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/* GTK - The GIMP Toolkit
* Copyright (C) 2014 Lieven van der Heide
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "gtkkineticscrolling.h"
#include <stdio.h>
#include "fallback-c89.c"
/*
* All our curves are second degree linear differential equations, and
* so they can always be written as linear combinations of 2 base
* solutions. c1 and c2 are the coefficients to these two base solutions,
* and are computed from the initial position and velocity.
*
* In the case of simple deceleration, the differential equation is
*
* y'' = -my'
*
* With m the resistence factor. For this we use the following 2
* base solutions:
*
* f1(x) = 1
* f2(x) = exp(-mx)
*
* In the case of overshoot, the differential equation is
*
* y'' = -my' - ky
*
* With m the resistance, and k the spring stiffness constant. We let
* k = m^2 / 4, so that the system is critically damped (ie, returns to its
* equilibrium position as quickly as possible, without oscillating), and offset
* the whole thing, such that the equilibrium position is at 0. This gives the
* base solutions
*
* f1(x) = exp(-mx / 2)
* f2(x) = t exp(-mx / 2)
*/
typedef enum {
GTK_KINETIC_SCROLLING_PHASE_DECELERATING,
GTK_KINETIC_SCROLLING_PHASE_OVERSHOOTING,
GTK_KINETIC_SCROLLING_PHASE_FINISHED,
} GtkKineticScrollingPhase;
struct _GtkKineticScrolling
{
GtkKineticScrollingPhase phase;
gdouble lower;
gdouble upper;
gdouble overshoot_width;
gdouble decel_friction;
gdouble overshoot_friction;
gdouble c1;
gdouble c2;
gdouble equilibrium_position;
gdouble t;
gdouble position;
gdouble velocity;
};
static void gtk_kinetic_scrolling_init_overshoot (GtkKineticScrolling *data,
gdouble equilibrium_position,
gdouble initial_position,
gdouble initial_velocity);
GtkKineticScrolling *
gtk_kinetic_scrolling_new (gdouble lower,
gdouble upper,
gdouble overshoot_width,
gdouble decel_friction,
gdouble overshoot_friction,
gdouble initial_position,
gdouble initial_velocity)
{
GtkKineticScrolling *data;
data = g_slice_new0 (GtkKineticScrolling);
data->lower = lower;
data->upper = upper;
data->decel_friction = decel_friction;
data->overshoot_friction = overshoot_friction;
if(initial_position < lower)
{
gtk_kinetic_scrolling_init_overshoot (data,
lower,
initial_position,
initial_velocity);
}
else if(initial_position > upper)
{
gtk_kinetic_scrolling_init_overshoot (data,
upper,
initial_position,
initial_velocity);
}
else
{
data->phase = GTK_KINETIC_SCROLLING_PHASE_DECELERATING;
data->c1 = initial_velocity / decel_friction + initial_position;
data->c2 = -initial_velocity / decel_friction;
data->t = 0;
data->position = initial_position;
data->velocity = initial_velocity;
}
return data;
}
void
gtk_kinetic_scrolling_free (GtkKineticScrolling *kinetic)
{
g_slice_free (GtkKineticScrolling, kinetic);
}
static void
gtk_kinetic_scrolling_init_overshoot (GtkKineticScrolling *data,
gdouble equilibrium_position,
gdouble initial_position,
gdouble initial_velocity)
{
data->phase = GTK_KINETIC_SCROLLING_PHASE_OVERSHOOTING;
data->equilibrium_position = equilibrium_position;
data->c1 = initial_position - equilibrium_position;
data->c2 = initial_velocity + data->overshoot_friction / 2 * data->c1;
data->t = 0;
}
gboolean
gtk_kinetic_scrolling_tick (GtkKineticScrolling *data,
gdouble time_delta,
gdouble *position)
{
switch(data->phase)
{
case GTK_KINETIC_SCROLLING_PHASE_DECELERATING:
{
gdouble last_position = data->position;
gdouble last_time = data->t;
gdouble exp_part;
data->t += time_delta;
exp_part = exp (-data->decel_friction * data->t);
data->position = data->c1 + data->c2 * exp_part;
data->velocity = -data->decel_friction * data->c2 * exp_part;
if(data->position < data->lower)
{
gtk_kinetic_scrolling_init_overshoot(data,data->lower,data->position,data->velocity);
}
else if (data->position > data->upper)
{
gtk_kinetic_scrolling_init_overshoot(data, data->upper, data->position, data->velocity);
}
else if (fabs(data->velocity) < 1 ||
(last_time != 0.0 && fabs(data->position - last_position) < 1))
{
data->phase = GTK_KINETIC_SCROLLING_PHASE_FINISHED;
data->position = round(data->position);
data->velocity = 0;
}
break;
}
case GTK_KINETIC_SCROLLING_PHASE_OVERSHOOTING:
{
gdouble exp_part, pos;
data->t += time_delta;
exp_part = exp(-data->overshoot_friction / 2 * data->t);
pos = exp_part * (data->c1 + data->c2 * data->t);
if (pos < data->lower - 50 || pos > data->upper + 50)
{
pos = CLAMP (pos, data->lower - 50, data->upper + 50);
gtk_kinetic_scrolling_init_overshoot (data, data->equilibrium_position, pos, 0);
}
else
data->velocity = data->c2 * exp_part - data->overshoot_friction / 2 * pos;
data->position = pos + data->equilibrium_position;
if(fabs (pos) < 0.1)
{
data->phase = GTK_KINETIC_SCROLLING_PHASE_FINISHED;
data->position = data->equilibrium_position;
data->velocity = 0;
}
break;
}
case GTK_KINETIC_SCROLLING_PHASE_FINISHED:
break;
}
if (position)
*position = data->position;
return data->phase != GTK_KINETIC_SCROLLING_PHASE_FINISHED;
}
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