path: root/java/awt/BasicStroke.java

/* BasicStroke.java -- 
   Copyright (C) 2002, 2003, 2004, 2005, 2006  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath 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, or (at your option)
any later version.

GNU Classpath 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.

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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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this exception to your version of the library, but you are not
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package java.awt;

import gnu.java.awt.java2d.CubicSegment;
import gnu.java.awt.java2d.LineSegment;
import gnu.java.awt.java2d.QuadSegment;
import gnu.java.awt.java2d.Segment;

import java.awt.geom.FlatteningPathIterator;
import java.awt.geom.GeneralPath;
import java.awt.geom.PathIterator;
import java.awt.geom.Point2D;
import java.util.Arrays;

/**
 * A general purpose {@link Stroke} implementation that can represent a wide
 * variety of line styles for use with subclasses of {@link Graphics2D}.
 * <p>
 * The line cap and join styles can be set using the options illustrated 
 * here:
 * <p>
 * <img src="doc-files/capjoin.png" width="350" height="180"
 * alt="Illustration of line cap and join styles" />
 * <p>
 * A dash array can be used to specify lines with alternating opaque and
 * transparent sections.
 */
public class BasicStroke implements Stroke
{
  /** 
   * Indicates a mitered line join style. See the class overview for an
   * illustration.
   */
  public static final int JOIN_MITER = 0;
  
  /** 
   * Indicates a rounded line join style. See the class overview for an
   * illustration.
   */
  public static final int JOIN_ROUND = 1;
  
  /** 
   * Indicates a bevelled line join style. See the class overview for an
   * illustration.
   */
  public static final int JOIN_BEVEL = 2;

  /** 
   * Indicates a flat line cap style. See the class overview for an
   * illustration.
   */
  public static final int CAP_BUTT = 0;
  
  /** 
   * Indicates a rounded line cap style. See the class overview for an
   * illustration.
   */
  public static final int CAP_ROUND = 1;
  
  /** 
   * Indicates a square line cap style. See the class overview for an
   * illustration.
   */
  public static final int CAP_SQUARE = 2;

  /** The stroke width. */
  private final float width;
  
  /** The line cap style. */
  private final int cap;
  
  /** The line join style. */
  private final int join;
  
  /** The miter limit. */
  private final float limit;
  
  /** The dash array. */
  private final float[] dash;
  
  /** The dash phase. */
  private final float phase;

  // The inner and outer paths of the stroke
  private Segment start, end;

  /**
   * Creates a new <code>BasicStroke</code> instance with the given attributes.
   *
   * @param width  the line width (>= 0.0f).
   * @param cap  the line cap style (one of {@link #CAP_BUTT}, 
   *             {@link #CAP_ROUND} or {@link #CAP_SQUARE}).
   * @param join  the line join style (one of {@link #JOIN_ROUND}, 
   *              {@link #JOIN_BEVEL}, or {@link #JOIN_MITER}).
   * @param miterlimit  the limit to trim the miter join. The miterlimit must be
   * greater than or equal to 1.0f.
   * @param dash The array representing the dashing pattern. There must be at
   * least one non-zero entry.
   * @param dashPhase is negative and dash is not null.
   *
   * @throws IllegalArgumentException If one input parameter doesn't meet
   * its needs.
   */
  public BasicStroke(float width, int cap, int join, float miterlimit,
                     float[] dash, float dashPhase)
  {
    if (width < 0.0f )
      throw new IllegalArgumentException("width " + width + " < 0");
    else if (cap < CAP_BUTT || cap > CAP_SQUARE)
      throw new IllegalArgumentException("cap " + cap + " out of range ["
					 + CAP_BUTT + ".." + CAP_SQUARE + "]");
    else if (miterlimit < 1.0f && join == JOIN_MITER)
      throw new IllegalArgumentException("miterlimit " + miterlimit
					 + " < 1.0f while join == JOIN_MITER");
    else if (join < JOIN_MITER || join > JOIN_BEVEL)
      throw new IllegalArgumentException("join " + join + " out of range ["
					 + JOIN_MITER + ".." + JOIN_BEVEL
					 + "]");
    else if (dashPhase < 0.0f && dash != null)
      throw new IllegalArgumentException("dashPhase " + dashPhase
					 + " < 0.0f while dash != null");
    else if (dash != null)
      if (dash.length == 0)
	throw new IllegalArgumentException("dash.length is 0");
      else
	{
	  boolean allZero = true;
	  
	  for ( int i = 0; i < dash.length; ++i)
	    {
	      if (dash[i] != 0.0f)
		{
		  allZero = false;
		  break;
		}
	    }
	  
	  if (allZero)
	    throw new IllegalArgumentException("all dashes are 0.0f");
	}

    this.width = width;
    this.cap = cap;
    this.join = join;
    limit = miterlimit;
    this.dash = dash == null ? null : (float[]) dash.clone();
    phase = dashPhase;
  }

  /**
   * Creates a new <code>BasicStroke</code> instance with the given attributes.
   *
   * @param width  the line width (>= 0.0f).
   * @param cap  the line cap style (one of {@link #CAP_BUTT}, 
   *             {@link #CAP_ROUND} or {@link #CAP_SQUARE}).
   * @param join  the line join style (one of {@link #JOIN_ROUND}, 
   *              {@link #JOIN_BEVEL}, or {@link #JOIN_MITER}).
   * @param miterlimit the limit to trim the miter join. The miterlimit must be
   * greater than or equal to 1.0f.
   * 
   * @throws IllegalArgumentException If one input parameter doesn't meet
   * its needs.
   */
  public BasicStroke(float width, int cap, int join, float miterlimit)
  {
    this(width, cap, join, miterlimit, null, 0);
  }

  /**
   * Creates a new <code>BasicStroke</code> instance with the given attributes.
   * The miter limit defaults to <code>10.0</code>.
   *
   * @param width  the line width (>= 0.0f).
   * @param cap  the line cap style (one of {@link #CAP_BUTT}, 
   *             {@link #CAP_ROUND} or {@link #CAP_SQUARE}).
   * @param join  the line join style (one of {@link #JOIN_ROUND}, 
   *              {@link #JOIN_BEVEL}, or {@link #JOIN_MITER}).
   * 
   * @throws IllegalArgumentException If one input parameter doesn't meet
   * its needs.
   */
  public BasicStroke(float width, int cap, int join)
  {
    this(width, cap, join, 10, null, 0);
  }

  /**
   * Creates a new <code>BasicStroke</code> instance with the given line
   * width.  The default values are:
   * <ul>
   * <li>line cap style: {@link #CAP_SQUARE};</li>
   * <li>line join style: {@link #JOIN_MITER};</li>
   * <li>miter limit: <code>10.0f</code>.
   * </ul>
   * 
   * @param width  the line width (>= 0.0f).
   * 
   * @throws IllegalArgumentException If <code>width</code> is negative.
   */
  public BasicStroke(float width)
  {
    this(width, CAP_SQUARE, JOIN_MITER, 10, null, 0);
  }

  /**
   * Creates a new <code>BasicStroke</code> instance.  The default values are:
   * <ul>
   * <li>line width: <code>1.0f</code>;</li>
   * <li>line cap style: {@link #CAP_SQUARE};</li>
   * <li>line join style: {@link #JOIN_MITER};</li>
   * <li>miter limit: <code>10.0f</code>.
   * </ul>
   */
  public BasicStroke()
  {
    this(1, CAP_SQUARE, JOIN_MITER, 10, null, 0);
  }
  
  /**
   * Creates a shape representing the stroked outline of the given shape.
   * THIS METHOD IS NOT YET IMPLEMENTED.
   * 
   * @param s  the shape.
   */
  public Shape createStrokedShape(Shape s)
  {
    PathIterator pi = s.getPathIterator(null);

    if( dash == null )
      return solidStroke( pi );

    return dashedStroke( pi );
  }

  /**
   * Returns the line width.
   * 
   * @return The line width.
   */
  public float getLineWidth()
  {
    return width;
  }

  /**
   * Returns a code indicating the line cap style (one of {@link #CAP_BUTT},
   * {@link #CAP_ROUND}, {@link #CAP_SQUARE}).
   * 
   * @return A code indicating the line cap style.
   */
  public int getEndCap()
  {
    return cap;
  }

  /**
   * Returns a code indicating the line join style (one of {@link #JOIN_BEVEL},
   * {@link #JOIN_MITER} or {@link #JOIN_ROUND}).
   * 
   * @return A code indicating the line join style.
   */
  public int getLineJoin()
  {
    return join;
  }

  /**
   * Returns the miter limit.
   * 
   * @return The miter limit.
   */
  public float getMiterLimit()
  {
    return limit;
  }

  /**
   * Returns the dash array, which defines the length of alternate opaque and 
   * transparent sections in lines drawn with this stroke.  If 
   * <code>null</code>, a continuous line will be drawn.
   * 
   * @return The dash array (possibly <code>null</code>).
   */
  public float[] getDashArray()
  {
    return dash;
  }

  /**
   * Returns the dash phase for the stroke.  This is the offset from the start
   * of a path at which the pattern defined by {@link #getDashArray()} is 
   * rendered.
   * 
   * @return The dash phase.
   */
  public float getDashPhase()
  {
    return phase;
  }

  /**
   * Returns the hash code for this object. The hash is calculated by
   * xoring the hash, cap, join, limit, dash array and phase values
   * (converted to <code>int</code> first with
   * <code>Float.floatToIntBits()</code> if the value is a
   * <code>float</code>).
   * 
   * @return The hash code.
   */
  public int hashCode()
  {
    int hash = Float.floatToIntBits(width);
    hash ^= cap;
    hash ^= join;
    hash ^= Float.floatToIntBits(limit);
   
    if (dash != null)
      for (int i = 0; i < dash.length; i++)
	hash ^=  Float.floatToIntBits(dash[i]);

    hash ^= Float.floatToIntBits(phase);

    return hash;
  }

  /**
   * Compares this <code>BasicStroke</code> for equality with an arbitrary 
   * object.  This method returns <code>true</code> if and only if:
   * <ul>
   * <li><code>o</code> is an instanceof <code>BasicStroke</code>;</li>
   * <li>this object has the same width, line cap style, line join style,
   * miter limit, dash array and dash phase as <code>o</code>.</li>
   * </ul>
   * 
   * @param o  the object (<code>null</code> permitted).
   * 
   * @return <code>true</code> if this stroke is equal to <code>o</code> and
   *         <code>false</code> otherwise.
   */
  public boolean equals(Object o)
  {
    if (! (o instanceof BasicStroke))
      return false;
    BasicStroke s = (BasicStroke) o;
    return width == s.width && cap == s.cap && join == s.join
      && limit == s.limit && Arrays.equals(dash, s.dash) && phase == s.phase;
  }

  private Shape solidStroke(PathIterator pi)
  {
    double[] coords = new double[6];
    double x, y, x0, y0;
    boolean pathOpen = false;
    GeneralPath output = new GeneralPath( );
    Segment[] p;
    x = x0 = y = y0 = 0;

    while( !pi.isDone() )
      {
        switch( pi.currentSegment(coords) )
          {
          case PathIterator.SEG_MOVETO:
            x0 = x = coords[0];
            y0 = y = coords[1];
            if( pathOpen )
              {
                capEnds();              
                convertPath(output, start);
                start = end = null;
                pathOpen = false;
              }
            break;

          case PathIterator.SEG_LINETO:
            p = (new LineSegment(x, y, coords[0], coords[1])).
              getDisplacedSegments(width/2.0);
            if( !pathOpen )
              {
                start = p[0];
                end = p[1];
                pathOpen = true;
              }
            else
              addSegments(p);

            x = coords[0];
            y = coords[1];
            break;

          case PathIterator.SEG_QUADTO:
            p = (new QuadSegment(x, y, coords[0], coords[1], coords[2], 
                                 coords[3])).getDisplacedSegments(width/2.0);
            if( !pathOpen )
              {
                start = p[0];
                end = p[1];
                pathOpen = true;
              }
            else
              addSegments(p);

            x = coords[2];
            y = coords[3];
            break;

          case PathIterator.SEG_CUBICTO:
            p = new CubicSegment(x, y, coords[0], coords[1],
                                 coords[2], coords[3],
                                 coords[4], coords[5]).getDisplacedSegments(width/2.0);
            if( !pathOpen )
              {
                start = p[0];
                end = p[1];
                pathOpen = true;
              }
            else
              addSegments(p);

            x = coords[4];
            y = coords[5];
            break;

          case PathIterator.SEG_CLOSE:
            if (x == x0 && y == y0)
              {
                joinSegments(new Segment[] { start.first, end.first });
              }
            else
              {
                p = (new LineSegment(x, y, x0, y0)).getDisplacedSegments(width / 2.0);
                addSegments(p);
              }
            convertPath(output, start);
            convertPath(output, end);
            start = end = null;
            pathOpen = false;
            output.setWindingRule(GeneralPath.WIND_EVEN_ODD);
            break;
          }
        pi.next();
      }

    if( pathOpen )
      {
        capEnds();
        convertPath(output, start);
      }
    return output;
  }

  private Shape dashedStroke(PathIterator pi)
  {
    // The choice of (flatnessSq == width / 3) is made to be consistent with
    // the flattening in CubicSegment.getDisplacedSegments
    FlatteningPathIterator flat = new FlatteningPathIterator(pi,
                                                             Math.sqrt(width / 3));

    // Holds the endpoint of the current segment (or piece of a segment)
    double[] coords = new double[2];

    // Holds end of the last segment
    double x, y, x0, y0;
    x = x0 = y = y0 = 0;

    // Various useful flags
    boolean pathOpen = false;
    boolean dashOn = true;
    boolean offsetting = (phase != 0);

    // How far we are into the current dash
    double distance = 0;
    int dashIndex = 0;

    // And variables to hold the final output
    GeneralPath output = new GeneralPath();
    Segment[] p;

    // Iterate over the FlatteningPathIterator
    while (! flat.isDone())
      {
        switch (flat.currentSegment(coords))
          {
          case PathIterator.SEG_MOVETO:
            x0 = x = coords[0];
            y0 = y = coords[1];

            if (pathOpen)
              {
                capEnds();
                convertPath(output, start);
                start = end = null;
                pathOpen = false;
              }

            break;

          case PathIterator.SEG_LINETO:
            boolean segmentConsumed = false;

            while (! segmentConsumed)
              {
                // Find the total remaining length of this segment
                double segLength = Math.sqrt((x - coords[0]) * (x - coords[0])
                                             + (y - coords[1])
                                             * (y - coords[1]));
                boolean spanBoundary = true;
                double[] segmentEnd = null;

                // The current segment fits entirely inside the current dash
                if ((offsetting && distance + segLength <= phase)
                    || distance + segLength <= dash[dashIndex])
                  {
                    spanBoundary = false;
                  }
                
                // Otherwise, we need to split the segment in two, as this
                // segment spans a dash boundry
                else
                  {
                    segmentEnd = (double[]) coords.clone();

                    // Calculate the remaining distance in this dash,
                    // and coordinates of the dash boundary
                    double reqLength;
                    if (offsetting)
                      reqLength = phase - distance;
                    else
                      reqLength = dash[dashIndex] - distance;

                    coords[0] = x + ((coords[0] - x) * reqLength / segLength);
                    coords[1] = y + ((coords[1] - y) * reqLength / segLength);
                  }

                if (offsetting || ! dashOn)
                  {
                    // Dash is off, or we are in offset - treat this as a
                    // moveTo
                    x0 = x = coords[0];
                    y0 = y = coords[1];

                    if (pathOpen)
                      {
                        capEnds();
                        convertPath(output, start);
                        start = end = null;
                        pathOpen = false;
                      }
                  }
                else
                  {
                    // Dash is on - treat this as a lineTo
                    p = (new LineSegment(x, y, coords[0], coords[1])).getDisplacedSegments(width / 2.0);

                    if (! pathOpen)
                      {
                        start = p[0];
                        end = p[1];
                        pathOpen = true;
                      }
                    else
                      addSegments(p);

                    x = coords[0];
                    y = coords[1];
                  }

                // Update variables depending on whether we spanned a
                // dash boundary or not
                if (! spanBoundary)
                  {
                    distance += segLength;
                    segmentConsumed = true;
                  }
                else
                  {
                    if (offsetting)
                      offsetting = false;
                    dashOn = ! dashOn;
                    distance = 0;
                    coords = segmentEnd;

                    if (dashIndex + 1 == dash.length)
                      dashIndex = 0;
                    else
                      dashIndex++;

                    // Since the value of segmentConsumed is still false,
                    // the next run of the while loop will complete the segment
                  }
              }
            break;

          // This is a flattened path, so we don't need to deal with curves
          }
        flat.next();
      }

    if (pathOpen)
      {
        capEnds();
        convertPath(output, start);
      }
    return output;
  }

  /**
   * Cap the ends of the path (joining the start and end list of segments)
   */
  private void capEnds()
  {
    Segment returnPath = end.last;

    end.reverseAll(); // reverse the path.
    end = null;
    capEnd(start, returnPath);
    start.last = returnPath.last;
    end = null;

    capEnd(start, start);
  }

  /**
   * Append the Segments in s to the GeneralPath p
   */
  private void convertPath(GeneralPath p, Segment s)
  {
    Segment v = s;
    p.moveTo((float)s.P1.getX(), (float)s.P1.getY());

    do
      {
        if(v instanceof LineSegment)
          p.lineTo((float)v.P2.getX(), (float)v.P2.getY());
        else if(v instanceof QuadSegment)
          p.quadTo((float)((QuadSegment)v).cp.getX(),
                   (float)((QuadSegment)v).cp.getY(),
                   (float)v.P2.getX(), 
                   (float)v.P2.getY());
        else if(v instanceof CubicSegment)
          p.curveTo((float)((CubicSegment)v).cp1.getX(),
                    (float)((CubicSegment)v).cp1.getY(),
                    (float)((CubicSegment)v).cp2.getX(),
                    (float)((CubicSegment)v).cp2.getY(),
                    (float)v.P2.getX(), 
                    (float)v.P2.getY());
        v = v.next;
      } while(v != s && v != null);

    p.closePath();
  }
  
  /**
   * Add the segments to start and end (the inner and outer edges of the stroke) 
   */
  private void addSegments(Segment[] segments)
  {
    joinSegments(segments);
    start.add(segments[0]);
    end.add(segments[1]);
  }

  private void joinSegments(Segment[] segments)
  {
    double[] p0 = start.last.cp2();
    double[] p1 = new double[]{start.last.P2.getX(), start.last.P2.getY()};
    double[] p2 = new double[]{segments[0].first.P1.getX(), segments[0].first.P1.getY()};
    double[] p3 = segments[0].cp1();
    Point2D p;

    p = lineIntersection(p0[0],p0[1],p1[0],p1[1],
                                 p2[0],p2[1],p3[0],p3[1], false);

    double det = (p1[0] - p0[0])*(p3[1] - p2[1]) - 
      (p3[0] - p2[0])*(p1[1] - p0[1]);

    if( det > 0 )
      {
        // start and segment[0] form the 'inner' part of a join, 
        // connect the overlapping segments
        joinInnerSegments(start, segments[0], p);
        joinOuterSegments(end, segments[1], p);
      }
    else
      {
        // end and segment[1] form the 'inner' part 
        joinInnerSegments(end, segments[1], p);
        joinOuterSegments(start, segments[0], p);
      }
  }

  /**
   * Make a cap between a and b segments, 
   * where a-->b is the direction of iteration.
   */
  private void capEnd(Segment a, Segment b)
  {
    double[] p0, p1;
    double dx, dy, l;
    Point2D c1,c2;

    switch( cap )
      {
      case CAP_BUTT:
        a.add(new LineSegment(a.last.P2, b.P1));
        break;

      case CAP_SQUARE:
        p0 = a.last.cp2();
        p1 = new double[]{a.last.P2.getX(), a.last.P2.getY()};
        dx = p1[0] - p0[0];
        dy = p1[1] - p0[1];
        l = Math.sqrt(dx * dx + dy * dy);
        dx = 0.5*width*dx/l;
        dy = 0.5*width*dy/l;
        c1 = new Point2D.Double(p1[0] + dx, p1[1] + dy);
        c2 = new Point2D.Double(b.P1.getX() + dx, b.P1.getY() + dy);
        a.add(new LineSegment(a.last.P2, c1));
        a.add(new LineSegment(c1, c2));
        a.add(new LineSegment(c2, b.P1));
        break;

      case CAP_ROUND:
        p0 = a.last.cp2();
        p1 = new double[]{a.last.P2.getX(), a.last.P2.getY()};
        dx = p1[0] - p0[0];
        dy = p1[1] - p0[1];
        l = Math.sqrt(dx * dx + dy * dy);
        dx = (2.0/3.0)*width*dx/l;
        dy = (2.0/3.0)*width*dy/l;
        c1 = new Point2D.Double(p1[0] + dx, p1[1] + dy);
        c2 = new Point2D.Double(b.P1.getX() + dx, b.P1.getY() + dy);
        a.add(new CubicSegment(a.last.P2, c1, c2, b.P1));
        break;
      }
    a.add(b);
  }

  /**
   * Returns the intersection of two lines, or null if there isn't one.
   * @param infinite - true if the lines should be regarded as infinite, false
   * if the intersection must be within the given segments.
   * @return a Point2D or null.
   */
  private Point2D lineIntersection(double X1, double Y1, 
                                   double X2, double Y2, 
                                   double X3, double Y3, 
                                   double X4, double Y4,
                                   boolean infinite)
  {
    double x1 = X1;
    double y1 = Y1;
    double rx = X2 - x1;
    double ry = Y2 - y1;

    double x2 = X3;
    double y2 = Y3;
    double sx = X4 - x2;
    double sy = Y4 - y2;

    double determinant = sx * ry - sy * rx;
    double nom = (sx * (y2 - y1) + sy * (x1 - x2));

    // lines can be considered parallel.
    if (Math.abs(determinant) < 1E-6)
      return null;

    nom = nom / determinant;

    // check if lines are within the bounds
    if(!infinite && (nom > 1.0 || nom < 0.0))
      return null;

    return new Point2D.Double(x1 + nom * rx, y1 + nom * ry);
  }

  /**
   * Join a and b segments, where a-->b is the direction of iteration.
   *
   * insideP is the inside intersection point of the join, needed for
   * calculating miter lengths.
   */
  private void joinOuterSegments(Segment a, Segment b, Point2D insideP)
  {
    double[] p0, p1;
    double dx, dy, l;
    Point2D c1,c2;

    switch( join )
      {
      case JOIN_MITER:
        p0 = a.last.cp2();
        p1 = new double[]{a.last.P2.getX(), a.last.P2.getY()};
        double[] p2 = new double[]{b.P1.getX(), b.P1.getY()};
        double[] p3 = b.cp1();
        Point2D p = lineIntersection(p0[0],p0[1],p1[0],p1[1],p2[0],p2[1],p3[0],p3[1], true);
        if( p == null || insideP == null )
          a.add(new LineSegment(a.last.P2, b.P1));
        else if((p.distance(insideP)/width) < limit)
          {
            a.add(new LineSegment(a.last.P2, p));
            a.add(new LineSegment(p, b.P1));
          } 
        else
          {
            // outside miter limit, do a bevel join.
            a.add(new LineSegment(a.last.P2, b.P1));
          }
        break;

      case JOIN_ROUND:
        p0 = a.last.cp2();
        p1 = new double[]{a.last.P2.getX(), a.last.P2.getY()};
        dx = p1[0] - p0[0];
        dy = p1[1] - p0[1];
        l = Math.sqrt(dx * dx + dy * dy);
        dx = 0.5*width*dx/l;
        dy = 0.5*width*dy/l;
        c1 = new Point2D.Double(p1[0] + dx, p1[1] + dy);

        p0 = new double[]{b.P1.getX(), b.P1.getY()};
        p1 = b.cp1();

        dx = p0[0] - p1[0]; // backwards direction.
        dy = p0[1] - p1[1];
        l = Math.sqrt(dx * dx + dy * dy);
        dx = 0.5*width*dx/l;
        dy = 0.5*width*dy/l;
        c2 = new Point2D.Double(p0[0] + dx, p0[1] + dy);
        a.add(new CubicSegment(a.last.P2, c1, c2, b.P1));
        break;

      case JOIN_BEVEL:
        a.add(new LineSegment(a.last.P2, b.P1));
        break;
      }
  }

  /**
   * Join a and b segments, removing any overlap
   */
  private void joinInnerSegments(Segment a, Segment b, Point2D p)
  {
    double[] p0 = a.last.cp2();
    double[] p1 = new double[] { a.last.P2.getX(), a.last.P2.getY() };
    double[] p2 = new double[] { b.P1.getX(), b.P1.getY() };
    double[] p3 = b.cp1();

    if (p == null)
      {
        // Dodgy.
        a.add(new LineSegment(a.last.P2, b.P1));
        p = new Point2D.Double((b.P1.getX() + a.last.P2.getX()) / 2.0,
                               (b.P1.getY() + a.last.P2.getY()) / 2.0);
      }
    else
      // This assumes segments a and b are single segments, which is
      // incorrect - if they are a linked list of segments (ie, passed in
      // from a flattening operation), this produces strange results!!
      a.last.P2 = b.P1 = p;
  }
}