Move jitterless scrolling logic

Moved the jitterless smooth scrolling logic out of JitterlessScrollPaneUI which wasn't the most logical place for it and into JitterlessScrollPane with the new PreciseMouseWheelListener inner class. JitterlessScrollPaneUI was then deleted and removed from themes/FlatLaf.properties

Author: Mystin

src/main/java/edu/rpi/legup/ui/JitterlessScrollPane.java

@@ -4,9 +4,16 @@
 import java.awt.Graphics;
 import java.awt.Graphics2D;
 import java.awt.GraphicsEnvironment;
+import java.awt.Rectangle;
+import java.awt.event.MouseWheelEvent;
+import java.awt.event.MouseWheelListener;
 import java.awt.geom.AffineTransform;
+import javax.swing.JScrollBar;
 import javax.swing.JScrollPane;
 import javax.swing.JViewport;
+import javax.swing.Scrollable;
+import javax.swing.SwingConstants;
+import javax.swing.UIManager;
 
 /**
  * The {@code JitterlessScrollPane} class is a {@code JScrollPane} that combats jittering of
@@ -21,15 +28,12 @@ public class JitterlessScrollPane extends JScrollPane {
 
     public JitterlessScrollPane() {
         super();
+        addMouseWheelListener(new PreciseWheelListener());
     }
 
     public JitterlessScrollPane(Component view) {
         super(view);
-    }
-
-    @Override
-    public String getUIClassID() {
-        return "JitterlessScrollPaneUI";
+        addMouseWheelListener(new PreciseWheelListener());
     }
 
     public void setFracOffsetX(double fracOffsetX) {
@@ -83,7 +87,7 @@ protected void paintChildren(Graphics graphics) {
 
             Graphics2D g = (Graphics2D) graphics.create();
 
-            // Get DPI scale from screen
+            // Get graphics environment scale from screen
             AffineTransform scaleDPI = GraphicsEnvironment
                     .getLocalGraphicsEnvironment()
                     .getDefaultScreenDevice()
@@ -102,4 +106,91 @@ protected void paintChildren(Graphics graphics) {
             g.dispose();
         }
     }
+
+    /**
+     * The {@code PreciseWheelListener} class is used by the {@code JitterlessScrollPane} class
+     * to intercept scrolling events from precise inputs like trackpads and uses them to give
+     * the {@code JitterlessScrollPane} sub-pixel scrolling accuracy and prevent "jumping".
+     */
+    protected class PreciseWheelListener implements MouseWheelListener {
+
+        @Override
+        public void mouseWheelMoved(MouseWheelEvent e) {
+
+            // Only intercept scroll wheel events from precise inputs and if enabled
+            if (
+                    isWheelScrollingEnabled() &&
+                            UIManager.getBoolean("ScrollPane.smoothScrolling") &&
+                            e.getPreciseWheelRotation() != e.getWheelRotation() &&
+                            viewport != null
+            ) {
+                // Modified code from com.formdev.flatlaf.ui.FlatScrollPaneUI#mouseWheelMovedSmooth
+                JScrollBar scrollbar = verticalScrollBar;
+                if (scrollbar == null || !scrollbar.isVisible() || e.isShiftDown()) {
+                    scrollbar = horizontalScrollBar;
+                    if (scrollbar == null || !scrollbar.isVisible()) {
+                        return;
+                    }
+                }
+
+                e.consume();
+
+                double rotation = e.getPreciseWheelRotation();
+                int unitIncrement;
+                int orientation = scrollbar.getOrientation();
+                Component view = viewport.getView();
+
+                if (view instanceof Scrollable scrollable) {
+
+                    Rectangle visibleRect = new Rectangle(viewport.getExtentSize());
+                    unitIncrement = scrollable.getScrollableUnitIncrement(visibleRect, orientation, 1);
+
+                    if (unitIncrement > 0) {
+
+                        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);
+                }
+
+                // Compute new position based on previous sub-pixel offset
+                double delta = rotation * unitIncrement * e.getScrollAmount() +
+                        ((orientation == SwingConstants.VERTICAL) ?
+                                getFracOffsetY() : getFracOffsetX());
+                int idelta = (int) Math.round(delta);
+
+                int value = scrollbar.getValue();
+                int minValue = scrollbar.getMinimum();
+                int maxValue = scrollbar.getMaximum() - scrollbar.getModel().getExtent();
+                int newValue = Math.max(minValue, Math.min(value + idelta, maxValue));
+
+                if (newValue != value) {
+                    scrollbar.setValue(newValue);
+                }
+
+                // Set new sub-pixel offset
+                double newFracOffset =
+                        (value + delta > minValue && value + delta < maxValue) ?
+                                delta - idelta : 0.0;
+                if (orientation == SwingConstants.VERTICAL) {
+                    setFracOffsetY(newFracOffset);
+                } else {
+                    setFracOffsetX(newFracOffset);
+                }
+            }
+        }
+    }
 }

src/main/java/edu/rpi/legup/ui/JitterlessScrollPaneUI.java

@@ -216,11 +216,6 @@ Expected.SvgIcon.borderColor = #232323
 [style]PopupMenu.dataSelection = background: #808080;
 
 
-# UI Delegate Mapping
-
-JitterlessScrollPaneUI = edu.rpi.legup.ui.JitterlessScrollPaneUI
-
-
 # Overrides of default flatlaf\FlatLaf.properties
 
 defaultFont = Roboto-Regular, 12