UIScale introduced

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatButtonBorder.java

@@ -25,6 +25,7 @@ import java.awt.Insets;
 import java.awt.Paint;
 import javax.swing.UIManager;
 import javax.swing.plaf.basic.BasicBorders;
+import com.formdev.flatlaf.util.UIScale;
 
 /**
  * Border for {@link javax.swing.JButton}.
@@ -42,7 +43,7 @@ public class FlatButtonBorder
 
 			float focusWidth = getFocusWidth();
 			float lineWidth = getLineWidth();
-			float arc = 6; //TODO
+			float arc = UIScale.scale( 6f ); //TODO
 
 			g2.setPaint( getBorderColor( c ) );
 			FlatUIUtils.drawRoundRectangle( g2, x, y, width, height, focusWidth, lineWidth, arc );
@@ -66,7 +67,7 @@ public class FlatButtonBorder
 
 	@Override
 	public Insets getBorderInsets( Component c, Insets insets ) {
-		int w = Math.round( getFocusWidth() + getLineWidth() );
+		int w = UIScale.round( getFocusWidth() + getLineWidth() );
 
 		insets = super.getBorderInsets( c, insets );
 		insets.top += w;
@@ -78,11 +79,11 @@ public class FlatButtonBorder
 
 	protected float getFocusWidth() {
 		//TODO
-		return 2;
+		return UIScale.scale( 2f );
 	}
 
 	protected float getLineWidth() {
 		//TODO
-		return 1;
+		return UIScale.scale( 1f );
 	}
 }

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatButtonUI.java

@@ -28,6 +28,7 @@ import javax.swing.JComponent;
 import javax.swing.UIManager;
 import javax.swing.plaf.ComponentUI;
 import javax.swing.plaf.basic.BasicButtonUI;
+import com.formdev.flatlaf.util.UIScale;
 import sun.swing.SwingUtilities2;
 
 /**
@@ -61,8 +62,8 @@ public class FlatButtonUI
 					FlatUIUtils.setRenderingHints( g2 );
 
 					//TODO
-					float focusWidth = 2;
+					float focusWidth = UIScale.scale( 2f );
-					float arc = 6;
+					float arc = UIScale.scale( 6f );
 
 					g2.setColor( getBackground( c ) );
 					FlatUIUtils.fillRoundRectangle( g2, 0, 0, c.getWidth(), c.getHeight(), focusWidth, arc );

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

@@ -17,6 +17,7 @@
 package com.formdev.flatlaf.util;
 
 import java.util.Locale;
+import java.util.StringTokenizer;
 
 /**
  * Provides information about the current system.
@@ -29,11 +30,43 @@ public class SystemInfo
 	public static final boolean IS_MAC;
 	public static final boolean IS_LINUX;
 
+	public static final boolean IS_JAVA_9_OR_LATER;
+
+	public static final boolean IS_JETBRAINS_JVM;
+
 	static {
 		String osName = System.getProperty( "os.name" ).toLowerCase( Locale.ENGLISH );
 
 		IS_WINDOWS = osName.startsWith( "windows" );
 		IS_MAC = osName.startsWith( "mac" );
 		IS_LINUX = osName.startsWith( "linux" );
+
+		int javaVersion = scanVersion( System.getProperty( "java.version" ) );
+		IS_JAVA_9_OR_LATER = (javaVersion >= toVersion( 9, 0, 0, 0 ));
+
+		IS_JETBRAINS_JVM = System.getProperty( "java.vm.vendor", "Unknown" )
+			.toLowerCase( Locale.ENGLISH ).contains( "jetbrains" );
+	}
+
+	private static int scanVersion( String version ) {
+		int major = 1;
+		int minor = 0;
+		int micro = 0;
+		int patch = 0;
+		try {
+			StringTokenizer st = new StringTokenizer( version, "._-+" );
+			major = Integer.parseInt( st.nextToken() );
+			minor = Integer.parseInt( st.nextToken() );
+			micro = Integer.parseInt( st.nextToken() );
+			patch = Integer.parseInt( st.nextToken() );
+		} catch( Exception ex ) {
+			// ignore
+		}
+
+		return toVersion( major, minor, micro, patch );
+	}
+
+	private static int toVersion( int major, int minor, int micro, int patch ) {
+		return (major << 24) + (minor << 16) + (micro << 8) + patch;
 	}
 }

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

@@ -0,0 +1,188 @@
+/*
+ * Copyright 2019 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.formdev.flatlaf.util;
+
+import java.awt.Font;
+import java.awt.GraphicsEnvironment;
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
+import java.lang.reflect.Method;
+import javax.swing.LookAndFeel;
+import javax.swing.UIManager;
+
+/**
+ * Two scaling modes are supported for HiDPI displays:
+ *
+ * 1) system scaling mode
+ *
+ * This mode is supported since Java 9 on all platforms and in some Java 8 VMs
+ * (e.g. Apple and JetBrains). The JRE determines the scale factor per-display and
+ * adds a scaling transformation to the graphics object.
+ * E.g. invokes {@code java.awt.Graphics2D.scale( 1.5, 1.5 )} for 150%.
+ * So the JRE does the scaling itself.
+ * E.g. when you draw a 10px line, a 15px line is drawn on screen.
+ * The scale factor may be different for each connected display.
+ *
+ * 2) user scaling mode
+ *
+ * This mode is for Java 8 compatibility and can be removed when changing minimum
+ * required Java version to 9.
+ * The user scale factor is computed based on the used font.
+ * The JRE does not scale anything.
+ * So we have to invoke {@link #scale(float)} where necessary.
+ * There is only one user scale factor for all displays.
+ *
+ * @author Karl Tauber
+ */
+public class UIScale
+{
+	private static final boolean DEBUG = false;
+
+	//---- system scaling (Java 9) --------------------------------------------
+
+	private static Boolean jreHiDPI;
+
+	private static boolean isJreHiDPIEnabled() {
+		if( jreHiDPI != null )
+			return jreHiDPI;
+
+		jreHiDPI = false;
+
+		if( SystemInfo.IS_JAVA_9_OR_LATER ) {
+			// Java 9 and later supports per-monitor scaling
+			jreHiDPI = true;
+		} else if( SystemInfo.IS_JETBRAINS_JVM ) {
+			// IntelliJ IDEA ships its own JetBrains Java 8 JRE that may supports per-monitor scaling
+			// see com.intellij.ui.JreHiDpiUtil.isJreHiDPIEnabled()
+			try {
+				GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
+				Class<?> sunGeClass = Class.forName( "sun.java2d.SunGraphicsEnvironment" );
+				if( sunGeClass.isInstance( ge ) ) {
+					Method m = sunGeClass.getDeclaredMethod( "isUIScaleOn" );
+					jreHiDPI = (Boolean) m.invoke( ge );
+				}
+			} catch( Throwable ex ) {
+				// ignore
+			}
+		}
+
+		return jreHiDPI;
+	}
+
+	//---- user scaling (Java 8) ----------------------------------------------
+
+	private static float scaleFactor = 1;
+
+	static {
+		if( isEnabled() ) {
+			// listener to update scale factor if LaF changed or if Label.font changed
+			// (e.g. option "Override default fonts" in IntelliJ IDEA)
+			PropertyChangeListener listener = new PropertyChangeListener() {
+				@Override
+				public void propertyChange( PropertyChangeEvent e ) {
+					String propName = e.getPropertyName();
+					if( "lookAndFeel".equals( propName ) ) {
+						// it is not necessary (and possible) to remove listener of old LaF defaults
+						if( e.getNewValue() instanceof LookAndFeel )
+							UIManager.getLookAndFeelDefaults().addPropertyChangeListener( this );
+						updateScaleFactor();
+					} else if( "Label.font".equals( propName ) )
+						updateScaleFactor();
+				}
+			};
+			UIManager.addPropertyChangeListener( listener );
+			UIManager.getLookAndFeelDefaults().addPropertyChangeListener( listener );
+
+			updateScaleFactor();
+		}
+	}
+
+	private static void updateScaleFactor() {
+		if( !isEnabled() )
+			return;
+
+		// use font size to calculate scale factor (instead of DPI)
+		// because even if we are on a HiDPI display it is not sure
+		// that a larger font size is set by the current LaF
+		// (e.g. can avoid large icons with small text)
+		Font font = UIManager.getFont( "Label.font" );
+
+		// default font size
+		float fontSizeDivider = 12f;
+
+		if( SystemInfo.IS_WINDOWS ) {
+			// Windows LaF uses Tahoma font rather than the actual Windows system font (Segoe UI),
+			// and its size is always ca. 10% smaller than the actual system font size.
+			// Tahoma 11 is used at 100%
+			if( "Tahoma".equals( font.getFamily() ) )
+				fontSizeDivider = 11f;
+		} else if( SystemInfo.IS_LINUX ) {
+			// default font size for Unity and Gnome is 15
+			fontSizeDivider = 15f;
+		}
+
+		setUserScaleFactor( font.getSize() / fontSizeDivider );
+	}
+
+	private static boolean isEnabled() {
+		if( isJreHiDPIEnabled() )
+			return false; // disable user scaling if JRE scales
+
+		// same as in IntelliJ IDEA
+		String hidpi = System.getProperty( "hidpi" );
+		return (hidpi != null) ? Boolean.parseBoolean( hidpi ) : true;
+	}
+
+	public static float getUserScaleFactor() {
+		return scaleFactor;
+	}
+
+	private static void setUserScaleFactor( float scaleFactor ) {
+		if( scaleFactor <= 1f )
+			scaleFactor = 1f;
+		else // round scale factor to 1/4
+			scaleFactor = Math.round( scaleFactor * 4f ) / 4f;
+
+		UIScale.scaleFactor = scaleFactor;
+
+		if( DEBUG )
+			System.out.println( "HiDPI scale factor " + scaleFactor );
+	}
+
+	public static float scale( float value ) {
+		return (scaleFactor == 1) ? value : (value * scaleFactor);
+	}
+
+	public static int scale( int value ) {
+		return (scaleFactor == 1) ? value : round( value * scaleFactor );
+	}
+
+	public static float unscale( float value ) {
+		return (scaleFactor == 1f) ? value : (value / scaleFactor);
+	}
+
+	public static int unscale( int value ) {
+		return (scaleFactor == 1f) ? value : round( value / scaleFactor );
+	}
+
+	public static int round( float value ) {
+		// subtracting 0.01 gives "better" results in some cases
+		//   e.g. 2px * 125% = 2px instead of 3px
+		//     or 1px * 150% = 1px instead of 2px
+		return Math.round( value - 0.01f );
+	}
+}

flatlaf-core/src/test/java/com/formdev/flatlaf/FlatComponentsTest.java

@@ -37,7 +37,7 @@ public class FlatComponentsTest
 
 		JOptionPane.showMessageDialog( null,
 			new FlatComponentsTest(),
-			"FlatComponentsTest",
+			"FlatComponentsTest (Java " + System.getProperty( "java.version" ) + ")",
 			JOptionPane.PLAIN_MESSAGE );
 	}