lumiera_documentation/src/lib/time/quantiser.cpp

/*
  Quantiser  -  aligning time values to a time grid

   Copyright (C)
     2010,            Hermann Vosseler <Ichthyostega@web.de>

  **Lumiera** is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; either version 2 of the License, or (at your
  option) any later version. See the file COPYING for further details.

* *****************************************************************/


/** @file quantiser.cpp
 ** Implementation of support functions to create grid-aligned time and timecode values
 */


#include "lib/time/quantiser.hpp"
#include "lib/time/timevalue.hpp"
#include "lib/time/timequant.hpp"
#include "lib/time.h"

#include <boost/rational.hpp>

using boost::rational_cast;
using std::string;


namespace error = lumiera::error;

namespace lib {
namespace time {
  
  
  PQuant
  getDefaultGridFallback()
  {
    static PQuant globalDefaultGrid (new FixedFrameQuantiser(1));
    return globalDefaultGrid;                                                    ///////////////////////TICKET #810
  };
  
  
  
  
  
  Grid::~Grid() { } // hint to emit the VTable here...
  
  
  /* Note: the ctor QuTime(TimeValue, Symbol) and the static function
   *       PQuant Quantiser::retrieve (Symbol) are defined in common-services.cpp
   *       To use this special convenience shortcuts, you need to link against liblumieracore.so
   *       This allows to use the Advice-system to retrieve grid definitions directly from the session  
   */
  
  
  /**
   * build a quantised time value by explicitly specifying a
   * grid alignment facility and without any hidden reference
   * to the Lumiera session. This is mainly intended for
   * debugging and unit testing.
   */
  QuTime::QuTime (TimeValue raw, PQuant quantisation_to_use)
    : Time(raw)
    , quantiser_(quantisation_to_use)
    { }
  
  
  
  /** Create a quantiser based on a fixed constant spaced grid, rooted at the reference point
   *  as origin of the scale. Quantisation then means to determine the grid interval containing
   *  a given raw time value. Here, the grid interval number zero \em starts at the origin;
   *  each interval includes its lower bound and excludes its upper bound.*/
  FixedFrameQuantiser::FixedFrameQuantiser (FrameRate const& frames_per_second, TimeValue referencePoint)
    : origin_(referencePoint)
    , raster_(__ensure_nonzero(frames_per_second.duration()))
    { }
  
  FixedFrameQuantiser::FixedFrameQuantiser (Duration const& frame_duration,     TimeValue referencePoint)
    : origin_(referencePoint)
    , raster_(__ensure_nonzero(frame_duration))
    { }
  
  
  
  
  /** convenience shortcut: \em materialise a raw time value
   *  based on this grid or time axis, but returning a raw time value. 
   *  Implemented as combination of the #gridPoint and #timeOf operations,
   *  i.e. we quantise into this scale, but transform the result back onto
   *  the global raw time value scale.
   * @warning this operation incurs information loss. Values may be rounded
   *          and / or clipped, according to the grid used. And, contrary to
   *          a QuTime value, the information about the actual grid is
   *          discarded. Please resist the temptation to abuse this
   *          operation to "just get a simple number", without
   *          understanding what quantisation means!
   */
  TimeValue
  Quantiser::materialise  (TimeValue const& raw)  const
  {
    return timeOf (gridPoint (raw));
  }
  
  
  
  /** grid quantisation (alignment).
   *  Determine the next lower grid interval start point,
   *  using a simple constant spaced time grid defined by
   *  origin and framerate stored within this quantiser.
   * @warning returned frame count might exceed the valid
   *      range when converting back into a TimeValue.
   * @see #lumiera_quantise_frames
   */
  FrameCnt
  FixedFrameQuantiser::gridPoint (TimeValue const& rawTime)  const
  {
    return lumiera_quantise_frames (_raw(rawTime), _raw(origin_), _raw(raster_));
  }
  
  
  /** transform into the local time scale grid aligned.
   *  The actual calculation first determines the number
   *  of the grid interval containing the given rawTime,
   *  then followed by multiplying this interval number
   *  with the grid spacing.
   * @return time of the start point of the grid interval
   *      containing the rawTime, _relative to the origin_
   *      of the time scale used by this quantiser.
   * @warning returned time values are limited by the
   *      valid range of lumiera::Time  
   * @see #lumiera_quantise_time
   */
  TimeValue
  FixedFrameQuantiser::gridLocal (TimeValue const& rawTime)  const
  {
    return TimeValue (lumiera_quantise_time (_raw(rawTime), _raw(origin_), _raw(raster_)));
  }
  
  
  /** calculate time value of a grid interval (frame) start point
   * @return time point measured in Lumiera internal time 
   * @warning returned time values are limited by the
   *      valid range of lumiera::Time
   */
  TimeValue
  FixedFrameQuantiser::timeOf (FrameCnt gridPoint)  const
  {
    return TimeValue (lumiera_time_of_gridpoint (gridPoint, _raw(origin_), _raw(raster_)));
  }
  
  
  /** calculate time coordinates of a time spec relative to this quantised time scale
   * @param gridTime seconds relative to the origin of this scale
   * @param gridOffset additional offset in grid intervals (frames)
   * @return time point measured in Lumiera internal time 
   * @warning returned time values are limited by the
   *      valid range of lumiera::Time
   */
  TimeValue
  FixedFrameQuantiser::timeOf (FSecs gridTime, int gridOffset)  const
  {
    Time gt(gridTime);
    TimeVar timePoint = gt + origin_;
    timePoint += gridOffset * Offset(raster_);
    return timePoint;
  }
  
  
  
  
  LUMIERA_ERROR_DEFINE (UNKNOWN_GRID, "referring to an undefined grid or scale in value quantisation");
  
  
  
}} // lib::time