Cannot enable ligatures (JetBrains Mono font)

[tferr]

JetBrains mono is a much-improved font for coding, featuring many readability features such as coding-specific ligatures. I am not able to use this font properly in RSyntaxTextArea.

Take this snippet that requires FlatLaf and the FlatLaf JetBrains Mono distribution (direct downloadable jars for both dependencies: flatlaf, flatlaf-fonts-jetbrains-mono):

import java.awt.Font;
import java.awt.font.TextAttribute;
import java.util.*;
import javax.swing.*;

import org.fife.ui.rsyntaxtextarea.RSyntaxTextArea;

import com.formdev.flatlaf.fonts.jetbrains_mono.FlatJetBrainsMonoFont;
import com.formdev.flatlaf.util.FontUtils;

public class Test {

	public Test() {
		FlatJetBrainsMonoFont.install();
		run(new JTextArea());
		run(new RSyntaxTextArea());
	}

	void run(final JTextArea ta) {
		final Font f = FontUtils.getCompositeFont(FlatJetBrainsMonoFont.FAMILY, Font.PLAIN, 40);
		final Map<TextAttribute, Object> textAttributes = new HashMap<>();
		textAttributes.put(TextAttribute.KERNING, TextAttribute.KERNING_ON);
		textAttributes.put(TextAttribute.LIGATURES, TextAttribute.LIGATURES_ON);
		ta.setFont(f.deriveFont(textAttributes));
		ta.setText("Current font: " + ta.getFont().getFontName() + "\nligatures: ## <> => ++ ~~ <= >= <=> ->>");
		JFrame frame = new JFrame(ta.getClass().getSimpleName());
		frame.getContentPane().add(ta);
		frame.pack();
		frame.setVisible(true);
	}

	public static void main(final String[] args) {
		new Test();
	}

The ligatures do render in JTextArea:

..but not in a RSyntaxTextArea:

Why is that? I could not find any obvious signs that TextAttributes are being overridden in the code base.

[tferr]

pinging @DevCharly in case they have experienced this elsewhere

[DevCharly]

I'm actually surprised that ligatures work in Swing 😮
Didn't know TextAttribute.LIGATURES...

So I tried to enable ligatures in FlatLaf Theme Editor, which uses RSyntaxTextArea, and it works 😮

I think the reason is that FlatLaf Theme Editor uses a subclass of org.fife.ui.rsyntaxtextarea.SyntaxScheme, which always uses the same font that has the ligatures attribute.

There are several places in SyntaxScheme where a new font is created using family, style and size, but without attributes. I think the ligature attribute is lost there. E.g.

RSyntaxTextArea/RSyntaxTextArea/src/main/java/org/fife/ui/rsyntaxtextarea/SyntaxScheme.java

Lines 445 to 449 in 9097e51

	StyleContext sc = StyleContext.getDefaultStyleContext();
	Font boldFont = sc.getFont(baseFont.getFamily(), Font.BOLD,
	baseFont.getSize());
	Font italicFont = sc.getFont(baseFont.getFamily(), Font.ITALIC,
	baseFont.getSize());

or

RSyntaxTextArea/RSyntaxTextArea/src/main/java/org/fife/ui/rsyntaxtextarea/SyntaxScheme.java

Lines 109 to 110 in 9097e51

	StyleContext sc = StyleContext.getDefaultStyleContext();
	style.font = sc.getFont(font.getFamily(), s, font.getSize());

To fix this, and keep the usage of StyleContext.getFont(), it is probably necessary to additionally invoke font.deriveFont(Map attributes) to reapply some font attributes of the base font.

[tferr]

Thanks a lot for this. I'm closing it, as this is a reasonable workaround.

[bobbylight]

I'll reopen this to make the necessary changes in SyntaxScheme pointed out above. Thanks folks for this!