ModderDojo Topic 7: Planning and Building a Complex Structure Mod in Minecraft


This topic continues from ModderDojo Topic 6: JavaScript Operators and ScriptCraftJS Drone Functions.

Sharing a Server:

In previous weeks before we stopped for Christmas, some people struggled to make progress through no fault of their own: they were hampered by CanaryMod crashing a lot on some people’s computers.

To work around this, everyone can connect to my computer as the Minecraft server, and I will also create a shared folder on the computer so you can drop your mods into it.

Please review these notes from several weeks ago: Topic 2: Connecting to Each Other’s Servers.

This Week’s Challenge:

This week (and for the next week or two), your challenge is build a substantial mod in ScriptCraft that, when you run it, will create an impressive-looking structure!

A key step to success here is planning and design: as I have said before, a  programmer’s most important tools are paper and pencils, for figuring out what you want to create before you write code for it.

You should review the following:




ModderDojo Athenry Topic 6: JavaScript Operators and ScriptCraftJS Drone Functions


Operators in any programming language are used when you want to calculate something new: they operate on values. variables, or expressions to produce a new value.

Since ScriptCraft is built on the JavaScript langauge, it uses standard JavaScript operators. As it happens, many other programming languages (including C, C++ and Java) use the same operators or very similar ones.

JavaScript Operators

Drone Functions:

As we have seen before, in ScriptCraft you use a drone to do your building for you. The drone has functions that are part of it.

Here are some of the main drone functions that are useful when building your mods:

ScriptCraft Drone Functions

You can find lots more about these and other functions in the ScriptCraft API Reference:

Example: Build a Pyramid

This example is based on a very nice program writing by Ruaidhri from Coderdojo Athenry last year, updated slightly because some ScriptCraft commands have changed in the meantime.

// Copyright Ruaidhri from ModderDojo Athenry,
// slightly updated by Michael and Alex.
// Builds a pyramid with entrance and lights inside.

exports.pyramid = function()
echo('making a pyramid');
var d = new Drone(self); // 'self' means start drone beside me


var size=31;

// Make the walls
while (size > 0)

// Entrance

// Lights inside
var t = 0;
while (t<4)
t = t + 1;

ModderDojo Topic 4: Moving from Scratch to JavaScript


Note: some individual topics are short: we got most of the way through the first 3 in our taster session. See this post:

JavaScript is a well-established programming language, mainly used in web development. ScriptCraft is a Minecraft mod that allows you to write JavaScript code for building structures in Minecraft and writing new Minecraft mods. (So it’s a mod for creating other mods.)

Steps 1-3: Install ScriptCraft, Learn how to Connect to a Server, and Create a First Mod

We covered these steps in the first two weeks:

  1. Getting Started with ScriptCraft and JavaScript
  2. How to Connect to Each Other’s Servers
  3. Creating our First ScriptCraft Mods

To try out ScriptCraft, look back at the introductory posts here:

Step 4: Comparing JavaScript to Scratch

Some people criticise Scratch as being “childish”, but I don’t agree. While it is designed so that even 8 year olds can use it, it is still has all of the key features of ‘adult’ programming languages, as listed in the image at the top of this post.

(Technically, any programming language with variables, decision and loops is Turing Complete.)

This means that, if you already know how to write a Scratch programs that use these features, you will be able to apply that knowledge to any other language, such as JavaScript. The syntax of JavaScript is different, but it uses the same computational thinking.





  • Even though they have basic ideas in common, every programming language has its own specific commands that relate to its purpose: Scratch is focused on 2D games and animations, while ScriptCraft is focused on operating inside Minecraft, and JavaScript generally is used for interactive websites.
  • the echo command that features in these slides is not a standard JavaScript command, it is just used in ScriptCraft to display things on your screen in Minecraft.  Everything else is standard JavaScript.

Minecraft Modding Taster Session – Week 1


This season at CoderDojo Athenry, the advanced groups are all starting with taster sessions of the various topics we will cover.

In Week 1, the topic we are covering is Minecraft Modding using JavaScript.

Here are the notes:

  1. Getting Started with ScriptCraft and JavaScript
  2. How to Connect to Each Other’s Servers
  3. Creating our First ScriptCraft Mods

Coming up next week: in introduction to Raspberry Pi and Electronics

Summer Project- Athenry Castle in Minecraft


A lot of you had a chance to see the Minecraft Project that some of our Ninjas worked on over the Summer weeks in Athenry Castle a couple of weeks ago.

As part of heritage week, Ruaidhrí, Eiblinn, Eoin, Darragh and Luke built a 13th century replica of Athenry Castle in Minecraft.

Athenry Castle Minecrafters

I promised a link to download the World and the Mods used, so here is a link to Dropbox where you will find all the files.

See you all Saturday! (September 19th)


ModderDojo Countries Mod: How to Upload Files to GitHub

Thanks to Ninja James for these excellent and detailed instructions, and for setting up a GitHub repository for us to share our code when working on the Countries Mod.

How to stage files to a repository.

WARNING: Please upload your mod in a folder with your topic.

Step 1. Create a folder with the name of the topic your doing for the country mod.

Step 2. Install git =, keep pressing next as we will not need any changes to the installation.

Step 3. For example I have my folder on my desktop, so I right click my desktop and click “GIT GUI”. A box should pop up.

Step 4. Click “Clone existing repository”, The source location is the git repo its self, so in the box put this :

Now the Target directory is your folder, click browse and find your folder, for example mine would be on the desktop, its called biomes, select your folder.

Example : My target dir is C:/Users/coderdojo/Desktop/Test Git/Biomes.

Click Clone, This may take a couple of minutes depending on your internet speed.git

Step 5. A window should pop up, looks like this ——->


For this example im going to put 2 files in my CLONED FOLDER!. WARNING: Put your your forge files in a folder with your name. Then once your have done that click [RESCAN], your forge files should pop up. Then click [STAGE CHANGED] and click [YES], all your files should move into the [GREEN AREA]. In the box that says [COMMIT MESSAGE], put a message that is related to your Topic in the mod.

Step 6. Click [COMMIT] after you have written your message.

Your files in the [GREEN AREA] should not be there.

Step 7. Now click [PUSH], a box should pop up click push again!

It should ask for my details… Username = FrictionlessPortals

My Password, you will have to ask me through skype, Due to security reasons.

If it says [SUCESS] you’ve sucessfully put your files on github!

If you want more help add me on skype as hypixel.jamertheredstonegamer.

ScriptCraft – An Exploding Chickens Mod

A few weeks ago we were lucky enough to have a visit from YouTuber and professional Minecraft modder (for the HyPixel server) codename_B (a.k.a. VladToBeHere, a.k.a. Ben).

Ben (left) addresses CoderDojo Athenry. ,Also pictured: Auburn, Ben's girlfriend, and our own Michael Madden

Ben (left) addresses CoderDojo Athenry. Also pictured: Auburn, Ben’s girlfriend, and our own Michael Madden

Ben is an extraordinary programmer who just breathes code. On his YouTube channel he regularly creates a complete MineCraft plugin in only sixty seconds!

After addressing the entire Dojo, Ben showed our modder group and a few other more advanced coders how to make a quick plugin which causes chickens to explode when a player kills them.

Ben’s mod was written in Java and used the Bukkit API to interface with MineCraft.

Porting the Plugin to ScriptCraft

ScriptCraft is built on top of Bukkit. Because of this, almost all the Bukkit API is available for use in ScriptCraft. I believe there are a few Java-only bits in Bukkit, but I haven’t encountered them.

I realized that, in theory at least, it should be possible to port Ben’s plugin to ScriptCraft. In practice, it proved to be more straightforward than I could have hoped. If you don’t already know Java, ScriptCraft is a great place to start if you want to create MineCraft mods.

ScriptCraft and Bukkit References

When writing something new, you’ll need to be able to look-up things that you are not familiar with. Two references I used for this script, apart from Ben’s original code, were:

  1. ScriptCraft API
  2. Bukkit API (from Spigot)

Browsing these resources is also a good way to see what can be done and to thereby generate new ideas.

Anatomy of the Plugin

The plugin is composed of four parts:

  1. Two variables to represent the Bukkit types which represent chickens and players respectively
  2. A loading function which we will run when the plugin loads
  3. An event handling function which will be called whenever one entity damages another
  4. A call to the loading function, at the bottom of the file, to make it run as soon as ScriptCraft reads it

Let’s talk about each of these parts in turn.

Variables to Represent Bukkit Types

After a require(‘events’) line (to make sure we can reference the events object), there are two lines as follows:

var bkPlayer = org.bukkit.entity.Player;
var bkChicken = org.bukkit.entity.Chicken;

These are ‘types’ which represent an entity of type Player and an entity of type Chicken respectively. We’ll use them in a bit to determine, when we’re told one entity has damaged another, that it was a Player entity causing damage to a Chicken entity.

The Loading Function

The next part of the script is the loading function. It’s short and really only does two things:

  1. Announces that the plugin has loaded by printing a message to the console
  2. Tells Bukkit that we’d like a function of our own to be run each time that a particular event occurs. In this case it’s the event that fires every time one entity damages another.

Here’s the code:

// The function which will run when we load this module
var _loadMod = function()
  // Announce ourselves to the console
  console.log("Exploding Chickens: [Loading ScriptCraft Mod]");

  // Tie our code into the event that fires every time one entity damages another

We’re passing events.entityDamageByEntity() the name of our function we’d like to have run. That function (_entityDamageByEntity) and this function (_loadMod) both have underscores at the start of their names. It’s a JavaScript convention which indicates that we’re never be calling these functions by name from outside this file. They’re private or internal functions.

The Event Handling Function

This is the most complex part of the module, but not terribly so. Here’s the code:

// The code that we want to run each time one entity damages another
var _entityDamageByEntity = function(event)
  // Find out, from the event, who's getting damaged and who did the damage
  var damagedEntity = event.getEntity();
  var damagingEntity = event.getDamager();
  // If it's a chicken getting damaged by a player, game on...
  if (damagedEntity instanceof bkChicken && damagingEntity instanceof bkPlayer)
    // Announce in the console that we've detected a player damaging a chicken
    console.log("Exploding Chickens: [A player damaged a chicken]");
    // Schedule a task to run in five seconds.
    server.scheduler.scheduleSyncDelayedTask(__plugin, function() 
      // Check to see if the damage brings the chicken's health
      // down to, or below, zero. If so, it's dead...
      if (damagedEntity.getHealth() - event.getDamage() <= 0)
        // Get the chicken's location
        var loc = damagedEntity.location;

        // Create an explosion at the chicken's location. 
        // A big one..., 10.0);
    }, 20 * 5);

What does it do?

  1. Gets the entity that caused the damage and the entity that was damaged and check to see if they’re a player and a chicken respectively
  2. If they are a player and a chicken, Schedule a task to run in aprox. five seconds. This task can result in an explosion, so it’s nice to have a little “getting away” time.
  3. When our task runs, see if the amount of damage inflicted was enough to bring the chicken’s health down to zero (or below) and if it was, make a massive explosion where the chicken was.

The Bukkit function scheduler.scheduleSyncDelayedTask() needs a reference to the plugin which is asking for the task to be scheduled. In this case it’s ScriptCraft and there is a special automatic variable, __plugin, which ScriptCraft can use to refer to itself when it needs to.

And that’s pretty much it!

Getting it All Going

The last line in the file is just a call to our _loadMod() function. This will get run immediately by ScriptCraft when it read it, setting the mod into action:

// Run this script as soon as the file's loaded


Here’s the mod in action:

Sorry chickens*.

The script file can be downloaded from here. I hope this inspires you to create your own server mods using ScriptCraft.



* The author is a vegetarian and general soft touch who even tends to feel bad about exploding virtual animals…


ModderDojo Countries Mod Week 1: Making a start on a large group project mod


In the ModderDojo group, we have started to work on a large group project to develop a mod with different aspects to it.

Following on from brainstorming session in recent weeks, we have decided to build a Countries Mod: there will be multiple different countries, each with different terrains, buildings and items such as food, clothing and weapons. We hope to have portals and an airplane to move between countries. Some parts will be implemented in Java and others in JavaScript. It should be exciting to work together and produce something impressive!

To plan the project and track our progress, we will use a project dashboard as shown above: items planned but not started are in white; items underway are in yellow; items completed are in green; any that we decide to drop will be in grey.

The young people of the ModderDojo group are also arranging a code repository and communications using skype between team members, and are planning to set up a server with  the mod on it and prepare one or more a mod review videos as it gets developed.

I am greatly impressed with the group’s ideas, enthusiasm, and capabilities!

Below are my slides from when we kicked off the project, the first couple of which referred back to when we started the stream in September.



Automatically Generated ScriptCraft to Draw An Image


Having done tagger.js, I thought “wouldn’t it be nice not to have to specify the design by hand?”

I started thinking about how cool it would be to have a way to take an image file and use that to define the design that tagger.js was going to spray.

The first thing that I determined was that, as far as I can see, there isn’t any built-in support for the various image formats (GIF, JPEG, PNG, etc.) in ScriptCraft. OK, so what then? Well, web browsers are great at handling images in all kinds of different formats. The HTML5 canvas element is good for playing around with bitmaps and on top of all that, JavaScript is supported for the coding part!

So, with very little previous experience and plenty of Googling, I decided to make a web page which would allow the user to enter a file’s name, press a few buttons and a ScriptCraft script would appear, as if by magic. Development was pretty smooth, baring one significant road-bump which I’ll describe. I’m not going to go into details about how the HTML file was made, but it should be clear enough if you want to read it. I will however describe the process of colour mapping.

HTML5 and a Tale of Tainted Canvases

Say what? An odd problem I quickly hit was that I couldn’t just specify an image file from just anywhere (using HTTP:). In fact, even worse, when I directly loaded my HTML page in my browser (using FILE:), I couldn’t even load up an image file which was in the same directory as the HTML page.

More Googling followed. Turns out that the browser was trying to protect me from “cross-origin data”, which is a security risk. Luckily there was an easy solution. I downloaded a small web server application and used that to serve my HTML page, which eliminated the issue. The web-server I chose was Mongoose, because it’s a single application, light and fast, but you can use another web-server if you prefer.

Testing in Chrome

I used Google Chrome as my browser for developing and testing this webpage. Chrome has a JavaScript console, which greatly simplifies debugging scripts. It can be found from the menu to the right of the address bar, at More Tools > JavaScript Console. Among other features, It allows you to set breakpoints and watch the value of variables as the script executes. It will also show you errors in your code, where it finds them.

Colour Mapping

The most important part of this script is mapping the colour of each pixel in the original image to an equivalent block in MineCraft. For this example, I have restricted myself to the 16 wool colours. So, for every pixel in the original image, I have to choose the MineCraft wool block that’s the closest in colour.

MineCraft Wool Palette

MineCraft Wool Palette

The colours we are going to match against are above. If you’re curious, here’s how I generated this MineCraft palette, I laid all 16 MineCraft wool blocks in order, from white to black, and then took a screenshot. This screenshot was, of course, influenced by the lighting in MineCraft at the time I took the screenshot and each block had the wool texture applied to (i.e. they weren’t just one flat colour). I did some further image manipulation to improve the palette. I applied a strong blur effect to downplay the effect of the texture and then I used my image editors Histogram Stretch functionality to make sure that the whitest and blackest colours were pushed towards true white and true black. Finally I sampled one point on each block and that became my representative colour.

These colours, in RGB format, became an array in the JavaScript inside my webpage:

var paletteRGB = [[255, 255, 255], 
                  [222, 146, 79],
                  [177, 98, 186],
                  [115, 152, 197],
                  [178, 185, 60],
                  [76, 179, 67],
                  [213, 151, 159],
                  [51, 51, 51],
                  [164, 180, 170],
                  [44, 109, 122],
                  [116, 68, 167],
                  [30, 50, 113],
                  [59, 43, 14],
                  [35, 62, 15],
                  [132, 53, 40],
                  [0, 0, 0]];

RGB (Red/Green/Blue) is a common way to represent colour. Its three numerical values, each of which can range between 0 and 255, represent the relative strengths of the Red, Green and Blue channels. We can think of this as a co-ordinate system, with the R, G and B values as axes.

RGB Colour Space Imagined as a Cube

Description: RGB Colour Space Imagined as a Cube. Author: SharkD. Source:

The image above shows what this looks like. Pure white is on the corner nearest to us. The opposite corner, which we can’t see, is pure black. Colours aren’t just on the surface of this cube either, If we were to cut through it at any plane, we would see all the colours on the inside as well.

Therefore, the difference between two colours can be thought of as the distance between two points in RGB space. It’s Pythagoras’ Theorem again, as we saw in the rainbowk.js project, but in 3D. All we have to do is take the colour of each pixel in the input image, calculate how far is is from each MineCraft wool colour and pick the wool colour which is the closest in distance; that will be the most similar.

Easy right? Well, almost. Turns out, our eyes don’t quite work that way. We’re not as sensitive to changes in some colours as we are in others. We’re most sensitive to changes in shades of blue, and least sensitive to changes in shades of green. If asked to pick by eye, we might make a different choice for the “closest” colour than then one given by mathematics alone. Luckily, scientists have worked out factors which account for this. If you look in the final script you’ll see that there are factors which are used to weight (make more important) the difference in some colours than others. You don’t need to understand how these numbers were arrived at, just understand why they are there.

// It's Pythagoras' theorem again, but weighted.
function weightedDistanceSquaredRgb(r0, g0, b0, r1, g1, b1)
  // These weights are used to convert RGB -> YUV and are useful here
  // to enhance the perceived closeness of two colours
  var weightR = 0.299;
  var weightG = 0.587;
  var weightB = 0.114;
  // Distance between two points in space: sqrt(x^2 + y^2 + z^2)
  return distanceSquared(r0 * weightR, g0 * weightG, b0 * weightB,
                         r1 * weightR, g1 * weightG, b1 * weightB);

By the way, notice that we’re returning the distance squared here. It’s a common programming shortcut if we’re just checking for the nearest thing. If something has the closest distance, it will also have the smallest distance squared. Doing the square root calculation isn’t worth it – so we don’t.

Downloading and Running

The ZIP file containing this HTML file (image_process.html) and a few sample images can be downloaded from here. Remember, you’ll have to use a web-server to view this webpage and have it be able to process the images. Feel free to try your own images, just copy them into the same directory as the HTML file first, and remember to keep them small as every pixel becomes a MineCraft block. My sample images are all around 40px wide.

What’s Next?

Next week we’ll extend this little application to add optional transparency to the output and merge it with tagger.js so our image is sprayed onto the environment.