Source for gnu.java.awt.GradientPaintContext

   1: /* GradientPaintContext.java --
   2:    Copyright (C) 2005, Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package gnu.java.awt;
  39: 
  40: import java.awt.geom.Point2D;
  41: import java.awt.image.ColorModel;
  42: import java.awt.image.Raster;
  43: import java.awt.image.WritableRaster;
  44: import java.awt.PaintContext;
  45: import java.awt.Color;
  46: 
  47: /**
  48:  * A {@link PaintContext} used by the {@link GradientPaint} class.
  49:  */
  50: public class GradientPaintContext implements PaintContext
  51: {
  52: 
  53:   // This implementation follows the technique described in
  54:   // "Java(tm) 2D Graphics" by Jonathan Knudsen (O'Reilly 1999).
  55: 
  56:   /** The x-coordinate of the anchor point for color 1. */
  57:   private final float x1;
  58: 
  59:   /** The y-coordinate of the anchor point for color 1. */
  60:   private final float y1;
  61: 
  62:   /** Color 1. */
  63:   private final Color c1;
  64: 
  65:   /** The x-coordinate of the anchor point for color 2. */
  66:   private final float x2;
  67: 
  68:   /** The y-coordinate of the anchor point for color 2. */
  69:   private final float y2;
  70: 
  71:   /** Color 2. */
  72:   private final Color c2;
  73: 
  74:   /** A flag indicating whether the gradient is cyclic or acyclic. */
  75:   private final boolean cyclic;
  76: 
  77:   /** The length of the gradient line - computed from the two anchor points. */
  78:   private final double length;
  79: 
  80:   /**
  81:    * Creates a new instance.
  82:    *
  83:    * @param x1  the x-coordinate for the anchor point for color 1.
  84:    * @param y1  the y-coordinate for the anchor point for color 1.
  85:    * @param c1  color 1.
  86:    * @param x2  the x-coordinate for the anchor point for color 2.
  87:    * @param y2  the y-coordinate for the anchor point for color 2.
  88:    * @param c2  color 2.
  89:    * @param cyclic  a flag that determines whether the gradient is cyclic
  90:    *                or acyclic.
  91:    */
  92:   public GradientPaintContext(float x1, float y1, Color c1,
  93:                               float x2, float y2, Color c2, boolean cyclic)
  94:   {
  95:     this.x1 = x1;
  96:     this.y1 = y1;
  97:     this.c1 = c1;
  98:     this.x2 = x2;
  99:     this.y2 = y2;
 100:     this.c2 = c2;
 101:     this.cyclic = cyclic;
 102:     length = Point2D.distance(x1, y1, x2, y2);
 103:   }
 104: 
 105:   /**
 106:    * Return the color model of this context. It may be different from the
 107:    * hint specified during createContext, as not all contexts can generate
 108:    * color patterns in an arbitrary model.
 109:    *
 110:    * @return the context color model
 111:    */
 112:   public ColorModel getColorModel()
 113:   {
 114:     return ColorModel.getRGBdefault();
 115:   }
 116: 
 117:   /**
 118:    * Return a raster containing the colors for the graphics operation.
 119:    *
 120:    * @param x the x-coordinate, in device space
 121:    * @param y the y-coordinate, in device space
 122:    * @param w the width, in device space
 123:    * @param h the height, in device space
 124:    * @return a raster for the given area and color
 125:    */
 126:   public Raster getRaster(int x, int y, int w, int h) {
 127:     ColorModel cm = getColorModel();
 128:     WritableRaster raster = cm.createCompatibleWritableRaster(w, h);
 129:     int[] data = new int[w * h * 4];
 130:     double pd2 = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
 131:     for (int r = 0; r < h; r++) {
 132:       for (int c = 0; c < w; c++) {
 133:         double u = 0.0;
 134:         if (pd2 != 0)
 135:           u = (((x + c) - x1) * (x2 - x1) + ((y + r) - y1) * (y2 - y1))
 136:                   / Math.sqrt(pd2);
 137:         double ratio = u / length;
 138:         if (cyclic)
 139:           ratio = Math.abs(ratio - Math.floor((ratio + 1.0) / 2.0) * 2.0);
 140:         else
 141:           ratio = Math.max(0.0, Math.min(1.0, ratio));
 142:         int base = (r * w + c) * 4;
 143:         data[base] = (int) (c1.getRed() + ratio * (c2.getRed() - c1.getRed()));
 144:         data[base + 1]
 145:           = (int) (c1.getGreen() + ratio * (c2.getGreen() - c1.getGreen()));
 146:         data[base + 2]
 147:           = (int) (c1.getBlue() + ratio * (c2.getBlue() - c1.getBlue()));
 148:         data[base + 3]
 149:           = (int) (c1.getAlpha() + ratio * (c2.getAlpha() - c1.getAlpha()));
 150:       }
 151:     }
 152:     raster.setPixels(0, 0, w, h, data);
 153:     return raster;
 154:   }
 155: 
 156:   /**
 157:    * Release the resources allocated for the paint (none in this
 158:    * implementation).
 159:    */
 160:   public void dispose() {
 161:     // nothing to do
 162:   }
 163: 
 164: }