src/java.desktop/macosx/classes/sun/lwawt/macosx/CPlatformResponder.java

*** 42,51 ****
--- 42,54 ----
  final class CPlatformResponder {
  
      private final PlatformEventNotifier eventNotifier;
      private final boolean isNpapiCallback;
      private int lastKeyPressCode = KeyEvent.VK_UNDEFINED;
+     private static final double DELTA_THRESHOLD = 0.8;
+     private double accumulatedDeltaX;
+     private double accumulatedDeltaY;
  
      CPlatformResponder(final PlatformEventNotifier eventNotifier,
                         final boolean isNpapiCallback) {
          this.eventNotifier = eventNotifier;
          this.isNpapiCallback = isNpapiCallback;
*** 87,127 ****
      /**
       * Handles scroll events.
       */
      void handleScrollEvent(final int x, final int y, final int absX,
                             final int absY, final int modifierFlags,
!                            final double deltaX, final double deltaY) {
          int jmodifiers = NSEvent.nsToJavaModifiers(modifierFlags);
          final boolean isShift = (jmodifiers & InputEvent.SHIFT_DOWN_MASK) != 0;
  
          // Vertical scroll.
          if (!isShift && deltaY != 0.0) {
!             dispatchScrollEvent(x, y, absX, absY, jmodifiers, deltaY);
          }
          // Horizontal scroll or shirt+vertical scroll.
          final double delta = isShift && deltaY != 0.0 ? deltaY : deltaX;
          if (delta != 0.0) {
              jmodifiers |= InputEvent.SHIFT_DOWN_MASK;
!             dispatchScrollEvent(x, y, absX, absY, jmodifiers, delta);
          }
      }
  
      private void dispatchScrollEvent(final int x, final int y, final int absX,
                                       final int absY, final int modifiers,
!                                      final double delta) {
          final long when = System.currentTimeMillis();
          final int scrollType = MouseWheelEvent.WHEEL_UNIT_SCROLL;
          final int scrollAmount = 1;
-         int wheelRotation = (int) delta;
-         int signum = (int) Math.signum(delta);
-         if (signum * delta < 1) {
-             wheelRotation = signum;
-         }
          // invert the wheelRotation for the peer
          eventNotifier.notifyMouseWheelEvent(when, x, y, absX, absY, modifiers,
                                              scrollType, scrollAmount,
!                                             -wheelRotation, -delta, null);
      }
  
      /**
       * Handles key events.
       */
--- 90,158 ----
      /**
       * Handles scroll events.
       */
      void handleScrollEvent(final int x, final int y, final int absX,
                             final int absY, final int modifierFlags,
!                            final double deltaX, final double deltaY,
!                            final int scrollMask) {
          int jmodifiers = NSEvent.nsToJavaModifiers(modifierFlags);
          final boolean isShift = (jmodifiers & InputEvent.SHIFT_DOWN_MASK) != 0;
  
+         int roundDeltaX = (int) Math.round(deltaX);
+         int roundDeltaY = (int) Math.round(deltaY);
+ 
+         if ((scrollMask & NSEvent.SCROLL_MASK_TRACKPAD) != 0) {
+             if ((scrollMask & NSEvent.SCROLL_MASK_PHASE_BEGAN) != 0) {
+                 accumulatedDeltaX = deltaX;
+                 accumulatedDeltaY = deltaY;
+             } else {
+                 accumulatedDeltaX += deltaX;
+                 accumulatedDeltaY += deltaY;
+             }
+ 
+             if (Math.abs(accumulatedDeltaX) > DELTA_THRESHOLD) {
+                 roundDeltaX = (int) Math.round(accumulatedDeltaX);
+                 accumulatedDeltaX -= roundDeltaX;
+             }
+ 
+             if (Math.abs(accumulatedDeltaY) > DELTA_THRESHOLD) {
+                 roundDeltaY = (int) Math.round(accumulatedDeltaY);
+                 accumulatedDeltaY -= roundDeltaY;
+             }
+         } else {
+             if (roundDeltaX == 0 && deltaX != 0) {
+                 roundDeltaX = deltaX > 0 ? 1 : -1;
+             }
+ 
+             if (roundDeltaY == 0 && deltaY != 0) {
+                 roundDeltaY = deltaY > 0 ? 1 : -1;
+             }
+         }
+ 
          // Vertical scroll.
          if (!isShift && deltaY != 0.0) {
!             dispatchScrollEvent(x, y, absX, absY, jmodifiers, roundDeltaY, deltaY);
          }
          // Horizontal scroll or shirt+vertical scroll.
          final double delta = isShift && deltaY != 0.0 ? deltaY : deltaX;
+         final int roundDelta = isShift && roundDeltaY != 0.0 ? roundDeltaY : roundDeltaX;
          if (delta != 0.0) {
              jmodifiers |= InputEvent.SHIFT_DOWN_MASK;
!             dispatchScrollEvent(x, y, absX, absY, jmodifiers, roundDelta, delta);
          }
      }
  
      private void dispatchScrollEvent(final int x, final int y, final int absX,
                                       final int absY, final int modifiers,
!                                      final int roundDelta, final double delta) {
          final long when = System.currentTimeMillis();
          final int scrollType = MouseWheelEvent.WHEEL_UNIT_SCROLL;
          final int scrollAmount = 1;
          // invert the wheelRotation for the peer
          eventNotifier.notifyMouseWheelEvent(when, x, y, absX, absY, modifiers,
                                              scrollType, scrollAmount,
!                                             -roundDelta, -delta, null);
      }
  
      /**
       * Handles key events.
       */