benchmarking dartbox2d

Joel Webber wrote this excellent blog post in which he tests native versions of Box2D against Javascript implementations. Perhaps unsurprisingly, he discovered that native code is around 20 times faster than JavaScript.

Having just released DartBox2d, I was curious to see how Dart stacks up against these results. It should be noted that the Dart version has diverged a little from the original port to make it more Dart-like. My measurements didn’t show any significant performance change between the current version and the initial port.

I’m using the same test as Joel, taken from his github repo, and have committed the Dart source used back into the tree, so you can check it out here. The JavaScript there, and used below, was generated using frog rather than dartc as it generates smaller, more readable output. The Dart VM does not currently support any references to dart:dom or dart:html so running those required some massaging of the code. Specifically, commenting out all of dartbox2d/callbacks/CanvasDraw.dart and removing all references to Canvas from Bench2d.dart.

All of the data and the graphs can be seen here.


First, JavaScript generated from Dart using frog vs hand-written Box2D-web JavaScript:

This is on a linear scale, unlike Joel’s graphs, as the difference between the traces is much smaller. However, the raw frame times are higher, which is probably due to the different machines we’re running on. The results, though, are still clear: Box2D-web runs at an average 104 ms/frame while the JS generated by frog from Dart is running at 135 ms/frame. There’s significant variation in both implementations (standard deviation is ~18 – 19 ms in both cases) which is either inherent in the simulation or indicates garbage collection running.


Given the difference Joel saw between the Java VM and Javascript, with the Java VM running 10 times faster than JavaScript, it is tempting to compare Dart compiled to JavaScript with Dart running natively in a VM in Dartium.

There’s a massive 4800 ms frame that I had to cut off to see detail across all the samples. I think this is some part of the VM being initialized and blocking the process, but it’s hard to tell.

There’s some other really interesting things to note here. Firstly, the VM performance improves over time, which is not something that I’ve seen in other tests. It’s also faster than the generated JavaScript and the hand-written Box2D-Web JavaScript at it’s fastest, however there is massive variance due to a periodic slowdown. It’s running at an average 119 ms per frame but the standard deviation is a massive 300 ms. I haven’t looked into the Dart VM but I’m going to throw out a guess that this is some garbage collection kicking in every few frames.


Here are all three results together for comparison:

With a little optimization work in DartBox2d, and maybe a little work on the code generation in Dart, I think it’s possible to get Dart-generated-JavaScript to get close to the performance of hand-written JavaScript. However, it’s also clear that the Dart VM, even in its current state, has the potential to outperform both.