Added section on event-driven programming and lookup tables to young persons' guide
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# The Young Person's Guide to Programming in Minecraft
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## Table of Contents
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* [Introduction](#introduction)
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* [Installation](#installation)
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* [Learning Javascript](#learning-javascript)
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* [First Steps](#first-steps)
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* [Variables](#variables)
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* [Functions](#functions)
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* [Building stuff in Minecraft](#building-stuff-in-minecraft)
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* [Common Block Materials](#common-block-materials)
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* [Dimensions](#dimensions)
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* [More Shapes](#more-shapes)
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* [The Drone Object](#the-drone-object)
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* [Movement](#movement)
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* [Chaining - Combining Building and Movement](#chaining---combining-building-and-movement)
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* [Exercise - Build a simple dwelling](#exercise---build-a-simple-dwelling)
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* [Remembering where you started](#remembering-where-you-started)
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* [Saving your work](#saving-your-work)
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* [Your first Minecraft Mod!](#your-first-minecraft-mod)
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* [Parameters](#parameters)
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* [true or false](#true-or-false)
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* [More fun with `true` or `false`](#more-fun-with-true-or-false)
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* [...and Again, and Again, and Again,...](#and-again-and-again-and-again)
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* [Counting to 100](#counting-to-100)
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* [Saying "Hi!" to every player](#saying-hi-to-every-player)
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* [While Loops](#while-loops)
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* [`utils.foreach()` - Yet another way to process Arrays](#utilsforeach---yet-another-way-to-process-arrays)
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* [Exercise](#exercise)
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* [Putting `for` loops to use - Building a Skyscraper](#putting-for-loops-to-use---building-a-skyscraper)
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* [Making Decisions](#making-decisions)
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* [Event-Driven programming](#event-driven-programming)
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* [Stop listening to events](#stop-listening-to-events)
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* [Keeping Score - Lookup tables in Javascript](#keeping-score---lookup-tables-in-javascript)
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* [Next Steps](#next-steps)
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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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@ -98,7 +133,7 @@ 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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/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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@ -110,8 +145,8 @@ called `location`. We can use that name like this...
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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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...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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@ -121,7 +156,7 @@ 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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/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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@ -135,7 +170,7 @@ execute this command...
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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 "free" variables created for you by ScriptCraft. One such variable is
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are handy *free* variables created for you by ScriptCraft. One such variable is
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`self`, it contains information about the current player (that's you)...
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/js echo ( self )
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@ -258,7 +293,7 @@ ground, then type the following and hit enter...
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... This will change the targeted block to wood. What's happened here
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is the `box()` function has created a single new wooden
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block. `blocks` is another one of those "free" variables you get in
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block. `blocks` is another one of those *free* variables you get in
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ScriptCraft, you can see a list of block materials by typing ...
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/js blocks.
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@ -274,21 +309,21 @@ 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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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 or `blocks.cobblestone`
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* "5" - Wooden Planks or `blocks.oak`
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* "5:2" - Birch wood Planks (light wood) or `blocks.birch`
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* "98" - Stone bricks or `blocks.brick.stone`
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* "45" - Red bricks or `blocks.brick.red`
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* "68" - Sign or `blocks.sign`
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* "102" - Glass panes (for windows) or `blocks.glass_pane`
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* '4' - Cobblestone or `blocks.cobblestone`
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* '5' - Wooden Planks or `blocks.oak`
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* '5:2' - Birch wood Planks (light wood) or `blocks.birch`
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* '98' - Stone bricks or `blocks.brick.stone`
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* '45' - Red bricks or `blocks.brick.red`
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* '68' - Sign or `blocks.sign`
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* '102' - Glass panes (for windows) or `blocks.glass_pane`
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You can create a single wooden block using the numeric values or the `blocks` variable. For example...
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/js box( "5" )
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/js box( '5' )
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... and ...
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@ -375,7 +410,7 @@ A series of 2 boxes is created 3 blocks apart.
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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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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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@ -393,14 +428,14 @@ Your dwelling should end up looking something like this...
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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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`'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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/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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`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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@ -440,7 +475,7 @@ 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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exports.greet = function(player){
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player.sendMessage("Hi " + player.name);
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player.sendMessage('Hi ' + player.name);
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}
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... then save the file in a new directory
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@ -455,7 +490,7 @@ type...
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... to reload all of the server plugins. Your mod has just been
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loaded. Try it out by typing this command...
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/js greet()
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/js greet(self)
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... it should display ...
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@ -473,7 +508,7 @@ when creating more complex mods.
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The `exports` variable is a special variable you can use in your mod
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to provide functions, objects and variables for others to use. If you
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want to provide something for other programmers to use, you should
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"export" it using the special `exports` variable. The syntax is
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*export* it using the special `exports` variable. The syntax is
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straightforward and you can use the same `exports` variable to export
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one or more functions, objects or variables. For example...
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@ -490,9 +525,9 @@ one or more functions, objects or variables. For example...
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and `snowball()` which can be invoked from the in-game prompt like
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this `/js egg(self)` or `/js snowball(self)`.
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### Parameters
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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()`
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greeting other than 'Hi ' you can change the code in the `greet()`
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function, or better still, you can use *Parameters*. Parameters are
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values you provide to a function so that the function behaves
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differently each time it is called.
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@ -508,11 +543,11 @@ Change the `greet()` function so that it looks like this...
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... Save your greet.js file and issue the `/js refresh()` command in
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minecraft. Now enter the following command in Minecraft...
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greet("Hello ",self);
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greet('Hello ',self);
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... Now try ...
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greet("Dia Dhuit ",self);
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greet('Dia Dhuit ',self);
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... you should see the following messages in your chat window...
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@ -523,7 +558,7 @@ minecraft. Now enter the following command in Minecraft...
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they're called. As you'll see later, Parameters are very useful when
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changing the behaviour of MineCraft.
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### true or false
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## true or false
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Try entering each of the following statements and make a note of the
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answers given by minecraft...
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@ -567,7 +602,7 @@ things...
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... try comparing some more numbers yourself - say for example,
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compare the ages of your friends or siblings to your own age.
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### More fun with `true` or `false`
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## More fun with `true` or `false`
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You can find out if you can Fly in minecraft by typing the following statement...
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/js self.allowFlight
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@ -616,14 +651,14 @@ called `API` calls - these are calls to functions and methods in
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Minecraft - you can read more about these on the [CraftBukkit API
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Reference][cbapi].)
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### ...and Again, and Again, and Again,...
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## ...and Again, and Again, and Again,...
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One of the things Computers are really good at is
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repetition. Computers don't get tired or bored of doing the same thing
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over and over again. Loops are handy, if you want to run the same
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code over and over again, each time with a different value.
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#### Counting to 100
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### Counting to 100
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At the in-game command prompt (hint: press 't') type the following then hit Enter...
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@ -651,11 +686,11 @@ The `for` statement is useful when you want to repeat something over and over. I
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remember, an Array is just a list of things, for example - the players
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connnected to a server, the worlds of a server and so on.
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#### Saying "Hi!" to every player
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### Saying "Hi!" to every player
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At the in-game command prompt type the following then hit Enter...
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/js for (var i = 0;i < server.onlinePlayers.length; i++){ server.onlinePlayers[i].sendMessage("Hi!"); }
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/js for (var i = 0;i < server.onlinePlayers.length; i++){ server.onlinePlayers[i].sendMessage('Hi!'); }
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... Lets look at these statements in more detail. We had to enter the
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statements on a single line at the in-game command prompt but the
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@ -664,7 +699,7 @@ statements could be written like this...
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var players = server.onlinePlayers;
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for (var i = 0; i < players.length; i++) {
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var player = players[i];
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player.sendMessage("Hi!");
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player.sendMessage('Hi!');
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}
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... On the first line, a new variable `players` is created from the
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@ -698,7 +733,7 @@ the bottom of the file...
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var players = server.onlinePlayers;
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for (var i = 0; i < players.length; i++) {
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var player = players[i];
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player.sendMessage("Hi!");
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player.sendMessage('Hi!');
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}
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}
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@ -709,7 +744,7 @@ loop and arrays. Arrays and `for` loops are used heavily in all types
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of software, in fact there probably isn't any software that doesn't
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use `for` loops and Arrays to get things done.
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### While Loops
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## While Loops
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Another way to repeat things over and over is to use a `while`
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loop. The following `while` loop counts to 100...
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@ -752,7 +787,7 @@ a matter of personal taste, `for` loops are more commonly used with
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Arrays but as you see from the example above, `while` loops can also
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loop over Arrays.
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### `utils.foreach()` - Yet another way to process Arrays
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## `utils.foreach()` - Yet another way to process Arrays
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Both the `for` statement and `while` statement are standard commonly
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used javascript statements used for looping. ScriptCraft also comes
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@ -805,7 +840,7 @@ utils.foreach() function...
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}
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);
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#### Exercise
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### Exercise
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Try changing the above function so that different sounds are played
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instead of a Cat's Meow. You'll need to lookup the [CraftBukkit API's
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Sound class][soundapi] to see all of the possible sounds that can be
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@ -816,7 +851,7 @@ provides `for` and `while` statements for looping and many javascript
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libraries also provide their own custom looping functions. You should
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use what you feel most comfortable with.
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### Putting `for` loops to use - Building a Skyscraper
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## Putting `for` loops to use - Building a Skyscraper
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For loops can be used to build enormous structures. In this next
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exercise I'm going to use a for loop to build a skyscraper. This
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@ -849,7 +884,7 @@ type the following...
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return this.move('myskyscraper'); // return to where we started
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};
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load("../drone/drone.js");
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load('../drone/drone.js');
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Drone.extend('myskyscraper',myskyscraper);
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... so this takes a little explaining. First I create a new function
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@ -885,7 +920,7 @@ that out, creating an entire city of blocks of skyscrapers is the next
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logical step. Of course, Minecraft doesn't have the same constraints
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as real-world densely populated areas so let your imagination go wild.
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### Making Decisions
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## Making Decisions
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All the programs we have seen so far have been fairly predictable - they went
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straight through the statements, and then went back to the beginning again. This is
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@ -893,7 +928,7 @@ not very useful. In practice the computer would be expected to make decisions an
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act accordingly. The javascript statement used for making decisions is `if`.
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While standing on the ground in-game, type the following at the command prompt...
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/js if ( self.flying ) { echo("Hey, You are flying!"); }
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/js if ( self.flying ) { echo('Hey, You are flying!'); }
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... No message should appear on screen. That is - `Hey, You are
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flying!` should *not* appear on screen. Now double-tap the `space`
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@ -903,7 +938,7 @@ enter the same statement again (If you don't want to type the same
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statement again, just press `/` then press the `UP` cursor key on your
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keyboard, the statement you entered previously should reappear.
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/js if ( self.flying ) { echo("Hey, You are flying!"); }
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/js if ( self.flying ) { echo('Hey, You are flying!'); }
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... this time the following message should have appeared on your screen...
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@ -919,7 +954,7 @@ What if you wanted to display a message only if a condition is *not*
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true ? For example to only display a message if the player is *not*
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flying...
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/js if ( ! self.flying ) { echo ("You are not flying."); }
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/js if ( ! self.flying ) { echo ('You are not flying.'); }
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... This code differs in that now there's a `!` (the exclamation mark)
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before `self.flying`. The `!` symbol negates (returns the opposite of)
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@ -948,7 +983,183 @@ whether or not you're currently flying. Type the `/js flightStatus()`
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command while on the ground and while flying. The message displayed in
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each case should be different.
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### Next Steps
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## Event-Driven programming
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So far we've written code which executes when you invoke the `/js `
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command. What if - for example - you want to have some special
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behaviour which occurs when a player joins the game? What if you
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wanted to display a custom welcome message (in addition to the MotD -
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message-of-the-day which is configurable in your server.properties
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file) ? This is where *Event-Driven Programming* comes
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in. Event-Driven Programming is just a fancy way of saying 'Do this
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when that happens' where 'this' is a function you define, and 'that'
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is some event which occurs. There are hundreds of events in the
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minecraft game...
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* Every time someone joins the server - that's an event!
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* Every time someone breaks a block - that's an event!
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* Every time someone shoots an arrow - that's an event! and so on...
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You can write a function which will be called whenever a specific type
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of event occurs, it's probably best to illustrate this by example. The
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following code sends a message to any player who breaks a block in the
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game...
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events.on('block.BlockBreakEvent', function (listener, event) {
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var breaker = event.player;
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breaker.sendMessage('You broke a block');
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});
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The `events.on()` function is how you *register* a function which you
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want to be called whenever a particular type of event occurs. In the
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above code the first parameter `'block.BlockBreakEvent'` is the type
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of event I want to listen for and the second parameter is the function
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I want to be called when that event occurs. The function I want called
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in turn takes 2 parameters. The `event` object has all the information
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about the event which just occurred. I can tell who broke the block
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and send a message to the player. The important thing to note is that
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the function defined above will not be called until a player breaks a
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block. Try it - save the above code in a new file in the
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`scriptcraft/plugins` directory then type `/js refresh()` to reload
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scriptcraft. Then break a block in the game and you should see the
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message 'You broke a block'.
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There are many types of events you can listen for in Minecraft. You can
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browse [all possible Bukkit events][bkevts] (click the 'Next
|
||||
Package' and 'Previous Package' links to browse).
|
||||
|
||||
It's important to note that when browsing the Bukkit API's
|
||||
[org.bukkit.event][bkevts] package, if you see a class called
|
||||
'org.bukkit.events.entity.EntityShootBowEvent', then when calling
|
||||
`events.on()` you can listen to such an event using either the fully
|
||||
qualified Class name...
|
||||
|
||||
events.on(org.bukkit.events.entity.EntityShootBowEvent, function( listener, event) {
|
||||
...
|
||||
});
|
||||
|
||||
or an abbreviated name in string form...
|
||||
|
||||
events.on('entity.EntityShootBowEvent', function( listener, event) {
|
||||
...
|
||||
});
|
||||
|
||||
If the `events.on()` function gets a String (text) as its first
|
||||
parameter it automatically converts it to the appropriate Class by
|
||||
prepending the 'org.bukkit.events' package.
|
||||
|
||||
For custom events (events which aren't in the org.bukkit.event tree)
|
||||
just specify the fully qualified class name instead. E.g. ...
|
||||
|
||||
events.on ( net.yourdomain.events.YourEvent, function(listener, event ) {
|
||||
...
|
||||
});
|
||||
|
||||
### Stop listening to events.
|
||||
|
||||
If you want an event handler to only execute once, you can remove the handler like this...
|
||||
|
||||
events.on('block.BlockBreakEvent', function(listener, evt) {
|
||||
var breaker = evt.player;
|
||||
breaker.sendMessage('You broke a block');
|
||||
evt.handlers.unregister( listener );
|
||||
});
|
||||
|
||||
The `evt.handlers.unregister( listener );` statement will remove this
|
||||
function from the list of listeners for this event.
|
||||
|
||||
## Keeping Score - Lookup tables in Javascript
|
||||
|
||||
In the *Event-Driven Programming* section, I defined a function which
|
||||
displayed a message to players every time they broke a block. Imagine
|
||||
if I wanted to keep a count of how many blocks each player has broken?
|
||||
This is where Javascript's Objecct literals come in handy. An object
|
||||
literal in javascript is simply a way of creating a new Object
|
||||
on-the-fly in your code. This is an example...
|
||||
|
||||
var myNewObject = { name: 'walter', country: 'Ireland' };
|
||||
|
||||
... I created a new object with two properties 'name' and
|
||||
'country'. The notation used to create this object is called JSON
|
||||
which is short for JavaScript Object Notation. If I want to find out
|
||||
the 'country' property of the myNewObject variable there are a few
|
||||
ways I can do it...
|
||||
|
||||
var playerCountry = myNewObject.country;
|
||||
|
||||
... or ...
|
||||
|
||||
var playerCountry = myNewObject['country']
|
||||
|
||||
... JavaScript lets you access any object property using either
|
||||
dot-notation ( `object.property` ) or by index ( `object['property']`
|
||||
). The result in both cases is the same - playerCountry will be
|
||||
'Ireland'. When accessing the object by indexing, the property doesn't
|
||||
even have to be a string literal - it can be a variable like this...
|
||||
|
||||
var propertyName = 'country';
|
||||
var propertyValue = myNewObject[propertyName];
|
||||
|
||||
... in the above example, the propertyName variable is used when
|
||||
indexing. What this means is that every object in JavaScript can act
|
||||
like a lookup table? What's a lookup table? A table you 'look up' of
|
||||
course. This is a table of names and scores...
|
||||
|
||||
Name Score
|
||||
-------- -----
|
||||
walter 5
|
||||
tom 6
|
||||
jane 8
|
||||
bart 7
|
||||
|
||||
... If I want to find Jane's score, I look *down* the list of names in
|
||||
the name column until I find 'jane' then look *across* to get her
|
||||
score. In Javascript, an object which stored such a table would look
|
||||
like this...
|
||||
|
||||
var scoreboard = {
|
||||
walter: 5,
|
||||
tom: 6,
|
||||
jane: 8,
|
||||
bart: 7
|
||||
};
|
||||
|
||||
... and if I wanted to write a function which took a player name as a
|
||||
parameter and returned their score, I'd do it like this...
|
||||
|
||||
function getScore(player){
|
||||
return scoreboard[ player ];
|
||||
}
|
||||
|
||||
... I might call such a function like this...
|
||||
|
||||
var janesScore = getScore('jane'); // returns 8
|
||||
|
||||
... putting it all together, a hypothetical scoreboard.js mdoule might
|
||||
look something like this...
|
||||
|
||||
var utils = require('utils');
|
||||
var scores = {};
|
||||
|
||||
exports.initialise = function(names){
|
||||
scores = {};
|
||||
utils.foreach(names, function(name){
|
||||
scores[name] = 0;
|
||||
});
|
||||
};
|
||||
|
||||
/* changes score by diff e.g. to add 6 to the player's current score
|
||||
updateScore('walter',6); // walter's new score = 5 + 6 = 11.
|
||||
*/
|
||||
exports.updateScore = function(name, diff){
|
||||
scores[name] += diff;
|
||||
};
|
||||
|
||||
exports.getScore = function(name){
|
||||
return scores[name];
|
||||
};
|
||||
|
||||
## Next Steps
|
||||
|
||||
This guide is meant as a gentle introduction to programming and
|
||||
modding Minecraft using the Javascript Programming Language.
|
||||
|
|
@ -974,10 +1185,10 @@ different objects and methods available for use by ScriptCraft.
|
|||
[cbapi]: http://jd.bukkit.org/beta/apidocs/
|
||||
[boole]: http://en.wikipedia.org/wiki/George_Boole
|
||||
[soundapi]: http://jd.bukkit.org/beta/apidocs/org/bukkit/Sound.html
|
||||
[ap]: http://walterhiggins.net/blog/ScriptCraft-1-Month-later
|
||||
[ap]: Anatomy-of-a-Plugin.md
|
||||
[api]: API-Reference.md
|
||||
[twl]: http://www.barebones.com/products/textwrangler/
|
||||
|
||||
[bkevts]: http://jd.bukkit.org/dev/apidocs/org/bukkit/event/package-summary.html
|
||||
[img_echo_date]: img/ypgpm_echo_date.png
|
||||
[img_3d_shapes]: img/ypgpm_3dshapes.jpg
|
||||
[img_whd]: img/ypgpm_whd.jpg
|
||||
|
|
|
|||
Reference in a new issue