In this lab you will program robots to play Minecraft and optimize their operation by using multiple threads to control multiple robots. You are provided a modded version of Minecraft which allows you to connect to a running game world to obtain a robot called a “turtle”. When you close the connection, the robot disappears. You may also open multiple connections to obtain multiple robots which can then work in parallel.

The setup is based on the turtles in the mod ComputerCraft and as such provides the same API. A small example demonstrating some of the turtles' functions is included in your files.

Even though most tasks can be solved using only one turtle, parallelization is the key to do them quickly. This introduces a few synchronization issues that you need to deal with: how to divide the task among the turtles and how to prevent turtles from crashing into each other.

Don't worry, if you've never played Minecraft before. There is a lot of content to the game, but for this lab you just need to know that the world is made of a 3D grid of blocks, which can be mined (“dug”) to obtain them as “item” in one's inventory, allowing one to place them somewhere else.

• Before opening Eclipse or Minecraft, run /opt/Uebungen/turtles/setup.sh.
• Run Eclipse and Minecraft from the “start menu”.
• Log into Minecraft (we will provide you with accounts for this lab) and launch the game using the “forge” profile (set in the bottom left of the launcher).
• Open a singleplayer world, for example the one we pre-installed for you. Turtles may now be created by connecting on the port 7473.

Run and read through the example program (“TurtleMain”). If you can't find the turtle moving about, try printing its location using System.out.println(turtle.getLocation()).

• In Minecraft the y coordinate is used for the height axis: near 0 you will encounter indestructible bedrock blocks, while ocean level is 64.
• By pressing F3 in Minecraft an overlay showing various information can be displayed. This is particularly useful for finding a certain coordinate.

Your first real task is to build a simple 3x1x3 grid (i.e., horizontal, height 1) of blocks at height y = 90 centered right above the spawning location. The goal here is to get accustomed to the API. Keep in mind that turtles need to collect some blocks before being able to place any!

• Once turtles start placing blocks in the correct spots, the progress of the building will be displayed in in-game chat.
• If a turtle function call fails (i.e., returns false), you can use the getFailureReason() method to obtain a string containing the reason. The reason will also be output to stderr.
• A turtle can interact with the 3 blocks in front of, above and below them. To access other blocks it needs to move or turn.
• Turtles have an inventory of 16 slots labeled 1 through 16, all starting out empty. A slot can hold up to 64 of any single block type. When a block is mined it is placed in the first slot of its type (if there is any) or into the first empty slot (if there is not). Use the select(int slot) function to choose which slot is used for actions, e.g., for placing blocks from.
• We extended the Turtle API by 2 additional methods to allow a turtle to determine its position and orientation in the world: getLocation() and getFacing().

Setup: Copy /home/lab/local-data/turtles/exercise2/ComputerCraft.cfg over the existing file of the same name in /home/lab/.minecraft/config, and restart Minecraft.

Now that you have understood the basics, it is time to add some parallelization! Build tower hollow of height 10 with a 5×5 area and a few holes in the side (see whiteboard). The tower should be made of cobblestone only (block name minecraft:cobblestone). Again, the tower should start at y = 90 and be centered around the spawning location.

Try to complete this task as quickly as possible by using as many turtles as you can handle! On world seed qwer 60 seconds is a good time. The assistants' record is 43.1 seconds.

• Use getItemDetail() to find out what materials you picked up.
• All function calls are blocking, i.e., they only return once the operation is complete or has failed.
• In Java, two strings a and b are compared by calling a.equals(b).

The room will be divided into two teams, each of which will be provided a server. The goal is to collaboratively build a cobblestone pyramid larger than that of the other team!

This is a very open-ended task. Feel free to focus on smaller parts of the problem, such as the efficient harvesting of cobblestone from the game world.

• When creating a world, you may want to turn cheats on to allow you to switch to spectator mode.
• Entering the command “/gamemode 3” enables you to fly around (press 'T' to open a text box in game).
• A random seed for a world without much obstruction near the spawn point is qwer.
• If something goes wrong, you can easily get a clean world by selecting an existing one from the menu and choosing “Re-Create”.
• Singleplayer worlds pause when the window loses focus unless you select “Open to LAN” in the menu.