine can be heav­ily opti­mized with lim­ited work, for exam­ple most of the data pushed on the stack is going to be used right away! More details on this on the next issue...

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