TBH it's a small demo - I've heard while JS engines these days are fast, they still struggle with complex physics simulations. I can't see any performance details/improvements noted in this release - anyone got figures?

Untrue, I used a port of Box2d (not this port, our own version) to build an "HTML5" game for sony, see link - http://www.youtube.com/watch?v=AicnuLQxHoQ

Unfortunately the game was taken down due to the Japan situation. Understandable.

Under Safari i was able to simulate ~80 live physics objects in a high collision environment at full frame render, bound to the DOM at 60fps on reasonable hardware 6 months ago (safari still has the fastest DOM paint time out there now).

Even when using Firefox 3.6 i could manage around 20 dynamic objects.

No CSS3 animation, just math and re-paints.

Javascript Math is not slow (at all), its generally the DOM/Canvas slowing you down.

If you've ever used the C++ Box2D, you'll have been able to create hundreds of objects just fine. 80 still isn't much!

Of course! This is now nearly possible in Chrome/Safari/FF5, but the limiting factor is still primarily re-paint time rather than the simulation itself.

Really? Even with FF5's hardware accelerated canvas?

the game looks awesome, any plans for a re-release?

It's also worth checking out GWTBox2d, which is actually Java code run through GWT, and runs surprisingly well: http://gwtbox2d.appspot.com/

I'm really impressed with what JS can do these days...