Grid.java

/*
Violet - A program for editing UML diagrams.

Copyright (C) 2002 Cay S. Horstmann (http://horstmann.com)

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

package com.horstmann.violet.framework;

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Stroke;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;

/**
   A grid to which points and rectangles can be "snapped". The
   snapping operation moves a point to the nearest grid point.
*/
public class Grid
{
   /**
      Constructs a grid with no grid points.
   */
   public Grid()
   {
      setGrid(0, 0);
   }
   
   /**
      Sets the grid point distances in x- and y-direction
      @param x the grid point distance in x-direction
      @param y the grid point distance in y-direction
   */
   public void setGrid(double x, double y)
   {
      gridx = x;
      gridy = y;
   }
   
   /**
      Draws this grid inside a rectangle.
      @param g2 the graphics context
      @param bounds the bounding rectangle
   */
   public void draw(Graphics2D g2, Rectangle2D bounds)
   {
      Color PALE_BLUE = new Color(0.9F, 0.8F, 0.9F);
      Color oldColor = g2.getColor();
      g2.setColor(PALE_BLUE);
      Stroke oldStroke = g2.getStroke();
      for (double x = bounds.getX(); x < bounds.getMaxX(); x += gridx)
         g2.draw(new Line2D.Double(x, bounds.getY(), x, bounds.getMaxY()));
      for (double y = bounds.getY(); y < bounds.getMaxY(); y += gridy)
         g2.draw(new Line2D.Double(bounds.getX(), y, bounds.getMaxX(), y));
      g2.setStroke(oldStroke);
      g2.setColor(oldColor);
   }

   /**
      Snaps a point to the nearest grid point
      @param p the point to snap. After the call, the 
      coordinates of p are changed so that p falls on the grid.
   */
   public void snap(Point2D p)
   {
      double x;
      if (gridx == 0)
         x = p.getX();
      else
         x = Math.round(p.getX() / gridx) * gridx;
      double y;
      if (gridy == 0)
         y = p.getY();
      else
         y = Math.round(p.getY() / gridy) * gridy;
         
      p.setLocation(x, y);
   }

   /**
      Snaps a rectangle to the nearest grid points
      @param r the rectangle to snap. After the call, the 
      coordinates of r are changed so that all of its corners
      falls on the grid.
   */
   public void snap(Rectangle2D r)
   {
      double x;
      double w;
      if (gridx == 0)
      {
         x = r.getX();
         w = r.getWidth();
      }
      else
      {
         x = Math.round(r.getX() / gridx) * gridx;
         w = Math.ceil(r.getWidth() / (2 * gridx)) * (2 * gridx);
      }
      double y;
      double h;
      if (gridy == 0)
      {
         y = r.getY();
         h = r.getHeight();
      }
      else
      {
         y = Math.round(r.getY() / gridy) * gridy;
         h = Math.ceil(r.getHeight() / (2 * gridy)) * (2 * gridy);
      }
         
      r.setFrame(x, y, w, h);      
   }

   private double gridx;
   private double gridy;
}