Building a Turtle Program Step by Step: Creating a Building Pattern

In this blog, we will break down a Lua turtle program and rebuild it step by step to create an easy-to-understand version. The program uses a turtle in ComputerCraft (CC) to build a pattern of blocks in a specified size.

The original program is as follows:

lua

local maxX, maxY = ...

function right()
    turtle.turnRight()
    turtle.forward()
    turtle.turnLeft()
end

function left()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnRight()
end

maxX = tonumber(maxX)
maxY = tonumber(maxY)

turtle.select(1)
turtle.place()

for y = 1, maxY do
    for x = 1, maxX do
        if x < maxX then
            if y % 2 == 1 then
                right()
            else
                left()
            end
            turtle.place()
        end
    end
    if y < maxY then
        turtle.up()
    end
    turtle.place()
end

for y = maxY, 1, -1 do
    if y > 1 then
        turtle.down()
    end
end

if maxY % 2 == 1 then
    turtle.turnLeft()
    for x = maxX, 1, -1 do
        if x > 1 then
            turtle.forward()
        end
    end
    turtle.turnRight()
end

Step 1: Setting the Maximum Size The program starts by defining two variables, maxX and maxY, which represent the maximum width and height of the pattern, respectively. These values are received as input parameters.

lua

local maxX, maxY = ...

Step 2: Defining Movement Functions To simplify the code, we can extract the repetitive movement logic into separate functions. The right() function turns the turtle to the right, moves it forward, and then turns it to the left. Similarly, the left() function turns the turtle to the left, moves it forward, and then turns it to the right.

lua

function right()
    turtle.turnRight()
    turtle.forward()
    turtle.turnLeft()
end

function left()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnRight()
end

Step 3: Converting Input to Numbers Next, the code converts the maxX and maxY variables from strings to numbers using the tonumber() function.

lua

maxX = tonumber(maxX)
maxY = tonumber(maxY)

Step 4: Placing the First Block The turtle is then selected and instructed to place a block using the turtle.select(1) and turtle.place() functions. This sets the block type in the turtle’s inventory slot 1 and places a block in front of it.

lua

turtle.select(1)
turtle.place()

Step 5: Building the Pattern The program uses nested loops to build the pattern. The outer loop iterates over the y variable from 1 to maxY, and the inner loop iterates over the x variable from 1 to maxX.

lua

for y = 1, maxY do
    for x = 1, maxX do
        -- Code to be added in the next steps
    end
    -- Code to be added in the next steps
end

Step 6: Alternating Movement and Block Placement Within the inner loop, there is a conditional statement that checks if x is less than maxX. If true, it determines whether the turtle should turn right or left based on the value of y using the modulus operator %.

lua

if x < maxX then
    if y % 2 == 1 then
        right()
    else
        left()
    end
    turtle.place()
end

Step 7: Moving Up and Placing a Block After each row is completed, the program checks if y is less than maxY. If true, it moves the turtle up and places a block at the new level using the turtle.up() and turtle.place() functions.

lua

if y < maxY then
    turtle.up()
end
turtle.place()

Step 8: Moving Down to the Starting Level Once all the rows are completed, the program uses a loop to move the turtle back down to the starting level. It iterates over the y variable in reverse from maxY to 1 and moves the turtle down with the turtle.down() function.

lua

for y = maxY, 1, -1 do
    if y > 1 then
        turtle.down()
    end
end

Step 9: Handling Odd Number of Rows If the number of rows (maxY) is odd, the turtle needs to move to the left side of the pattern after reaching the bottom-right corner. The program achieves this by turning the turtle left, moving it backward to the starting column, and then turning it right again.

lua

if maxY % 2 == 1 then
    turtle.turnLeft()
    for x = maxX, 1, -1 do
        if x > 1 then
            turtle.forward()
        end
    end
    turtle.turnRight()
end