Android example source code file (DirectionPoint.java)

This example Android source code file (DirectionPoint.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

ambiguousdirection, directionpoint, horizonal, unknown, vertical

The DirectionPoint.java Android example source code

/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.android.divideandconquer;

/**
 * To specify a dividing line, a user hits the screen and drags in a
 * certain direction.  Once the line has been drawn long enough and mostly
 * in a particular direction (vertical, or horizontal), we can decide we
 * know what they mean.  Otherwise, it is unknown.
 *
 * This is also nice because if the user decides they don't want to send
 * a dividing line, they can just drag their finger back to where they first
 * touched and let go, cancelling.
 */
public class DirectionPoint {
    enum AmbiguousDirection {
        Vertical,
        Horizonal,
        Unknown
    }

    private float mX;
    private float mY;

    private float endLineX;
    private float endLineY;

    public DirectionPoint(float x, float y) {
        mX = x;
        mY = y;
        endLineX = x;
        endLineY = y;
    }

    public void updateEndPoint(float x, float y) {
        endLineX = x;
        endLineY = y;
    }


    public float getX() {
        return mX;
    }

    public float getY() {
        return mY;
    }

    /**
     * We know the direction when the line is at leat 20 pixels long,
     * and the angle is no more than PI / 6 away from a definitive direction.
     */
    public AmbiguousDirection getDirection() {
        float dx = endLineX - mX;
        double distance = Math.hypot(dx, endLineY - mY);
        if (distance < 10) {
            return AmbiguousDirection.Unknown;
        }
        double angle = Math.acos(dx / distance);
        double thresh = Math.PI / 6;
        if ((angle < thresh || (angle > (Math.PI - thresh)))) {
            return AmbiguousDirection.Horizonal;
        }
        if ((angle > 2 * thresh) && angle < 4*thresh) {
            return AmbiguousDirection.Vertical;
        }
        return AmbiguousDirection.Unknown;
    }
}