Android Open Source - paperchains Spring Dynamics

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License

The source code is released under:
Apache License
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Java Source Code

/*
 * Copyright (c) 2010, Sony Ericsson Mobile Communication AB. All rights reserved.
 */*from  ww w. ja  v a  2s . co  m*/
 * 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;

/**
 * SpringDynamics is a Dynamics object that uses friction and spring physics to snap to boundaries and give a natural
 * and organic dynamic.
 */
public class SpringDynamics extends Dynamics {

  /**
   * Friction factor
   */
  private float mFriction;

  /**
   * Spring stiffness factor
   */
  private float mStiffness;

  /**
   * Spring damping
   */
  private float mDamping;

  /**
   * Set friction parameter, friction physics are applied when inside of snap bounds.
   *
   * @param friction Friction factor
   */
  public void setFriction(float friction) {
    mFriction = friction;
  }

  /**
   * Set spring parameters, spring physics are applied when outside of snap bounds.
   *
   * @param stiffness    Spring stiffness
   * @param dampingRatio Damping ratio, < 1 underdamped, > 1 overdamped
   */
  public void setSpring(float stiffness, float dampingRatio) {
    mStiffness = stiffness;
    mDamping = dampingRatio * 2 * (float) Math.sqrt(stiffness);
  }

  /**
   * Calculate acceleration at the current state
   *
   * @return Current acceleration
   */
  private float calculateAcceleration() {
    float acceleration;

    final float distanceFromLimit = getDistanceToLimit();
    if (distanceFromLimit != 0) {
      acceleration = distanceFromLimit * mStiffness - mDamping * mVelocity;
    } else {
      acceleration = -mFriction * mVelocity;
    }

    return acceleration;
  }

  @Override
  protected void onUpdate(int dt) {
    // Calculate dt in seconds as float
    final float fdt = dt / 1000f;

    // Calculate current acceleration
    final float a = calculateAcceleration();

    // Calculate next position based on current velocity and acceleration
    mPosition += mVelocity * fdt + .5f * a * fdt * fdt;

    // Update velocity
    mVelocity += a * fdt;
  }

}
Java Source Code List
