SnapToGrid.java

/*******************************************************************************
 * Copyright (c) 2003, 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
 *******************************************************************************/
package org.eclipse.gef;

import org.eclipse.draw2d.geometry.Dimension;
import org.eclipse.draw2d.geometry.Point;
import org.eclipse.draw2d.geometry.PrecisionRectangle;

/**
 * A helper used to perform snapping to a grid, which is specified on the
 * graphical viewer via the various properties defined in this class. This
 * helper can be used in conjunction with the
 * {@link org.eclipse.gef.tools.DragEditPartsTracker DragEditPartsTracker} when
 * dragging editparts within a graphical viewer. When snapping a rectangle, the
 * edges of the rectangle will snap along gridlines.
 * <P>
 * This helper does not keep up with changes made to the graphical viewer's
 * properties. Clients should instantiate a new helper each time one is
 * requested and not hold on to instances of the helper, if the grid properties
 * specified on the viewer are subject to change.
 * 
 * @author Randy Hudson
 * @author Pratik Shah
 * @since 3.0
 * @see org.eclipse.gef.editparts.GridLayer
 */
public class SnapToGrid extends SnapToHelper {

	/**
	 * A viewer property indicating whether the snap function is enabled. The
	 * value must be a Boolean.
	 */
	public static final String PROPERTY_GRID_ENABLED = "SnapToGrid.isEnabled"; //$NON-NLS-1$

	/**
	 * A viewer property indicating whether the grid should be displayed. The
	 * value must be a Boolean.
	 */
	public static final String PROPERTY_GRID_VISIBLE = "SnapToGrid.isVisible"; //$NON-NLS-1$
	/**
	 * A viewer property indicating the grid spacing. The value must be a
	 * {@link Dimension}.
	 */
	public static final String PROPERTY_GRID_SPACING = "SnapToGrid.GridSpacing"; //$NON-NLS-1$
	/**
	 * A viewer property indicating the grid's origin. The value must be a
	 * {@link Point}.
	 */
	public static final String PROPERTY_GRID_ORIGIN = "SnapToGrid.GridOrigin"; //$NON-NLS-1$

	/**
	 * The default grid size if the viewer does not specify a size.
	 * 
	 * @see #PROPERTY_GRID_SPACING
	 */
	public static final int DEFAULT_GRID_SIZE = 12;

	/**
	 * @deprecated use DEFAULT_GRID_SIZE
	 */
	public static final int DEFAULT_GAP = DEFAULT_GRID_SIZE;

	/**
	 * The graphical part whose content's figure defines the grid.
	 */
	protected GraphicalEditPart container;

	/**
	 * The horizontal interval for the grid
	 */
	protected int gridX;

	/**
	 * The vertical interval for the grid
	 */
	protected int gridY;

	/**
	 * The origin of the grid.
	 */
	protected Point origin;

	/**
	 * Constructs a gridded snap helper on the given editpart. The editpart
	 * should be the graphical editpart whose contentspane figure is used as the
	 * reference for the grid.
	 * 
	 * @param container
	 *            the editpart which the grid is on
	 */
	public SnapToGrid(GraphicalEditPart container) {
		this.container = container;
		Dimension spacing = (Dimension) container.getViewer().getProperty(
				PROPERTY_GRID_SPACING);
		if (spacing != null) {
			gridX = spacing.width;
			gridY = spacing.height;
		}
		if (gridX == 0)
			gridX = DEFAULT_GRID_SIZE;
		if (gridY == 0)
			gridY = DEFAULT_GRID_SIZE;
		Point loc = (Point) container.getViewer().getProperty(
				PROPERTY_GRID_ORIGIN);
		if (loc != null)
			origin = loc;
		else
			origin = new Point();
	}

	/**
	 * @see SnapToHelper#snapRectangle(Request, int, PrecisionRectangle,
	 *      PrecisionRectangle)
	 */
	public int snapRectangle(Request request, int snapLocations,
			PrecisionRectangle rect, PrecisionRectangle result) {

		rect = rect.getPreciseCopy();
		makeRelative(container.getContentPane(), rect);
		PrecisionRectangle correction = new PrecisionRectangle();
		makeRelative(container.getContentPane(), correction);

		if (gridX > 0 && (snapLocations & EAST) != 0) {
			correction.setPreciseWidth(correction.preciseWidth()
					- Math.IEEEremainder(rect.preciseRight() - origin.x - 1,
							gridX));
			snapLocations &= ~EAST;
		}

		if ((snapLocations & (WEST | HORIZONTAL)) != 0 && gridX > 0) {
			double leftCorrection = Math.IEEEremainder(rect.preciseX()
					- origin.x, gridX);
			correction.setPreciseX(correction.preciseX() - leftCorrection);
			if ((snapLocations & HORIZONTAL) == 0) {
				correction.setPreciseWidth(correction.preciseWidth()
						+ leftCorrection);
			}
			snapLocations &= ~(WEST | HORIZONTAL);
		}

		if ((snapLocations & SOUTH) != 0 && gridY > 0) {
			correction.setPreciseHeight(correction.preciseHeight()
					- Math.IEEEremainder(rect.preciseBottom() - origin.y - 1,
							gridY));
			snapLocations &= ~SOUTH;
		}

		if ((snapLocations & (NORTH | VERTICAL)) != 0 && gridY > 0) {
			double topCorrection = Math.IEEEremainder(rect.preciseY()
					- origin.y, gridY);
			correction.setPreciseY(correction.preciseY() - topCorrection);
			if ((snapLocations & VERTICAL) == 0) {
				correction.setPreciseHeight(correction.preciseHeight()
						+ topCorrection);
			}
			snapLocations &= ~(NORTH | VERTICAL);
		}

		makeAbsolute(container.getContentPane(), correction);
		result.setPreciseX(result.preciseX() + correction.preciseX());
		result.setPreciseY(result.preciseY() + correction.preciseY());
		result.setPreciseWidth(result.preciseWidth()
				+ correction.preciseWidth());
		result.setPreciseHeight(result.preciseHeight()
				+ correction.preciseHeight());
		return snapLocations;
	}

}