mixer.cpp

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/*
 * This file is part of OpenTTD.
 * 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.
 * 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.
 * 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/>.
 */
 
#include "stdafx.h"
#include <mutex>
#include <atomic>
#include "core/math_func.hpp"
#include "framerate_type.h"
#include "mixer.h"
#include "settings_type.h"
 
#include "safeguards.h"
 
struct MixerChannel {
  /* pointer to allocated buffer memory */
  int8_t *memory;
 
  /* current position in memory */
  uint32_t pos;
  uint32_t frac_pos;
  uint32_t frac_speed;
  uint32_t samples_left;
 
  /* Mixing volume */
  int volume_left;
  int volume_right;
 
  bool is16bit;
};
 
static std::atomic<uint8_t> _active_channels;
static MixerChannel _channels[8];
static uint32_t _play_rate = 11025;
static uint32_t _max_size = UINT_MAX;
static MxStreamCallback _music_stream = nullptr;
static std::mutex _music_stream_mutex;
static std::atomic<uint8_t> _effect_vol;
 
static const int MAX_VOLUME = 32767;
 
template <typename T>
static int RateConversion(T *b, int frac_pos)
{
  return ((b[0] * ((1 << 16) - frac_pos)) + (b[1] * frac_pos)) >> 16;
}
 
template <typename T>
static void mix_int16(MixerChannel *sc, int16_t *buffer, uint samples, uint8_t effect_vol)
{
  /* Shift required to get sample value into range for the data type. */
  const uint SHIFT = sizeof(T) * CHAR_BIT;
 
  if (samples > sc->samples_left) samples = sc->samples_left;
  sc->samples_left -= samples;
  assert(samples > 0);
 
  const T *b = (const T *)sc->memory + sc->pos;
  uint32_t frac_pos = sc->frac_pos;
  uint32_t frac_speed = sc->frac_speed;
  int volume_left = sc->volume_left * effect_vol / 255;
  int volume_right = sc->volume_right * effect_vol / 255;
 
  if (frac_speed == 0x10000) {
    /* Special case when frac_speed is 0x10000 */
    do {
      buffer[0] = Clamp(buffer[0] + (*b * volume_left  >> SHIFT), -MAX_VOLUME, MAX_VOLUME);
      buffer[1] = Clamp(buffer[1] + (*b * volume_right >> SHIFT), -MAX_VOLUME, MAX_VOLUME);
      b++;
      buffer += 2;
    } while (--samples > 0);
  } else {
    do {
      int data = RateConversion(b, frac_pos);
      buffer[0] = Clamp(buffer[0] + (data * volume_left  >> SHIFT), -MAX_VOLUME, MAX_VOLUME);
      buffer[1] = Clamp(buffer[1] + (data * volume_right >> SHIFT), -MAX_VOLUME, MAX_VOLUME);
      buffer += 2;
      frac_pos += frac_speed;
      b += frac_pos >> 16;
      frac_pos &= 0xffff;
    } while (--samples > 0);
  }
 
  sc->frac_pos = frac_pos;
  sc->pos = b - (const T *)sc->memory;
}
 
static void MxCloseChannel(uint8_t channel_index)
{
  _active_channels.fetch_and(~(1 << channel_index), std::memory_order_release);
}
 
void MxMixSamples(void *buffer, uint samples)
{
  PerformanceMeasurer framerate(PFE_SOUND);
  static uint last_samples = 0;
  if (samples != last_samples) {
    framerate.SetExpectedRate((double)_play_rate / samples);
    last_samples = samples;
  }
 
  /* Clear the buffer */
  memset(buffer, 0, sizeof(int16_t) * 2 * samples);
 
  {
    std::lock_guard<std::mutex> lock{ _music_stream_mutex };
    /* Fetch music if a sampled stream is available */
    if (_music_stream) _music_stream((int16_t*)buffer, samples);
  }
 
  /* Apply simple x^3 scaling to master effect volume. This increases the
   * perceived difference in loudness to better match expectations. effect_vol
   * is expected to be in the range 0-127 hence the division by 127 * 127 to
   * get back into range. */
  uint8_t effect_vol_setting = _effect_vol.load(std::memory_order_relaxed);
  uint8_t effect_vol = (effect_vol_setting *
                      effect_vol_setting *
                      effect_vol_setting) / (127 * 127);
 
  /* Mix each channel */
  uint8_t active = _active_channels.load(std::memory_order_acquire);
  for (uint8_t idx : SetBitIterator(active)) {
    MixerChannel *mc = &_channels[idx];
    if (mc->is16bit) {
      mix_int16<int16_t>(mc, (int16_t*)buffer, samples, effect_vol);
    } else {
      mix_int16<int8_t>(mc, (int16_t*)buffer, samples, effect_vol);
    }
    if (mc->samples_left == 0) MxCloseChannel(idx);
  }
}
 
MixerChannel *MxAllocateChannel()
{
  uint8_t currently_active = _active_channels.load(std::memory_order_acquire);
  uint8_t available = ~currently_active;
  if (available == 0) return nullptr;
 
  uint8_t channel_index = FindFirstBit(available);
 
  MixerChannel *mc = &_channels[channel_index];
  free(mc->memory);
  mc->memory = nullptr;
  return mc;
}
 
void MxSetChannelRawSrc(MixerChannel *mc, int8_t *mem, size_t size, uint rate, bool is16bit)
{
  mc->memory = mem;
  mc->frac_pos = 0;
  mc->pos = 0;
 
  mc->frac_speed = (rate << 16) / _play_rate;
 
  if (is16bit) size /= 2;
 
  /* adjust the magnitude to prevent overflow */
  while (size >= _max_size) {
    size >>= 1;
    rate = (rate >> 1) + 1;
  }
 
  mc->samples_left = (uint)size * _play_rate / rate;
  mc->is16bit = is16bit;
}
 
void MxSetChannelVolume(MixerChannel *mc, uint volume, float pan)
{
  /* Use sinusoidal pan to maintain overall sound power level regardless
   * of position. */
  mc->volume_left = (uint)(sin((1.0 - pan) * M_PI / 2.0) * volume);
  mc->volume_right = (uint)(sin(pan * M_PI / 2.0) * volume);
}
 
 
void MxActivateChannel(MixerChannel *mc)
{
  uint8_t channel_index = mc - _channels;
  _active_channels.fetch_or((1 << channel_index), std::memory_order_release);
}
 
uint32_t MxSetMusicSource(MxStreamCallback music_callback)
{
  std::lock_guard<std::mutex> lock{ _music_stream_mutex };
  _music_stream = music_callback;
  return _play_rate;
}
 
 
bool MxInitialize(uint rate)
{
  std::lock_guard<std::mutex> lock{ _music_stream_mutex };
  _play_rate = rate;
  _max_size  = UINT_MAX / _play_rate;
  _music_stream = nullptr; /* rate may have changed, any music source is now invalid */
  return true;
}
 
void SetEffectVolume(uint8_t volume)
{
  _effect_vol.store(volume, std::memory_order_relaxed);
}