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# The Young Person's Guide to Programming in Minecraft
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## 2013/01/08 17:26
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## Draft
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### Introduction
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Minecraft is an open-ended 3D game where you can build and craft
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anything you like. Minecraft can be extended and enhanced using 'Mods'
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(short for 'modifications') - additional bits of code that are added
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to the Game. ScriptCraft is one such Mod - it lets you program in
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Javacript right within the game, making it possible to ...
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* Build using simple javascript statements.
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* Extend the game in other interesting ways - add new Items, change
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the game behaviour and create mini-games.
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Minecraft can be played in single-player or multi-player mode (with
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friends). Most people play Minecraft in Multi-player mode where
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players connect to a Minecraft Server on the internet or locally
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(running on the player's computer).
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![Cottages created using ScriptCraft in MineCraft][img_cr]
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### Installation
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CraftBukkit is a version of the Minecraft server software which allows
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easy addition of 'Mods' and extensions to Minecraft. ScriptCraft is a
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'Mod' for use with CraftBukkit. Adding Mods to Minecraft can be
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difficult but CraftBukkit makes it easy. Follow these steps to
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Install ScriptCraft on your computer...
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1. [Download and install CraftBukkit][dlbuk].
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2. [Download the ScriptCraft Mod][sc-plugin]. Then copy it to the
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`craftbukkit/plugins` folder you created in step 1.
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3. Start the CraftBukkit server.
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4. In the CraftBukkit command window type `op {your_username}` and hit
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enter, replacing {your_username} with your own minecraft
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username. This will give you `operator` access meaning you can perform
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more commands than are normally available in Minecraft.
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5. In the CraftBukkit command window type `js 1 + 1` and hit enter. You should see `> 2` .
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... Congratulations! You just installed your own Minecraft Server with
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the ScriptCraft Mod and are now ready to begin programming in Minecraft.
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Normally, Minecraft Mods are written in Java. This makes writing your
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own extension or game rules difficult because you must first learn Java.
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Java is different enough from Javascript. With the ScriptCraft plug-in
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installed, you don't have to learn Java, you can extend and customize
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Minecraft your way using Javascript. Javascript is easier to learn than
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Java but it's also more flexible and powerful and is used for creating
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interactive web sites and many other applications.
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### Learning Javascript
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To begin creating cool stuff in Minecraft using ScriptCraft, you don't
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*have* to know much JavaScript. ScriptCraft comes with lots of functions
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to help you create buildings of any size, and lets you experiment while
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you play. However, as you learn Javascript you will be able to create
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cooler stuff in Minecraft - not just buildings, you'll be able to add
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new rules and items to the game - even create mini-games for you and
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your friends. If you want to get started learning JavaScript, check out
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this [fun Javascript Tutorial][ce]. If you want to dive right in to
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ScriptCraft, read on...
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### First Steps
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If you don't already know Javascript, don't worry, you'll learn a little
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about Programming and Javascript along the way. You've set up a
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Minecraft server and are ready to connect ...
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1. Launch Minecraft (keep the Bukkit Command window open).
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2. Click 'Multi-Player'
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3. Click 'Add Server'
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4. Type any name you like in the name field then type `localhost` in the
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address field. `localhost` is a special internet address that points to
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your own computer.
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5. Click 'Join Server' to join the craftbukkit server.
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6. Once you've joined the game, press the `/` key located at the bottom
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right of your keyboard. A prompt will appear. Type the following then
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press enter: `js 1 + 1` The number 2 should be displayed.
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... Well Done! You've just confirmed you can run Javascript code from
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within the Minecraft Console.
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### Variables
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A variable is how you name something for the computer (and you the
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programmer) to remember. You create a new variable in Javascript using
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the `var` keyword...
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/js var location = "Blackrock Castle"
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... creates a new variable called `location` and stores the text
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`Blackrock Castle` in it. Now the computer has a new item in its memory
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called `location`. We can use that name like this...
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/js echo( location )
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... and the following is displayed...
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Blackrock Castle
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...You might be wondering where the `""` (called double-quotes) went.
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When telling the computer to store some text, you have to put `"`
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(that's the double-quote character - press Shift+2) at the start and end
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of the text. The computer doesn't store these quote characters, only the
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text between them. The computer will store the variables while the
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Minecraft Server is running. Repeat the last command you entered by
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pressing the `/` key then the UP arrow key on your keyboard, then
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pressing enter. You can repeat that statement as many times as you like
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and the computer will always display the same value. You can change the
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value like this...
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/js location = "Mahon Point"
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...notice this time I didn't use the `var` keyword. I didn't need to.
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The `var` keyword is only needed when you first create the variable. Now
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execute this command...
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/js echo( location )
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...and it displays...
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Mahon Point
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Variables can be created and changed easily in Javascript. Along with
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the variables you'll create in your in-game commands and scripts, there
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are handy variables created for you by ScriptCraft. One such variable is
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`self`, it contains information about the current player...
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/js echo ( self )
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... displays the following...
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CraftPlayer{name=walterh}
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... for me but the message displayed will be different for every player.
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### Functions
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ScriptCraft comes with a couple of extra functions not normally found in
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Javascript. These functions will help you build new structures and
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buildings which would otherwise take hours to build by hand. Before
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looking at the building functions let's look at the `echo()` function.
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`echo()` - as its name implies - will echo back at you whatever you
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tell it. For example, type ...
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/js echo('Hello')
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... and the game will display...
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Hello
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... type ...
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/js echo( 5 + 7 )
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... and the game will display...
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12
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... While you can now use Minecraft to help with Maths homework - I
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don't recommend it. Homework and Minecraft don't mix! The `echo()`
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function will display anything you tell it to - Text, Numbers and other types...
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/js echo( new Date() )
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... prints today's date. If the statement above looks confusing - don't
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worry - `new Date()` creates a new date object - I'll talk about objects
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later ...
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Tue Jan 08 2013 20:53:37 GMT-0000 (GMT)
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![Today's Date][img_echo_date]
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`echo()` is a very useful function but it is not part of the
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Javascript Language. You can't use it outside of Minecraft. There are
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many other functions in Javascript all of which you can also
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use in Minecraft. For example...
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/js Math.max( 6, 11 )
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... returns the larger of the 2 numbers you give it (max is short for
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maximum). While...
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/js Math.min( 6, 11 )
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... returns the smaller of the 2 numbers. That's another thing -
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functions can `return` stuff. You can store the result of a function
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(what it returns) in a variable like this...
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/js var biggest = Math.max( 6, 11 )
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... Now type...
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/js biggest
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... Not all Javascript functions return data but most do. As well as
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the functions provided to you by the Javascript Language and
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ScriptCraft, you can write your own functions like this...
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/js function whatTimeIsIt () { return new Date() }
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... Here you've created a new `function` called `whatTimeIsIt` and
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told the function it should return a new `Date` object every time it's
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called. You'll notice the above statement didn't actually do anything
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- it certainly didn't display the current time. That's because all
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you've done is is say what the function should do when it's called,
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you haven't called it yet. To call the function...
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/js whatTimeIsIt()
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... The current time is displayed. Congrats! You've just written your
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first Javascript function - you're well on your way to becoming a
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Minecraft Modder :-) There are many functions for working with Text,
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numbers and dates in Javascript...
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/js Math.random()
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... prints out a random number every time you call it. Try it! Then press
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the `/` key then the UP Arrow key to repeat the last statement in your
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in-game console. You'll see the number displayed is different each
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time. Think of Math.random() as a Dice with many many sides. You can
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rely on it to never return the same value twice.
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### Building stuff in Minecraft
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Now we get to the fun stuff - creating structures and buildings in
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Minecraft. Building by hand is fun but tedious when you want to build
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big - Towers, Castles and Fortresses. That's where ScriptCraft comes in.
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ScriptCraft comes with a couple of javascript functions that can be
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combined to build interesting things. Let's start small though to get a
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feel for how ScriptCraft's building functions work. The function you'll
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probably use most for building is called `box()` and - as its name
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implies - it is used to create cubes and cuboids of any size. A cube is
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a 3D shape whose sides are all the same length. A cuboid is a 3D shape
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whose width, height and length can differ.
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![3D Shapes][img_3d_shapes]
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You can create a Cube or a Cuboid in ScriptCraft using the `box()`
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function. You must tell the function what material you want the shape to
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be made of. For example, in the game, point the cross hairs at the
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ground, then type the following and hit enter...
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/js box("5")
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... This will change the targeted block to wood. What's happened here is
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the `box()` function has created a single new wooden block. The text
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`"5"` is taken by Minecraft to mean Wood. You can see many more
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materials and the number Minecraft uses for them by visiting the
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[Minecraft Data Values][mcdv] site.
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### Common Block Materials
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In Minecraft Programming, Materials aren't known by their name,
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instead numbers (sometimes 2 numbers) are used to indicate which
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material should be used. For example the number 2 is grass, 1 is
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cobblestone etc, while 5 is wood (oak). There are different types of
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wood so the text "5:1" means Spruce, "5:2" means Birch and "5:3" means
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Jungle wood. There are many different materials in the Minecraft world, the most
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commonly used materials for building are:
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* "4" - Cobblestone
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* "5" - Wooden Planks
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* "5:2" - Birch wood Planks (light wood)
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* "98" - Stone bricks
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* "45" - Red bricks
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* "68" - Doors
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* "102" - Glass panes (for windows)
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For reference, here is a chart of all of the blocks (not items) in the Minecraft
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world...
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![Minecraft Data Values][img_dv]
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### Dimensions
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`box()` can do more than just
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create single blocks - it can create cubes and cuboids of any
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size. Take a look at the following picture which shows how shapes are
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measured in 3D space. There are 3 dimensions (or sizes) to consider.
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1. Width
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2. Height
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3. Depth (or length) - not to be confused with how deep underground a
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mine-shaft can go. Think of Depth (or length if you prefer) as how far
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away you want something to extend.
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![Width, Height and Depth][img_whd]
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### More shapes
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* `box0( block, width, height, depth )` - creates an empty box (with the
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insides hollowed out - perfect for dwellings. `box0` will remove both
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the floor and ceiling too.
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* `cylinder( block, radius, height )` - creates cylinders, perfect for
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Chimneys.
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* `cylinder0( block, radius, height )` - creates empty cylinders -
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perfect for Towers. `cylinder0` will remove both the floor and
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ceiling too.
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* `prism( block, width, depth )` - creates a Prism - good for roofs.
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* `prism0( block, width, depth )` - creates an empty prism.
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### The Drone Object
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ScriptCraft is a Minecraft Mod that lets you execute Javascript code
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in the game. It also lets you write your own Mod in Javacript. One
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such mod that comes bundled with ScriptCraft is called the `Drone`
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mod. The `Drone` is an (invsible) object you create every time you
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execute any of the building or movement functions. When you execute...
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/js box(5,3,2,4)
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... a new `Drone` object is created and does the work of building on
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your behalf. Think of a `Drone` as something like a remote control
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plane that can move about freely and build things for you. Moving the
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Drone is easy...
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### Movement
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* `up( numberOfBlocks )` - moves the Drone Up. For example: `up()`
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will move the Drone 1 block up. You can tell it how many blocks to
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move if you want it to move more than one block.
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* `down( numberOfBlocks )` - moves the Drone Down.
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* `left( numberOfBlocks )` - moves the Drone Left.
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* `right( numberOfBlocs )` - moves the Drone Right.
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* `fwd( numberOfBlocs )` - moves the Drone Forward (away from the player).
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* `back( numberOfBlocs )` - moves the Drone Back (towards the player)
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* `turn( numberOfTurns )` - Turns the Drone Clock-wise (right). For example:
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`turn()` will make the Drone turn right 90 degrees. `turn(2)` will
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make the Drone turn twice so that it is facing in the opposite
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direction.
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#### Chaining - combining bulding and movement.
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You can make a Drone move around before and after building by
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*daisy-chaining* the building and movement functions together. In the
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game, point at the ground then type the following...
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/js up(1).box(5).fwd(3).box(5)
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A series of 2 boxes is created 3 blocks apart.
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![Two Boxes 3 blocks apart][img_2boxes]
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### Excercise - Build a simple dwelling
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OK. You know enough now about the `Drone` functions to be able to
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build a simple dwelling. The dwelling should be a hollow building with
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a sloped roof. *Don't worry about doors or windows for now*. The walls
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should be made of Cobblestone ("4") and the roof made of wood ("5"). You can use
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the following `Drone` functions to create a dwelling 7 blocks wide by
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3 blocks high by 6 blocks long with a wooden sloped roof. It's up
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to you to figure out how.
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* `up()`
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* `box0()`
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* `prism0()`
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Your dwelling should end up looking something like this...
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![Excercise Dwelling][img_ed]
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### Remembering where you started.
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Sometimes when you're building something big that requires lots of
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manoeuvering by your Drone, you need to leave breadcrumbs as you go so
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your `Drone` can return to where it started. Every new Drone has a
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`"start"` checkpoint that it can return to by executing
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`move("start")` ...
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/js box("5").up(3).left(4).box("1").turn(3).fwd(5).right().box("1").move("start")
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... A genius would have trouble figuring out how to get back
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to where they started. Fortunately, they don't have to - the
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`move("start")` function will take the Drone back to its starting
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point.
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* `chkpt( breadCrumb )` - Leaves a mark at your Drone's current
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location so it can return there later. Think of it as giving a name
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to the place where your Drone is located. `chkpt` is short for
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Check-Point - a place in a game where you usually save your
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progress.
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* `move( breadCrumb )` - Moves your Drone to a location you named
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using `chkpt()` . It brings your Drone back to the place where you
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saved it.
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Both `chkpt()` and `mark()` are useful for when you want to build
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complex things that require your Drone to move about a lot ( for
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example, Castles, mansions, palaces, etc).
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### Saving your work
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You can build cool things using the in-game command-prompt and the
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`/js` command but sooner or later you'll probably want to build
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something more complex and save your commands so you can run them
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again when you quit the game and start it up again.
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[Notepad++][np] Is a special text editor (like Notepad which comes
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installed on every Windows machine) that is well suited for writing
|
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code. If you don't already have it on your machine, you can [install
|
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Notepad++ here][np]. I recommend using NotePad++ rather than plain old
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Notepad because it understands Javascript.
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### Your First Minecraft Mod!
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So, You've learnt a little bit about Javascript and what the Drone()
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object can do, let's use that knowledge to create a Minecraft Mod!
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Once you've installed Notepad++, Launch it, create a new file and type the following...
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function greet(){
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echo("Hi " + self.name);
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}
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... then save the file in a new directory
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`craftbukkit/js-plugins/{your_name}` (replace {your_name} with your
|
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own name) and call the file `greet.js` (be sure to change the file-type
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option to '*.* All Files' when saving or NotePad++ will add a '.txt'
|
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extension to the filename. Now switch back to the Minecraft game and
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type...
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/reload
|
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... to reload all of the server plugins. Your mod has just been loaded. Try it out by typing this command...
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|
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/js greet()
|
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... it should display ...
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||||
|
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Hi {your-username-here}
|
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|
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... where {your-username-here} will be replaced with your own
|
||||
minecraft username. Congratulations - You've just written your very
|
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first Minecraft Mod! With ScriptCraft installed, writing Minecraft
|
||||
Mods is as simple as writing a new javascript function and saving it
|
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in a file in the js-plugins directory. This function will now be
|
||||
avaible every time you launch minecraft.
|
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|
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#### Parameters
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If you want to change the `greet()` function so that it displays a
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greeting other than "Hi " you can change the code in the `greet()`
|
||||
function, or better still, you can use *Parameters*. Parameters are
|
||||
values you provide to a function so that the function behaves
|
||||
differently each time it is called.
|
||||
|
||||
![greeting][img_greet]
|
||||
|
||||
Change the `greet()` function so that it looks like this...
|
||||
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||||
function greet( greeting ) {
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echo( greeting + self.name );
|
||||
}
|
||||
|
||||
... Save your greet.js file and issue the /reload command in
|
||||
minecraft. Now enter the following command in Minecraft...
|
||||
|
||||
greet("Hello ");
|
||||
|
||||
... Now try ...
|
||||
|
||||
greet("Dia Dhuit ");
|
||||
|
||||
... you should see the following messages in your chat window...
|
||||
|
||||
Hello {your name}
|
||||
Dia Dhuit {your name}
|
||||
|
||||
... Parameters let you provide different values to functions each time
|
||||
they're called. As you'll see later, Parameters are very useful when
|
||||
changing the behaviour of MineCraft.
|
||||
|
||||
### true or false
|
||||
|
||||
Try entering each of the following statements and make a note of the
|
||||
answers given by minecraft...
|
||||
|
||||
/js 1 < 2
|
||||
|
||||
/js 1 > 2
|
||||
|
||||
... the answer given by the first statement ( `1 < 2` ) should be
|
||||
`true` since 1 is less than 2. The `<` symbol - usually found near the
|
||||
bottom right of your keyboard - means test to see if something is less
|
||||
than another so `1 < 2` is a way of asking the computer "is 1 less
|
||||
than 2 ?". This is a silly example of course since we know 1 is less
|
||||
than 2 but when dealing with variables we might not know in advance
|
||||
what its value is or whether it's greater than (bigger) or less than
|
||||
(smaller) another number or value. The result of the 2nd statement (`1 > 2`)
|
||||
should be `false` since 1 is not greater than 2. Now try this...
|
||||
|
||||
/js 1 = 2
|
||||
|
||||
... The result won't be what you expected. You'll see an Error message
|
||||
- that's OK. What's happened here is I've tried to test to see if 1 is
|
||||
equal to 2 but I've made one of the most common mistakes even
|
||||
experienced programmers make. If you want to test to see if two things
|
||||
are the same, you use `==` that's two equals signs right next to each
|
||||
other. Let's try again...
|
||||
|
||||
/js 1 == 2
|
||||
|
||||
... this time you should get an answer `false` since 1 obviously isn't
|
||||
equal to 2. These are the different *operators* used when comparing
|
||||
things...
|
||||
|
||||
* `<` Is less than ?
|
||||
* `>` Is greater than ?
|
||||
* `==` Is equal to ?
|
||||
* `<=` Is less than or equal to ?
|
||||
* `>=` Is greather than or equal to ?
|
||||
* `!=` Is not equal to ?
|
||||
|
||||
... try comparing some more numbers yourself - say for example,
|
||||
compare the ages of your friends or siblings to your own age.
|
||||
|
||||
#### More fun with `true` or `false`
|
||||
You can find out if you can Fly in minecraft by typing the following statement...
|
||||
|
||||
/js self.allowFlight
|
||||
|
||||
... the result will be `true` or `false` depending on whether you can
|
||||
fly or not. You can turn on and off your ability to fly by setting
|
||||
your `allowFlight` property to `true` or `false`. Try it...
|
||||
|
||||
/js self.allowFlight = true
|
||||
|
||||
... Now you can fly! To turn off flight...
|
||||
|
||||
/js self.allowFlight = false
|
||||
|
||||
... and you come crashing down to earth. This is just one example of
|
||||
how `true` and `false` are used throughout ScriptCraft - these are
|
||||
called `boolean` values - named after [George Boole][boole], a 19th Century
|
||||
Maths Professor at University College Cork. There are plenty more
|
||||
examples of boolean values in Minecraft. You can find out if monsters
|
||||
are allowed in your minecraft world by typing the following
|
||||
statement...
|
||||
|
||||
/js self.location.world.allowMonsters
|
||||
|
||||
... The result of this statement will be either `false` (Phew!) or
|
||||
`true` (Yikes!) depending on how your server has been
|
||||
configured. However, typing the following statement doesn't work as
|
||||
expected...
|
||||
|
||||
/js self.location.world.allowMonsters = true
|
||||
|
||||
... This statement won't work as expected - it will give an Error
|
||||
message. This is because sometimes we can read variables but we can't
|
||||
change them the same way we read them (this is because of how
|
||||
Javascript, Java and the CraftBukkit API work together). To turn on or
|
||||
off the spawning of monsters, type the following...
|
||||
|
||||
/js self.location.world.setSpawnFlags(false, true)
|
||||
|
||||
... the `setSpawnFlags()` method takes 2 parameters, the first
|
||||
parameter says whether or not monsters can spawn, and the 2nd says
|
||||
whether or not Animals can spawn. (SIDENOTE: You may be wondering how
|
||||
to change other aspects of the Minecraft game - pretty much all
|
||||
aspects of the game can be changed. Changes are made using what are
|
||||
called `API` calls - these are calls to functions and methods in
|
||||
Minecraft - you can read more about these on the [CraftBukkit API
|
||||
Reference][cbapi].)
|
||||
|
||||
### ...and Again, and Again, and Again,...
|
||||
|
||||
One of the things Computers are really good at is
|
||||
repetition. Computers don't get tired or bored of doing the same thing
|
||||
over and over again. Loops are handy, if you want to run the same
|
||||
code over and over again, each time with a different value.
|
||||
|
||||
#### Counting to 100
|
||||
|
||||
At the in-game command prompt (hint: press 't') type the following then hit Enter...
|
||||
|
||||
/js for (var i = 1 ; i <= 100 ; i = i + 1) { echo( i ); }
|
||||
|
||||
... The above code will count from 1 to 100. The first thing you'll
|
||||
notice if you run the above code is how quickly the count
|
||||
happened. You're probably curious how long it would take to count to
|
||||
1000. Try it out for yourself. Change the above line of code so that
|
||||
it counts to 1000 instead of 100. If you're feeling adventurous, see
|
||||
how long it takes to count to ten thousand, one hundred thousand or even one million.
|
||||
|
||||
The `for` statement is useful when you want to repeat something over and over. It has 4 parts...
|
||||
|
||||
1. The initialiser: `var i = 1` - this happens once at the start of the loop.
|
||||
2. The test: `i <= 100` - this happens at the start of each run around the loop. If the test fails, then the loop ends.
|
||||
3. The increment: `i = i + 1` - this happens at the end of each run
|
||||
around the loop. If you didn't have a statement here, the loop might
|
||||
never finish. `i = i + 1` is often written as `i++` - it's shorter
|
||||
and does basically the same thing.
|
||||
4. The body - everything that appears between the `{` and `}` (opening and closing curly braces).
|
||||
|
||||
|
||||
`for` loops becomes very useful when you combine it with Arrays -
|
||||
remember, an Array is just a list of things, for example - the players
|
||||
connnected to a server, the worlds of a server and so on.
|
||||
|
||||
#### Saying "Hi!" to every player
|
||||
|
||||
At the in-game command prompt type the following then hit Enter...
|
||||
|
||||
/js for (var i = 0;i < server.onlinePlayers.length; i++){ server.onlinePlayers[i].sendMessage("Hi!"); }
|
||||
|
||||
... Lets look at these statements in more detail. We had to enter the
|
||||
statements on a single line at the in-game command prompt but the
|
||||
statements could be written like this...
|
||||
|
||||
var players = server.onlinePlayers;
|
||||
for (var i = 0; i < players.length; i++) {
|
||||
var player = players[i];
|
||||
player.sendMessage("Hi!");
|
||||
}
|
||||
|
||||
... On the first line, a new variable `players` is created from the
|
||||
server object's onlinePlayers property. `players` is more concise and
|
||||
easier to type than the long-winded `server.onlinePlayers`. On the
|
||||
second line, the for loop is declared, a counter variable `i` is set
|
||||
to 0 (zero - arrays in javascript start at 0 not 1) and each time
|
||||
around the loop is tested to see if it's less than the number of
|
||||
players online. At the end of each run around the loop the `i`
|
||||
variable is incremented (increased by 1) so that the next player can
|
||||
be messaged. Inside the body of the for loop (everything between the
|
||||
opening `{` and closing `}` curly braces) the `players[i]` expression
|
||||
refers to the player in the players array at position[i]. Imagine
|
||||
there are 4 players online on a minecraft server, the `players` array
|
||||
might look like this...
|
||||
|
||||
* players[0] = 'CrafterJohn'
|
||||
* players[1] = 'MinerPaul'
|
||||
* players[2] = 'ExplorerRingo'
|
||||
* players[3] = 'TraderGeorge'
|
||||
|
||||
... in this case `players.length` will be 4 (since there are 4 online
|
||||
players), the for-loop will go around 4 times starting from position 0
|
||||
and going all the way up to position 3, sending a message to each of
|
||||
the players in the array. It's time for a new scriptcraft
|
||||
function. Open the `hi.js` file you created earlier (using NotePad++ ,
|
||||
TextWrangler or your editor of choice) and add the following code at
|
||||
the bottom of the file...
|
||||
|
||||
function hiAll(){
|
||||
var players = server.onlinePlayers;
|
||||
for (var i = 0; i < players.length; i++) {
|
||||
var player = players[i];
|
||||
player.sendMessage("Hi!");
|
||||
}
|
||||
}
|
||||
|
||||
... save the file, at the in-game command prompt type `reload` and
|
||||
then type `/js hiAll()`. This will send the message `Hi!` to all of
|
||||
the players connected to your server. You've done this using a `for`
|
||||
loop and arrays. Arrays and `for` loops are used heavily in all types
|
||||
of software, in fact there probably isn't any software that doesn't
|
||||
use `for` loops and Arrays to get things done.
|
||||
|
||||
#### While Loops
|
||||
|
||||
Another way to repeat things over and over is to use a `while`
|
||||
loop. The following `while` loop counts to 100...
|
||||
|
||||
var i = 1;
|
||||
while (i <= 100){
|
||||
echo( i );
|
||||
i = i + 1;
|
||||
}
|
||||
|
||||
A `while` loop will repeat until its condition is `false` - the
|
||||
condition in the above example is `i <= 100` so while i is less than
|
||||
or equal to 100 the code within the `while` block (everything between
|
||||
the starting `{` and ending `}` curly braces) will run. It's important
|
||||
that you change the variable being tested in a while loop, otherwise
|
||||
the while loop will never it - it will run forever. Try running the
|
||||
following code...
|
||||
|
||||
/js var i = 1; while (i <= 100){ echo( i ); }
|
||||
|
||||
The code above will contine printing out the number 1 until the end of
|
||||
time (or until you unplug your computer). That's because the `i`
|
||||
variable is never incremented (remember - incrementing just means
|
||||
adding 1 to it) so i will always be 1 and never changes meaning the
|
||||
loop goes on forever. Again - this is a mistake even experienced programmers sometimes make.
|
||||
|
||||
Just like `for` loops, `while` loops can be also be used to loop
|
||||
through arrays. The following loop prints out all of the players on
|
||||
the server...
|
||||
|
||||
var players = server.onlinePlayers;
|
||||
var i = 0;
|
||||
while ( i < players.length ) {
|
||||
echo( players[i] );
|
||||
i = i + 1;
|
||||
}
|
||||
|
||||
... whether you chose to use a `for` loop or a `while` loop is largely
|
||||
a matter of personal taste, `for` loops are more commonly used with
|
||||
Arrays but as you see from the example above, `while` loops can also
|
||||
loop over Arrays.
|
||||
|
||||
#### `utils.foreach()` - Yet another way to process Arrays
|
||||
|
||||
Both the `for` statement and `while` statement are standard commonly
|
||||
used javascript statements used for looping. ScriptCraft also comes
|
||||
with a special function for looping called `utils.foreach()`.
|
||||
utils.foreach() is a convenience function, you don't have to use it if
|
||||
you prefer the syntax of javascript's `for` and `while`
|
||||
loops. utils.foreach() takes two parameters...
|
||||
|
||||
1. An array
|
||||
2. A function which will be called for each item in the array.
|
||||
|
||||
...that's right, you can pass functions as parameters in javascript!
|
||||
Let's see it in action, the following code will `echo()` (print) the
|
||||
name of each online player...
|
||||
|
||||
utils.foreach( server.onlinePlayers, echo );
|
||||
|
||||
... in the above example, the list of online players is processed one
|
||||
at a time and each item (player) is passed to the `echo`
|
||||
function. Note here that I used `echo` not `echo()`. The round braces
|
||||
() are used to call the function. If I want to pass the function as a
|
||||
parameter, I just use the function name without the round braces. The
|
||||
above example uses a named function which already exists ( `echo` ),
|
||||
you can also create new functions on-the-fly and pass them to the
|
||||
utils.foreach() function...
|
||||
|
||||
/*
|
||||
give every player the ability to fly.
|
||||
*/
|
||||
utils.foreach( server.onlinePlayers,
|
||||
function (player) {
|
||||
player.setAllowFlight(true);
|
||||
}
|
||||
);
|
||||
|
||||
Loops are a key part of programming in any language. Javascript
|
||||
provides `for` and `while` statements for looping and many javascript
|
||||
libraries also provide their own custom looping functions. You should
|
||||
use what you feel most comfortable with.
|
||||
|
||||
TODO
|
||||
### Making Decisions
|
||||
TODO
|
||||
|
||||
#### if then else
|
||||
TODO
|
||||
|
||||
[buk]: http://wiki.bukkit.org/Setting_up_a_server
|
||||
[dlbuk]: http://dl.bukkit.org/
|
||||
[sc-plugin]: files/scriptcraft/
|
||||
[ce]: http://www.codecademy.com/
|
||||
[mcdv]: http://www.minecraftwiki.net/wiki/Data_values
|
||||
[np]: http://notepad-plus-plus.org/
|
||||
[cbapi]: http://jd.bukkit.org/beta/apidocs/
|
||||
[boole]: http://en.wikipedia.org/wiki/George_Boole
|
||||
|
||||
[img_echo_date]: img/ypgpm_echo_date.png
|
||||
[img_3d_shapes]: img/ypgpm_3dshapes.jpg
|
||||
[img_whd]: img/ypgpm_whd.jpg
|
||||
[img_dv]: img/ypgpm_datavalues.png
|
||||
[img_ed]: img/ypgpm_ex_dwell.png
|
||||
[img_2boxes]: img/ypgpm_2boxes.png
|
||||
[img_cr]: img/ypgpm_mc_cr.png
|
||||
[img_greet]: img/ypgpm_greet.png
|
||||
|
||||
## Categories
|
||||
Minecraft, Programming, ScriptCraft
|
Reference in a new issue