how to set mousewheel and arrow button scroll speed equal

[LittleRave]

I've experienced that when I set

scrollPane.getVerticalScrollBar().setUnitIncrement(50);

I can change the scroll speed of a JScrollPane, but there's always a difference between scrolling with the mousewheel and scrolling with the arrow buttons of the scrollbar. With the arrow buttons I always geht 1/3 of the mousewheel scroll speed.
Is there a way to set them equal?

[zweibieren]

It will interfere with user expectations if you tinker with the amount of wheel scrolling.
That said, here's a version of JScrollPane that has a method, setUnitsToScroll(int),
that sets the number of "units" that the mouse wheel moves.
Typically, a unit is one line of text.

/*
 *
cryptic comment in JavaDocs for MouseWheelListener:
				The MouseWheelEvent offers methods for conforming
				to the underlying platform settings. These platform settings
				can be changed at any time by the user.
				MouseWheelEvents reflect the most recent settings.
http://java.sun.com/docs/books/tutorial/uiswing/events/mousewheellistener.html
				The amount that the mouse wheel scrolls is also platform dependent.
				 Both the type and amount of scrolling may be settable
				 via the mouse control panel for your platform.
 *
 */

package Test;

import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import javax.swing.*;

/**
     A hacked version of JScrollPane that permits modification of MouseWheelEvents.
 * In particular, the getUnitsToScroll() method can return an arbitrary amount.
 */
public class HansackedScrollPane extends JScrollPane implements MouseWheelListener {

	public HansackedScrollPane() { 
		super();
	}

	int unitsToScroll = 0;
	int getUnitsToScroll() { return unitsToScroll; }
	void setUnitsToScroll(int units) { unitsToScroll = units; }

	@Override
	public void addNotify() {
		super.addNotify();
		mangleWheel();
	}

	MouseWheelListener[] realListeners;
	/**
	 * Intercept mouse wheel events so we can tinker with getUnitsToScroll()
	 */
	private void mangleWheel() {
		realListeners = getMouseWheelListeners();
		for (MouseWheelListener mwl : realListeners)
			removeMouseWheelListener(mwl);
		addMouseWheelListener(this);
	}

	public void mouseWheelMoved(MouseWheelEvent e) {
		// System.out.println("wheel rolled " + e.getWheelRotation());
		MouseWheelEvent mwe = new WheelHack(e);
		for (MouseWheelListener mwl : realListeners)
			mwl.mouseWheelMoved(mwe);
	}
	/**
	 * A clone of MouseWheelEvent with modified getUnitsToScroll()
	 */
	class WheelHack extends MouseWheelEvent {
		private WheelHack(MouseWheelEvent e) {
			super((Component)e.getSource(), e.getID(),
					e.getWhen(), e.getModifiers(),
					e.getX(), e.getY(), e.getXOnScreen(), e.getYOnScreen(),
					e.getClickCount(), e.isPopupTrigger(),
					e.getScrollType(), e.getScrollAmount(),
					e.getWheelRotation());
		}
		@Override
		public int getUnitsToScroll() {
			if (unitsToScroll == 0)   // not set by client yet, use system value
				unitsToScroll = super.getUnitsToScroll();
			return unitsToScroll;
		}
	}


    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
		// some text to scroll
		JTextArea text = new JTextArea();
		for (int i = 0; i < 1000; i++)
			text.append("" + i + "\n");

		// create scrollpane to be tested
		final HansackedScrollPane subject = new HansackedScrollPane();
		subject.setUnitsToScroll(25);
		subject.setViewportView(text);

		javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
				// create and run frame
				JFrame frame = new JFrame("ScrollTest");
				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frame.setContentPane(subject);
				frame.setPreferredSize(new Dimension(91, 500));
				frame.pack();
				frame.setVisible(true);
            }
        });
    }
}

[LittleRave]

But this won't adjust the scroll speed of the arrow buttons, will it? I want to speed them both up, but have them at the same speed

[zweibieren]

But this won't adjust the scroll speed of the arrow buttons, will it? I want to speed them both up, but have them at the same speed

Give someone the moon and they want the sun ;-)
This is it for me this year.
Cheers until twenty-ten.

/*

 * This demo show how to adjust the scroll amount for ARROW and WHEEL

 	set ARROW_SCROLL_PIXELS to a number of pixels
				to scroll for clicking an arrow at the end of a scrollbar
	set WHEEL_SCROLL_PIXELS to a number of pixels
				to scroll each time the mouse wheel is rolled one click

 * BACKGROUND - the way scrolling usually works
 *
 * There are four scrolling operations:
 *   -- BAR - click above or below the thumb in the scrollbar
 *   -- PAGE - pageup/pagedown buttons    ("scrollUp" action)
 *   -- ARROW - click an arrow at top or bottom of scrollbar
 *   -- WHEEL - roll the mouse wheel
 *
 * Of these, BAR and PAGE scroll by getScrollableBlockIncrement()
 *			For JTextArea, this is the height of the screen space.
 * ARROW scrolls by Scrollable.getScrollableUnitIncr()
 *			For JTextArea this is the getRowHeight()
 * WHEEL scrolls by a mutiple of Scrollable.getScrollableUnitIncr
 *       (the multiple is specified by the user on the control panel (not in Java)

 
 * The file below has two JComponents and an interface.
 * (They should be in three separate files instead of all nested in one.)
 * They are:
 * 
 *    class HansackedScrollPane extends JScrollPane
 *			The constructor has an argument which is 
 *			the number of pixels to scroll for a mouse wheel roll of one click.
 *			This number is only approximate unless the object
 *			being scrolled implements the interface WackyScrollUnit.
 * 
 *    interface WackyScrollUnit
 *			A JComponent that implements this interface
 *			will do a more accurate job of scrolling exactly the number
 *			of pixels specified for wheel scrolls. It must also override
 *			getScrollableUnitIncrement
 *
 *   class HansackedTextArea extends JTextArea
 *			The constructor has a parameter to specify
 *			the number of pixels to be scrolled
 *			for each click on the arrows in a scrollbar.

 */

package Test;

import java.awt.Component;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import javax.swing.*;

/**
     A hacked version of JScrollPane that permits modification of MouseWheelEvents.
 *  The amount to scroll for a wheel rool-click is specified in the constructor.
 */
public class HansackedScrollPane extends JScrollPane implements MouseWheelListener {

	Scrollable scrollee = null;

	int wheelUnitsIncr;
	int getUnitsForWheelStep() { return wheelUnitsIncr; }
	void setUnitsForWheelStep(int units) { wheelUnitsIncr = units; }

	/**
	 * Construct a JScrollPane with non-standard scrolling by the mouse wheel.
	 * @param u
	 */
	public HansackedScrollPane(int u) {
		super();
		wheelUnitsIncr = u;
	}

	@Override
	public void setViewportView(Component view) {
		if (view instanceof Scrollable)
			scrollee = (Scrollable)view;
		super.setViewportView(view);
	}

	@Override
	public void addNotify() {
		super.addNotify();
		mangleWheel();
	}

	MouseWheelListener[] realListeners;
	/**
	 * Intercept mouse wheel events so we can tinker with getUnitsToScroll()
	 */
	private void mangleWheel() {
		realListeners = getMouseWheelListeners();
		for (MouseWheelListener mwl : realListeners)
			removeMouseWheelListener(mwl);
		addMouseWheelListener(this);
	}

	public void mouseWheelMoved(MouseWheelEvent e) {
		// System.out.println("wheel rolled " + e.getWheelRotation());
		MouseWheelEvent mwe 
				= (scrollee == null) ? e : new WheelHack(e);
		for (MouseWheelListener mwl : realListeners)
			mwl.mouseWheelMoved(mwe);
	}
	/**
	 * A clone of MouseWheelEvent that forces a block scroll
	 */
	class WheelHack extends MouseWheelEvent {
		private WheelHack(MouseWheelEvent e) {
			super((Component)e.getSource(), e.getID(),
					e.getWhen(), e.getModifiers(),
					e.getX(), e.getY(), e.getXOnScreen(), e.getYOnScreen(),
					e.getClickCount(), e.isPopupTrigger(),

					MouseWheelEvent.WHEEL_UNIT_SCROLL,		//	instead of e.getScrollType(),
					computeDistance(e),											//  instead of e.getScrollAmount(),
					e.getWheelRotation() < 0 ? -1 : 1);					// instead of e.getWheelRotation());
		}
	}

	// helper for WheelHack
	int computeDistance(MouseWheelEvent e) {
		if (scrollee instanceof WackyScrollUnit) {
			((WackyScrollUnit)scrollee).setTempUnit(wheelUnitsIncr);
			return 1;
		}

		// return  floor(total / scrollable.getScrollableUnitIncrement())
		int direction = e.getWheelRotation() < 0 ? -1 : 1;
		int unitIncr = scrollee.getScrollableUnitIncrement(
				getViewport().getViewRect(),
				SwingConstants.VERTICAL, direction);
		return wheelUnitsIncr/unitIncr;
	}

	/**
 *			A JComponent that implements this interface
 *			will do a more accurate job of scrolling exactly the number
 *			of pixels specified for wheel scrolls. It must also override
 *			getScrollableUnitIncrement
	 */
	interface WackyScrollUnit {
		void setTempUnit(int u);
		//public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction);
	}

	/**
 *			The constructor has a parameter to specify
 *			the number of pixels to be scrolled
 *			for each click on the arrows in a scrollbar.
	 *
	 *		The setTempUnit method helps with mouse wheelk scrolling
	 */
	static class HansackedTextArea extends JTextArea implements WackyScrollUnit {

		int unitsIncr;
		int getUnitsIncr() { return unitsIncr; }
		void setUnitsIncr(int u) { unitsIncr = u; }

		boolean tempUnitSet = false;   // if true, getScrollableUnitIncrement responds with tempUnit, once
		int tempUnit;								// phoney value to return from getScriollableUnitIncrement
		public void setTempUnit(int u) {
			tempUnitSet = true;
			tempUnit = u;
		}

		HansackedTextArea(int u) {
			super();
			unitsIncr = u;
		}
		@Override
		public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
			if (tempUnitSet) {
				tempUnitSet = false;
				return tempUnit;
			}
			return unitsIncr;  // pixels to scroll for a unit (an ARROW scroll)
		}
		@Override
		public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
			if (orientation != SwingConstants.VERTICAL)
				return super.getScrollableBlockIncrement(visibleRect, orientation, direction);
			return visibleRect.height;    // pixels to scroll   for PAGE and BAR
		}
	}

	// parameters for scrolling
	final static int ARROW_SCROLL_PIXELS = 91;
	final static int WHEEL_SCROLL_PIXELS = 200;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
		// some text to scroll
		JTextArea text;
		text = new HansackedTextArea(ARROW_SCROLL_PIXELS);
		for (int i = 0; i < 1000; i++)
			text.append("" + i + "\n");

		// create scrollpane to be tested
		final HansackedScrollPane subject
				= new HansackedScrollPane(WHEEL_SCROLL_PIXELS);
		subject.setViewportView(text);

		javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
				// create and run frame
				JFrame frame = new JFrame("ScrollTest");
				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				subject.setBorder(BorderFactory.createEmptyBorder(2,5,2,0));
				frame.setContentPane(subject);
				frame.setPreferredSize(new Dimension(45, 500));
				frame.pack();
				frame.setVisible(true);
            }
        });
    }

}

[LittleRave]

Give someone the moon and they want the sun ;-)

It's winter! Who doesn't want the sun? :D
Thanks a lot, will have a look at it when I solved my current problem.

[LittleRave]

Hmm... I don't have a JTextArea but a JPanel in my JScrollPane, so I can't override the getScrollableUnitIncrement function, that's why it's not working ...

[camickr]

I don't have a JTextArea but a JPanel in my JScrollPane, so I can't override the getScrollableUnitIncrement function, that's why it's not working

Sure you can. You can implement the Scrollable interface on any component. ScrollablePanel provides a generic solution and is easily customizable.

@zweibieren - in about 3 weeks my next blog entry will be on a "Mouse Wheel Controller", which uses some of the concepts you introduced in your first solution to control the mouse wheel scroll amount. I will be giving you credit for some of the ideas in case you want to check it out.

[LittleRave]

I cannot extend from ScrollablePanel class because I've already extended from JLayeredPane. I have to paint something in front of all added components of the panel so this is necessary, isn't it?.
But I will try to make use of the Scrollable interface.
Thanks for the suggestion :).


EDIT: I've realized that JLayeredPane only works with a null layout, so I can't use it and found a different solution ... Now when I get back to this issue I'm gonna try the ScrollablePanel extension. Thanks again