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       1                 :            : /*
       2                 :            :  * Copyright (C) 2014 Lieven van der Heide
       3                 :            :  * Copyright (C) 2021 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
       4                 :            :  *
       5                 :            :  * This library is free software; you can redistribute it and/or
       6                 :            :  * modify it under the terms of the GNU Lesser General Public
       7                 :            :  * License as published by the Free Software Foundation; either
       8                 :            :  * version 2.1 of the License, or (at your option) any later version.
       9                 :            :  *
      10                 :            :  * This library is distributed in the hope that it will be useful,
      11                 :            :  * but WITHOUT ANY WARRANTY; without even the implied warranty of
      12                 :            :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13                 :            :  * Lesser General Public License for more details.
      14                 :            :  *
      15                 :            :  * You should have received a copy of the GNU Lesser General Public
      16                 :            :  * License along with this library; if not, write to the Free Software
      17                 :            :  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
      18                 :            :  */
      19                 :            : 
      20                 :            : #include "shumate-kinetic-scrolling-private.h"
      21                 :            : 
      22                 :            : #include <math.h>
      23                 :            : #include <stdio.h>
      24                 :            : 
      25                 :            : /*
      26                 :            :  * All our curves are second degree linear differential equations, and
      27                 :            :  * so they can always be written as linear combinations of 2 base
      28                 :            :  * solutions. c1 and c2 are the coefficients to these two base solutions,
      29                 :            :  * and are computed from the initial position and velocity.
      30                 :            :  *
      31                 :            :  * In the case of simple deceleration, the differential equation is
      32                 :            :  *
      33                 :            :  *   y'' = -my'
      34                 :            :  *
      35                 :            :  * With m the resistance factor. For this we use the following 2
      36                 :            :  * base solutions:
      37                 :            :  *
      38                 :            :  *   f1(x) = 1
      39                 :            :  *   f2(x) = exp(-mx)
      40                 :            :  *
      41                 :            :  * In the case of overshoot, the differential equation is
      42                 :            :  *
      43                 :            :  *   y'' = -my' - ky
      44                 :            :  *
      45                 :            :  * With m the resistance, and k the spring stiffness constant. We let
      46                 :            :  * k = m^2 / 4, so that the system is critically damped (ie, returns to its
      47                 :            :  * equilibrium position as quickly as possible, without oscillating), and offset
      48                 :            :  * the whole thing, such that the equilibrium position is at 0. This gives the
      49                 :            :  * base solutions
      50                 :            :  *
      51                 :            :  *   f1(x) = exp(-mx / 2)
      52                 :            :  *   f2(x) = t exp(-mx / 2)
      53                 :            : */
      54                 :            : 
      55                 :            : typedef enum {
      56                 :            :   SHUMATE_KINETIC_SCROLLING_PHASE_DECELERATING,
      57                 :            :   SHUMATE_KINETIC_SCROLLING_PHASE_FINISHED,
      58                 :            : } ShumateKineticScrollingPhase;
      59                 :            : 
      60                 :            : struct _ShumateKineticScrolling
      61                 :            : {
      62                 :            :   ShumateKineticScrollingPhase phase;
      63                 :            :   double lower;
      64                 :            :   double upper;
      65                 :            :   double overshoot_width;
      66                 :            :   double decel_friction;
      67                 :            :   double overshoot_friction;
      68                 :            : 
      69                 :            :   double c1;
      70                 :            :   double c2;
      71                 :            :   double equilibrium_position;
      72                 :            : 
      73                 :            :   double t_s;
      74                 :            :   double position;
      75                 :            :   double velocity;
      76                 :            : };
      77                 :            : 
      78                 :            : static inline double
      79                 :          0 : us_to_s (double t)
      80                 :            : {
      81                 :          0 :   return t / 1000000.0;
      82                 :            : }
      83                 :            : 
      84                 :            : ShumateKineticScrolling *
      85                 :          0 : shumate_kinetic_scrolling_new (double decel_friction,
      86                 :            :                                double initial_velocity)
      87                 :            : {
      88                 :          0 :   ShumateKineticScrolling *data;
      89                 :            : 
      90                 :          0 :   data = g_new0 (ShumateKineticScrolling, 1);
      91                 :          0 :   data->phase = SHUMATE_KINETIC_SCROLLING_PHASE_DECELERATING;
      92                 :          0 :   data->decel_friction = decel_friction;
      93                 :          0 :   data->c1 = initial_velocity / decel_friction;
      94                 :          0 :   data->c2 = -data->c1;
      95                 :          0 :   data->t_s = 0.0;
      96                 :          0 :   data->position = 0.0;
      97                 :          0 :   data->velocity = initial_velocity;
      98                 :            : 
      99                 :          0 :   return data;
     100                 :            : }
     101                 :            : 
     102                 :            : void
     103                 :          0 : shumate_kinetic_scrolling_free (ShumateKineticScrolling *kinetic)
     104                 :            : {
     105                 :          0 :   g_free (kinetic);
     106                 :          0 : }
     107                 :            : 
     108                 :            : gboolean
     109                 :          0 : shumate_kinetic_scrolling_tick (ShumateKineticScrolling *data,
     110                 :            :                                 double                   time_delta_us,
     111                 :            :                                 double                  *position)
     112                 :            : {
     113         [ #  # ]:          0 :   switch(data->phase)
     114                 :            :     {
     115                 :          0 :     case SHUMATE_KINETIC_SCROLLING_PHASE_DECELERATING:
     116                 :            :       {
     117                 :          0 :         double last_position = data->position;
     118                 :          0 :         double last_time_ms = data->t_s;
     119                 :          0 :         double exp_part;
     120                 :            : 
     121                 :          0 :         data->t_s += us_to_s (time_delta_us);
     122                 :            : 
     123                 :          0 :         exp_part = exp (-data->decel_friction * data->t_s);
     124                 :          0 :         data->position = data->c1 + data->c2 * exp_part;
     125                 :          0 :         data->velocity = -data->decel_friction * data->c2 * exp_part;
     126                 :            : 
     127   [ #  #  #  # ]:          0 :         if (fabs (data->velocity) < 1.0 ||
     128         [ #  # ]:          0 :             (last_time_ms != 0.0 && fabs (data->position - last_position) < 1.0))
     129                 :            :           {
     130                 :          0 :             data->phase = SHUMATE_KINETIC_SCROLLING_PHASE_FINISHED;
     131                 :          0 :             data->position = round (data->position);
     132                 :          0 :             data->velocity = 0;
     133                 :            :           }
     134                 :            :         break;
     135                 :            :       }
     136                 :            : 
     137                 :            :     case SHUMATE_KINETIC_SCROLLING_PHASE_FINISHED:
     138                 :            :     default:
     139                 :            :       break;
     140                 :            :     }
     141                 :            : 
     142         [ #  # ]:          0 :   if (position)
     143                 :          0 :     *position = data->position;
     144                 :            : 
     145                 :          0 :   return data->phase != SHUMATE_KINETIC_SCROLLING_PHASE_FINISHED;
     146                 :            : }