Notes & Strumline - Friday Night Funkin'

Overview

The notes system handles note rendering, hit detection, and strumline management. The Strumline class manages receptors, notes, and sustains for a single player, while NoteSprite represents individual notes.

Class Hierarchy

FlxSpriteGroup
  └── Strumline
        ├── notes (FlxTypedSpriteGroup<NoteSprite>)
        ├── holdNotes (FlxTypedSpriteGroup<SustainTrail>)
        ├── strumlineNotes (FlxTypedSpriteGroup<StrumlineNote>)
        └── noteSplashes (FlxTypedSpriteGroup<NoteSplash>)

FunkinSprite
  └── NoteSprite

Strumline

A group of sprites that handles receptors, notes, and note splashes for a given player.

Constants

Strumline.DIRECTIONS = [LEFT, DOWN, UP, RIGHT];
Strumline.STRUMLINE_SIZE = 104; // pixels
Strumline.NOTE_SPACING = 112; // pixels (104 + 8)
Strumline.KEY_COUNT = 4;

Properties

isPlayer

Bool

Whether this strumline is controlled by player input (true) or CPU (false)

scrollSpeed

Float

default:"1.0"

Scroll speed multiplier for notes

isDownscroll

Bool

Whether notes scroll downward instead of upward

notes

FlxTypedSpriteGroup<NoteSprite>

Active notes heading toward the strumline

holdNotes

FlxTypedSpriteGroup<SustainTrail>

Active hold/sustain notes

strumlineNotes

FlxTypedSpriteGroup<StrumlineNote>

The receptor arrows (4 directions)

noteData

Array<SongNoteData>

Note data from the chart

showNotesplash

Bool

default:"true"

Whether to show note splash effects on sick hits

Methods

`new(noteStyle:NoteStyle, isPlayer:Bool, ?scrollSpeed:Float)`

Creates a new strumline.

var playerStrumline = new Strumline(noteStyle, true, 1.5);
var opponentStrumline = new Strumline(noteStyle, false, 1.5);

noteStyle

NoteStyle

required

Note style for visuals (e.g., “funkin”, “pixel”)

isPlayer

Bool

required

True for player-controlled, false for CPU

scrollSpeed

Float

Initial scroll speed multiplier

`applyNoteData(data:Array<SongNoteData>):Void`

Loads note data from a chart.

// Load notes for this strumline
var playerNotes = chartData.notes.filter(n -> n.getMustHitNote());
strumline.applyNoteData(playerNotes);

data

Array<SongNoteData>

required

Array of note data from the chart

`addNoteData(note:SongNoteData, sort:Bool = true):Void`

Adds a single note to the strumline.

var newNote:SongNoteData = {
  time: 1000.0,
  data: 2, // UP
  length: 0.0
};
strumline.addNoteData(newNote);

`pressKey(dir:NoteDirection, keyCode:Int):Void`

Registers a key press.

// Called by input system
strumline.pressKey(NoteDirection.LEFT, FlxKey.A);

`releaseKey(dir:NoteDirection, ?keyCode:Int):Void`

Registers a key release.

strumline.releaseKey(NoteDirection.LEFT, FlxKey.A);

// Release all keys for this direction
strumline.releaseKey(NoteDirection.LEFT);

`isKeyHeld(dir:NoteDirection):Bool`

Checks if a direction is being held.

if (strumline.isKeyHeld(NoteDirection.DOWN)) {
  trace('Down is held!');
}

`hitNote(note:NoteSprite, removeNote:Bool = true):Void`

Marks a note as hit.

strumline.hitNote(note, true); // Hit and remove
strumline.hitNote(note, false); // Hit but keep visible

note

NoteSprite

required

The note that was hit

removeNote

Bool

default:"true"

If true, removes note immediately. If false, makes it transparent.

`killNote(note:NoteSprite):Void`

Kills a note (for misses or cleanup).

strumline.killNote(note);

`playConfirm(direction:NoteDirection):Void`

Plays the confirm animation on a receptor.

strumline.playConfirm(NoteDirection.LEFT);

`playPress(direction:NoteDirection):Void`

Plays the press animation on a receptor.

strumline.playPress(NoteDirection.UP);

`playStatic(direction:NoteDirection):Void`

Returns a receptor to its static/idle state.

strumline.playStatic(NoteDirection.RIGHT);

`playNoteSplash(direction:NoteDirection):Void`

Plays a note splash effect.

// On sick rating
strumline.playNoteSplash(NoteDirection.DOWN);

`getNotesMayHit():Array<NoteSprite>`

Returns notes within the hit window.

var hittableNotes = strumline.getNotesMayHit();
for (note in hittableNotes) {
  // Check for inputs
}

`clean():Void`

Resets the strumline, removing all notes and resetting state.

// When restarting
strumline.clean();

`vwooshNotes():Void`

Animates all notes flying off-screen (for restarts).

strumline.vwooshNotes();

`vwooshInNotes():Void`

Animates notes flying in from off-screen.

strumline.vwooshInNotes();

`resetScrollSpeed(?newScrollSpeed:Float):Void`

Resets scroll speed to chart default or specified value.

strumline.resetScrollSpeed(); // Use chart speed
strumline.resetScrollSpeed(2.0); // Set to 2.0x

NoteSprite

Represents a single note heading toward the strumline.

Properties

strumTime

Float

Time when the note should be hit (milliseconds)

length

Float

default:"0.0"

Hold note length in milliseconds (0 for single notes)

direction

NoteDirection

Direction of the note (LEFT, DOWN, UP, RIGHT)

kind

Null<String>

Note kind (e.g., “alt”, “hurt”) for special behavior

noteData

SongNoteData

Reference to the chart data for this note

hasBeenHit

Bool

default:"false"

True if the note has been hit

hasMissed

Bool

default:"false"

True if the note was missed

mayHit

Bool

default:"false"

True if the note is within the hit window

tooEarly

Bool

default:"false"

True if the note is before the hit window

scoreable

Bool

default:"true"

Whether this note contributes to score/accuracy

isHoldNote

Bool

True if this is a hold note (length > 0)

holdNoteSprite

SustainTrail

Reference to the hold note sprite

Methods

`new(noteStyle:NoteStyle, direction:Int = 0)`

Creates a new note sprite.

var note = new NoteSprite(noteStyle, NoteDirection.LEFT);

`setupNoteGraphic(noteStyle:NoteStyle):Void`

Sets up the note’s visual appearance.

note.setupNoteGraphic(pixelNoteStyle);

`getParam(name:String):Null<Dynamic>`

Retrieves a custom parameter value.

var customValue = note.getParam('scrollMult');
if (customValue != null) {
  scrollSpeed *= customValue;
}

`desaturate():Void`

Desaturates the note (used after hitting).

note.desaturate(); // Make it grayscale

`setHue(hue:Float):Void`

Changes the note’s hue.

note.setHue(180.0); // Shift color

Hit Detection

Hit Window

Notes can be hit within a time window defined by Constants.HIT_WINDOW_MS:

var hitWindow = Constants.HIT_WINDOW_MS; // e.g., 166.67ms

if (Math.abs(note.strumTime - Conductor.songPosition) <= hitWindow) {
  // Note is hittable
}

Judgement Timing

Typical timing windows:

Sick: ±45ms
Good: ±90ms
Bad: ±135ms
Shit: ±166ms

Hold Notes (SustainTrail)

Hold notes are rendered as trails that follow regular notes:

Properties

sustainLength: Remaining length in milliseconds
fullSustainLength: Original total length
hitNote: Whether the note head was hit
missedNote: Whether the hold was dropped
cover: Visual cover that appears when holding

Behavior

Note head must be hit first
Hold note clips as it’s held
Dropped if key is released early
Completed when sustainLength reaches 0

Usage Examples

Creating a Strumline

// Create strumlines for both players
var noteStyle = NoteStyleRegistry.instance.fetchEntry('funkin');

var playerStrumline = new Strumline(noteStyle, true, 1.0);
playerStrumline.x = 730;
playerStrumline.y = 100;

var opponentStrumline = new Strumline(noteStyle, false, 1.0);
opponentStrumline.x = 100;
opponentStrumline.y = 100;

// Load note data
var chart = SongRegistry.instance.parseEntryChartData(songId, difficulty);
var playerNotes = chart.notes.filter(n -> n.getMustHitNote());
var opponentNotes = chart.notes.filter(n -> !n.getMustHitNote());

playerStrumline.applyNoteData(playerNotes);
opponentStrumline.applyNoteData(opponentNotes);

Handling Input

// On key press
if (controls.NOTE_LEFT_P) {
  playerStrumline.pressKey(NoteDirection.LEFT, FlxKey.A);
  
  var hittableNotes = playerStrumline.getNotesMayHit()
    .filter(n -> n.direction == NoteDirection.LEFT);
  
  if (hittableNotes.length > 0) {
    var note = hittableNotes[0];
    var diff = Math.abs(note.strumTime - Conductor.songPosition);
    
    if (diff <= 45) {
      // Sick hit!
      playerStrumline.hitNote(note);
      playerStrumline.playNoteSplash(NoteDirection.LEFT);
    }
  }
}

// On key release
if (controls.NOTE_LEFT_R) {
  playerStrumline.releaseKey(NoteDirection.LEFT, FlxKey.A);
}

Custom Note Behavior

// Create a note with custom parameters
var bombNote:SongNoteData = {
  time: 2000.0,
  data: 1, // DOWN
  length: 0.0,
  kind: 'hurt',
  params: [
    { name: 'damage', value: 0.5 }
  ]
};

strumline.addNoteData(bombNote);

// Later, check note kind
if (note.kind == 'hurt') {
  var damage = note.getParam('damage') ?? 0.1;
  health -= damage;
}

Best Practices

Always check note.mayHit before allowing hits. Notes outside the hit window should not be hittable.

Use getNotesMayHit() to get only notes that can currently be hit, avoiding unnecessary iteration.

The strumline automatically recycles note sprites for performance. Don’t destroy notes manually unless absolutely necessary.

Core

Audio

Play

Data

Modding

​Overview

​Class Hierarchy

​Strumline

​Constants

​Properties

​Methods

​new(noteStyle:NoteStyle, isPlayer:Bool, ?scrollSpeed:Float)

​applyNoteData(data:Array<SongNoteData>):Void

​addNoteData(note:SongNoteData, sort:Bool = true):Void

​pressKey(dir:NoteDirection, keyCode:Int):Void

​releaseKey(dir:NoteDirection, ?keyCode:Int):Void

​isKeyHeld(dir:NoteDirection):Bool

​hitNote(note:NoteSprite, removeNote:Bool = true):Void

​killNote(note:NoteSprite):Void

​playConfirm(direction:NoteDirection):Void

​playPress(direction:NoteDirection):Void

​playStatic(direction:NoteDirection):Void

​playNoteSplash(direction:NoteDirection):Void

​getNotesMayHit():Array<NoteSprite>

​clean():Void

​vwooshNotes():Void

​vwooshInNotes():Void

​resetScrollSpeed(?newScrollSpeed:Float):Void

​NoteSprite

​Properties

​Methods

​new(noteStyle:NoteStyle, direction:Int = 0)

​setupNoteGraphic(noteStyle:NoteStyle):Void

​getParam(name:String):Null<Dynamic>

​desaturate():Void

​setHue(hue:Float):Void

​Hit Detection

​Hit Window

​Judgement Timing

​Hold Notes (SustainTrail)

​Properties

​Behavior

​Usage Examples

​Creating a Strumline

​Handling Input

​Custom Note Behavior

​Best Practices

Build docs developers (and LLMs) love

Overview

Class Hierarchy

Strumline

Constants

Properties

Methods

`new(noteStyle:NoteStyle, isPlayer:Bool, ?scrollSpeed:Float)`

`applyNoteData(data:Array<SongNoteData>):Void`

`addNoteData(note:SongNoteData, sort:Bool = true):Void`

`pressKey(dir:NoteDirection, keyCode:Int):Void`

`releaseKey(dir:NoteDirection, ?keyCode:Int):Void`

`isKeyHeld(dir:NoteDirection):Bool`

`hitNote(note:NoteSprite, removeNote:Bool = true):Void`

`killNote(note:NoteSprite):Void`

`playConfirm(direction:NoteDirection):Void`

`playPress(direction:NoteDirection):Void`

`playStatic(direction:NoteDirection):Void`

`playNoteSplash(direction:NoteDirection):Void`

`getNotesMayHit():Array<NoteSprite>`

`clean():Void`

`vwooshNotes():Void`

`vwooshInNotes():Void`

`resetScrollSpeed(?newScrollSpeed:Float):Void`

NoteSprite

Properties

Methods

`new(noteStyle:NoteStyle, direction:Int = 0)`

`setupNoteGraphic(noteStyle:NoteStyle):Void`

`getParam(name:String):Null<Dynamic>`

`desaturate():Void`

`setHue(hue:Float):Void`

Hit Detection

Hit Window

Judgement Timing

Hold Notes (SustainTrail)

Properties

Behavior

Usage Examples

Creating a Strumline

Handling Input

Custom Note Behavior

Best Practices