You might know Mark Johns ( from his indie titles like Space Barnacle. Here, he talks to about his recent involvement in the development of Tap Tap Dance.

This new touch-based music game for iPhone and iPod Touch features visual themes designed by fellow indie creator cactus and Kevin Coulton and a soundtrack that includes The Chemical Brothers, Daft Punk, Basement Jaxx, and more.

Can you provide some background on how Tap Tap Dance came about, and how you became part of the development team?

Before Apple released it's officially sanctioned SDK, a team of hackers figured out a way to reverse engineer their way past the security on the device, and opened up a path for developing unofficial apps for 'jailbroken' iPhones. One of those apps was a rhythm game called "Tap Tap Revolution", written by Nate True.

Not long after Apple released the official SDK, Tapulous, an iPhone based startup, bought the game, rechristened it Tap Tap Revenge, and released it as a free game on the iTunes App Store. Since then, the game has been downloaded by over 3 million different people, and something like 100,000 unique people play it every day. As of today, it is the most popular free application on the iPhone and iPod Touch.

Tap Tap Revenge, as it is now, is written in straight Cocoa, and all its graphics are rendered in software on the CPU. It works pretty well, but it's slow compared to what what can be done if you take advantage of the 3d graphics chip on the phone.

I was hired to rewrite the game from scratch in OpenGL, actually to supplement work with a very talented guy in Montreal, named Guy English, who had already begun to put it together. Tap Tap Dance is the first game we're releasing which takes advantage of this new engine. The first thing you'll notice is that it plays a lot smoother, and we have the power to do lots more nice little effects without chugging down the machine.

Tell us about the music tracks you've solicited for Tap Tap Dance.

The music for Tap Tap Dance got lined up as Guy and I were working on the new TTR engine. It was put together by this great guy, Bruno Guez, an accomplished DJ and producer. When I saw that we had these great tracks from artists like Daft Punk, Justice, Digitalism, Chemical Brothers, and Basement Jaxx, I got really excited. I knew we should do something special for it, because these are artists whose songs I have and play in my own iTunes collection. I thought it'd be cool if we moved in a direction where we were creating something like interactive music videos, with rhythm game mechanics influencing their playback.

I'd always wanted to collaborate with cactus, and I've worked with Kevin before on numerous projects (Space Barnacle, Rotrix, and a number of as yet unreleased Doomlaser games). I asked Jonatan (cactus) if he was interested, showed him the tracks, and asked him to pick one and make some visuals for it. Basically anything he wanted. And then I tried my best to get his vision into the game. He did the Disco Lies track, by Moby, remixed by The Dusty Kids Fears.

I'd also like to say that the cactus theme isn't quite done. Jonatan gave me way more awesome stuff than I could put in, but we plan on getting as much of it in as we can in the next update to the game.

What about gameplay?

There are four difficulty levels in Tap Tap Dance: Easy, Medium, Hard, and Expert. Each difficulty level has a playlist, with one special track at the end. We've been referring to them as Boss Tracks in-house. You play a few of the normal tracks on a difficulty level, and if you do well (above an 85% on 50% of them), you'll unlock the boss track, which has one of these special themes. And when you beat the boss track, you unlock the next difficulty level. Kevin did the boss tracks for Easy and Hard, and Cactus did the boss track for Medium.

Any new features then?

Tap Tap Dance sticks to the tried and true mechanics of Tap Tap Revenge, with a few additions. We've added multi-tap notes, and Tap and Hold, which really opens up gameplay possibilities. Nick and I wanted the difficulty progression to be somewhat akin to learning to play piano, or another chorded musical instrument, from the ground up, in a very abstract way. So on easy, you start out tapping one note at a time, and on the boss track, Technologic by Daft Punk, with a theme by Kevin Coulton and myself, we introduce the multitap, which you see a lot of on medium.

On cactus' boss track, that Moby - Disco Lies remix, we introduce tap and hold. For the hard boss track, the 2001 ending-inspired seven minute Justice track, remixed by Soulwax, we combine all these mechanics, so you've got tap and hold - chords, using your other finger to tap rhythms from other elements of the song, and switch up the rhythms to follow the song's various instrumentation, hopefully creating a very epic experience. Somewhere between a music video, the light show at a rock show, and the Tap Tap Revenge we know and love.

How many songs will be included?

10. Each of the ten tracks is on multiple playlists, with harder difficulty and a more complex level as you progress. In easy, you only have four songs. Unlocking the new difficulty levels by beating the boss tracks unlocks all the songs.

The boss track for hard is Phantom Pt II by Justice, remixed by Soulwax, which is 7 minutes and 23 seconds long, and has an epic visual theme, created by Kevin Coulton and scripted by myself. We also did the first pass on the actual tap track level in my dining room. It was given the professional treatment by Nick Gallant, the guy who made the levels for all the songs, and pretty much all of the Tap Tap Revenge songs to date. He also wrote this song "Turn Yourself Around" which is the de facto theme song for Tap Tap Revenge. He's pretty integral to the project, and a great guy to work with.

Any additional modes?

Tap Tap Dance has a two-player mode, where you can play the game in-person with a friend. Basically you've got rails on either side of the screen, and you play against a friend, and see who's the baddest. It works quite well on car trips, trains, diners, that sort of thing. You can play all the songs you unlock in the single player story mode.