Become a Minecraft VJ

Everyone has played Minecraft. You will all have built amazing structures, designed cunning traps and even created elaborate cart lines controlled by redstone switches. How many of you have performed with Minecraft? We bet you didn’t know that you could use Minecraft to create amazing visuals just like a professional VJ.

If your only way of modifying Minecraft was with the mouse, you’d have a tough time changing things fast enough. Luckily for you your Raspberry Pi comes with a version of Minecraft that can be controlled with code. It also comes with an app called Sonic Pi which makes coding Minecraft not only easy but also incredibly fun.

In today’s article we’ll be showing you some of the tips and tricks that we’ve used to create performances in night clubs and music venues around the world.

Let’s get started…

Getting Started

Let’s start with a simple warm up exercise to refresh ourselves with the basics. First up, crack open your Raspberry Pi and then fire up both Minecraft and Sonic Pi. In Minecraft, create a new world, and in Sonic Pi choose a fresh buffer and write in this code:

mc_message "Let's get started..."

Hit the Run button and you’ll see the message over in the Minecraft window. OK, we’re ready to start, let’s have some fun……

Sand Storms

When we’re using Minecraft to create visuals we try and think about what will both look interesting and also be easy to generate from code. One nice trick is to create a sand storm by dropping sand blocks from the sky. For that all we need are a few basic fns:

• sleep - for inserting a delay between actions
• mc_location - to find our current location
• mc_set_block- to place sand blocks at a specific location
• rrand - to allow us to generate random values within a range
• live_loop - to allow us to continually make it rain sand

If you’re unfamiliar with any of the built-in fns such as rrand, just type the word into your buffer, click on it and then hit the keyboard combo Control-i to bring up the built-in documentation. Alternatively you can navigate to the lang tab in the Help system and then look up the fns directly along with all the other exciting things you can do.

Let’s make it rain a little first before unleashing the full power of the storm. Grab your current location and use it to create a few sand blocks up in the sky nearby:

x, y, z = mc_location
mc_set_block :sand, x, y + 20, z + 5
sleep 2
mc_set_block :sand, x, y + 20, z + 6
sleep 2
mc_set_block :sand, x, y + 20, z + 7
sleep 2
mc_set_block :sand, x, y + 20, z + 8

When you hit Run, you might have to look around a little as the blocks may start falling down behind you depending on which direction you’re currently facing. Don’t worry, if you missed them just hit Run again for another batch of sand rain - just make sure you’re looking the right way!

Let’s quickly review what’s going on here. On the first line we grabbed Steve’s location as coordinates with the fn mc_location and placed them into the vars x, y, and z. Then on the next lines we used the mc_set_block fn to place some sand at the same coordinates as Steve but with some modifications. We chose the same x coordinate, a y coordinate 20 blocks higher and then successively larger z coordinates so the sand dropped in a line away from Steve.

Why don’t you take that code and start playing around with it yourself? Try adding more lines, changing the sleep times, try mixing :sand with :gravel and choose different coordinates. Just experiment and have fun!

Live Loops Unleashed

OK, it’s time to get the storm raging by unleashing the full power of the live_loop - Sonic Pi’s magical ability which unleashes the full power of live coding - changing code on-the-fly whilst it’s running!

live_loop :sand_storm do
  x, y, z = mc_location
  xd = rrand(-10, 10)
  zd = rrand(-10, 10)
  co = rrand(70, 130)
  synth :cnoise, attack: 0, release: 0.125, cutoff: co
  mc_set_block :sand, x + xd, y+20, z+zd
  sleep 0.125
end

What fun! We’re looping round pretty quickly (8 times a second) and during each loop we’re finding Steve’s location like before but then generating 3 random values:

• xd - the difference for x which will be between -10 and 10
• zd - the difference for z also between -10 and 10
• co - a cutoff value for the low pass filter between 70 and 130

We then use those random values in the fns synth and mc_set_block giving us sand falling in random locations around Steve along with a percussive rain-like sound from the :cnoise synth.

For those of you new to live loops - this is where the fun really starts with Sonic Pi. Whilst the code is running and the sand is pouring down, try changing one of the values, perhaps the sleep time to 0.25 or the :sand block type to :gravel. Now hit run again. Hey Presto! Things changed without the code stopping. This is your gateway to performing like a real VJ. Keep practising and changing things around. How different can you make the visuals without stopping the code?

Epic Block Patterns

Finally, another great way of generating interesting visuals is to generate huge patterned walls to fly towards and close by. For this effect we’ll need to move from placing the blocks randomly to placing them in an ordered manner. We can do this by nesting two sets of iteration (hit the Help button and navigate to section 5.2 of the tutorial “Iteration and Loops” for more background on iteration). The funny |xd| after the do means that xd will be set for each value of the iteration. So the first time it will be 0, then 1, then 2… etc. By nesting two lots of iteration together like this we can generate all the coordinates for a square. We can then randomly choose block types from a ring of blocks for an interesting effect:

x, y, z = mc_location
bs = (ring :gold, :diamond, :glass)
10.times do |xd|
  10.times do |yd|
    mc_set_block bs.choose, x + xd, y + yd, z
  end
end

Pretty neat. Whilst we’re having fun here, try changing bs.choose to bs.tick to move from a random pattern to a more regular one. Try changing the block types and the more adventurous of you might want to try sticking this within a live_loop so that the patterns keep changing automatically.

Now, for the VJ finale - change the two 10.times to 100.times and hit Run. Kaboom! A Huge gigantic wall of randomly placed bricks. Imagine how long it would take you to build that manually with your mouse! Double-tap space to enter fly-mode and start swooping by for some great visual effects. Don’t stop here though - use your imagination to conjure up some cool ideas and then use the coding power of Sonic Pi to make it real. When you’ve practised enough dim the lights and put on a VJ show for your friends!