Dogcows Code - chaz/yoink/blob - src/moof/interpolator.hh

   1
   2 /*]  Copyright (c) 2009-2010, Charles McGarvey  [**************************
   3 **]  All rights reserved.
   4 *
   5 * vi:ts=4 sw=4 tw=75
   6 *
   7 * Distributable under the terms and conditions of the 2-clause BSD license;
   8 * see the file COPYING for a complete text of the license.
   9 *
  10 **************************************************************************/
  11
  12 #ifndef _MOOF_INTERPOLATOR_HH_
  13 #define _MOOF_INTERPOLATOR_HH_
  14
  15 /**
  16  * \file interpolator.hh
  17  * Functions and classes concerning interpolations between values.
  18  */
  19
  20 #include <moof/math.hh>
  21
  22
  23 namespace moof {
  24
  25
  26 /**
  27  * Interpolators should inherit from this base class to get some free
  28  * functionality.  Subclasses of this base class will implement their own
  29  * interpolation functions.
  30  */
  31 template <class F, class T = scalar>
  32 class interpolator
  33 {
  34 public:
  35
  36         /**
  37          * Interpolation mode.
  38          */
  39         enum mode
  40         {
  41                 stop            = 0,    /// Interpolator will stop when done.
  42                 repeat          = 1,    /// Interpolator will go back to the beginning.
  43                 oscillate       = 2             /// Interpolator will reverse direction.
  44         };
  45
  46
  47         /**
  48          * Construct an uninitialized interpolator.
  49          */
  50         interpolator() :
  51                 is_done_(true) {}
  52
  53         /**
  54          * Construct an interpolator.
  55          * \param a The initial value.
  56          * \param b The target value.
  57          * \param t The duration of the interpolation.
  58          * \param mode The interpolation mode.
  59          */
  60         interpolator(const T& a, const T& b, scalar t = 1.0, mode mode = stop) :
  61                 state_(a),
  62                 prior_(a),
  63                 a_(a),
  64                 b_(b),
  65                 alpha_(SCALAR(0.0)),
  66                 scale_(SCALAR(1.0) / t),
  67                 mode_(mode),
  68                 is_done_(false) {}
  69
  70         /**
  71          * Initialize the interpolator.  Any interpolation already being
  72          * tracked by this object will be replaced with a new interpolation
  73          * based on the initialization arguments.
  74          * \param a The initial value.
  75          * \param b The target value.
  76          * \param t The duration of the interpolation.
  77          * \param mode The interpolation mode.
  78          */
  79         void init(const T& a, const T& b, scalar t = 1.0, mode mode = stop)
  80         {
  81                 a_ = a;
  82                 b_ = b;
  83                 alpha_ = 0.0;
  84                 scale_ = 1.0 / t;
  85                 mode_ = mode;
  86                 is_done_ = false;
  87         }
  88
  89
  90         /**
  91          * Update the interpolation state with a timeslice.
  92          * \param t The total time in seconds.
  93          * \param dt The number of seconds passed since the last call to
  94          * update.
  95          */
  96         void update(scalar t, scalar dt)
  97         {
  98                 if (!is_done_)
  99                 {
 100                         alpha_ += dt * scale_;
 101                         prior_ = state_;
 102                         state_ = function_(a_, b_, alpha_);
 103
 104                         if (alpha_ > 1.0)
 105                         {
 106                                 switch (mode_)
 107                                 {
 108                                         case stop:
 109                                                 alpha_ = SCALAR(1.0);
 110                                                 is_done_ = true;
 111                                                 break;
 112                                         case repeat:
 113                                                 alpha_ -= SCALAR(1.0);
 114                                                 break;
 115                                         case oscillate:
 116                                                 alpha_ = SCALAR(2.0) - alpha_;
 117                                                 scale_ = -scale_;
 118                                                 break;
 119                                 }
 120                         }
 121                         else if (alpha_ < 0.0)
 122                         {
 123                                 switch (mode_)
 124                                 {
 125                                         case stop:
 126                                                 alpha_ = SCALAR(0.0);
 127                                                 is_done_ = true;
 128                                                 break;
 129                                         case repeat:
 130                                                 alpha_ += SCALAR(1.0);
 131                                                 break;
 132                                         case oscillate:
 133                                                 alpha_ = -alpha_;
 134                                                 scale_ = -scale_;
 135                                                 break;
 136                                 }
 137                         }
 138                 }
 139         }
 140
 141
 142         /**
 143          * Get the interpolated value.
 144          * \return The interpolated value.
 145          */
 146         T state() const
 147         {
 148                 return state_;
 149         }
 150
 151         /**
 152          * Get the interpolated value interpolated between two updates.
 153          * \param alpha The fraction between updates.
 154          * \return The interpolated value.
 155          */
 156         T state(scalar alpha) const
 157         {
 158                 return lerp(prior_, state_, alpha);
 159         }
 160
 161         /**
 162          * Get whether or not the interpolation is done.  This will only return
 163          * true if the interpolation mode is stop.
 164          * \return True if the interpolation has finished.
 165          */
 166         bool is_done() const
 167         {
 168                 return is_done_;
 169         }
 170
 171
 172 private:
 173
 174         T       state_;
 175         T       prior_;
 176         T       a_;
 177         T       b_;
 178
 179         F       function_;
 180
 181         scalar  alpha_;
 182         scalar  scale_;
 183         mode    mode_;
 184         bool    is_done_;
 185 };
 186
 187
 188 struct linear_interpolation_function
 189 {
 190         template <class T>
 191         T operator () (const T& a, const T& b, scalar alpha)
 192         {
 193                 return lerp(a, b, alpha);
 194         }
 195 };
 196
 197
 198 typedef interpolator<linear_interpolation_function> lerp_scalar;
 199
 200
 201 } // namespace moof
 202
 203 #endif // _MOOF_INTERPOLATOR_HH_
 204