Monday, 6 May 2013

How the cello controls the game in Cello Fortress

The most unique aspect of Cello Fortress is how a cellist does a live performance in front of an audience, while at the same time controlling a game. This is completely different from other music games, in which the musician usually plays on a fake plastic instrument, and even if he plays a real instrument, he does nothing but imitate an existing song. In most such other music games, there is hardly any real gameplay: just points based on how well you played the song.

Cello Fortress is a completely different affair: here the cellist is controlling a real game, with real choice and interaction. Depending on what his opponents do, the cellist plays different notes. The cellist can even do things like baiting the opponents with a certain attack and then switching to another.

So how does that work? What does the cellist need to do to trigger the various attacks? Check this trailer to see (and hear!) how it works:

Live video footage in the trailer shot by Games at the Indie Games Concert.

Here is an overview of the attacks as explained in the trailer:
  • Slow high notes: long range guns
  • Slow chords: homing missiles
  • Fast high notes: machine guns*
  • Fast chords: double machine guns*
  • Dissonant chords: flamethrowers
  • Slow low notes: create mines
  • Fast low notes: mines move towards the player
  • Special melody 1: obliterate left half of screen
  • Special melody 2: obliterate right half of screen
*Playing even faster notes increases the speed of the machine guns.

The key thing to realise, is that the first seven of these attacks allow the cellist to play many different styles, melodies and rhythms, and still achieve that attack. The number of possibilities with "slow high notes" is literally infinite. This is a crucial aspect to the game, since it allows the cellist to improvise in many different ways, keeping each match of Cello Fortress fresh and varied. Having so much freedom also allows an experienced cellist to play fluently from one attack to the other.

There is real gameplay and choice in this. For example, something I often do when playing the cello in Cello Fortress, is play something slow to dare players to get close to my cannons. As soon as they do, I switch to fast chords to damage them from short range.

The special melodies are each 8 notes and have been defined beforehand. The fun in these is that the attack is announced when the 4th note is played, but the damage is not actually done until the 8th note is played. Players who pay close attention can hear the attack coming after only two notes, and thus flee before it even happens.

I can play the melody faster or slower to make the attack happen earlier or later. From a gameplay perspective, one would assume I always attack as quickly as possible, but my goal is actually not purely to win: I want to entertain the players and the audience. So I sometimes deliberately let them live to give them a more fun experience. This can be seen around 1:33 in the trailer: I make the final note very long to allow that player to escape. Just like in a film, the best moments are not when the hero dies, but when he narrowly escapes.

These controls were specifically chosen because they combine music and control in a natural way. Achieving this was more difficult than it may seem. In my very first prototype, the cello simply shot one bullet for every note, and the direction of the bullet depended on the pitch of the note. This turned out to play horribly: whenever the players moved from the left to the right, the cellist had to play a scale from low to high. When they moved back, the notes also had to go back from high to low. This made it completely impossible to play anything that sounded like good music.

Another thing I tweaked a lot is the mapping of which pattern triggers which attack. The current controls work quite well on an emotional level: the attack is linked to the feeling of the music. Slow, low notes often sound quite tense and sad on a cello (especially with the specific types of melodies I personally usually play), and alternating between slow and fast notes creates an awesomely menacing atmosphere. This can be seen in the trailer from around 1:00. Creating tension this way works incredibly well: I performed with Cello Fortress in front of an audience of several hundred people at the Indie Games Concert, and the noises from the audience made it clear that they experienced the tension very strongly.

A note I should make on this trailer, is that in the real game, there is a slight delay between the music the cello plays and the moment the guns react to it. This is because analysing music in real-time takes a bit of time. To make the trailer more understandable, I have moved the sound a bit to make the music fit the gameplay exactly.

While I am already performing with it, I am also still working on Cello Fortress to improve it. So what is next? My focus for the coming period is first creating real graphics, and after that I want to add a couple more attacks for the cellist. In the meanwhile, I hope more events, venues and exhibits will contact me to perform with Cello Fortress! Check for tour dates and contact info!


  1. Couldn't you distribute pre-arranged cello songs for the game so non-cellists can play without you/another musician?

    Additionally, are you thinking about other instruments at all?

    1. I definitely could pre-record songs, but it would lose a lot of the fun: I cannot react to the players that way. Also, the performance is very much part of what makes it cool. Without the live musician, it loses it most important part. Still, could be a nice extra at some point! :)

      I have been thinking about trying other instruments, yes. Especially violin and viola could work really well, I expect, and maybe wind instruments as well.

  2. As a cellist, I want to download this game badly. As a UX researcher, I want to help. If you open this up to do user testing, please let me know.