The Mirin Template

The NotITG Mirin Template. Easily create modfiles using Lua.

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For loops

At its core, a for loop is a “repeat” instruction, that means “do thing Y, X many times”, with a few special rules about how it counts, defined by you.

The general structure is this:

for i = Start, End, StepSize do
  --do some stuff with i,
  --which starts at Start,
  --and goes until End,
  --with StepSize being the increment per "step"
end

The “i” part is the most important here. Everything within the for block is happening repeatedly for each value of i. Note: if StepSize is 1, it doesn’t have to be declared.

A quick example:

for i = 0, 10, 2 do
  print('HELLO, THIS IS STEP '..i)
end

(Note: .. is concatenation, which combines two strings)

This is going to print 6 things to the console.

HELLO, THIS IS STEP 0
HELLO, THIS IS STEP 2
HELLO, THIS IS STEP 4
HELLO, THIS IS STEP 6
HELLO, THIS IS STEP 8
HELLO, THIS IS STEP 10

Note: The start and end values are inclusive, which is why this prints 6 times instead of 5.

Another example:

for i = 0, 5 do
  print('2 to the power of '..i..' is '..math.pow(2, i))
end

This will print the following:

to the power of 0 is 1
to the power of 1 is 2
to the power of 2 is 4
to the power of 3 is 8
to the power of 4 is 16
to the power of 5 is 32

The ability to do things multiple times has many applications in programming, but it’s particularly useful in mods. If you’re working in tables (as is the case with every modern template), you can add lots of things to a table at the same time.

Let’s say for example, you want to move players back and forth every 4 beats, starting at beat 200:

for i = 200, 232, 4 do
  ease {i, 2, outCubic, 100, 'z'}
  ease {i + 2, 2, outCubic, 0, 'z'}
end

Starting at beat 200, this is going to move the playfields 100 pixels towards the camera, then at beat 202 move back to the starting position. Because of the for loop, this code will be run again, but with i = 204, making the playfields move forward again at 204 and back again at 206. This will carry on until i is greater than 231 (causing it to not run at beat 232, as the condition will have been satisfied by the time it reaches that point).

This is a very basic overview on how a for loop works and what it can be used for. There are many other things, like for i,v in pairs/ipairs or while loops, but this should give you a good start. For more information on how for loops work, click here.

Original explanation written by Taro