Panel: support painting background with rounded corners (issue #367)

FlatLineBorder: support rounded corners

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

@@ -582,17 +582,18 @@ class UIDefaultsLoader
 
 	private static Object parseBorder( String value, Function<String, String> resolver, List<ClassLoader> addonClassLoaders ) {
 		if( value.indexOf( ',' ) >= 0 ) {
-			// top,left,bottom,right[,lineColor[,lineThickness]]
+			// top,left,bottom,right[,lineColor[,lineThickness[,arc]]]
 			List<String> parts = splitFunctionParams( value, ',' );
 			Insets insets = parseInsets( value );
 			ColorUIResource lineColor = (parts.size() >= 5)
 				? (ColorUIResource) parseColorOrFunction( resolver.apply( parts.get( 4 ) ), resolver, true )
 				: null;
-			float lineThickness = (parts.size() >= 6) ? parseFloat( parts.get( 5 ), true ) : 1f;
+			float lineThickness = (parts.size() >= 6 && !parts.get( 5 ).isEmpty()) ? parseFloat( parts.get( 5 ), true ) : 1f;
+			int arc = (parts.size() >= 7) ? parseInteger( parts.get( 6 ), true ) : 0;
 
 			return (LazyValue) t -> {
 				return (lineColor != null)
-					? new FlatLineBorder( insets, lineColor, lineThickness )
+					? new FlatLineBorder( insets, lineColor, lineThickness, arc )
 					: new FlatEmptyBorder( insets );
 			};
 		} else

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

@@ -37,15 +37,18 @@ public class FlatLineBorder
 {
 	private final Color lineColor;
 	private final float lineThickness;
+	/** @since 2 */ private final int arc;
 
 	public FlatLineBorder( Insets insets, Color lineColor ) {
-		this( insets, lineColor, 1f );
+		this( insets, lineColor, 1f, 0 );
 	}
 
-	public FlatLineBorder( Insets insets, Color lineColor, float lineThickness ) {
+	/** @since 2 */
+	public FlatLineBorder( Insets insets, Color lineColor, float lineThickness, int arc ) {
 		super( insets );
 		this.lineColor = lineColor;
 		this.lineThickness = lineThickness;
+		this.arc = arc;
 	}
 
 	public Color getLineColor() {
@@ -56,13 +59,18 @@ public class FlatLineBorder
 		return lineThickness;
 	}
 
+	/** @since 2 */
+	public int getArc() {
+		return arc;
+	}
+
 	@Override
 	public void paintBorder( Component c, Graphics g, int x, int y, int width, int height ) {
 		Graphics2D g2 = (Graphics2D) g.create();
 		try {
 			FlatUIUtils.setRenderingHints( g2 );
 			FlatUIUtils.paintOutlinedComponent( g2, x, y, width, height,
-				0, 0, 0, scale( getLineThickness() ), 0, null, getLineColor(), null );
+				0, 0, 0, scale( getLineThickness() ), scale( getArc() ), null, getLineColor(), null );
 		} finally {
 			g2.dispose();
 		}

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

@@ -16,14 +16,18 @@
 
 package com.formdev.flatlaf.ui;
 
+import java.awt.Graphics;
+import java.awt.Graphics2D;
 import java.beans.PropertyChangeListener;
 import java.util.Map;
 import javax.swing.JComponent;
 import javax.swing.JPanel;
 import javax.swing.plaf.ComponentUI;
 import javax.swing.plaf.basic.BasicPanelUI;
+import com.formdev.flatlaf.ui.FlatStylingSupport.Styleable;
 import com.formdev.flatlaf.ui.FlatStylingSupport.StyleableUI;
 import com.formdev.flatlaf.util.LoggingFacade;
+import com.formdev.flatlaf.util.UIScale;
 
 /**
  * Provides the Flat LaF UI delegate for {@link javax.swing.JPanel}.
@@ -32,7 +36,7 @@ import com.formdev.flatlaf.util.LoggingFacade;
  *
  * @uiDefault Panel.font				Font	unused
  * @uiDefault Panel.background			Color	only used if opaque
- * @uiDefault Panel.foreground			Color
+ * @uiDefault Panel.foreground			Color	unused
  * @uiDefault Panel.border				Border
  *
  * @author Karl Tauber
@@ -41,6 +45,9 @@ public class FlatPanelUI
 	extends BasicPanelUI
 	implements StyleableUI
 {
+	// only used via styling (not in UI defaults)
+	/** @since 2 */ @Styleable protected int arc = -1;
+
 	private final boolean shared;
 	private PropertyChangeListener propertyChangeListener;
 	private Map<String, Object> oldStyleValues;
@@ -113,4 +120,34 @@ public class FlatPanelUI
 	public Map<String, Class<?>> getStyleableInfos( JComponent c ) {
 		return FlatStylingSupport.getAnnotatedStyleableInfos( this );
 	}
+
+	@Override
+	public void update( Graphics g, JComponent c ) {
+		// fill background
+		if( c.isOpaque() ) {
+			int width = c.getWidth();
+			int height = c.getHeight();
+			int arc = (this.arc >= 0)
+				? this.arc
+				: ((c.getBorder() instanceof FlatLineBorder)
+					? ((FlatLineBorder)c.getBorder()).getArc()
+					: 0);
+
+			// fill background with parent color to avoid garbage in rounded corners
+			if( arc > 0 )
+				FlatUIUtils.paintParentBackground( g, c );
+
+			g.setColor( c.getBackground() );
+			if( arc > 0 ) {
+				// fill rounded rectangle if having rounded corners
+				Object[] oldRenderingHints = FlatUIUtils.setRenderingHints( g );
+				FlatUIUtils.paintComponentBackground( (Graphics2D) g, 0, 0, width, height,
+					0, UIScale.scale( arc ) );
+				FlatUIUtils.resetRenderingHints( g, oldRenderingHints );
+			} else
+				g.fillRect( 0, 0, width, height );
+		}
+
+		paint( g, c );
+	}
 }