/*

 * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code 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.  Oracle designates this

 * 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

 * or visit www.oracle.com if you need additional information or have any

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 */

package java.awt.geom;

import java.util.*;

/**

 * A utility class to iterate over the path segments of an arc

 * through the PathIterator interface.

 *

 * @author      Jim Graham

 */

class ArcIterator implements PathIterator {

    double x, y, w, h, angStRad, increment, cv;

    AffineTransform affine;

    int index;

    int arcSegs;

    int lineSegs;

    ArcIterator(Arc2D a, AffineTransform at) {

        this.w = a.getWidth() / 2;

        this.h = a.getHeight() / 2;

        this.x = a.getX() + w;

        this.y = a.getY() + h;

        this.angStRad = -Math.toRadians(a.getAngleStart());

        this.affine = at;

        double ext = -a.getAngleExtent();

        if (ext >= 360.0 || ext <= -360) {

            arcSegs = 4;

            this.increment = Math.PI / 2;

            // btan(Math.PI / 2);

            this.cv = 0.5522847498307933;

            if (ext < 0) {

                increment = -increment;

                cv = -cv;

            }

        } else {

            arcSegs = (int) Math.ceil(Math.abs(ext) / 90.0);

            this.increment = Math.toRadians(ext / arcSegs);

            this.cv = btan(increment);

            if (cv == 0) {

                arcSegs = 0;

            }

        }

        switch (a.getArcType()) {

        case Arc2D.OPEN:

            lineSegs = 0;

            break;

        case Arc2D.CHORD:

            lineSegs = 1;

            break;

        case Arc2D.PIE:

            lineSegs = 2;

            break;

        }

        if (w < 0 || h < 0) {

            arcSegs = lineSegs = -1;

        }

    }

    /**

     * 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 > arcSegs + lineSegs;

    }

    /**

     * 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++;

    }

    /*

     * btan computes the length (k) of the control segments at

     * the beginning and end of a cubic bezier that approximates

     * a segment of an arc with extent less than or equal to

     * 90 degrees.  This length (k) will be used to generate the

     * 2 bezier control points for such a segment.

     *

     *   Assumptions:

     *     a) arc is centered on 0,0 with radius of 1.0

     *     b) arc extent is less than 90 degrees

     *     c) control points should preserve tangent

     *     d) control segments should have equal length

     *

     *   Initial data:

     *     start angle: ang1

     *     end angle:   ang2 = ang1 + extent

     *     start point: P1 = (x1, y1) = (cos(ang1), sin(ang1))

     *     end point:   P4 = (x4, y4) = (cos(ang2), sin(ang2))

     *

     *   Control points:

     *     P2 = (x2, y2)

     *     | x2 = x1 - k * sin(ang1) = cos(ang1) - k * sin(ang1)

     *     | y2 = y1 + k * cos(ang1) = sin(ang1) + k * cos(ang1)

     *

     *     P3 = (x3, y3)

     *     | x3 = x4 + k * sin(ang2) = cos(ang2) + k * sin(ang2)

     *     | y3 = y4 - k * cos(ang2) = sin(ang2) - k * cos(ang2)

     *

     * The formula for this length (k) can be found using the

     * following derivations:

     *

     *   Midpoints:

     *     a) bezier (t = 1/2)

     *        bPm = P1 * (1-t)^3 +

     *              3 * P2 * t * (1-t)^2 +

     *              3 * P3 * t^2 * (1-t) +

     *              P4 * t^3 =

     *            = (P1 + 3P2 + 3P3 + P4)/8

     *

     *     b) arc

     *        aPm = (cos((ang1 + ang2)/2), sin((ang1 + ang2)/2))

     *

     *   Let angb = (ang2 - ang1)/2; angb is half of the angle

     *   between ang1 and ang2.

     *

     *   Solve the equation bPm == aPm

     *

     *     a) For xm coord:

     *        x1 + 3*x2 + 3*x3 + x4 = 8*cos((ang1 + ang2)/2)

     *

     *        cos(ang1) + 3*cos(ang1) - 3*k*sin(ang1) +

     *        3*cos(ang2) + 3*k*sin(ang2) + cos(ang2) =

     *        = 8*cos((ang1 + ang2)/2)

     *

     *        4*cos(ang1) + 4*cos(ang2) + 3*k*(sin(ang2) - sin(ang1)) =

     *        = 8*cos((ang1 + ang2)/2)

     *

     *        8*cos((ang1 + ang2)/2)*cos((ang2 - ang1)/2) +

     *        6*k*sin((ang2 - ang1)/2)*cos((ang1 + ang2)/2) =

     *        = 8*cos((ang1 + ang2)/2)

     *

     *        4*cos(angb) + 3*k*sin(angb) = 4

     *

     *        k = 4 / 3 * (1 - cos(angb)) / sin(angb)

     *

     *     b) For ym coord we derive the same formula.

     *

     * Since this formula can generate "NaN" values for small

     * angles, we will derive a safer form that does not involve

     * dividing by very small values:

     *     (1 - cos(angb)) / sin(angb) =

     *     = (1 - cos(angb))*(1 + cos(angb)) / sin(angb)*(1 + cos(angb)) =

     *     = (1 - cos(angb)^2) / sin(angb)*(1 + cos(angb)) =

     *     = sin(angb)^2 / sin(angb)*(1 + cos(angb)) =

     *     = sin(angb) / (1 + cos(angb))

     *

     */

    private static double btan(double increment) {

        increment /= 2.0;

        return 4.0 / 3.0 * Math.sin(increment) / (1.0 + Math.cos(increment));

    }

    /**

     * 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("arc iterator out of bounds");

        }

        double angle = angStRad;

        if (index == 0) {

            coords[0] = (float) (x + Math.cos(angle) * w);

            coords[1] = (float) (y + Math.sin(angle) * h);

            if (affine != null) {

                affine.transform(coords, 0, coords, 0, 1);

            }

            return SEG_MOVETO;

        }

        if (index > arcSegs) {

            if (index == arcSegs + lineSegs) {

                return SEG_CLOSE;

            }

            coords[0] = (float) x;

            coords[1] = (float) y;

            if (affine != null) {

                affine.transform(coords, 0, coords, 0, 1);

            }

            return SEG_LINETO;

        }

        angle += increment * (index - 1);

        double relx = Math.cos(angle);

        double rely = Math.sin(angle);

        coords[0] = (float) (x + (relx - cv * rely) * w);

        coords[1] = (float) (y + (rely + cv * relx) * h);

        angle += increment;

        relx = Math.cos(angle);

        rely = Math.sin(angle);

        coords[2] = (float) (x + (relx + cv * rely) * w);

        coords[3] = (float) (y + (rely - cv * relx) * h);

        coords[4] = (float) (x + relx * w);

        coords[5] = (float) (y + rely * 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("arc iterator out of bounds");

        }

        double angle = angStRad;

        if (index == 0) {

            coords[0] = x + Math.cos(angle) * w;

            coords[1] = y + Math.sin(angle) * h;

            if (affine != null) {

                affine.transform(coords, 0, coords, 0, 1);

            }

            return SEG_MOVETO;

        }

        if (index > arcSegs) {

            if (index == arcSegs + lineSegs) {

                return SEG_CLOSE;

            }

            coords[0] = x;

            coords[1] = y;

            if (affine != null) {

                affine.transform(coords, 0, coords, 0, 1);

            }

            return SEG_LINETO;

        }

        angle += increment * (index - 1);

        double relx = Math.cos(angle);

        double rely = Math.sin(angle);

        coords[0] = x + (relx - cv * rely) * w;

        coords[1] = y + (rely + cv * relx) * h;

        angle += increment;

        relx = Math.cos(angle);

        rely = Math.sin(angle);

        coords[2] = x + (relx + cv * rely) * w;

        coords[3] = y + (rely - cv * relx) * h;

        coords[4] = x + relx * w;

        coords[5] = y + rely * h;

        if (affine != null) {

            affine.transform(coords, 0, coords, 0, 3);

        }

        return SEG_CUBICTO;

    }

}