ScrollPane: increase viewport width for rounded border to remove/reduce gap between view and vertical scrollbar

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

@@ -454,6 +454,26 @@ public class FlatScrollPaneUI
 		paint( g, c );
 	}
 
+	@Override
+	public void paint( Graphics g, JComponent c ) {
+		Border viewportBorder = scrollpane.getViewportBorder();
+		if( viewportBorder != null ) {
+			Rectangle r = scrollpane.getViewportBorderBounds();
+			int padding = getBorderLeftRightPadding( scrollpane );
+			JScrollBar vsb = scrollpane.getVerticalScrollBar();
+			if( padding > 0 &&
+				vsb != null && vsb.isVisible() &&
+				scrollpane.getLayout() instanceof FlatScrollPaneLayout &&
+				((FlatScrollPaneLayout)scrollpane.getLayout()).canIncreaseViewportWidth( scrollpane ) )
+			{
+				boolean ltr = scrollpane.getComponentOrientation().isLeftToRight();
+				int extraWidth = Math.min( padding, vsb.getWidth() );
+				viewportBorder.paintBorder( scrollpane, g, r.x - (ltr ? 0 : extraWidth), r.y, r.width + extraWidth, r.height );
+			} else
+				viewportBorder.paintBorder( scrollpane, g, r.x, r.y, r.width, r.height );
+		}
+	}
+
 	/** @since 1.3 */
 	public static boolean isPermanentFocusOwner( JScrollPane scrollPane ) {
 		Component view = getView( scrollPane );
@@ -488,6 +508,13 @@ public class FlatScrollPaneUI
 			: 0;
 	}
 
+	private static int getBorderLeftRightPadding( JScrollPane scrollPane ) {
+		Border border = scrollPane.getBorder();
+		return (border instanceof FlatScrollPaneBorder)
+			? ((FlatScrollPaneBorder)border).getLeftRightPadding( scrollPane )
+			: 0;
+	}
+
 	//---- class Handler ------------------------------------------------------
 
 	/**
@@ -533,23 +560,46 @@ public class FlatScrollPaneUI
 			super.layoutContainer( parent );
 
 			JScrollPane scrollPane = (JScrollPane) parent;
-			Border border = scrollPane.getBorder();
-			int padding;
-			if( border instanceof FlatScrollPaneBorder &&
-				(padding = ((FlatScrollPaneBorder)border).getLeftRightPadding( scrollPane )) > 0 )
-			{
-				JScrollBar vsb = getVerticalScrollBar();
-				if( vsb != null && vsb.isVisible() ) {
-					// move vertical scrollbar to trailing edge
-					Insets insets = scrollPane.getInsets();
-					Rectangle r = vsb.getBounds();
-					int y = Math.max( r.y, insets.top + padding );
-					int y2 = Math.min( r.y + r.height, scrollPane.getHeight() - insets.bottom - padding );
-					boolean ltr = scrollPane.getComponentOrientation().isLeftToRight();
+			int padding = getBorderLeftRightPadding( scrollPane );
+			if( padding > 0 && vsb != null && vsb.isVisible() ) {
+				// move vertical scrollbar to trailing edge
+				Insets insets = scrollPane.getInsets();
+				Rectangle r = vsb.getBounds();
+				int y = Math.max( r.y, insets.top + padding );
+				int y2 = Math.min( r.y + r.height, scrollPane.getHeight() - insets.bottom - padding );
+				boolean ltr = scrollPane.getComponentOrientation().isLeftToRight();
 
-					vsb.setBounds( r.x + (ltr ? padding : -padding), y, r.width, y2 - y );
+				vsb.setBounds( r.x + (ltr ? padding : -padding), y, r.width, y2 - y );
+
+				// increase width of viewport, column header and horizontal scrollbar
+				if( canIncreaseViewportWidth( scrollPane ) ) {
+					int extraWidth = Math.min( padding, vsb.getWidth() );
+					resizeViewport( viewport, extraWidth, ltr );
+					resizeViewport( colHead, extraWidth, ltr );
+					resizeViewport( hsb, extraWidth, ltr );
 				}
 			}
 		}
+
+		boolean canIncreaseViewportWidth( JScrollPane scrollPane ) {
+			return scrollPane.getComponentOrientation().isLeftToRight()
+				? !isCornerVisible( upperRight ) && !isCornerVisible( lowerRight )
+				: !isCornerVisible( upperLeft ) && !isCornerVisible( lowerLeft );
+		}
+
+		private static boolean isCornerVisible( Component corner ) {
+			return corner != null &&
+				corner.getWidth() > 0 &&
+				corner.getHeight() > 0 &&
+				corner.isVisible();
+		}
+
+		private static void resizeViewport( Component c, int extraWidth, boolean ltr ) {
+			if( c == null )
+				return;
+
+			Rectangle vr = c.getBounds();
+			c.setBounds( vr.x - (ltr ? 0 : extraWidth), vr.y, vr.width + extraWidth, vr.height );
+		}
 	}
 }

flatlaf-testing/src/main/java/com/formdev/flatlaf/testing/FlatRoundedScrollPaneTest.java

@@ -24,6 +24,8 @@ import java.util.Arrays;
 import java.util.stream.Collectors;
 import javax.swing.*;
 import javax.swing.border.Border;
+import javax.swing.border.CompoundBorder;
+import javax.swing.border.MatteBorder;
 import javax.swing.table.AbstractTableModel;
 import javax.swing.tree.*;
 import com.formdev.flatlaf.FlatClientProperties;
@@ -212,6 +214,19 @@ public class FlatRoundedScrollPaneTest
 			: "?" );
 	}
 
+	private void viewportBorderChanged() {
+		Border viewportBorder = viewportBorderCheckBox.isSelected()
+			? new CompoundBorder(
+				new MatteBorder( 1, 1, 0, 0, Color.red ),
+				new MatteBorder( 0, 0, 1, 1, Color.blue ) )
+			: null;
+		for( JScrollPane scrollPane : allJScrollPanes ) {
+			scrollPane.setViewportBorder( viewportBorder );
+			scrollPane.revalidate();
+			scrollPane.repaint();
+		}
+	}
+
 	private void initComponents() {
 		// JFormDesigner - Component initialization - DO NOT MODIFY  //GEN-BEGIN:initComponents
 		splitPane2 = new JSplitPane();
@@ -247,6 +262,7 @@ public class FlatRoundedScrollPaneTest
 		cornersCheckBox = new JCheckBox();
 		columnHeaderCheckBox = new JCheckBox();
 		horizontalScrollBarCheckBox = new JCheckBox();
+		viewportBorderCheckBox = new JCheckBox();
 		rowHeaderCheckBox = new JCheckBox();
 		verticalScrollBarCheckBox = new JCheckBox();
 
@@ -437,6 +453,11 @@ public class FlatRoundedScrollPaneTest
 			horizontalScrollBarCheckBox.addActionListener(e -> horizontalScrollBarChanged());
 			panel3.add(horizontalScrollBarCheckBox, "cell 4 0");
 
+			//---- viewportBorderCheckBox ----
+			viewportBorderCheckBox.setText("Viewport border");
+			viewportBorderCheckBox.addActionListener(e -> viewportBorderChanged());
+			panel3.add(viewportBorderCheckBox, "cell 2 1");
+
 			//---- rowHeaderCheckBox ----
 			rowHeaderCheckBox.setText("Row Header");
 			rowHeaderCheckBox.addActionListener(e -> rowHeaderChanged());
@@ -485,6 +506,7 @@ public class FlatRoundedScrollPaneTest
 	private JCheckBox cornersCheckBox;
 	private JCheckBox columnHeaderCheckBox;
 	private JCheckBox horizontalScrollBarCheckBox;
+	private JCheckBox viewportBorderCheckBox;
 	private JCheckBox rowHeaderCheckBox;
 	private JCheckBox verticalScrollBarCheckBox;
 	// JFormDesigner - End of variables declaration  //GEN-END:variables

flatlaf-testing/src/main/java/com/formdev/flatlaf/testing/FlatRoundedScrollPaneTest.jfd

@@ -1,4 +1,4 @@
-JFDML JFormDesigner: "8.1.0.0.283" Java: "19.0.2" encoding: "UTF-8"
+JFDML JFormDesigner: "8.1.1.0.298" Java: "19.0.2" encoding: "UTF-8"
 
 new FormModel {
 	contentType: "form/swing"
@@ -216,6 +216,13 @@ new FormModel {
 				}, new FormLayoutConstraints( class net.miginfocom.layout.CC ) {
 					"value": "cell 4 0"
 				} )
+				add( new FormComponent( "javax.swing.JCheckBox" ) {
+					name: "viewportBorderCheckBox"
+					"text": "Viewport border"
+					addEvent( new FormEvent( "java.awt.event.ActionListener", "actionPerformed", "viewportBorderChanged", false ) )
+				}, new FormLayoutConstraints( class net.miginfocom.layout.CC ) {
+					"value": "cell 2 1"
+				} )
 				add( new FormComponent( "javax.swing.JCheckBox" ) {
 					name: "rowHeaderCheckBox"
 					"text": "Row Header"