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

/*******************************************************************************
 * Copyright (c) 2004, 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.editparts;

import org.eclipse.draw2d.ColorConstants;
import org.eclipse.draw2d.FigureUtilities;
import org.eclipse.draw2d.FreeformLayer;
import org.eclipse.draw2d.Graphics;
import org.eclipse.draw2d.IFigure;
import org.eclipse.draw2d.geometry.Dimension;
import org.eclipse.draw2d.geometry.Point;

import org.eclipse.gef.SnapToGrid;

/**
 * This is a layer that displays the grid. The default grid color is
 * {@link org.eclipse.draw2d.ColorConstants#lightGray light gray}. To change the
 * grid color, set the foreground color for this layer.
 * 
 * @author Pratik Shah
 * @since 3.0
 */
public class GridLayer extends FreeformLayer {

	/**
	 * Field indicating the horizontal grid spacing
	 */
	protected int gridX = SnapToGrid.DEFAULT_GRID_SIZE;
	/**
	 * Field for the vertical grid spacing
	 */
	protected int gridY = SnapToGrid.DEFAULT_GRID_SIZE;

	/**
	 * Field indicating what the grid origin is. This is used simply to
	 * determine the offset from 0,0.
	 */
	protected Point origin = new Point();

	/**
	 * Constructor Sets the default grid color: ColorConstants.lightGray
	 */
	public GridLayer() {
		super();
		setForegroundColor(ColorConstants.lightGray);
	}

	/**
	 * Overridden to indicate no preferred size. The grid layer should not
	 * affect the size of the layered pane in which it is placed.
	 * 
	 * @see org.eclipse.draw2d.Figure#getPreferredSize(int, int)
	 */
	public Dimension getPreferredSize(int wHint, int hHint) {
		return new Dimension();
	}

	/**
	 * @see org.eclipse.draw2d.Figure#paintFigure(org.eclipse.draw2d.Graphics)
	 */
	protected void paintFigure(Graphics graphics) {
		super.paintFigure(graphics);
		paintGrid(graphics);
	}

	/**
	 * Paints the grid. Sub-classes can override to customize the grid's look.
	 * If this layer is being used with SnapToGrid, this method will only be
	 * invoked when the {@link SnapToGrid#PROPERTY_GRID_VISIBLE visibility}
	 * property is set to true.
	 * 
	 * @param g
	 *            The Graphics object to be used to do the painting
	 * @see FigureUtilities#paintGrid(Graphics, IFigure, Point, int, int)
	 */
	protected void paintGrid(Graphics g) {
		FigureUtilities.paintGrid(g, this, origin, gridX, gridY);
	}

	/**
	 * Sets the origin of the grid. The origin is used only to determine the
	 * offset from 0,0.
	 * 
	 * @param p
	 *            the origin
	 */
	public void setOrigin(Point p) {
		if (p == null)
			p = new Point();
		if (!origin.equals(p)) {
			origin = p;
			repaint();
		}
	}

	/**
	 * Sets the horizontal and vertical spacing of the grid. A grid spacing of 0
	 * will be replaced with the {@link SnapToGrid#DEFAULT_GRID_SIZE default}
	 * spacing. A negative spacing will cause no grid lines to be drawn for that
	 * dimension.
	 * 
	 * @param spacing
	 *            A Dimension representing the horizontal (width) and vertical
	 *            (height) gaps
	 */
	public void setSpacing(Dimension spacing) {
		if (spacing == null)
			spacing = new Dimension(SnapToGrid.DEFAULT_GRID_SIZE,
					SnapToGrid.DEFAULT_GRID_SIZE);
		if (!spacing.equals(gridX, gridY)) {
			gridX = spacing.width != 0 ? spacing.width : gridX;
			gridY = spacing.height != 0 ? spacing.height : gridY;
			repaint();
		}
	}

}