Smooth Scrolling improved

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

@@ -112,6 +112,7 @@ public abstract class FlatLaf
 	private PopupFactory oldPopupFactory;
 	private MnemonicHandler mnemonicHandler;
 	private boolean subMenuUsabilityHelperInstalled;
+	private boolean smoothScrollingHelperInstalled;
 
 	private Consumer<UIDefaults> postInitialization;
 	private List<Function<Object, Object>> uiDefaultsGetters;
@@ -271,6 +272,9 @@ public void initialize() {
 
 		// install submenu usability helper
 		subMenuUsabilityHelperInstalled = SubMenuUsabilityHelper.install();
+
+		// install smooth scrolling helper
+		smoothScrollingHelperInstalled = SmoothScrollingHelper.install();
 
 		// listen to desktop property changes to update UI if system font or scaling changes
 		if( SystemInfo.isWindows ) {
@@ -364,6 +368,12 @@ public void uninitialize() {
 			subMenuUsabilityHelperInstalled = false;
 		}
 
+		// uninstall smooth scrolling helper
+		if( smoothScrollingHelperInstalled ) {
+			SmoothScrollingHelper.uninstall();
+			smoothScrollingHelperInstalled = false;
+		}
+
 		// restore default link color
 		new HTMLEditorKit().getStyleSheet().addRule( "a, address { color: blue; }" );
 		postInitialization = null;

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

@@ -132,6 +132,14 @@ public interface FlatSystemProperties
 	 */
 	String ANIMATION = "flatlaf.animation";
 
+	/**
+	 * Specifies whether smooth scrolling is enabled.
+	 * <p>
+	 * <strong>Allowed Values</strong> {@code false} and {@code true}<br>
+	 * <strong>Default</strong> {@code true}
+	 */
+	String SMOOTH_SCROLLING = "flatlaf.smoothScrolling";
+
 	/**
 	 * Specifies whether vertical text position is corrected when UI is scaled on HiDPI screens.
 	 * <p>

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

@@ -0,0 +1,209 @@
+/*
+ * Christopher Deckers ([email protected])
+ * http://www.nextencia.net
+ * 
+ * See the file "readme.txt" for information on usage and redistribution of
+ * this file, and for a DISCLAIMER OF ALL WARRANTIES.
+ */
+package com.formdev.flatlaf;
+
+import java.awt.AWTEvent;
+import java.awt.Component;
+import java.awt.Container;
+import java.awt.Rectangle;
+import java.awt.Toolkit;
+import java.awt.event.AWTEventListener;
+import java.awt.event.ComponentEvent;
+import java.awt.event.KeyEvent;
+import java.awt.event.MouseEvent;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.Set;
+import javax.swing.JComponent;
+import javax.swing.JScrollBar;
+import javax.swing.JScrollPane;
+import javax.swing.JViewport;
+import javax.swing.RepaintManager;
+import javax.swing.SwingUtilities;
+import com.formdev.flatlaf.util.Animator;
+
+/**
+ * @author Christopher Deckers
+ */
+public class SmoothScrollingHelper implements AWTEventListener
+{
+
+	private static SmoothScrollingHelper instance;
+
+	static synchronized boolean install() {
+		if( instance != null )
+			return false;
+		instance = new SmoothScrollingHelper();
+		long eventMask = AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK | AWTEvent.MOUSE_WHEEL_EVENT_MASK | AWTEvent.KEY_EVENT_MASK;
+		Toolkit.getDefaultToolkit().addAWTEventListener(instance, eventMask);
+		return true;
+	}
+
+	static synchronized void uninstall() {
+		if( instance == null )
+			return;
+		Toolkit.getDefaultToolkit().removeAWTEventListener(instance);
+		instance = null;
+	}
+
+	@Override
+	public void eventDispatched( AWTEvent event ) {
+		if( event instanceof ComponentEvent && ((ComponentEvent)event).getComponent() instanceof JScrollBar ) {
+			// Do not disconnect blit scroll mode when e.g. dragging the scroll bar.
+			return;
+		}
+		if( Animator.useAnimation() && FlatSystemProperties.getBoolean( FlatSystemProperties.SMOOTH_SCROLLING, true ) ) {
+			boolean isHoldingScrollModeBlocked = false;
+			switch(event.getID()) {
+			    case MouseEvent.MOUSE_MOVED:
+			    case MouseEvent.MOUSE_ENTERED:
+			    case MouseEvent.MOUSE_EXITED:
+			        if(isBlitScrollModeBlocked) {
+			            int modifiersEx = ((MouseEvent)event).getModifiersEx();
+			            if((modifiersEx & (MouseEvent.BUTTON1_DOWN_MASK | MouseEvent.BUTTON2_DOWN_MASK | MouseEvent.BUTTON3_DOWN_MASK)) == 0) {
+			                // If the scroll mode was blocked for dragging, let's release if we receive a non-drag-related event (i.e. drag is done).
+			                for( JViewport viewport: viewportSet ) {
+			                    setBlitScrollModeBlocked( viewport, false );
+			                    setInSmoothScrolling( viewport, false );
+			                }
+			                isBlitScrollModeBlocked = false;
+			            }
+			        }
+			        break;
+				case MouseEvent.MOUSE_PRESSED:
+				case MouseEvent.MOUSE_DRAGGED:
+					isHoldingScrollModeBlocked = true;
+					// Fall through
+				case MouseEvent.MOUSE_RELEASED:
+				case MouseEvent.MOUSE_CLICKED:
+				case MouseEvent.MOUSE_WHEEL:
+				case KeyEvent.KEY_PRESSED:
+				case KeyEvent.KEY_RELEASED:
+				case KeyEvent.KEY_TYPED:
+					boolean isBlitScrollModeBlocked_ = isBlitScrollModeBlocked;
+					if(!isBlitScrollModeBlocked_) {
+						Component c = ((ComponentEvent)event).getComponent();
+						for( JViewport viewport: viewportSet ) {
+							Container scrollPane = viewport.getParent();
+							if(scrollPane == c || scrollPane.isAncestorOf( c )) {
+								setInSmoothScrolling( viewport, true );
+							}
+							setBlitScrollModeBlocked( viewport, true );
+						}
+						isBlitScrollModeBlocked = true;
+					}
+					if( !isHoldingScrollModeBlocked && ( !isBlitScrollModeBlocked_ || event.getID() == MouseEvent.MOUSE_RELEASED )) {
+						SwingUtilities.invokeLater( () -> {
+							for( JViewport viewport: viewportSet ) {
+								setBlitScrollModeBlocked( viewport, false );
+								setInSmoothScrolling( viewport, false );
+							}
+							isBlitScrollModeBlocked = false;
+						} );
+					}
+					break;
+			}
+		}
+	}
+
+	private boolean isBlitScrollModeBlocked;
+
+	public static synchronized void setBlitScrollModeBlocked( JViewport viewport, boolean isBlocked ) {
+		if( instance == null )
+			return;
+		String clientPropertyName = "_flatlaf.originalScrollMode";
+		if( isBlocked ) {
+			int scrollMode = viewport.getScrollMode();
+			if( scrollMode == JViewport.BLIT_SCROLL_MODE ) {
+				viewport.putClientProperty( clientPropertyName , scrollMode );
+				viewport.setScrollMode( JViewport.SIMPLE_SCROLL_MODE );
+			}
+		} else {
+			Integer scrollMode = (Integer)viewport.getClientProperty( clientPropertyName );
+			if( scrollMode != null ) {
+				viewport.setScrollMode( scrollMode );
+				viewport.putClientProperty( clientPropertyName , null );
+			}
+		}
+	}
+
+	public static void setScrollBarValueWithOptionalRepaint(JViewport viewport, JScrollBar scrollbar, int value) {
+		Container viewportParent = null;
+		Rectangle dirtyRegion = null;
+		viewportParent = viewport == null? null: viewport.getParent();
+		dirtyRegion = viewportParent instanceof JComponent? RepaintManager.currentManager( viewport ).getDirtyRegion((JComponent)viewportParent ): null;
+		int scrollMode = viewport.getScrollMode();
+		if(scrollMode == JViewport.BLIT_SCROLL_MODE) {
+			viewport.setScrollMode( JViewport.SIMPLE_SCROLL_MODE );
+		}
+		scrollbar.setValue( value );
+		if(scrollMode == JViewport.BLIT_SCROLL_MODE) {
+			viewport.setScrollMode( JViewport.BLIT_SCROLL_MODE );
+		}
+		if(dirtyRegion != null && dirtyRegion.width == 0 && dirtyRegion.height == 0) {
+			// There was no dirty region. Let's restore that state for blit scroll mode to work.
+			RepaintManager.currentManager( viewport ).markCompletelyClean( (JComponent)viewportParent );
+		}
+	}
+
+	public static synchronized boolean isInBlockedBlitScrollMode( JViewport viewport ) {
+		if( instance == null )
+			return false;
+		String clientPropertyName = "_flatlaf.originalScrollMode";
+		return viewport.getClientProperty( clientPropertyName ) != null && viewport.getScrollMode() == JViewport.SIMPLE_SCROLL_MODE;
+	}
+
+	public static synchronized void allowBlitScrollModeTemporarily( JViewport viewport, boolean isAllowed ) {
+		if( instance == null )
+			return;
+		// When mouse is dragged, blit scroll mode is deactivated so that drag timers that provoke more scrolling do not repaint at wrong position.
+		// The FlatLaf animator re-activates the blit scroll mode just for its timed operation.
+		String clientPropertyName = "_flatlaf.originalScrollMode";
+		if(viewport.getClientProperty( clientPropertyName ) != null) {
+			if(isAllowed) {
+				viewport.setScrollMode( JViewport.BLIT_SCROLL_MODE );
+			} else {
+				viewport.setScrollMode( JViewport.SIMPLE_SCROLL_MODE );
+			}
+		}
+	}
+
+	public static synchronized boolean isInSmoothScrolling( JViewport viewport ) {
+		if( instance == null )
+			return false;
+		String clientPropertyName = "_flatlaf.inSmoothScrolling";
+		return viewport != null && viewport.getClientProperty( clientPropertyName ) != null;
+	}
+
+	private static synchronized void setInSmoothScrolling( JViewport viewport, boolean isInSmoothScrolling ) {
+		if( instance == null )
+			return;
+		String clientPropertyName = "_flatlaf.inSmoothScrolling";
+		viewport.putClientProperty( clientPropertyName , isInSmoothScrolling? Boolean.TRUE: null);
+	}
+
+	private static Set<JViewport> viewportSet = Collections.newSetFromMap(new IdentityHashMap<JViewport, Boolean>());
+
+	public static synchronized void registerViewport( JViewport viewport ) {
+		if( instance == null )
+			return;
+		if(viewport.getParent() instanceof JScrollPane) {
+			viewportSet.add( viewport );
+		}
+	}
+
+	public static synchronized void unregisterViewport( JViewport viewport ) {
+		if( instance == null )
+			return;
+		if( instance.isBlitScrollModeBlocked ) {
+			instance.setBlitScrollModeBlocked( viewport, false );
+		}
+		viewportSet.remove( viewport );
+	}
+
+}