com.almeros.android.multitouch.MoveGestureDetector Maven / Gradle / Ivy

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package com.almeros.android.multitouch;

import android.content.Context;
import android.graphics.PointF;
import android.view.MotionEvent;

/**
 * @author Almer Thie (code.almeros.com)
 * Copyright (c) 2013, Almer Thie (code.almeros.com)
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
 *
 *  Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
 *  Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer
 *  in the documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 */
public class MoveGestureDetector extends BaseGestureDetector {

    /**
     * Listener which must be implemented which is used by MoveGestureDetector
     * to perform callbacks to any implementing class which is registered to a
     * MoveGestureDetector via the constructor.
     *
     * @see MoveGestureDetector.SimpleOnMoveGestureListener
     */
    public interface OnMoveGestureListener {
        public boolean onMove(MoveGestureDetector detector);
        public boolean onMoveBegin(MoveGestureDetector detector);
        public void onMoveEnd(MoveGestureDetector detector);
    }

    /**
     * Helper class which may be extended and where the methods may be
     * implemented. This way it is not necessary to implement all methods
     * of OnMoveGestureListener.
     */
    public static class SimpleOnMoveGestureListener implements OnMoveGestureListener {
        public boolean onMove(MoveGestureDetector detector) {
            return false;
        }

        public boolean onMoveBegin(MoveGestureDetector detector) {
            return true;
        }

        public void onMoveEnd(MoveGestureDetector detector) {
            // Do nothing, overridden implementation may be used
        }
    }

    private static final PointF FOCUS_DELTA_ZERO = new PointF();

    private final OnMoveGestureListener mListener;

    private PointF mCurrFocusInternal;
    private PointF mPrevFocusInternal;
    private PointF mFocusExternal = new PointF();
    private PointF mFocusDeltaExternal = new PointF();


    public MoveGestureDetector(Context context, OnMoveGestureListener listener) {
        super(context);
        mListener = listener;
    }

    @Override
    protected void handleStartProgressEvent(int actionCode, MotionEvent event) {
        switch (actionCode) {
            case MotionEvent.ACTION_DOWN:
                resetState(); // In case we missed an UP/CANCEL event

                mPrevEvent = MotionEvent.obtain(event);
                mTimeDelta = 0;

                updateStateByEvent(event);
                break;

            case MotionEvent.ACTION_MOVE:
                mGestureInProgress = mListener.onMoveBegin(this);
                break;
        }
    }

    @Override
    protected void handleInProgressEvent(int actionCode, MotionEvent event) {
        switch (actionCode) {
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mListener.onMoveEnd(this);
                resetState();
                break;

            case MotionEvent.ACTION_MOVE:
                updateStateByEvent(event);

                // Only accept the event if our relative pressure is within
                // a certain limit. This can help filter shaky data as a
                // finger is lifted.
                if (mCurrPressure / mPrevPressure > PRESSURE_THRESHOLD) {
                    final boolean updatePrevious = mListener.onMove(this);
                    if (updatePrevious) {
                        mPrevEvent.recycle();
                        mPrevEvent = MotionEvent.obtain(event);
                    }
                }
                break;
        }
    }

    protected void updateStateByEvent(MotionEvent curr) {
        super.updateStateByEvent(curr);

        final MotionEvent prev = mPrevEvent;

        // Focus intenal
        mCurrFocusInternal = determineFocalPoint(curr);
        mPrevFocusInternal = determineFocalPoint(prev);

        // Focus external
        // - Prevent skipping of focus delta when a finger is added or removed
        boolean mSkipNextMoveEvent = prev.getPointerCount() != curr.getPointerCount();
        mFocusDeltaExternal = mSkipNextMoveEvent ? FOCUS_DELTA_ZERO : new PointF(mCurrFocusInternal.x - mPrevFocusInternal.x,  mCurrFocusInternal.y - mPrevFocusInternal.y);

        // - Don't directly use mFocusInternal (or skipping will occur). Add
        // unskipped delta values to mFocusExternal instead.
        mFocusExternal.x += mFocusDeltaExternal.x;
        mFocusExternal.y += mFocusDeltaExternal.y;
    }

    /**
     * Determine (multi)finger focal point (a.k.a. center point between all
     * fingers)
     *
     * @param MotionEvent e
     * @return PointF focal point
     */
    private PointF determineFocalPoint(MotionEvent e) {
        // Number of fingers on screen
        final int pCount = e.getPointerCount();
        float x = 0f;
        float y = 0f;

        for (int i = 0; i < pCount; i++) {
            x += e.getX(i);
            y += e.getY(i);
        }

        return new PointF(x / pCount, y / pCount);
    }

    public float getFocusX() {
        return mFocusExternal.x;
    }

    public float getFocusY() {
        return mFocusExternal.y;
    }

    public PointF getFocusDelta() {
        return mFocusDeltaExternal;
    }

}