Drop shadows:

- reworked drop shadows implementation to support 4-sided shadows
- use 4-sided shadow for internal frames
- made shadows configurable in UI defaults
- made shadows dark in dark themes

(issue #94)

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

@@ -29,6 +29,12 @@ import com.formdev.flatlaf.util.UIScale;
 
 /**
  * Paints a drop shadow border around the component.
+ * Supports 1-sided, 2-side, 3-sided or 4-sided drop shadows.
+ * <p>
+ * The shadow insets allow specifying drop shadow thickness for each side.
+ * A zero or negative value hides the drop shadow on that side.
+ * A negative value can be used to indent the drop shadow on corners.
+ * E.g. -4 on left indents drop shadow at top-left and bottom-left corners by 4 pixels.
  *
  * @author Karl Tauber
  */
@@ -36,10 +42,10 @@ public class FlatDropShadowBorder
 	extends FlatEmptyBorder
 {
 	private final Color shadowColor;
-	private final int shadowSize;
-	private final int cornerInset;
-	private final int shadowAlpha;
+	private final Insets shadowInsets;
+	private final float shadowOpacity;
 
+	private final int shadowSize;
 	private Image shadowImage;
 	private Color lastShadowColor;
 	private double lastSystemScaleFactor;
@@ -50,26 +56,36 @@ public class FlatDropShadowBorder
 	}
 
 	public FlatDropShadowBorder( Color shadowColor ) {
-		this( shadowColor, 4, 4, 128 );
+		this( shadowColor, 4, 0.5f );
 	}
 
-	public FlatDropShadowBorder( Color shadowColor, int shadowSize, int cornerInset, int shadowAlpha ) {
-		super( new Insets( 0, 0, shadowSize, shadowSize ) );
+	public FlatDropShadowBorder( Color shadowColor, int shadowSize, float shadowOpacity ) {
+		this( shadowColor, new Insets( -shadowSize, -shadowSize, shadowSize, shadowSize ), shadowOpacity );
+	}
+
+	public FlatDropShadowBorder( Color shadowColor, Insets shadowInsets, float shadowOpacity ) {
+		super( Math.max( shadowInsets.top, 0 ), Math.max( shadowInsets.left, 0 ),
+			Math.max( shadowInsets.bottom, 0 ), Math.max( shadowInsets.right, 0 ) );
 		this.shadowColor = shadowColor;
-		this.shadowSize = shadowSize;
-		this.cornerInset = cornerInset;
-		this.shadowAlpha = shadowAlpha;
+		this.shadowInsets = shadowInsets;
+		this.shadowOpacity = shadowOpacity;
+
+		shadowSize = Math.max(
+			Math.max( shadowInsets.left, shadowInsets.right ),
+			Math.max( shadowInsets.top, shadowInsets.bottom ) );
 	}
 
 	@Override
 	public void paintBorder( Component c, Graphics g, int x, int y, int width, int height ) {
+		if( shadowSize <= 0 )
+			return;
+
 		HiDPIUtils.paintAtScale1x( (Graphics2D) g, x, y, width, height, this::paintImpl );
 	}
 
 	private void paintImpl( Graphics2D g, int x, int y, int width, int height, double scaleFactor ) {
 		Color shadowColor = (this.shadowColor != null) ? this.shadowColor : g.getColor();
-		int shadowSize = (int) Math.ceil( UIScale.scale( this.shadowSize ) * scaleFactor );
-		int cornerInset = (int) Math.ceil( UIScale.scale( this.cornerInset ) * scaleFactor );
+		int shadowSize = scale( this.shadowSize, scaleFactor );
 
 		// create and cache shadow image
 		float userScaleFactor = UIScale.getUserScaleFactor();
@@ -78,7 +94,7 @@ public class FlatDropShadowBorder
 			lastSystemScaleFactor != scaleFactor ||
 			lastUserScaleFactor != userScaleFactor )
 		{
-			shadowImage = createShadowImage( shadowColor, shadowSize, shadowAlpha,
+			shadowImage = createShadowImage( shadowColor, shadowSize, shadowOpacity,
 				(float) (scaleFactor * userScaleFactor) );
 			lastShadowColor = shadowColor;
 			lastSystemScaleFactor = scaleFactor;
@@ -87,55 +103,103 @@ public class FlatDropShadowBorder
 
 /*debug
 		int m = shadowImage.getWidth( null );
+		Color oldColor = g.getColor();
 		g.setColor( Color.lightGray );
 		g.drawRect( x - m - 1, y - m - 1, m + 1, m + 1 );
 		g.setColor( Color.white );
 		g.fillRect( x - m, y - m, m, m );
 		g.drawImage( shadowImage, x - m, y - m, null );
+		g.setColor( oldColor );
 debug*/
 
-		int x1c = x + cornerInset;
-		int y1c = y + cornerInset;
-		int x1cs = x1c + shadowSize;
-		int y1cs = y1c + shadowSize;
+		int left = scale( shadowInsets.left, scaleFactor );
+		int right = scale( shadowInsets.right, scaleFactor );
+		int top = scale( shadowInsets.top, scaleFactor );
+		int bottom = scale( shadowInsets.bottom, scaleFactor );
 
-		int x2s = x + width;
-		int y2s = y + height;
-		int x2 = x2s - shadowSize;
-		int y2 = y2s - shadowSize;
+		// shadow outer coordinates
+		int x1o = x - Math.min( left, 0 );
+		int y1o = y - Math.min( top, 0 );
+		int x2o = x + width + Math.min( right, 0 );
+		int y2o = y + height + Math.min( bottom, 0 );
+
+		// shadow inner coordinates
+		int x1i = x1o + shadowSize;
+		int y1i = y1o + shadowSize;
+		int x2i = x2o - shadowSize;
+		int y2i = y2o - shadowSize;
 
 		int wh = (shadowSize * 2) - 1;
 		int center = shadowSize - 1;
 
-		// left-bottom edge
-		g.drawImage( shadowImage, x1c, y2, x1cs, y2s,
-			0, center, shadowSize, wh, null );
+		// left-top edge
+		if( left > 0 || top > 0 ) {
+			g.drawImage( shadowImage, x1o, y1o, x1i, y1i,
+				0, 0, center, center, null );
+		}
 
-		// bottom shadow
-		g.drawImage( shadowImage, x1cs, y2, x2, y2s,
-			center, center, center + 1, wh, null );
-
-		// right-bottom edge
-		g.drawImage( shadowImage, x2, y2, x2s, y2s,
-			center, center, wh, wh, null );
-
-		// right shadow
-		g.drawImage( shadowImage, x2, y1cs, x2s, y2,
-			center, center, wh, center + 1, null );
+		// top shadow
+		if( top > 0 ) {
+			g.drawImage( shadowImage, x1i, y1o, x2i, y1i,
+				center, 0, center + 1, center, null );
+		}
 
 		// right-top edge
-		g.drawImage( shadowImage, x2, y1c, x2s, y1cs,
-			center, 0, wh, shadowSize, null );
+		if( right > 0 || top > 0 ) {
+			g.drawImage( shadowImage, x2i, y1o, x2o, y1i,
+				center, 0, wh, center, null );
+		}
+
+		// left shadow
+		if( left > 0 ) {
+			g.drawImage( shadowImage, x1o, y1i, x1i, y2i,
+				0, center, center, center + 1, null );
+		}
+
+		// right shadow
+		if( right > 0 ) {
+			g.drawImage( shadowImage, x2i, y1i, x2o, y2i,
+				center, center, wh, center + 1, null );
+		}
+
+		// left-bottom edge
+		if( left > 0 || bottom > 0 ) {
+			g.drawImage( shadowImage, x1o, y2i, x1i, y2o,
+				0, center, center, wh, null );
+		}
+
+		// bottom shadow
+		if( bottom > 0 ) {
+			g.drawImage( shadowImage, x1i, y2i, x2i, y2o,
+				center, center, center + 1, wh, null );
+		}
+
+		// right-bottom edge
+		if( right > 0 || bottom > 0 ) {
+			g.drawImage( shadowImage, x2i, y2i, x2o, y2o,
+				center, center, wh, wh, null );
+		}
+	}
+
+	private int scale( int value, double scaleFactor ) {
+		return (int) Math.ceil( UIScale.scale( value ) * scaleFactor );
 	}
 
 	private static BufferedImage createShadowImage( Color shadowColor, int shadowSize,
-		int shadowAlpha, float scaleFactor )
+		float shadowOpacity, float scaleFactor )
 	{
 		int shadowRGB = shadowColor.getRGB() & 0xffffff;
+		int shadowAlpha = (int) (255 * shadowOpacity);
 		Color startColor = new Color( shadowRGB | ((shadowAlpha & 0xff) << 24), true );
 		Color midColor = new Color( shadowRGB | (((shadowAlpha / 2) & 0xff) << 24), true );
 		Color endColor = new Color( shadowRGB, true );
 
+/*debug
+		startColor = Color.red;
+		midColor = Color.green;
+		endColor = Color.blue;
+debug*/
+
 		int wh = (shadowSize * 2) - 1;
 		int center = shadowSize - 1;
 

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

@@ -112,8 +112,16 @@ public class FlatInternalFrameUI
 		private final Color activeBorderColor = UIManager.getColor( "InternalFrame.activeBorderColor" );
 		private final Color inactiveBorderColor = UIManager.getColor( "InternalFrame.inactiveBorderColor" );
 		private final int borderLineWidth = FlatUIUtils.getUIInt( "InternalFrame.borderLineWidth", 1 );
+		private final boolean dropShadowPainted = UIManager.getBoolean( "InternalFrame.dropShadowPainted" );
 
-		private final FlatDropShadowBorder dropShadowBorder = new FlatDropShadowBorder();
+		private final FlatDropShadowBorder activeDropShadowBorder = new FlatDropShadowBorder(
+			UIManager.getColor( "InternalFrame.activeDropShadowColor" ),
+			UIManager.getInsets( "InternalFrame.activeDropShadowInsets" ),
+			FlatUIUtils.getUIFloat( "InternalFrame.activeDropShadowOpacity", 0.5f ) );
+		private final FlatDropShadowBorder inactiveDropShadowBorder = new FlatDropShadowBorder(
+			UIManager.getColor( "InternalFrame.inactiveDropShadowColor" ),
+			UIManager.getInsets( "InternalFrame.inactiveDropShadowInsets" ),
+			FlatUIUtils.getUIFloat( "InternalFrame.inactiveDropShadowOpacity", 0.5f ) );
 
 		public FlatInternalFrameBorder() {
 			super( UIManager.getInsets( "InternalFrame.borderMargins" ) );
@@ -150,10 +158,17 @@ public class FlatInternalFrameUI
 				g2.setColor( f.isSelected() ? activeBorderColor : inactiveBorderColor );
 
 				// paint drop shadow
-				Insets dropShadowInsets = dropShadowBorder.getBorderInsets();
-				dropShadowBorder.paintBorder( c, g2, (int) rx, (int) ry,
-					(int) rwidth + dropShadowInsets.right,
-					(int) rheight + dropShadowInsets.bottom );
+				if( dropShadowPainted ) {
+					FlatDropShadowBorder dropShadowBorder = f.isSelected()
+						? activeDropShadowBorder : inactiveDropShadowBorder;
+
+					Insets dropShadowInsets = dropShadowBorder.getBorderInsets();
+					dropShadowBorder.paintBorder( c, g2,
+						(int) rx - dropShadowInsets.left,
+						(int) ry - dropShadowInsets.top,
+						(int) rwidth + dropShadowInsets.left + dropShadowInsets.right,
+						(int) rheight + dropShadowInsets.top + dropShadowInsets.bottom );
+				}
 
 				// paint border
 				g2.fill( FlatUIUtils.createRectangle( rx, ry, rwidth, rheight, lineWidth ) );

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

@@ -29,6 +29,7 @@ import javax.swing.JComponent;
 import javax.swing.Popup;
 import javax.swing.PopupFactory;
 import javax.swing.SwingUtilities;
+import javax.swing.UIManager;
 import javax.swing.border.Border;
 import com.formdev.flatlaf.util.SystemInfo;
 
@@ -49,6 +50,9 @@ public class FlatPopupFactory
 	public Popup getPopup( Component owner, Component contents, int x, int y )
 		throws IllegalArgumentException
 	{
+		if( !UIManager.getBoolean( "Popup.dropShadowPainted" ) && !SystemInfo.IS_MAC )
+			return super.getPopup( owner, contents, x, y );
+
 		// always use heavy weight popup because the drop shadow increases
 		// the popup size and may overlap the window bounds
 		Popup popup = getHeavyWeightPopup( owner, contents, x, y );
@@ -129,7 +133,10 @@ public class FlatPopupFactory
 			parent = (JComponent) p;
 			oldBorder = parent.getBorder();
 			oldOpaque = parent.isOpaque();
-			parent.setBorder( new FlatDropShadowBorder( null, 4, 4, 32 ) ); //TODO
+			parent.setBorder( new FlatDropShadowBorder(
+				UIManager.getColor( "Popup.dropShadowColor" ),
+				UIManager.getInsets( "Popup.dropShadowInsets" ),
+				FlatUIUtils.getUIFloat( "Popup.dropShadowOpacity", 0.5f ) ) );
 			parent.setOpaque( false );
 
 			window = SwingUtilities.windowForComponent( contents );

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatDarkLaf.properties

@@ -158,6 +158,9 @@ InternalFrame.closePressedBackground=darken(Actions.Red,10%,lazy)
 InternalFrame.closeHoverForeground=#fff
 InternalFrame.closePressedForeground=#fff
 
+InternalFrame.activeDropShadowOpacity=0.5
+InternalFrame.inactiveDropShadowOpacity=0.75
+
 
 #---- List ----
 
@@ -187,6 +190,12 @@ MenuItemCheckBox.icon.disabledCheckmarkColor=#606060
 PasswordField.capsLockIconColor=#ffffff64
 
 
+#---- Popup ----
+
+Popup.dropShadowColor=#000
+Popup.dropShadowOpacity=0.25
+
+
 #---- PopupMenu ----
 
 PopupMenu.borderColor=#5e5e5e

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLaf.properties

@@ -261,6 +261,13 @@ InternalFrame.maximizeIcon=com.formdev.flatlaf.icons.FlatInternalFrameMaximizeIc
 InternalFrame.minimizeIcon=com.formdev.flatlaf.icons.FlatInternalFrameMinimizeIcon
 InternalFrame.windowBindings=null
 
+# drop shadow
+InternalFrame.dropShadowPainted=true
+InternalFrame.activeDropShadowColor=null
+InternalFrame.activeDropShadowInsets=5,5,6,6
+InternalFrame.inactiveDropShadowColor=null
+InternalFrame.inactiveDropShadowInsets=3,3,4,4
+
 
 #---- InternalFrameTitlePane ----
 
@@ -362,6 +369,12 @@ PasswordField.echoChar=\u2022
 PasswordField.capsLockIcon=com.formdev.flatlaf.icons.FlatCapsLockIcon
 
 
+#---- Popup ----
+
+Popup.dropShadowPainted=true
+Popup.dropShadowInsets=-4,-4,4,4
+
+
 #---- PopupMenu ----
 
 PopupMenu.border=com.formdev.flatlaf.ui.FlatPopupMenuBorder

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLightLaf.properties

@@ -165,6 +165,9 @@ InternalFrame.closePressedBackground=darken(Actions.Red,10%,lazy)
 InternalFrame.closeHoverForeground=#fff
 InternalFrame.closePressedForeground=#fff
 
+InternalFrame.activeDropShadowOpacity=0.25
+InternalFrame.inactiveDropShadowOpacity=0.5
+
 
 #---- List ----
 
@@ -194,6 +197,12 @@ MenuItemCheckBox.icon.disabledCheckmarkColor=#ABABAB
 PasswordField.capsLockIconColor=#00000064
 
 
+#---- Popup ----
+
+Popup.dropShadowColor=#000
+Popup.dropShadowOpacity=0.15
+
+
 #---- PopupMenu ----
 
 PopupMenu.borderColor=#adadad