2 * Copyright (C) 2017 Robin Gareus <robin@gareus.org>
3 * Copyright (C) 1999 Paul Davis
5 * This program is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU General Public License
7 * as published by the Free Software Foundation; either version 2
8 * of the License, or (at your option) any later version.
10 * This program 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
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 #ifndef __pbd_control_math_h__
21 #define __pbd_control_math_h__
26 /* map gain-coeff [0..2] to position [0..1] */
28 gain_to_position (double g)
33 return pow ((6.0 * log (g) / log (2.0) + 192.0) / 198.0, 8.0);
36 /* map position [0..1] to gain-coeff [0..2] */
38 position_to_gain (double pos)
43 return exp (((pow (pos, 1.0 / 8.0) * 198.0) - 192.0) / 6.0 * log (2.0));
46 /* map position [0..1] to parameter [lower..upper] on a logarithmic scale */
48 position_to_logscale (double pos, double lower, double upper)
50 assert (upper > lower && lower * upper > 0);
51 assert (pos >= 0.0 && pos <= 1.0);
52 return lower * pow (upper / lower, pos);
55 /* map parameter [lower..upper] to position [0..1] on a logarithmic scale*/
57 logscale_to_position (double val, double lower, double upper)
59 assert (upper > lower && lower * upper > 0);
60 assert (val >= lower && val <= upper);
61 return log (val / lower) / log (upper / lower);
65 logscale_to_position_with_steps (double val, double lower, double upper, uint32_t steps)
68 double v = logscale_to_position (val, lower, upper) * (steps - 1.0);
69 return round (v) / (steps - 1.0);
73 position_to_logscale_with_steps (double pos, double lower, double upper, uint32_t steps)
76 double p = round (pos * (steps - 1.0)) / (steps - 1.0);
77 return position_to_logscale (p, lower, upper);
82 interpolate_linear (double from, double to, double fraction)
84 return from + (fraction * (to - from));
88 interpolate_logarithmic (double from, double to, double fraction, double lower, double upper)
90 // this is expensive -- optimize
91 double l0 = logscale_to_position (from, lower, upper);
92 double l1 = logscale_to_position (to, lower, upper);
93 return position_to_logscale (l0 + fraction * (l1 - l0), lower, upper);
97 interpolate_gain (double from, double to, double fraction, double upper)
99 // this is expensive -- optimize
100 double g0 = gain_to_position (from * 2. / upper);
101 double g1 = gain_to_position (to * 2. / upper);
102 return position_to_gain (g0 + fraction * (g1 - g0)) * upper / 2.;