Linux: fixed scaling if GDK_SCALE environment variable is set or if running on JetBrains Runtime (issue #69)

CHANGELOG.md

@@ -1,6 +1,12 @@
 FlatLaf Change Log
 ==================
 
+## Unreleased
+
+- Linux: Fixed scaling if `GDK_SCALE` environment variable is set or if running
+  on JetBrains Runtime. (issue #69)
+
+
 ## 0.28
 
 - PasswordField: Warn about enabled Caps Lock.

flatlaf-core/src/main/java/com/formdev/flatlaf/LinuxFontPolicy.java

@@ -17,6 +17,7 @@
 package com.formdev.flatlaf;
 
 import java.awt.Font;
+import java.awt.GraphicsConfiguration;
 import java.awt.GraphicsEnvironment;
 import java.awt.Toolkit;
 import java.io.BufferedReader;
@@ -31,6 +32,7 @@ import java.util.logging.Level;
 import javax.swing.text.StyleContext;
 import com.formdev.flatlaf.util.StringUtils;
 import com.formdev.flatlaf.util.SystemInfo;
+import com.formdev.flatlaf.util.UIScale;
 
 /**
  * @author Karl Tauber
@@ -99,6 +101,10 @@ class LinuxFontPolicy
 	}
 
 	private static double getGnomeFontScale() {
+		// do not scale font here if JRE scales
+		if( isSystemScaling() )
+			return 1;
+
 		// see class com.sun.java.swing.plaf.gtk.PangoFonts background information
 
 		Object value = Toolkit.getDefaultToolkit().getDesktopProperty( "gnome.Xft/DPI" );
@@ -168,7 +174,7 @@ class LinuxFontPolicy
 
 		// font dpi
 		int dpi = 96;
-		if( forceFontDPI != null ) {
+		if( forceFontDPI != null && !isSystemScaling() ) {
 			try {
 				dpi = Integer.parseInt( forceFontDPI );
 				if( dpi <= 0 )
@@ -247,4 +253,15 @@ class LinuxFontPolicy
 		}
 		return null;
 	}
+
+	/**
+	 * Returns true if the JRE scales, which is the case if:
+	 *   - environment variable GDK_SCALE is set and running on Java 9 or later
+	 *   - running on JetBrains Runtime 11 or later and scaling is enabled in system Settings
+	 */
+	private static boolean isSystemScaling() {
+		GraphicsConfiguration gc = GraphicsEnvironment.getLocalGraphicsEnvironment()
+			.getDefaultScreenDevice().getDefaultConfiguration();
+		return UIScale.getSystemScaleFactor( gc ) > 1;
+	}
 }