miranda makes things! Tiny DDR logic

Tiny DDR logic

For this week I wanted to make a pipeline for going from the most common file format for DDR songs / levels to playable game logic in Arduino that can detect how off a user’s keypress is (in milliseconds) from the true timing of the note and map this to a score using the scoring guide.

First, I found the most downloaded simfile off zenius-i-vanisher and downloaded the .zip file for the level. Inside the file, I found:

A bit more about the .sm file. The format of it looks like this:

//----- song ID: xeph -----//
#TITLE:Xepher;
#ARTIST:Tatsh;
#BANNER:Xepher.png;
#BACKGROUND:Xepher-bg.png;
#CDTITLE:./CDTITLES/BeatmaniaIIDX.png;
#MUSIC:Xepher.ogg;
#SAMPLESTART:33.9;
#SAMPLELENGTH:15;
#BPMS:0=170;

//---------------dance-single - ----------------
#NOTES:
     dance-single:
     :
     Beginner:
     4:
     :
0000
0000
0000
0000
,
... 
1000
0000
0000
1001
,
0000
0000
0000
0110
,
...

The BPMS property specifies the BPM and the note where that BPM begins (to be able to handle tempo changes mid-song). In the example above we have a consistent BPM of 170.

The notes are encoded in a way I can’t seem to find documentation for, but luckily there is a handy Python simfile library which contains a handy timing engine to decode the note metadata and time (in seconds) from the note information.

Each of the TimedNotes looks like this:

TimedNote(time=8.471, note=Note(beat=Beat(24), column=0, note_type=NoteType.TAP))

We have the time (in seconds), and inside of the Note object, the beat, column (arrow direction, where 0 is left, 1 is down, 2 is up, 3 is right) and note type, which for the beginner tracks is always TAP, but could also be, e.g. HOLD_HEAD or TAIL to define the beginning and end of a note which is held across multiple beats. My code converts this into a plaintext file which represents a table with three columns, where each row is one arrow: the timing of the arrow (in milliseconds since song start), the note type, and the arrow direction. Here is an example simfile which is the input to my parsing script and here is the .txt output for the beginner level of that simfile.

To quickly test if this works, I wrote a small .ino file which simply loads the parsed data structure, starts a millisecond counter, and prints the arrow type and direction to the Serial Monitor when the arrows are meant to be pressed. Since I couldn’t figure out how to add a .txt file into Wokwi I just hardcoded the array into the code itself. It’s not a particularly exciting demo, but it works!

Onwards…