Boris Smus

interaction engineering

An onslaught of mobile HTML games

HTML5 games are really picking up. Casual Girl Gamer recently produced a nice list of impressive titles. The modern web platform (namely, fast javascript and canvas) is incredibly promising to a game developer. The advantages that it brings are huge: no installation required, and ubiquitous cross platform compatibility. I took a practical look at games in the HTML5 mobile space, taking Onslaught!, a particularly fun and well written game, and porting it to Android/iPhone.

Perhaps porting is too strong a word here. Onslaught! runs and performs reasonably well on my Nexus One running Android 2.2.1. The only problem is that the game uses keyboard input, making it completely unplayable on mobile devices. Luckily, the controls are quite simple, and only require a directional pad and two buttons. So I decided to build an on-screen virtual game controller, not unlike those found in many native iPhone games. At first I was inclined to build the controls by extending the game itself (using the canvas element), but then decided that an HTML-based approach is better (since it saves the trouble of hit detection), and might even work as a generic controller for other games.

Hoping to create a general game controller for Android/iPhone, I sought to generate keyboard events from JavaScript, based on touch input. While this is possible if your key event handlers are written in a particular framework (say jQuery), it seems to be generally impossible for security reasons. I wrote an Onslaught!-specific controller that should be easy to port to any other game. The controller simply embeds the Onslaught! game in it's original 640x480 resolution, which is then scaled to the device size using the meta viewport element. The result is a mobile game that's playable on Nexus One, and not-quite-playable on iPod Touch (2nd gen) due to slower JavaScript execution. These are the only two devices I currently have access to, so I would appreciate it if you could try it on your Android or iOS device (in landscape mode) and let me know how it goes!


I ran into a few stumbling blocks as I was developing and testing this port, most of which involve the Android browser on Nexus One running Android 2.2.1.

  1. Very immature touch event (ontouchstart, ontouchend, etc) support. In fact, the browser doesn't seem to support multi-touch at all (ie. only one touch can be registered at a time). In contrast, Safari for iOS supports multitouch events quite well. For complete details, see this quirksmode writeup and this bug report.
  2. The Android browser completely ignores many properties in the meta viewport element's content attribute. Specifically, the browser doesn't react to initial-scale, minimum-scale, maximum-scale and width. As a result, I had to hack around this issue by abusing an Android-only property called target-densityDpi. I suspect that I may be doing something wrong here, since it's a pretty fundamental issue. Still I logged a bug.
  3. Less significant but still noteworthy, the CSS :active selector does not activate on the Android browser (at least for div elements). The reference implementation is iOS, where a touchstart event on a div element causes it to become :active until a touchend event.

In the short term, HTML as a gaming platform is emerging as a real Flash killer. In the long term, I wouldn't be surprised if HTML games will be widely played on Mac, PC, TV console, and mobile phone platforms. Whatever happens, browsers will continue to be pushed to conform to modern specifications and perform ever better, making mobile rich web applications more and more feasible.

In closing, many thanks to Lost Decade Games team for writing such a sweet game and not obfuscating the JavaScript! Oh, and a reminder that if you're working on a HTML game, be sure to submit it to Mozilla's Game On contest, then add some touch controls and submit it to this mobile HTML game contest. Let the games begin!