SwipeRecognizer.java

/*
 * Copyright 2012 Daniel Kurka
 *
 * 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.googlecode.mgwt.dom.client.recognizer.swipe;

import com.google.gwt.core.client.GWT;
import com.google.gwt.dom.client.Touch;
import com.google.gwt.event.dom.client.TouchCancelEvent;
import com.google.gwt.event.dom.client.TouchEndEvent;
import com.google.gwt.event.dom.client.TouchMoveEvent;
import com.google.gwt.event.dom.client.TouchStartEvent;
import com.google.gwt.event.shared.HasHandlers;

import com.googlecode.mgwt.dom.client.event.touch.TouchCopy;
import com.googlecode.mgwt.dom.client.event.touch.TouchHandler;
import com.googlecode.mgwt.dom.client.recognizer.EventPropagator;
import com.googlecode.mgwt.dom.client.recognizer.swipe.SwipeEvent.DIRECTION;

public class SwipeRecognizer implements TouchHandler {

  private static EventPropagator DEFAULT_EVENT_PROPAGATOR;

  private final HasHandlers source;

  private EventPropagator eventPropagator;

  private final int minDistance;

  private final int threshold;

  private int touchCount;

  private enum State {
    INVALID, READY, FINDER_DOWN, FOUND_DIRECTION
  }

  private State state;

  private DIRECTION direction;

  private int lastDistance;

  private int x;

  private int y;

  /**
   * construct a swipe recognizer
   *
   * @param source the source to fire events on
   */
  public SwipeRecognizer(HasHandlers source) {
    this(source, 40);
  }

  /**
   * construct a swipe recognizer
   *
   * @param source the source to fire events on
   * @param minDistance the minimum distance to cover before this counts as a swipe
   */
  public SwipeRecognizer(HasHandlers source, int minDistance) {
    this(source, minDistance, 10);
  }

  /**
   * construct a swipe recognizer
   *
   * @param source the source to fire events on
   * @param minDistance the minimum distance to cover before this counts as a swipe
   * @param threshold the initial threshold before swipe start is fired
   */
  public SwipeRecognizer(HasHandlers source, int minDistance, int threshold) {
    if (source == null)
      throw new IllegalArgumentException("source can not be null");

    if (minDistance <= 0 || minDistance < threshold) {
      throw new IllegalArgumentException("minDistance > 0 and minDistance > threshold");
    }

    if (threshold <= 0) {
      throw new IllegalArgumentException("threshold > 0");
    }

    this.source = source;
    this.minDistance = minDistance;
    this.threshold = threshold;
    this.touchCount = 0;
    state = State.READY;
  }

  @Override
  public void onTouchStart(TouchStartEvent event) {
    touchCount++;

    switch (state) {
      case INVALID:
        break;

      case READY:
        state = State.FINDER_DOWN;

        x = event.getTouches().get(0).getPageX();
        y = event.getTouches().get(0).getPageY();
        break;

      case FINDER_DOWN:
      default:
        state = State.INVALID;
        break;
    }
  }

  @Override
  public void onTouchMove(TouchMoveEvent event) {
    Touch touch = event.getTouches().get(0);

    switch (state) {
      case INVALID:

        break;
      case READY:
        // WTF?
        state = State.INVALID;
        break;
      case FINDER_DOWN:

        // log(" X: " + touch.getPageX() + " old: " + touchStart.getPageX() + " test: " + x);

        if (Math.abs(touch.getPageX() - x) >= threshold) {
          state = State.FOUND_DIRECTION;

          direction = touch.getPageX() - x > 0 ? DIRECTION.LEFT_TO_RIGHT : DIRECTION.RIGHT_TO_LEFT;

          SwipeStartEvent swipeStartEvent =
              new SwipeStartEvent(TouchCopy.copy(touch), touch.getPageX() - x, direction);

          getEventPropagator().fireEvent(source, swipeStartEvent);

        } else {
          if (Math.abs(touch.getPageY() - y) >= threshold) {
            state = State.FOUND_DIRECTION;

            direction = touch.getPageY() - y > 0 ? DIRECTION.TOP_TO_BOTTOM : DIRECTION.BOTTOM_TO_TOP;

            SwipeStartEvent swipeStartEvent =
                new SwipeStartEvent(TouchCopy.copy(touch), touch.getPageY() - y, direction);

            getEventPropagator().fireEvent(source, swipeStartEvent);

          }

        }
        break;

      case FOUND_DIRECTION:

        switch (direction) {
          case TOP_TO_BOTTOM:
          case BOTTOM_TO_TOP:
            lastDistance = Math.abs(touch.getPageY() - y);
            getEventPropagator().fireEvent(
                source,
                new SwipeMoveEvent(TouchCopy.copy(touch), lastDistance > minDistance,
                    lastDistance, direction));
            break;

          case LEFT_TO_RIGHT:
          case RIGHT_TO_LEFT:
            lastDistance = Math.abs(touch.getPageX() - x);
            getEventPropagator().fireEvent(
                source,
                new SwipeMoveEvent(TouchCopy.copy(touch), lastDistance > minDistance,
                    lastDistance, direction));

            break;

          default:
            break;
        }

        break;

      default:
        break;
    }
  }

  @Override
  public void onTouchEnd(TouchEndEvent event) {
    touchCount--;

    switch (state) {
      case FOUND_DIRECTION:
        getEventPropagator().fireEvent(source, new SwipeEndEvent(lastDistance > minDistance, lastDistance, direction));
        reset();
        break;
      default:
        reset();
        break;
    }
  }

  @Override
  public void onTouchCancel(TouchCancelEvent event) {
    touchCount--;
    if (touchCount <= 0) {
      reset();
    }
  }

  /**
   * the threshold before an event is fired (deadzone)
   *
   * @return the threshold in px
   */
  public int getThreshold() {
    return threshold;
  }

  /**
   * the distance that needs to be covered before counting as a swipe
   *
   * @return the distance in px
   */
  public int getMinDistance() {
    return minDistance;
  }

  private void reset() {
    state = State.READY;
    touchCount = 0;
  }

  // Visible for testing
  EventPropagator getEventPropagator() {
    if (eventPropagator == null) {
      if (DEFAULT_EVENT_PROPAGATOR == null) {
        DEFAULT_EVENT_PROPAGATOR = GWT.create(EventPropagator.class);
      }
      eventPropagator = DEFAULT_EVENT_PROPAGATOR;
    }
    return eventPropagator;
  }
}