interpolator.h

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//            Copyright (C) 2004-2007 by The Allacrost Project
//                         All Rights Reserved
//
// This code is licensed under the GNU GPL version 2. It is free software 
// and you may modify it and/or redistribute it under the terms of this license.
// See http://www.gnu.org/copyleft/gpl.html for details.

/*!****************************************************************************
 * \file    interpolator.h
 * \author  Raj Sharma, roos@allacrost.org
 * \brief   Header file for Interpolator class
 *
 * The Interpolator class can interpolate between a single and final value
 * using various methods (linear, fast, slow, etc.)
 *****************************************************************************/ 

#ifndef __INTERPOLATOR_HEADER__
#define __INTERPOLATOR_HEADER__

#include "defs.h"
#include "utils.h"

namespace hoa_video
{


/*!***************************************************************************
 *  \brief Interpolation metods are various ways to create smoothed values
 *         between two numbers, e.g. linear interpolation
 *****************************************************************************/

enum InterpolationMethod
{
  VIDEO_INTERPOLATE_INVALID = -1,
  
  VIDEO_INTERPOLATE_EASE = 0,
  VIDEO_INTERPOLATE_SRCA = 1,
  VIDEO_INTERPOLATE_SRCB = 2,
  VIDEO_INTERPOLATE_FAST = 3,
  VIDEO_INTERPOLATE_SLOW = 4,
  VIDEO_INTERPOLATE_LINEAR = 5,
  
  VIDEO_INTERPOLATE_TOTAL = 6
};


/*!***************************************************************************
 *  \brief class that lets you set up various kinds of interpolations.
 *         The basic way to use it is to set the interpolation method using
 *         SetMethod(), then call Start() with the values you want to
 *         interpolate between and the time to do it in.
 *****************************************************************************/
 
class Interpolator
{
public:

  /*!***************************************************************************
  *  \brief Constructor
  *****************************************************************************/
  Interpolator();

  /*!***************************************************************************
  *  \brief Begins interpolation
  * \param a start value of interpolation
  * \param b end value of interpolation
  * \param milliseconds amount of time to interpolate over
  * \return success/failure
  *****************************************************************************/
  bool Start(float a, float b, int32 milliseconds);

  /*!***************************************************************************
  *  \brief Sets the interpolation method.  If this is not called, VIDEO_INTERPOLATION_LINEAR
  *      is assumed
  * \param method interpolation method to use
  * \return success/failure
  *****************************************************************************/
  bool  SetMethod(InterpolationMethod method);
  
  /*!***************************************************************************
  *  \brief Gets the current interpolated value
  * \return the current interpolated value
  *****************************************************************************/
  float GetValue();
  
  /*!***************************************************************************
  *  \brief Increments time by frameTime and updates the interpolation
  * \param frame_time amount to update the time value by
  * \return success/failure
  *****************************************************************************/
  bool  Update(int32 frame_time);
  
  /*!***************************************************************************
  *  \brief Is interpolation finished?
  * \return true if done, false if not
  *****************************************************************************/
  bool  IsFinished();

private:

  /*!***************************************************************************
  *  \brief Interpolates logarithmically.  Increases quickly then levels off.
  * \param t float value to interpolate
  * \return interpolated value
  *****************************************************************************/
  float _FastTransform(float t);
  
  /*!***************************************************************************
  *  \brief Interpolates exponentially.  Increases slowly then skyrockets.
  * \param t float value to interpolate
  * \return interpolated value
  *****************************************************************************/
  float _SlowTransform(float t);
  
  /*!***************************************************************************
  *  \brief Interpolates periodically.  Increases slowly to 1.0 then back down to 0.0
  * \param t float value to interpolate
  * \return interpolated value
  *****************************************************************************/
  float _EaseTransform(float t);

  /*!***************************************************************************
  *  \brief Verifies the interpolation method is valid.
  * \return true for valid, false for not
  *****************************************************************************/
  bool _ValidMethod();
  
  InterpolationMethod _method;
  
  float _a, _b;
  
  int32   _current_time;
  
  int32   _end_time;
  
  bool  _finished;
  
  float _current_value;
  
}; // class Interpolator

}  // namespace hoa_video

#endif // !__INTERPOLATOR_HEADER__

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