Introduction

Thus far, we have used Scriptcraft to build cool structures in our Minecraft worlds, but the interaction has been a little one-sided. We’ve placed objects into the world, but we’ve never stopped to ask: “What’s already there?”.

That’s a powerful question to ask, because once we know what’s already in the world, our interaction with it becomes richer and opens up many new possibilities.

Objects in JavaScript

Objects in JavaScript have Properties and Methods. Properties are what they sound like; a value associated with object that we can get or set. Methods are actions, in the form of a function, that we can ask the object to perform.

If you thought of me as a Person object then you could imagine some of the Properties and Methods I might have. For Properties I might have things like Name, Age, Height, Weight, etc. An example of a Method I might have could be SayHi() [notice the round brackets after the name marking this as a method]. That would make me say “Hi!”. A method might have arguments, so it could be SayHiTo(“Dave”) which would make me say “Hi Dave!”. A method could equally calculate a value. An example might be CalculateBMI() which would calculate my Body Mass Index (BMI) value based on my Height and Weight properties. On second thoughts… scratch that idea. Exploring Existing Objects

How do we explore the objects in the ScriptCraft world? One way is to read the API documentation:

• Scriptcraft API Reference
• Bukkit API Reference

Another way is to look at the Scriptcraft code files themselves, especially drone.js.

Another handy, lazy, way to explore an object you already have a reference to in ScriptCraft is just to treat it like a string and pass it to self.sendMessage(). You’ll usually get a representation which shows some of the properties of the object and those properties’ values. It’s incomplete, but very quick and might show what you’re looking for.

Getting the Block Type

All of this was building to finding out, from Scriptcraft, what the block at a particular location is. Using a combination of the techniques listed above, I determined that I needed to call a method on the Bukkit World object called getBlockAt(). In Scriptcraft the server object has an array called worlds and the normal world is worlds[0]. For the curious; worlds[1] is the nether and worlds[2] is the end.

That’s everything we need to create a simple script to examine the block that we’re currently looking at. We can create a Drone, which is created at the block we are looking at by default, to get the location. Here is the main part of the code:

// Create a drone (will be placed at the block the player's looking at)
var d = new Drone();

// Gather information about the world, the drone's location
// and the block at the drone's location
var world = server.worlds[0];
var loc = d.getLocation();
var chunk = loc.chunk;
var block_info = world.getBlockAt(loc.x, loc.y, loc.z);

The remainder of the code is just printing this information to the console in a tidy way. We called it whats_that.js and it can be downloaded from here. The screenshot below shows it being run.

This will form the basis for some future projects.

Quick Final Note on Block Metadata

One final note and something that wasn’t discussed at our session last week: to fully define a block we need to know both its type and its metadata. Two wool blocks of different colours have the same type but different metadata values to distinguish them from one-and-other. Similarly steps use the metadata value to distinguish between the different possible orientations. You can use the whats_that() function to explore this.