src/java.desktop/share/classes/java/awt/geom/EllipseIterator.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
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 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 in the LICENSE file that
 * accompanied this code).
 *
 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.awt.geom;

import java.util.*;

/**
 * A utility class to iterate over the path segments of an ellipse
 * through the PathIterator interface.
 *
 * @author      Jim Graham
 */
class EllipseIterator implements PathIterator {
    double x, y, w, h;
    AffineTransform affine;
    int index;

    EllipseIterator(Ellipse2D e, AffineTransform at) {
        this.x = e.getX();
        this.y = e.getY();
        this.w = e.getWidth();
        this.h = e.getHeight();
        this.affine = at;
        if (w < 0 || h < 0) {
            index = 6;
        }
    }

    /**
     * Return the winding rule for determining the insideness of the
     * path.
     * @see #WIND_EVEN_ODD
     * @see #WIND_NON_ZERO
     */
    public int getWindingRule() {
        return WIND_NON_ZERO;
    }

    /**
     * Tests if there are more points to read.
     * @return true if there are more points to read
     */
    public boolean isDone() {
        return index > 5;
    }

    /**
     * Moves the iterator to the next segment of the path forwards
     * along the primary direction of traversal as long as there are
     * more points in that direction.
     */
    public void next() {
        index++;
    }

    // ArcIterator.btan(Math.PI/2)
    public static final double CtrlVal = 0.5522847498307933;

    /*
     * ctrlpts contains the control points for a set of 4 cubic
     * bezier curves that approximate a circle of radius 0.5
     * centered at 0.5, 0.5
     */
    private static final double pcv = 0.5 + CtrlVal * 0.5;
    private static final double ncv = 0.5 - CtrlVal * 0.5;
    private static double[][] ctrlpts = {
        {  1.0,  pcv,  pcv,  1.0,  0.5,  1.0 },
        {  ncv,  1.0,  0.0,  pcv,  0.0,  0.5 },
        {  0.0,  ncv,  ncv,  0.0,  0.5,  0.0 },
        {  pcv,  0.0,  1.0,  ncv,  1.0,  0.5 }
    };

    /**
     * Returns the coordinates and type of the current path segment in
     * the iteration.
     * The return value is the path segment type:
     * SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE.
     * A float array of length 6 must be passed in and may be used to
     * store the coordinates of the point(s).
     * Each point is stored as a pair of float x,y coordinates.
     * SEG_MOVETO and SEG_LINETO types will return one point,
     * SEG_QUADTO will return two points,
     * SEG_CUBICTO will return 3 points
     * and SEG_CLOSE will not return any points.
     * @see #SEG_MOVETO
     * @see #SEG_LINETO
     * @see #SEG_QUADTO
     * @see #SEG_CUBICTO
     * @see #SEG_CLOSE
     */
    public int currentSegment(float[] coords) {
        if (isDone()) {
            throw new NoSuchElementException("ellipse iterator out of bounds");
        }
        if (index == 5) {
            return SEG_CLOSE;
        }
        if (index == 0) {
            double[] ctrls = ctrlpts[3];
            coords[0] = (float) (x + ctrls[4] * w);
            coords[1] = (float) (y + ctrls[5] * h);
            if (affine != null) {
                affine.transform(coords, 0, coords, 0, 1);
            }
            return SEG_MOVETO;
        }
        double[] ctrls = ctrlpts[index - 1];
        coords[0] = (float) (x + ctrls[0] * w);
        coords[1] = (float) (y + ctrls[1] * h);
        coords[2] = (float) (x + ctrls[2] * w);
        coords[3] = (float) (y + ctrls[3] * h);
        coords[4] = (float) (x + ctrls[4] * w);
        coords[5] = (float) (y + ctrls[5] * h);
        if (affine != null) {
            affine.transform(coords, 0, coords, 0, 3);
        }
        return SEG_CUBICTO;
    }

    /**
     * Returns the coordinates and type of the current path segment in
     * the iteration.
     * The return value is the path segment type:
     * SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE.
     * A double array of length 6 must be passed in and may be used to
     * store the coordinates of the point(s).
     * Each point is stored as a pair of double x,y coordinates.
     * SEG_MOVETO and SEG_LINETO types will return one point,
     * SEG_QUADTO will return two points,
     * SEG_CUBICTO will return 3 points
     * and SEG_CLOSE will not return any points.
     * @see #SEG_MOVETO
     * @see #SEG_LINETO
     * @see #SEG_QUADTO
     * @see #SEG_CUBICTO
     * @see #SEG_CLOSE
     */
    public int currentSegment(double[] coords) {
        if (isDone()) {
            throw new NoSuchElementException("ellipse iterator out of bounds");
        }
        if (index == 5) {
            return SEG_CLOSE;
        }
        if (index == 0) {
            double[] ctrls = ctrlpts[3];
            coords[0] = x + ctrls[4] * w;
            coords[1] = y + ctrls[5] * h;
            if (affine != null) {
                affine.transform(coords, 0, coords, 0, 1);
            }
            return SEG_MOVETO;
        }
        double[] ctrls = ctrlpts[index - 1];
        coords[0] = x + ctrls[0] * w;
        coords[1] = y + ctrls[1] * h;
        coords[2] = x + ctrls[2] * w;
        coords[3] = y + ctrls[3] * h;
        coords[4] = x + ctrls[4] * w;
        coords[5] = y + ctrls[5] * h;
        if (affine != null) {
            affine.transform(coords, 0, coords, 0, 3);
        }
        return SEG_CUBICTO;
    }
}