LibGDX app cannot load TTF fonts due to "invalid padding"

I am new to LibGDX and trying to make a very simple game. But I soon ran into an issue when using BitmapFont. In my Game class, I load a BitmapFont like so:

private SpriteBatch batch;
private BitmapFont font;
    
@Override
public void create() {
    batch = new SpriteBatch();
    font = new BitmapFont(Gdx.files.internal("fonts/PlaypenSans-ExtraLight.ttf"));
    this.setScreen(new MainMenuScreen(this));
}

The TTF file was downloaded from Google Fonts. The result was the following error:

Exception in thread "main" com.badlogic.gdx.utils.GdxRuntimeException: Error loading font file: fonts/PlaypenSans-ExtraLight.ttf
        at com.badlogic.gdx.graphics.g2d.BitmapFont$BitmapFontData.load(BitmapFont.java:717)
        at com.badlogic.gdx.graphics.g2d.BitmapFont$BitmapFontData.<init>(BitmapFont.java:485)
        at com.badlogic.gdx.graphics.g2d.BitmapFont.<init>(BitmapFont.java:116)
        at com.badlogic.gdx.graphics.g2d.BitmapFont.<init>(BitmapFont.java:109)
        at com.ssage.pong.Pong.create(Pong.java:18)
        at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Window.initializeListener(Lwjgl3Window.java:416)
        at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Window.update(Lwjgl3Window.java:366)
        at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application.loop(Lwjgl3Application.java:192)
        at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application.<init>(Lwjgl3Application.java:166)
        at com.ssage.pong.desktop.DesktopLauncher.main(DesktopLauncher.java:16)
Caused by: com.badlogic.gdx.utils.GdxRuntimeException: Invalid padding.
        at com.badlogic.gdx.graphics.g2d.BitmapFont$BitmapFontData.load(BitmapFont.java:500)

I got the same error with other TTF files.

Using BitmapFont with the default constructor (so the default font) does work. I can't find anything about the "invalid padding error" online.

Solution

A BitmapFont is a class that wraps a bitmap-font, which is a text document describing where in a image each character is located (for example the default.fnt file from libGDX), it does not load TTF files.

If you want to use TTF files in your project, you should enable the freetype extension (you can pick it when you create your libGDX project), and then use the FreeTypeFontGenerator to generate a BitmapFont on the fly.

The libGDX freetype page has some good examples on how to do this, but essentially you

Create a FreeTypeFontGenerator passing the TTF file as a constructor argument.
Create a FreeTypeFontParameter object and set things like size on it.
Call generateFont on the FreeTypeFontGenerate object passing in the parameters, this will return a BitmapFont.
Dispose the FreeTypeFontGenerator`.