basicstroke.java

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/*
 * @(#)BasicStroke.java	1.37 01/12/03
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 only, as published by the Free Software Foundation. 
 * 
 * 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 version 2 for more details (a copy is
 * included at /legal/license.txt). 
 * 
 * You should have received a copy of the GNU General Public License
 * version 2 along with this work; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA 
 * 
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
 * Clara, CA 95054 or visit www.sun.com if you need additional
 * information or have any questions. 
 */

package java.awt;

/**
 * The <code>BasicStroke</code> class defines a basic set of rendering
 * attributes for the outlines of graphics primitives, which are rendered
 * with a {@link Graphics2D} object that has its Stroke attribute set to 
 * this <code>BasicStroke</code>.
 * The rendering attributes defined by <code>BasicStroke</code> describe 
 * the shape of the mark made by a pen drawn along the outline of a 
 * {@link Shape} and the decorations applied at the ends and joins of 
 * path segments of the <code>Shape</code>.
 * These rendering attributes include:
 * <dl compact>
 * <dt><i>width</i>
 * <dd>The pen width, measured perpendicularly to the pen trajectory.
 * <dt><i>end caps</i>
 * <dd>The decoration applied to the ends of unclosed subpaths and
 * dash segments.  Subpaths that start and end on the same point are
 * still considered unclosed if they do not have a CLOSE segment.
 * See {@link java.awt.geom.PathIterator#SEG_CLOSE SEG_CLOSE}
 * for more information on the CLOSE segment.
 * The three different decorations are: {@link #CAP_BUTT},
 * {@link #CAP_ROUND}, and {@link #CAP_SQUARE}.
 * <dt><i>line joins</i>
 * <dd>The decoration applied at the intersection of two path segments 
 * and at the intersection of the endpoints of a subpath that is closed
 * using {@link java.awt.geom.PathIterator#SEG_CLOSE SEG_CLOSE}.
 * The three different decorations are: {@link #JOIN_BEVEL}, 
 * {@link #JOIN_MITER}, and {@link #JOIN_ROUND}.
 * <dt><i>miter limit</i>
 * <dd>The limit to trim a line join that has a JOIN_MITER decoration.
 * A line join is trimmed when the ratio of miter length to stroke
 * width is greater than the miterlimit value.  The miter length is 
 * the diagonal length of the miter, which is the distance between 
 * the inside corner and the outside corner of the intersection.
 * The smaller the angle formed by two line segments, the longer 
 * the miter length and the sharper the angle of intersection.  The
 * default miterlimit value of 10.0f causes all angles less than 
 * 11 degrees to be trimmed.  Trimming miters converts
 * the decoration of the line join to bevel.
 * <dt><i>dash attributes</i>
 * <dd>The definition of how to make a dash pattern by alternating
 * between opaque and transparent sections.
 * </dl>
 * All attributes that specify measurements and distances controlling
 * the shape of the returned outline are measured in the same
 * coordinate system as the original unstroked <code>Shape</code> 
 * argument.  When a <code>Graphics2D</code> object uses a 
 * <code>Stroke</code> object to redefine a path during the execution 
 * of one of its <code>draw</code> methods, the geometry is supplied 
 * in its original form before the <code>Graphics2D</code> transform 
 * attribute is applied.  Therefore, attributes such as the pen width 
 * are interpreted in the user space coordinate system of the 
 * <code>Graphics2D</code> object and are subject to the scaling and 
 * shearing effects of the user-space-to-device-space transform in that 
 * particular <code>Graphics2D</code>.  
 * For example, the width of a rendered shape's outline is determined
 * not only by the width attribute of this <code>BasicStroke</code>, 
 * but also by the transform attribute of the 
 * <code>Graphics2D</code> object.  Consider this code:
 * <blockquote><tt>
 *      // sets the Graphics2D object's Tranform attribute
 *	g2d.scale(10, 10);
 *      // sets the Graphics2D object's Stroke attribute
 *      g2d.setStroke(new BasicStroke(1.5f));
 * </tt></blockquote>
 * Assuming there are no other scaling transforms added to the 
 * <code>Graphics2D</code> object, the resulting line 
 * will be approximately 15 pixels wide. 
 * As the example code demonstrates, a floating-point line 
 * offers better precision, especially when large transforms are 
 * used with a <code>Graphics2D</code> object.
 * When a line is diagonal, the exact width depends on how the 
 * rendering pipeline chooses which pixels to fill as it traces the 
 * theoretical widened outline.  The choice of which pixels to turn 
 * on is affected by the antialiasing attribute because the 
 * antialiasing rendering pipeline can choose to color 
 * partially-covered pixels. 
 * <p>
 * For more information on the user space coordinate system and the 
 * rendering process, see the <code>Graphics2D</code> class comments.
 * @see Graphics2D
 * @version 1.37, 12/03/01
 * @author Jim Graham
 */
public class BasicStroke implements Stroke {

    /**
     * Joins path segments by extending their outside edges until
     * they meet.
     */
    public final static int JOIN_MITER = 0;

    /**
     * Joins path segments by rounding off the corner at a radius
     * of half the line width.
     */
    public final static int JOIN_ROUND = 1;

    /**
     * Joins path segments by connecting the outer corners of their
     * wide outlines with a straight segment.
     */
    public final static int JOIN_BEVEL = 2;

    /**
     * Ends unclosed subpaths and dash segments with no added
     * decoration.
     */
    public final static int CAP_BUTT = 0;

    /**
     * Ends unclosed subpaths and dash segments with a round
     * decoration that has a radius equal to half of the width
     * of the pen.
     */
    public final static int CAP_ROUND = 1;

    /**
     * Ends unclosed subpaths and dash segments with a square
     * projection that extends beyond the end of the segment
     * to a distance equal to half of the line width.
     */
    public final static int CAP_SQUARE = 2;

    float width;

    int join;
    int cap;
    float miterlimit;

    float dash[];
    float dash_phase;

    /**
     * Constructs a new <code>BasicStroke</code> with the specified
     * attributes.
     * @param width the width of this <code>BasicStroke</code>.  The
     *         width must be greater than or equal to 0.0f.  If width is
     *         set to 0.0f, the stroke is rendered as the thinnest
     *         possible line for the target device and the antialias
     *         hint setting.
     * @param cap the decoration of the ends of a <code>BasicStroke</code>
     * @param join the decoration applied where path segments meet
     * @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
     * @param dash_phase the offset to start the dashing pattern
     * @throws IllegalArgumentException if <code>width</code> is negative
     * @throws IllegalArgumentException if <code>cap</code> is not either
     *         CAP_BUTT, CAP_ROUND or CAP_SQUARE
     * @throws IllegalArgumentException if <code>miterlimit</code> is less
     *         than 1 and <code>join</code> is JOIN_MITER
     * @throws IllegalArgumentException if <code>join</code> is not
     *         either JOIN_ROUND, JOIN_BEVEL, or JOIN_MITER
     * @throws IllegalArgumentException if <code>dash_phase</code>
     *         is negative and <code>dash</code> is not <code>null</code>
     * @throws IllegalArgumentException if the length of
     *         <code>dash</code> is zero
     * @throws IllegalArgumentException if dash lengths are all zero.
     */
    private BasicStroke(float width, int cap, int join, float miterlimit,
		       float dash[], float dash_phase) {
	if (width < 0.0f) {
	    throw new IllegalArgumentException("negative width");
	}
	if (cap != CAP_BUTT && cap != CAP_ROUND && cap != CAP_SQUARE) {
	    throw new IllegalArgumentException("illegal end cap value");
	}
	if (join == JOIN_MITER) {
	    if (miterlimit < 1.0f) {
		throw new IllegalArgumentException("miter limit < 1");
	    }
	} else if (join != JOIN_ROUND && join != JOIN_BEVEL) {
	    throw new IllegalArgumentException("illegal line join value");
	}
	if (dash != null) {
	    if (dash_phase < 0.0f) {
		throw new IllegalArgumentException("negative dash phase");
	    }
	    boolean allzero = true;
	    for (int i = 0; i < dash.length; i++) {
		float d = dash[i];
		if (d > 0.0) {
		    allzero = false;
		} else if (d < 0.0) {
		    throw new IllegalArgumentException("negative dash length");
		}
	    }
	    if (allzero) {
		throw new IllegalArgumentException("dash lengths all zero");
	    }
	}
	this.width	= width;
	this.cap	= cap;
	this.join	= join;
	this.miterlimit	= miterlimit;