Adds a circular arc to the given path by approximating it through a cubic Bezier curve on Canvas. - Android Graphics

Android examples for Graphics:Canvas

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Description

Adds a circular arc to the given path by approximating it through a cubic Bezier curve on Canvas.

Demo Code

/**/*from ww w  . j a va 2s.c o  m*/
 * ArcUtils.java
 *
 * Copyright (c) 2014 BioWink GmbH.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software. 
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 **/
//package com.java2s;

import android.graphics.Path;
import android.graphics.PointF;
import android.support.annotation.NonNull;

import static java.lang.Math.sqrt;

public class Main {
    /**
     * Adds a circular arc to the given path by approximating it through a cubic B?er curve.
     * <p/>
     * <p>
     * Note that this <strong>does not</strong> split the arc to better approximate it, for that see either:
     * <ul>
     * <li>{@link #createBezierArcDegrees(PointF, float, float, float, int, boolean,
     * Path)}</li>
     * <li>{@link #createBezierArcRadians(PointF, float, double, double, int, boolean,
     * Path)}</li>
     * </ul>
     * </p>
     * <p/>
     * For a technical explanation:
     * <a href="http://hansmuller-flex.blogspot.de/2011/10/more-about-approximating-circular-arcs.html">
     * http://hansmuller-flex.blogspot.de/2011/10/more-about-approximating-circular-arcs.html
     * </a>
     *
     * @param path        The path to add the arc to.
     * @param center      The center of the circle.
     * @param start       The starting point of the arc on the circle.
     * @param end         The ending point of the arc on the circle.
     * @param moveToStart If {@code true}, move to the starting point of the arc
     *                    (see: {@link Path#moveTo(float, float)}).
     *
     * @see #createBezierArcDegrees(PointF, float, float, float, int, boolean, Path)
     * @see #createBezierArcRadians(PointF, float, double, double, int, boolean, Path)
     */
    public static void addBezierArcToPath(@NonNull Path path,
            @NonNull PointF center, @NonNull PointF start,
            @NonNull PointF end, boolean moveToStart) {
        if (moveToStart) {
            path.moveTo(start.x, start.y);
        }
        if (start.equals(end)) {
            return;
        }

        final double ax = start.x - center.x;
        final double ay = start.y - center.y;
        final double bx = end.x - center.x;
        final double by = end.y - center.y;
        final double q1 = ax * ax + ay * ay;
        final double q2 = q1 + ax * bx + ay * by;
        final double k2 = 4d / 3d * (sqrt(2d * q1 * q2) - q2)
                / (ax * by - ay * bx);
        final float x2 = (float) (center.x + ax - k2 * ay);
        final float y2 = (float) (center.y + ay + k2 * ax);
        final float x3 = (float) (center.x + bx + k2 * by);
        final float y3 = (float) (center.y + by - k2 * bx);

        path.cubicTo(x2, y2, x3, y3, end.x, end.y);
    }
}

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