bundles/org.eclipse.gef/src/org/eclipse/gef/editparts/ViewportAutoexposeHelper.java

/*******************************************************************************
 * Copyright (c) 2000, 2010 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Intershop, Gunnar Wagenknecht - fix for 44288
 *******************************************************************************/
package org.eclipse.gef.editparts;

import org.eclipse.draw2d.PositionConstants;
import org.eclipse.draw2d.Viewport;
import org.eclipse.draw2d.geometry.Insets;
import org.eclipse.draw2d.geometry.Point;
import org.eclipse.draw2d.geometry.Rectangle;

import org.eclipse.gef.AutoexposeHelper;
import org.eclipse.gef.GraphicalEditPart;

/**
 * An implementation of {@link org.eclipse.gef.AutoexposeHelper} that performs
 * autoscrolling of a <code>Viewport</code> figure. This helper is for use with
 * graphical editparts that contain a viewport figure. This helper will search
 * the editpart and find the viewport. Autoscroll will occur when the detect
 * location is inside the viewport's bounds, but near its edge. It will continue
 * for as long as the location continues to meet these criteria. The autoscroll
 * direction is approximated to the nearest orthogonal or diagonal direction
 * (north, northeast, east, etc.).
 * 
 * @author hudsonr
 */
public class ViewportAutoexposeHelper extends ViewportHelper implements
		AutoexposeHelper {

	/** defines the range where autoscroll is active inside a viewer */
	private static final Insets DEFAULT_EXPOSE_THRESHOLD = new Insets(18);

	/** the last time an auto expose was performed */
	private long lastStepTime = 0;

	/** The insets for this helper. */
	private Insets threshold;

	/**
	 * Constructs a new helper on the given GraphicalEditPart. The editpart must
	 * have a <code>Viewport</code> somewhere between its <i>contentsPane</i>
	 * and its <i>figure</i> inclusively.
	 * 
	 * @param owner
	 *            the GraphicalEditPart that owns the Viewport
	 */
	public ViewportAutoexposeHelper(GraphicalEditPart owner) {
		super(owner);
		threshold = DEFAULT_EXPOSE_THRESHOLD;
	}

	/**
	 * Constructs a new helper on the given GraphicalEditPart. The editpart must
	 * have a <code>Viewport</code> somewhere between its <i>contentsPane</i>
	 * and its <i>figure</i> inclusively.
	 * 
	 * @param owner
	 *            the GraphicalEditPart that owns the Viewport
	 * @param threshold
	 *            the Expose Threshold to use when determing whether or not a
	 *            scroll should occur.
	 */
	public ViewportAutoexposeHelper(GraphicalEditPart owner, Insets threshold) {
		super(owner);
		this.threshold = threshold;
	}

	/**
	 * Returns <code>true</code> if the given point is inside the viewport, but
	 * near its edge.
	 * 
	 * @see org.eclipse.gef.AutoexposeHelper#detect(org.eclipse.draw2d.geometry.Point)
	 */
	public boolean detect(Point where) {
		lastStepTime = 0;
		Viewport port = findViewport(owner);
		Rectangle rect = Rectangle.SINGLETON;
		port.getClientArea(rect);
		port.translateToParent(rect);
		port.translateToAbsolute(rect);
		return rect.contains(where) && !rect.crop(threshold).contains(where);
	}

	/**
	 * Returns <code>true</code> if the given point is outside the viewport or
	 * near its edge. Scrolls the viewport by a calculated (time based) amount
	 * in the current direction.
	 * 
	 * todo: investigate if we should allow auto expose when the pointer is
	 * outside the viewport
	 * 
	 * @see org.eclipse.gef.AutoexposeHelper#step(org.eclipse.draw2d.geometry.Point)
	 */
	public boolean step(Point where) {
		Viewport port = findViewport(owner);

		Rectangle rect = Rectangle.SINGLETON;
		port.getClientArea(rect);
		port.translateToParent(rect);
		port.translateToAbsolute(rect);
		if (!rect.contains(where) || rect.crop(threshold).contains(where))
			return false;

		// set scroll offset (speed factor)
		int scrollOffset = 0;

		// calculate time based scroll offset
		if (lastStepTime == 0)
			lastStepTime = System.currentTimeMillis();

		long difference = System.currentTimeMillis() - lastStepTime;

		if (difference > 0) {
			scrollOffset = ((int) difference / 3);
			lastStepTime = System.currentTimeMillis();
		}

		if (scrollOffset == 0)
			return true;

		rect.crop(threshold);

		int region = rect.getPosition(where);
		Point loc = port.getViewLocation();

		if ((region & PositionConstants.SOUTH) != 0)
			loc.y += scrollOffset;
		else if ((region & PositionConstants.NORTH) != 0)
			loc.y -= scrollOffset;

		if ((region & PositionConstants.EAST) != 0)
			loc.x += scrollOffset;
		else if ((region & PositionConstants.WEST) != 0)
			loc.x -= scrollOffset;

		port.setViewLocation(loc);
		return true;
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	public String toString() {
		return "ViewportAutoexposeHelper for: " + owner; //$NON-NLS-1$
	}

}