Tuesday, September 16, 2014

MCPI-Scratch: A Scratch Extension application to program Minecraft

The last blog post - Scratch, Minecraft and Raspberry Pi: how they fit together - explained different alternatives for programming Minecraft using Scratch. Unfortunately the easy alternatives are currently limited running everything on a Raspberry Pi using an older version of Scratch.

So I've been messing around with the Extension capabilities in Scratch 2 and have a helper application that will allow you to manipulate Minecraft using a standalone Scratch 2 editor.

First a quick recap:

Scratch2 has a mechanism for interacting with external programs - the Scratch Extension Protocol.  Scratch speaks HTTP to a helper app running on the same machine which in turn can then interact with any other program. All the details are in that earlier blog post.

I've chosen to write the helper app in python which interacts with the Minecraft Pi Protocol. That gives flexibility to connect to either a local CraftBukkit server with the RaspberryJuice mod or to Minecraft Pi Edition. We have both setups and its been tested on both of them.


The code is available over on github and the README has the most up to date details about how to install and get started but I'll do a quick summary here also.

If you are comfortable with git then you know how to clone the repo. If not, then the easiest thing is to download the project as a zip file.

Download and install Scratch 2 offline editor.
  • Scratch and the helper app must be running on the same machine
Choose which Minecraft setup you wish to use. Either:
  • Minecraft Pi Edition or
  • CraftBukkit server with the RaspberryJuice mod

Getting Started

You will need to start the applications in the correct order.

1. Start Minecraft
  • This must be running before you start MCPI-Scratch because the application attempts to create a connection on startup and will fail if Minecraft is not running.
  • If you're using the Minecraft Pi Edition then you are done
  • If you are running the CraftBukkit server with the RaspberryJuice mod then you will need to use the Minecraft launcher to also start a client to connect to the server
  • The helper app needs a player in the world in order to orient itself and send position information back to Scratch
  • A useful tip is to use the t cmd to open the chat console in Minecraft and get control of the mouse so you can get to another application.
2. Start MCPI-Scratch. 
  • The application attempts to connect to localhost by default.
  • $ python ./mcpi-scratch.py
  • Use the -m host cmd-line arg to specify minecraft running on another machine
  • For instance, if you are connecting to Minecraft running on a Rasperry Pi (change the IP in the example for the IP address of your RPi)
  • $ python ./mcpi-scratch.py -m
3. Start Scratch. 
  • When the editor loads, shift-click the File menu and select Import experimental HTTP extension and select the file mcpi-scratch.s2e in the MCPI-Scratch install directory. This file specifies the new blocks to use in Scratch and the messages they send/receive with the MCPI-Scratch app.
  • You should now be able to select the More Blocks section in Scratch and see the Scratch Blocks that can be used in scripts

You should now be ready to write scripts to interact with Minecraft.


In the initial release I've only implemented blocks for the following commands
  • postToChat
  • getPlayerPos
  • setPlayerPos
  • setBlock: this includes a flag to set the block using absolute coordinates or relative to the player position
  • setBlocks
This is enough to get started. I'll add more blocks to represent the Minecraft Pi Protocol API if people are interested.

There is a good API reference at the StuffAboutCode blog and you can easily adapt the python examples from that blog to Scratch programs


The installation as a couple of sample scripts


The postToChat.sb2 script is a good way to test your set up.

Simply open that file from the scratchExamples directory, click on the script in the Scratch editor, and it should print a hello message in the minecraft chat console.

If this is working then you're ready to try the other blocks.


The simpleHouse.sb2 script creates a very simple square house using setBlocks block.

It also has some other statements to both clean up and test the other blocks.


An adaptation of the rainbow example that is popular in python api tutorials for minecraft
(it took a painfully long time to figure out that the sine function in python and Scratch operate on radians and degrees respectively - fun with debugging...)

That's it. Give it a whirl.

Thursday, September 4, 2014

Scratch, Minecraft and Raspberry Pi: how they fit together

My son has been learning programming with Scratch. But moving sprites around the screen will only keep his attention for so long, so we've been trying to figure out how to get Scratch programs to manipulate Minecraft. 

The short answer

The short answer is  "Yes, you can". The longer is answer is more involved and complicated so I thought I'd collect my notes for others that are trying to figure it out.

The longer answer

Can you get Scratch to manipulate Minecraft? 
Well, it depends on which version of Scratch you want to use and also which version of Minecraft you want to use. 

To understand all the combinations and consequences you need to understand a bit about how they interact.

Scratch doesn't interact with Minecraft directly. You need to use a Scratch extension to interact with an external program. That external program then provides the interaction between Scratch and Minecraft.

The complication is that the extension to Scratch and the API/MOD for Minecraft are dependent on the versions of the respective applications you want to use.

Lets start with the easiest alternative - do everything on a Raspberry Pi.

The good news is that it just works. You can go and grab a copy of all the necessary bits at scratch2mcpi

The installer has all the bits you need. Just fire it up, then copy and modify some of the example applications.

There is also a 2nd package you can get which provides a Scratch programming wrapper to Martin O'Hanlon's python library for Minecraft Turtle Graphics. Again, the whole lot can be downloaded as a single installer and you can see the example projects on the author's Scratch area.

To use scratch for minecraft turtle graphics you need to open one of the examples (or the template project), modify it as you want and save as a new project. (This limitation is due to the way Scratch on the RPi deals with external programs... As we shall see)

The not so good news is that these two packages are kind of limited and you need to use an older version of Scratch. To understand the limitations lets have a look at how it works.

The version of Scratch you get on the RPi is v1.4 but the current version of Scratch is now v2.0.

Unfortunately the latest standalone version of Scratch doesn't run on the RPi because its built on Adobe Air which doesn't run on the RPi architecture. So you're stuck with v1.4. 

The limitation is that the way Scratch handles interaction with external programs is pretty limited in v1.4 but has received a nice upgrade in v2.0. 

Scratch 1.4 uses its Remote Sensors Protocol to communicate with external applications. This provides low-level socket communication between Broadcast messages from Scratch 1.4 and the external app. There is a small python project, ScratchPy which talks that protocol. The scratch2mcpi project builds on scratchpy to speak to Minecraft.

However, Minecraft on the RPi is not the same as regular Minecraft. Minecraft Pi Edition is a cut-down version similar to the version of minecraft that you get on your phone or tablet (or ps3/xbox console). It provides an API (both python and java) which enables external programs to interact with the world using the Minecraft Pi Protocol. This protocol isn't available on regular minecraft, just the RPi version (* there is an exception which I'll come back to...).

So, the available software only lets you interact between Minecraft and Scratch programs on the RPi. 

But what if you want to use Scratch v2.0 or a version of Minecraft that is not the Pi Edition? At the moment you can't. The only way to use Scratch 2.0 is to run it somewhere other than a RPi (Mac, Win, or Linux(x86)).

Scratch2 has a new mechanism for interacting with external programs - the Scratch Extension Protocol. At this time you need to use a standalone (not web) version of Scratch though there are plans to make it possible to use the protocol from the webapp version of the scratch editor.

The extension protocol speaks HTTP to a helper app running on the same machine as Scratch. That helper app can then interact with any other program. This approach is more flexible than the Scratch v1.4 mechanism that works for scratch2mcpi.

There isn't (or I can't find) a Scratch 2 extension app that interacts with Minecraft. But here is how it should work:

Lets start with the helper app. When you define a helper app you have the opportunity to define your own blocks that can be used in Scratch scripts. When these blocks are used in the scripts Scratch sends http messages to the helper app - simple GET messages with the operation and data from the block passed along. The helper app can then pass these along to Minecraft. Its also possible to have blocks that listen to the helper app for incoming information. Scratch continuously polls the helper app for new information so you could read info from Minecraft and use it in a script (not super efficient but it works...)

This is all much nicer than the simple Broadcast messages that are available in Scratch v1.4.

As an example, here is a screenshot of a test helper app I've been toying with to test out communication with Minecraft. The "post to chat" block will send a message via the helper app to the Minecraft Pi edition API to print a message to the players chat window. There is also a block which polls the app to return the players position to use in a script.

Now we can cover the options this creates on the Minecraft side.
The helper app is just a small http server which listens for HTTP requests from Scratch and you can then do what you like. There are a number of alternatives for interacting with Minecraft.

  1. You could use the same mcpi api to communicate with Minecraft Pi Edition running on an RPi
  2. Or you could connect to a full Minecraft server that has a MOD to provide an API to external clients. For example, you could write a http server in Node and then use the node-minecraft npm or the ScriptCraft mod to integrate to Minecraft. 
  3. Finally you could actually use Minecraft Pi Protocol on a Minecraft server that isn't running on the RPi. The RaspberryJuice mod provides a slightly cut-down version of the Pi Protocol which allows you to integrate with the same API on both full servers and Pi Edition.

Next Steps

If you want to start using Scratch and Minecraft together, then you need to use one of the alternatives available on the Raspberry Pi. The next step is to see if I can get a Scratch2 helper app to expand those possibilities...