Android Open Source - paperchains Dynamics

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (c) 2010, Sony Ericsson Mobile Communication AB. All rights reserved.
 */*w  w  w.  j a  va  2  s .  c om*/
 * 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.
 *    * Neither the name of the Sony Ericsson Mobile Communication AB nor the names
 *      of its contributors may be used to endorse or promote products derived from
 *      this software without specific prior written permission.
 *
 * 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.
 */

package com.sonyericsson.zoom;

/**
 * Utility class used to handle flinging within a specified limit.
 */
public abstract class Dynamics {
  /**
   * The maximum delta time, in milliseconds, between two updates
   */
  private static final int MAX_TIMESTEP = 50;

  /**
   * The current position
   */
  protected float mPosition;

  /**
   * The current velocity
   */
  protected float mVelocity;

  /**
   * The current maximum position
   */
  protected float mMaxPosition = Float.MAX_VALUE;

  /**
   * The current minimum position
   */
  protected float mMinPosition = -Float.MAX_VALUE;

  /**
   * The time of the last update
   */
  protected long mLastTime = 0;

  /**
   * Sets the state of the dynamics object. Should be called before starting to call update.
   *
   * @param position The current position.
   * @param velocity The current velocity in pixels per second.
   * @param now      The current time
   */
  public void setState(final float position, final float velocity, final long now) {
    mVelocity = velocity;
    mPosition = position;
    mLastTime = now;
  }

  /**
   * Returns the current position. Normally used after a call to update() in order to get the updated position.
   *
   * @return The current position
   */
  public float getPosition() {
    return mPosition;
  }

  /**
   * Gets the velocity. Unit is in pixels per second.
   *
   * @return The velocity in pixels per second
   */
  public float getVelocity() {
    return mVelocity;
  }

  /**
   * Used to find out if the list is at rest, that is, has no velocity and is inside the the limits. Normally used to
   * know if more calls to update are needed.
   *
   * @param velocityTolerance Velocity is regarded as 0 if less than velocityTolerance
   * @param positionTolerance Position is regarded as inside the limits even if positionTolerance above or below
   * @return true if list is at rest, false otherwise
   */
  public boolean isAtRest(final float velocityTolerance, final float positionTolerance) {
    final boolean standingStill = Math.abs(mVelocity) < velocityTolerance;
    final boolean withinLimits = mPosition - positionTolerance < mMaxPosition && mPosition + positionTolerance >
        mMinPosition;
    return standingStill && withinLimits;
  }

  /**
   * Sets the maximum position.
   *
   * @param maxPosition The maximum value of the position
   */
  public void setMaxPosition(final float maxPosition) {
    mMaxPosition = maxPosition;
  }

  /**
   * Sets the minimum position.
   *
   * @param minPosition The minimum value of the position
   */
  public void setMinPosition(final float minPosition) {
    mMinPosition = minPosition;
  }

  /**
   * Updates the position and velocity.
   *
   * @param now The current time
   */
  public void update(final long now) {
    int dt = (int) (now - mLastTime);
    if (dt > MAX_TIMESTEP) {
      dt = MAX_TIMESTEP;
    }

    onUpdate(dt);

    mLastTime = now;
  }

  /**
   * Gets the distance to the closest limit (max and min position).
   *
   * @return If position is more than max position: distance to max position. If position is less than min position:
   * distance to min position. If within limits: 0
   */
  protected float getDistanceToLimit() {
    float distanceToLimit = 0;

    if (mPosition > mMaxPosition) {
      distanceToLimit = mMaxPosition - mPosition;
    } else if (mPosition < mMinPosition) {
      distanceToLimit = mMinPosition - mPosition;
    }

    return distanceToLimit;
  }

  /**
   * Updates the position and velocity.
   *
   * @param dt The delta time since last time
   */
  abstract protected void onUpdate(int dt);
}

Java Source Code List

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