ViewportAutoexposeHelper.java

/*******************************************************************************
 * Copyright (c) 2000, 2005 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; //$NON-NLS-1$
}

}