support smooth scrolling with touchpads and high precision mouse wheels (issue #27)

CHANGELOG.md

@@ -3,6 +3,8 @@ FlatLaf Change Log
 
 ## Unreleased
 
+- Support smooth scrolling with touchpads and high precision mouse wheels.
+  (issue #27)
 - Changed `.properties` file loading order: Now all core `.properties` files are
   loaded before loading addon `.properties` files. This makes it easier to
   overwrite core values in addons. Also, addon loading order can be specified.

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

@@ -14,15 +14,24 @@
  * limitations under the License.
  */
 
+/*
+ * Smooth scrolling code partly based on code from IntelliJ IDEA Community Edition,
+ * which is licensed under the Apache 2.0 license. Copyright 2000-2016 JetBrains s.r.o.
+ * See: https://github.com/JetBrains/intellij-community/blob/31e1b5a8e43219b9571951bab6457cfb3012e3ef/platform/platform-api/src/com/intellij/ui/components/SmoothScrollPane.java#L141-L185
+ *
+ */
 package com.formdev.flatlaf.ui;
 
 import java.awt.Component;
 import java.awt.Graphics;
 import java.awt.Insets;
+import java.awt.Rectangle;
 import java.awt.event.ContainerEvent;
 import java.awt.event.ContainerListener;
 import java.awt.event.FocusEvent;
 import java.awt.event.FocusListener;
+import java.awt.event.MouseWheelEvent;
+import java.awt.event.MouseWheelListener;
 import java.beans.PropertyChangeEvent;
 import java.beans.PropertyChangeListener;
 import javax.swing.BorderFactory;
@@ -34,6 +43,8 @@ import javax.swing.JTable;
 import javax.swing.JViewport;
 import javax.swing.LookAndFeel;
 import javax.swing.ScrollPaneConstants;
+import javax.swing.Scrollable;
+import javax.swing.SwingConstants;
 import javax.swing.UIManager;
 import javax.swing.plaf.ComponentUI;
 import javax.swing.plaf.basic.BasicScrollPaneUI;
@@ -50,6 +61,10 @@ import com.formdev.flatlaf.FlatClientProperties;
  * @uiDefault ScrollPane.border				Border
  * @uiDefault ScrollPane.viewportBorder		Border
  *
+ * <!-- FlatScrollPaneUI -->
+ *
+ * @uiDefault ScrollPane.smoothScrolling		boolean
+ *
  * @author Karl Tauber
  */
 public class FlatScrollPaneUI
@@ -94,6 +109,130 @@ public class FlatScrollPaneUI
 		handler = null;
 	}
 
+	@Override
+	protected MouseWheelListener createMouseWheelListener() {
+		return new BasicScrollPaneUI.MouseWheelHandler() {
+			@Override
+			public void mouseWheelMoved( MouseWheelEvent e ) {
+				// Note: Getting UI value "ScrollPane.smoothScrolling" here to allow
+				// applications to turn smooth scrolling on or off at any time
+				// (e.g. in application options dialog).
+				if( UIManager.getBoolean( "ScrollPane.smoothScrolling" ) &&
+					scrollpane.isWheelScrollingEnabled() &&
+					e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL &&
+					e.getPreciseWheelRotation() != 0 &&
+					e.getPreciseWheelRotation() != e.getWheelRotation() )
+				{
+					mouseWheelMovedSmooth( e );
+				} else
+					super.mouseWheelMoved( e );
+			}
+		};
+	}
+
+	private static final double EPSILON = 1e-5d;
+
+	private void mouseWheelMovedSmooth( MouseWheelEvent e ) {
+		// return if there is no viewport
+		JViewport viewport = scrollpane.getViewport();
+		if( viewport == null )
+			return;
+
+		// find scrollbar to scroll
+		JScrollBar scrollbar = scrollpane.getVerticalScrollBar();
+		if( scrollbar == null || !scrollbar.isVisible() || e.isShiftDown() ) {
+			scrollbar = scrollpane.getHorizontalScrollBar();
+			if( scrollbar == null || !scrollbar.isVisible() )
+				return;
+		}
+
+		// consume event
+		e.consume();
+
+		// get precise wheel rotation
+		double rotation = e.getPreciseWheelRotation();
+
+		// get unit and block increment
+		int unitIncrement;
+		int blockIncrement;
+		int orientation = scrollbar.getOrientation();
+		Component view = viewport.getView();
+		if( view instanceof Scrollable ) {
+			Scrollable scrollable = (Scrollable) view;
+
+			// Use (0, 0) view position to obtain constant unit increment of first item
+			// (which might otherwise be variable on smaller-than-unit scrolling).
+			Rectangle visibleRect = new Rectangle( viewport.getViewSize() );
+			unitIncrement = scrollable.getScrollableUnitIncrement( visibleRect, orientation, 1 );
+			blockIncrement = scrollable.getScrollableBlockIncrement( visibleRect, orientation, 1 );
+
+			if( unitIncrement > 0 ) {
+				// For the case that the first item (e.g. in a list) is larger
+				// than the other items, get the unit increment of the second item
+				// and use the smaller one.
+				if( orientation == SwingConstants.VERTICAL ) {
+					visibleRect.y += unitIncrement;
+					visibleRect.height -= unitIncrement;
+				} else {
+					visibleRect.x += unitIncrement;
+					visibleRect.width -= unitIncrement;
+				}
+				int unitIncrement2 = scrollable.getScrollableUnitIncrement( visibleRect, orientation, 1 );
+				if( unitIncrement2 > 0 )
+					unitIncrement = Math.min( unitIncrement, unitIncrement2 );
+			}
+		} else {
+			int direction = rotation < 0 ? -1 : 1;
+			unitIncrement = scrollbar.getUnitIncrement( direction );
+			blockIncrement = scrollbar.getBlockIncrement( direction );
+		}
+
+		// limit scroll amount (number of units to scroll) for small viewports
+		// (e.g. vertical scrolling in file chooser)
+		int scrollAmount = e.getScrollAmount();
+		int viewportWH = (orientation == SwingConstants.VERTICAL)
+			? viewport.getHeight()
+			: viewport.getWidth();
+		if( unitIncrement * scrollAmount > viewportWH )
+			scrollAmount = Math.max( viewportWH / unitIncrement, 1 );
+
+		// compute relative delta
+		double delta = rotation * scrollAmount * unitIncrement;
+		boolean adjustDelta = Math.abs( rotation ) < (1.0 + EPSILON);
+		double adjustedDelta = adjustDelta
+			? Math.max( -blockIncrement, Math.min( delta, blockIncrement ) )
+			: delta;
+
+		// compute new value
+		int value = scrollbar.getValue();
+		double minDelta = scrollbar.getMinimum() - value;
+		double maxDelta = scrollbar.getMaximum() - scrollbar.getModel().getExtent() - value;
+		double boundedDelta = Math.max( minDelta, Math.min( adjustedDelta, maxDelta ) );
+		int newValue = value + (int) Math.round( boundedDelta );
+
+		// set new value
+		if( newValue != value )
+			scrollbar.setValue( newValue );
+
+/*debug
+		System.out.println( String.format( "%4d  %9f / %4d %4d / %12f %5s %12f / %4d %4d %4d / %12f %12f %12f / %4d",
+			e.getWheelRotation(),
+			e.getPreciseWheelRotation(),
+			unitIncrement,
+			blockIncrement,
+			delta,
+			adjustDelta,
+			adjustedDelta,
+			value,
+			scrollbar.getMinimum(),
+			scrollbar.getMaximum(),
+			minDelta,
+			maxDelta,
+			boundedDelta,
+			newValue ) );
+*/
+	}
+
 	@Override
 	protected PropertyChangeListener createPropertyChangeListener() {
 		return new BasicScrollPaneUI.PropertyChangeHandler() {

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

@@ -311,6 +311,7 @@ ScrollBar.buttonDisabledArrowColor=$ComboBox.buttonDisabledArrowColor
 ScrollPane.border=com.formdev.flatlaf.ui.FlatBorder
 ScrollPane.background=$ScrollBar.track
 ScrollPane.fillUpperCorner=true
+ScrollPane.smoothScrolling=true
 
 
 #---- Separator ----