taverna-workbench-graph-view/src/main/java/net/sf/taverna/t2/workbench/views/graph/AutoScrollInteractor.java

package net.sf.taverna.t2.workbench.views.graph;

import static java.awt.event.InputEvent.BUTTON1_DOWN_MASK;
import static java.awt.event.InputEvent.BUTTON1_MASK;
import static java.awt.event.MouseEvent.BUTTON1;
import static java.awt.event.MouseEvent.MOUSE_DRAGGED;
import static java.awt.event.MouseEvent.MOUSE_PRESSED;
import static java.lang.System.currentTimeMillis;

import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.InputEvent;
import java.awt.event.MouseEvent;
import java.awt.geom.AffineTransform;
import java.util.Timer;
import java.util.TimerTask;

import org.apache.batik.swing.JSVGCanvas;
import org.apache.batik.swing.gvt.InteractorAdapter;
import org.apache.batik.swing.gvt.JGVTComponent;

/**
 * An interactor that scrolls the canvas view if the mouse is dragged to the
 * edge of the canvas.
 * 
 * @author David Withers
 */
public class AutoScrollInteractor extends InteractorAdapter {
	/**
	 * Defines the border around the canvas in which the auto scroll will become
	 * active.
	 */
	private static final int BORDER = 25;
	/**
	 * The interval, in milliseconds, between scroll events.
	 */
	private static final long SCROLL_INTERVAL = 100;

	private JSVGCanvas svgCanvas;
	private Dimension canvasSize;
	private int scrollX;
	private int scrollY;
	private int mouseX;
	private int mouseY;

	/**
	 * Component used to identify mouse events generated by this class
	 */
	private Component eventIdentifier = new Component() {
		private static final long serialVersionUID = -295542754718804222L;
	};

	private static Timer timer = new Timer("GraphAutoScrollTimer", true);

	private TimerTask task;

	/**
	 * Whether the interactor has finished.
	 */
	protected boolean finished = true;

	public AutoScrollInteractor(JSVGCanvas svgCanvas) {
		this.svgCanvas = svgCanvas;
	}

	@Override
	public boolean startInteraction(InputEvent ie) {
		int mods = ie.getModifiers();
		if (ie.getID() == MOUSE_PRESSED && (mods & BUTTON1_MASK) != 0) {
			AffineTransform transform = svgCanvas.getRenderingTransform();
			// check if we're zoomed in
			if (transform.getScaleX() > 1d || transform.getScaleY() > 1d) {
				canvasSize = svgCanvas.getSize();
				return true;
			}
		}
		return false;
	}

	@Override
	public boolean endInteraction() {
		return finished;
	}

	@Override
	public void mousePressed(final MouseEvent e) {
		if (startInteraction(e)) {
			finished = false;
			task = new TimerTask() {
				@Override
				public void run() {
					scrollTimerCallback(e);
				}
			};
			timer.schedule(task, 0, SCROLL_INTERVAL);
		}
	}

	/**
	 * Dispatches a mouse drag event that updates the mouse location by the
	 * amount that the canvas has been scrolled.
	 * 
	 * @param dragX
	 * @param dragY
	 */
	private void dispatchDragEvent(double dragX, double dragY) {
		int x = (int) (mouseX + dragX);
		int y = (int) (mouseY + dragY);
		MouseEvent mouseDragEvent = new MouseEvent(eventIdentifier,
				MOUSE_DRAGGED, currentTimeMillis(), BUTTON1_DOWN_MASK, x, y, 1,
				false, BUTTON1);
		svgCanvas.dispatchEvent(mouseDragEvent);
	}

	@Override
	public void mouseReleased(MouseEvent e) {
		if (!finished) {
			finished = true;
			scrollX = 0;
			scrollY = 0;
			if (task != null)
				task.cancel();
		}
	}

	@Override
	public void mouseDragged(MouseEvent e) {
		// ignore events generated by this class
		if (!finished && e.getSource() != eventIdentifier) {
			mouseX = e.getX();
			mouseY = e.getY();
			int minX = BORDER;
			int maxX = canvasSize.width - BORDER;
			int minY = BORDER;
			int maxY = canvasSize.height - BORDER;

			scrollX = (mouseX < minX) ? (minX - mouseX)
					: (mouseX > maxX) ? (maxX - mouseX) : 0;
			scrollY = (mouseY < minY) ? (minY - mouseY)
					: (mouseY > maxY) ? (maxY - mouseY) : 0;
		}
	}

	private void scrollTimerCallback(MouseEvent e) {
		double x = scrollX;
		double y = scrollY;
		if (x == 0 && y == 0)
			return;

		JGVTComponent c = (JGVTComponent) e.getSource();
		AffineTransform rt = (AffineTransform) c.getRenderingTransform()
				.clone();
		double currentTranslateX = rt.getTranslateX();
		double currentTranslateY = rt.getTranslateY();
		// the tranlation that will show the east edge
		double maxTranslateX = -((canvasSize.width * rt.getScaleX()) - canvasSize.width);
		// the translation that will show the south
		double maxTranslateY = -((canvasSize.height * rt.getScaleY()) - canvasSize.height);

		if (x > 0 && currentTranslateX + x > 0)
			// scroll left && not at west edge
			x = -currentTranslateX;
		else if (x < 0 && currentTranslateX + x < maxTranslateX)
			// scroll right && not at east edge
			x = maxTranslateX - currentTranslateX;

		if (y > 0 && currentTranslateY + y > 0)
			// scroll up && not at north edge
			y = -currentTranslateY;
		else if (y < 0 && currentTranslateY + y < maxTranslateY)
			// scroll down && not at south edge
			y = maxTranslateY - currentTranslateY;

		if (x != 0d || y != 0d) {
			AffineTransform at = AffineTransform.getTranslateInstance(x, y);
			rt.preConcatenate(at);
			c.setRenderingTransform(rt);
			dispatchDragEvent(x, y);
		}
	}
}