src/mixer.cpp

   1 /* $Id: mixer.cpp 20211 2010-07-24 10:14:39Z alberth $ */
   2
   3 /*
   4  * This file is part of OpenTTD.
   5  * OpenTTD 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, version 2.
   6  * OpenTTD 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.
   7  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   8  */
   9
  10 /** @file mixer.cpp Mixing of sound samples. */
  11
  12 #include "stdafx.h"
  13 #include <math.h>
  14 #include "core/math_func.hpp"
  15
  16 #include "safeguards.h"
  17
  18 struct MixerChannel {
  19         bool active;
  20
  21         /* pointer to allocated buffer memory */
  22         int8 *memory;
  23
  24         /* current position in memory */
  25         uint32 pos;
  26         uint32 frac_pos;
  27         uint32 frac_speed;
  28         uint32 samples_left;
  29
  30         /* Mixing volume */
  31         int volume_left;
  32         int volume_right;
  33
  34         bool is16bit;
  35 };
  36
  37 static MixerChannel _channels[8];
  38 static uint32 _play_rate = 11025;
  39 static uint32 _max_size = UINT_MAX;
  40
  41 /**
  42  * The theoretical maximum volume for a single sound sample. Multiple sound
  43  * samples should not exceed this limit as it will sound too loud. It also
  44  * stops overflowing when too many sounds are played at the same time, which
  45  * causes an even worse sound quality.
  46  */
  47 static const int MAX_VOLUME = 128 * 128;
  48
  49 /**
  50  * Perform the rate conversion between the input and output.
  51  * @param b the buffer to read the data from
  52  * @param frac_pos the position from the begin of the buffer till the next element
  53  * @tparam T the size of the buffer (8 or 16 bits)
  54  * @return the converted value.
  55  */
  56 template <typename T>
  57 static int RateConversion(T *b, int frac_pos)
  58 {
  59         return ((b[0] * ((1 << 16) - frac_pos)) + (b[1] * frac_pos)) >> 16;
  60 }
  61
  62 static void mix_int16(MixerChannel *sc, int16 *buffer, uint samples)
  63 {
  64         if (samples > sc->samples_left) samples = sc->samples_left;
  65         sc->samples_left -= samples;
  66         assert(samples > 0);
  67
  68         const int16 *b = (const int16 *)sc->memory + sc->pos;
  69         uint32 frac_pos = sc->frac_pos;
  70         uint32 frac_speed = sc->frac_speed;
  71         int volume_left = sc->volume_left;
  72         int volume_right = sc->volume_right;
  73
  74         if (frac_speed == 0x10000) {
  75                 /* Special case when frac_speed is 0x10000 */
  76                 do {
  77                         buffer[0] = Clamp(buffer[0] + (*b * volume_left  >> 16), -MAX_VOLUME, MAX_VOLUME);
  78                         buffer[1] = Clamp(buffer[1] + (*b * volume_right >> 16), -MAX_VOLUME, MAX_VOLUME);
  79                         b++;
  80                         buffer += 2;
  81                 } while (--samples > 0);
  82         } else {
  83                 do {
  84                         int data = RateConversion(b, frac_pos);
  85                         buffer[0] = Clamp(buffer[0] + (data * volume_left  >> 16), -MAX_VOLUME, MAX_VOLUME);
  86                         buffer[1] = Clamp(buffer[1] + (data * volume_right >> 16), -MAX_VOLUME, MAX_VOLUME);
  87                         buffer += 2;
  88                         frac_pos += frac_speed;
  89                         b += frac_pos >> 16;
  90                         frac_pos &= 0xffff;
  91                 } while (--samples > 0);
  92         }
  93
  94         sc->frac_pos = frac_pos;
  95         sc->pos = b - (const int16 *)sc->memory;
  96 }
  97
  98 static void mix_int8_to_int16(MixerChannel *sc, int16 *buffer, uint samples)
  99 {
 100         if (samples > sc->samples_left) samples = sc->samples_left;
 101         sc->samples_left -= samples;
 102         assert(samples > 0);
 103
 104         const int8 *b = sc->memory + sc->pos;
 105         uint32 frac_pos = sc->frac_pos;
 106         uint32 frac_speed = sc->frac_speed;
 107         int volume_left = sc->volume_left;
 108         int volume_right = sc->volume_right;
 109
 110         if (frac_speed == 0x10000) {
 111                 /* Special case when frac_speed is 0x10000 */
 112                 do {
 113                         buffer[0] = Clamp(buffer[0] + (*b * volume_left  >> 8), -MAX_VOLUME, MAX_VOLUME);
 114                         buffer[1] = Clamp(buffer[1] + (*b * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
 115                         b++;
 116                         buffer += 2;
 117                 } while (--samples > 0);
 118         } else {
 119                 do {
 120                         int data = RateConversion(b, frac_pos);
 121                         buffer[0] = Clamp(buffer[0] + (data * volume_left  >> 8), -MAX_VOLUME, MAX_VOLUME);
 122                         buffer[1] = Clamp(buffer[1] + (data * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
 123                         buffer += 2;
 124                         frac_pos += frac_speed;
 125                         b += frac_pos >> 16;
 126                         frac_pos &= 0xffff;
 127                 } while (--samples > 0);
 128         }
 129
 130         sc->frac_pos = frac_pos;
 131         sc->pos = b - sc->memory;
 132 }
 133
 134 static void MxCloseChannel(MixerChannel *mc)
 135 {
 136         mc->active = false;
 137 }
 138
 139 void MxMixSamples(void *buffer, uint samples)
 140 {
 141         MixerChannel *mc;
 142
 143         /* Clear the buffer */
 144         memset(buffer, 0, sizeof(int16) * 2 * samples);
 145
 146         /* Mix each channel */
 147         for (mc = _channels; mc != endof(_channels); mc++) {
 148                 if (mc->active) {
 149                         if (mc->is16bit) {
 150                                 mix_int16(mc, (int16*)buffer, samples);
 151                         } else {
 152                                 mix_int8_to_int16(mc, (int16*)buffer, samples);
 153                         }
 154                         if (mc->samples_left == 0) MxCloseChannel(mc);
 155                 }
 156         }
 157 }
 158
 159 MixerChannel *MxAllocateChannel()
 160 {
 161         MixerChannel *mc;
 162         for (mc = _channels; mc != endof(_channels); mc++) {
 163                 if (!mc->active) {
 164                         free(mc->memory);
 165                         mc->memory = nullptr;
 166                         return mc;
 167                 }
 168         }
 169         return nullptr;
 170 }
 171
 172 void MxSetChannelRawSrc(MixerChannel *mc, int8 *mem, size_t size, uint rate, bool is16bit)
 173 {
 174         mc->memory = mem;
 175         mc->frac_pos = 0;
 176         mc->pos = 0;
 177
 178         mc->frac_speed = (rate << 16) / _play_rate;
 179
 180         if (is16bit) size /= 2;
 181
 182         /* adjust the magnitude to prevent overflow */
 183         while (size >= _max_size) {
 184                 size >>= 1;
 185                 rate = (rate >> 1) + 1;
 186         }
 187
 188         mc->samples_left = (uint)size * _play_rate / rate;
 189         mc->is16bit = is16bit;
 190 }
 191
 192 /**
 193  * Set volume and pan parameters for a sound.
 194  * @param mc     MixerChannel to set
 195  * @param volume Volume level for sound, range is 0..16384
 196  * @param pan    Pan position for sound, range is 0..1
 197  */
 198 void MxSetChannelVolume(MixerChannel *mc, uint volume, float pan)
 199 {
 200         /* Use sinusoidal pan to maintain overall sound power level regardless
 201          * of position. */
 202         mc->volume_left = (uint)(sin((1.0 - pan) * M_PI / 2.0) * volume);
 203         mc->volume_right = (uint)(sin(pan * M_PI / 2.0) * volume);
 204 }
 205
 206
 207 void MxActivateChannel(MixerChannel *mc)
 208 {
 209         mc->active = true;
 210 }
 211
 212
 213 bool MxInitialize(uint rate)
 214 {
 215         _play_rate = rate;
 216         _max_size  = UINT_MAX / _play_rate;
 217         return true;
 218 }