Linux: support KDE (#1)

The Swing fonts are not updated when the user changes system font size (System Settings > Fonts > Force Font DPI). A application restart is necessary. This is the same behavior as in native KDE applications.

tested on Kubuntu 19.04

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

@@ -19,24 +19,39 @@
 import java.awt.Font;
 import java.awt.GraphicsEnvironment;
 import java.awt.Toolkit;
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.StringTokenizer;
 import javax.swing.text.StyleContext;
+import com.formdev.flatlaf.util.SystemInfo;
 
 /**
  * @author Karl Tauber
  */
 class LinuxFontPolicy
 {
  static Font getFont() {
+ return SystemInfo.IS_KDE ? getKDEFont() : getGnomeFont();
+ }
+
+ /**
+ * Gets the default font for Gnome.
+ */
+ private static Font getGnomeFont() {
  // see class com.sun.java.swing.plaf.gtk.PangoFonts background information
 
  Object fontName = Toolkit.getDefaultToolkit().getDesktopProperty( "gnome.Gtk/FontName" );
  if( !(fontName instanceof String) )
  fontName = "sans 10";
 
- String family = "";
- int style = Font.PLAIN;
- int size = 10;
+ String family = "";
+ int style = Font.PLAIN;
+ int size = 10;
 
  StringTokenizer st = new StringTokenizer( (String) fontName );
  while( st.hasMoreTokens() ) {
@@ -57,7 +72,7 @@ else if( Character.isDigit( word.charAt( 0 ) ) ) {
  }
 
  // scale font size
- double dsize = size * getSystemFontScale();
+ double dsize = size * getGnomeFontScale();
  size = (int) (dsize + 0.5);
  if( size < 1 )
  size = 1;
@@ -67,6 +82,10 @@ else if( Character.isDigit( word.charAt( 0 ) ) ) {
  if( logicalFamily != null )
  family = logicalFamily;
 
+ return createFont( family, style, size, dsize );
+ }
+
+ private static Font createFont( String family, int style, int size, double dsize ) {
  // using StyleContext.getFont() here because it uses
  // sun.font.FontUtilities.getCompositeFontUIResource()
  Font font = new StyleContext().getFont( family, style, size );
@@ -77,7 +96,7 @@ else if( Character.isDigit( word.charAt( 0 ) ) ) {
  return font;
  }
 
- private static double getSystemFontScale() {
+ private static double getGnomeFontScale() {
  // see class com.sun.java.swing.plaf.gtk.PangoFonts background information
 
  Object value = Toolkit.getDefaultToolkit().getDesktopProperty( "gnome.Xft/DPI" );
@@ -107,4 +126,123 @@ private static String mapFcName( String name ) {
  }
  return null;
  }
+
+ /**
+ * Gets the default font for KDE for KDE configuration files.
+ *
+ * The Swing fonts are not updated when the user changes system font size
+ * (System Settings > Fonts > Force Font DPI). A application restart is necessary.
+ * This is the same behavior as in native KDE applications.
+ *
+ * The "display scale factor" (kdeglobals: [KScreen] > ScaleFactor) is not used
+ * KDE also does not use it to calculate font size. Only forceFontDPI is used by KDE.
+ * If user changes "display scale factor" (System Settings > Display and Monitors >
+ * Displays > Scale Display), the forceFontDPI is also changed to reflect the scale factor.
+ */
+ private static Font getKDEFont() {
+ List<String> kdeglobals = readConfig( "kdeglobals" );
+ List<String> kcmfonts = readConfig( "kcmfonts" );
+
+ String generalFont = getConfigEntry( kdeglobals, "General", "font" );
+ String forceFontDPI = getConfigEntry( kcmfonts, "General", "forceFontDPI" );
+
+ String family = "sansserif";
+ int style = Font.PLAIN;
+ int size = 10;
+
+ if( generalFont != null ) {
+ List<String> strs = FlatLaf.split( generalFont, ',' );
+ try {
+ family = strs.get( 0 );
+ size = Integer.parseInt( strs.get( 1 ) );
+ if( "75".equals( strs.get( 4 ) ) )
+ style |= Font.BOLD;
+ if( "1".equals( strs.get( 5 ) ) )
+ style |= Font.ITALIC;
+ } catch( RuntimeException ex ) {
+ ex.printStackTrace();
+ }
+ }
+
+ // font dpi
+ int dpi = 96;
+ if( forceFontDPI != null ) {
+ try {
+ dpi = Integer.parseInt( forceFontDPI );
+ if( dpi <= 0 )
+ dpi = 96;
+ if( dpi < 50 )
+ dpi = 50;
+ } catch( NumberFormatException ex ) {
+ ex.printStackTrace();
+ }
+ }
+
+ // scale font size
+ double fontScale = dpi / 72.0;
+ double dsize = size * fontScale;
+ size = (int) (dsize + 0.5);
+ if( size < 1 )
+ size = 1;
+
+ return createFont( family, style, size, dsize );
+ }
+
+ private static List<String> readConfig( String filename ) {
+ File userHome = new File( System.getProperty( "user.home" ) );
+
+ // search for config file
+ String[] configDirs = {
+ ".config", // KDE 5
+ ".kde4/share/config", // KDE 4
+ ".kde/share/config"// KDE 3
+ };
+ File file = null;
+ for( String configDir : configDirs ) {
+ file = new File( userHome, configDir + "/" + filename );
+ if( file.isFile() )
+ break;
+ }
+ if( !file.isFile() )
+ return Collections.emptyList();
+
+ // read config file
+ ArrayList<String> lines = new ArrayList<>( 200 );
+ try( BufferedReader reader = new BufferedReader( new FileReader( file ) ) ) {
+ String line = null;
+ while( (line = reader.readLine()) != null )
+ lines.add( line );
+ } catch( IOException ex ) {
+ ex.printStackTrace();
+ }
+ return lines;
+ }
+
+ private static String getConfigEntry( List<String> config, String group, String key ) {
+ int groupLength = group.length();
+ int keyLength = key.length();
+ boolean inGroup = false;
+ for( String line : config ) {
+ if( !inGroup ) {
+ if( line.length() >= groupLength + 2 &&
+ line.charAt( 0 ) == '[' &&
+ line.charAt( groupLength + 1 ) == ']' &&
+ line.indexOf( group ) == 1 )
+ {
+ inGroup = true;
+ }
+ } else {
+ if( line.startsWith( "[" ) )
+ return null;
+
+ if( line.length() >= keyLength + 2 &&
+ line.charAt( keyLength ) == '=' &&
+ line.startsWith( key ) )
+ {
+ return line.substring( keyLength + 1 );
+ }
+ }
+ }
+ return null;
+ }
 }

flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java

@@ -40,6 +40,9 @@ public class SystemInfo
  // Java VMs
  public static final boolean IS_JETBRAINS_JVM;
 
+ // UI toolkits
+ public static final boolean IS_KDE;
+
  static {
  // platforms
  String osName = System.getProperty( "os.name" ).toLowerCase( Locale.ENGLISH );
@@ -58,6 +61,9 @@ public class SystemInfo
  // Java VMs
  IS_JETBRAINS_JVM = System.getProperty( "java.vm.vendor", "Unknown" )
  .toLowerCase( Locale.ENGLISH ).contains( "jetbrains" );
+
+ // UI toolkits
+ IS_KDE = (IS_LINUX && System.getenv( "KDE_FULL_SESSION" ) != null);
  }
 
  private static long scanVersion( String version ) {

flatlaf-core/src/main/java/com/formdev/flatlaf/util/UIScale.java

@@ -157,8 +157,8 @@ private static float computeScaleFactor( Font font ) {
  if( "Tahoma".equals( font.getFamily() ) )
  fontSizeDivider = 11f;
  } else if( SystemInfo.IS_LINUX ) {
- // default font size for Unity and Gnome is 15
- fontSizeDivider = 15f;
+ // default font size for Unity and Gnome is 15 and for KDE it is 13
+ fontSizeDivider = SystemInfo.IS_KDE ? 13f : 15f;
  }
 
  return font.getSize() / fontSizeDivider;