RootPane: give the root pane useful background, foreground and font

(fixes wrong background in title bar and menu bar when switching from Nimbus to FlatLaf)

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

@@ -393,6 +393,7 @@ public abstract class FlatLaf
 			"EditorPane.inactiveBackground",
 			"FormattedTextField.disabledBackground",
 			"PasswordField.disabledBackground",
+			"RootPane.background",
 			"Spinner.disabledBackground",
 			"TextArea.disabledBackground",
 			"TextArea.inactiveBackground",
@@ -411,7 +412,8 @@ public abstract class FlatLaf
 			"Spinner.disabledForeground",
 			"ToggleButton.disabledText" );
 		putDefaults( defaults, defaults.getColor( "textText" ),
-			"DesktopIcon.foreground" );
+			"DesktopIcon.foreground",
+			"RootPane.foreground" );
 
 		initFonts( defaults );
 		initIconColors( defaults, isDark() );
@@ -541,6 +543,9 @@ public abstract class FlatLaf
 			if( key instanceof String && (((String)key).endsWith( ".font" ) || ((String)key).endsWith( "Font" )) )
 				defaults.put( key, activeFont );
 		}
+
+		// add fonts that are not set in BasicLookAndFeel
+		defaults.put( "RootPane.font", activeFont );
 	}
 
 	private void initDefaultFont( UIDefaults defaults ) {

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

@@ -66,6 +66,9 @@ import com.formdev.flatlaf.util.UIScale;
  *
  * <!-- FlatWindowResizer -->
  *
+ * @uiDefault RootPane.font									Font	unused
+ * @uiDefault RootPane.background							Color
+ * @uiDefault RootPane.foreground							Color	unused
  * @uiDefault RootPane.borderDragThickness					int
  * @uiDefault RootPane.cornerDragWidth						int
  * @uiDefault RootPane.honorFrameMinimumSizeOnResize		boolean
@@ -126,8 +129,23 @@ public class FlatRootPaneUI
 	protected void installDefaults( JRootPane c ) {
 		super.installDefaults( c );
 
+		// Give the root pane useful background, foreground and font.
+		// Background is used for title bar and menu bar if native window decorations
+		// and unified background are enabled.
+		// Foreground and font are usually not used, but set for completeness.
+		// Not using LookAndFeel.installColorsAndFont() here because it will not work
+		// because the properties are null by default but inherit non-null values from parent.
+		if( !c.isBackgroundSet() || c.getBackground() instanceof UIResource )
+			c.setBackground( UIManager.getColor( "RootPane.background" ) );
+		if( !c.isForegroundSet() || c.getForeground() instanceof UIResource )
+			c.setForeground( UIManager.getColor( "RootPane.foreground" ) );
+		if( !c.isFontSet() || c.getFont() instanceof UIResource )
+			c.setFont( UIManager.getFont( "RootPane.font" ) );
+
 		// Update background color of JFrame or JDialog parent to avoid bad border
 		// on HiDPI screens when switching from light to dark Laf.
+		// Window background color is also used in native window decorations
+		// to fill background when window is initially shown or when resizing window.
 		// The background of JFrame is initialized in JFrame.frameInit() and
 		// the background of JDialog in JDialog.dialogInit(),
 		// but it was not updated when switching Laf.

flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/FlatInspector.java

@@ -474,9 +474,9 @@ public class FlatInspector
 		if( c instanceof JComponent )
 			appendRow( buf, "Border", toString( ((JComponent)c).getBorder(), classHierarchy ) );
 
-		appendRow( buf, "Background", toString( c.getBackground() ) );
+		appendRow( buf, "Background", toString( c.getBackground() ) + (c.isBackgroundSet() ? "" : "  NOT SET") );
-		appendRow( buf, "Foreground", toString( c.getForeground() ) );
+		appendRow( buf, "Foreground", toString( c.getForeground() ) + (c.isBackgroundSet() ? "" : "  NOT SET") );
-		appendRow( buf, "Font", toString( c.getFont() ) );
+		appendRow( buf, "Font", toString( c.getFont() ) + (c.isFontSet() ? "" : "  NOT SET") );
 
 		if( c instanceof JComponent ) {
 			try {

flatlaf-testing/dumps/uidefaults/FlatDarkLaf_1.8.0.txt

@@ -818,6 +818,7 @@ Resizable.resizeBorder         [lazy] 4,4,4,4  false    com.formdev.flatlaf.ui.F
 #---- RootPane ----
 
 RootPane.activeBorderColor     #4d5154  HSL 206   4  32    com.formdev.flatlaf.util.DerivedColor [UI]    lighten(7% autoInverse)
+RootPane.background            #3c3f41  HSL 204   4  25    javax.swing.plaf.ColorUIResource [UI]
 RootPane.border                [lazy] 1,1,1,1  false    com.formdev.flatlaf.ui.FlatRootPaneUI$FlatWindowBorder [UI]
 RootPane.borderDragThickness   5
 RootPane.cornerDragWidth       16
@@ -830,6 +831,8 @@ RootPane.defaultButtonWindowKeyBindings length=8    [Ljava.lang.Object;
     [5] press
     [6] ctrl released ENTER
     [7] release
+RootPane.font                  [active] $defaultFont [UI]
+RootPane.foreground            #bbbbbb  HSL   0   0  73    javax.swing.plaf.ColorUIResource [UI]
 RootPane.honorDialogMinimumSizeOnResize true
 RootPane.honorFrameMinimumSizeOnResize false
 RootPane.inactiveBorderColor   #484c4e  HSL 200   4  29    com.formdev.flatlaf.util.DerivedColor [UI]    lighten(5% autoInverse)

flatlaf-testing/dumps/uidefaults/FlatLightLaf_1.8.0.txt

@@ -823,6 +823,7 @@ Resizable.resizeBorder         [lazy] 4,4,4,4  false    com.formdev.flatlaf.ui.F
 #---- RootPane ----
 
 RootPane.activeBorderColor     #737373  HSL   0   0  45    com.formdev.flatlaf.util.DerivedColor [UI]    darken(50% autoInverse)
+RootPane.background            #f2f2f2  HSL   0   0  95    javax.swing.plaf.ColorUIResource [UI]
 RootPane.border                [lazy] 1,1,1,1  false    com.formdev.flatlaf.ui.FlatRootPaneUI$FlatWindowBorder [UI]
 RootPane.borderDragThickness   5
 RootPane.cornerDragWidth       16
@@ -835,6 +836,8 @@ RootPane.defaultButtonWindowKeyBindings length=8    [Ljava.lang.Object;
     [5] press
     [6] ctrl released ENTER
     [7] release
+RootPane.font                  [active] $defaultFont [UI]
+RootPane.foreground            #000000  HSL   0   0   0    javax.swing.plaf.ColorUIResource [UI]
 RootPane.honorDialogMinimumSizeOnResize true
 RootPane.honorFrameMinimumSizeOnResize false
 RootPane.inactiveBorderColor   #a6a6a6  HSL   0   0  65    com.formdev.flatlaf.util.DerivedColor [UI]    darken(30% autoInverse)

flatlaf-testing/dumps/uidefaults/FlatTestLaf_1.8.0.txt

@@ -833,6 +833,7 @@ Resizable.resizeBorder         [lazy] 4,4,4,4  false    com.formdev.flatlaf.ui.F
 
 #---- RootPane ----
 
+RootPane.background            #ccffcc  HSL 120 100  90    javax.swing.plaf.ColorUIResource [UI]
 RootPane.border                [lazy] 1,1,1,1  false    com.formdev.flatlaf.ui.FlatRootPaneUI$FlatWindowBorder [UI]
 RootPane.borderDragThickness   5
 RootPane.cornerDragWidth       16
@@ -845,6 +846,8 @@ RootPane.defaultButtonWindowKeyBindings length=8    [Ljava.lang.Object;
     [5] press
     [6] ctrl released ENTER
     [7] release
+RootPane.font                  [active] $defaultFont [UI]
+RootPane.foreground            #ff0000  HSL   0 100  50    javax.swing.plaf.ColorUIResource [UI]
 RootPane.honorDialogMinimumSizeOnResize true
 RootPane.honorFrameMinimumSizeOnResize false
 RootPaneUI                     com.formdev.flatlaf.ui.FlatRootPaneUI

flatlaf-theme-editor/src/main/resources/com/formdev/flatlaf/themeeditor/FlatLafUIKeys.txt

@@ -631,10 +631,13 @@ RangeSliderUI
 Resizable.resizeBorder
 RootPane.activeBorderColor
 RootPane.ancestorInputMap
+RootPane.background
 RootPane.border
 RootPane.borderDragThickness
 RootPane.cornerDragWidth
 RootPane.defaultButtonWindowKeyBindings
+RootPane.font
+RootPane.foreground
 RootPane.honorDialogMinimumSizeOnResize
 RootPane.honorFrameMinimumSizeOnResize
 RootPane.inactiveBorderColor