ref: 9ea6caad72938bbe113376ec6a5c2202728da6d5
dir: /src/Backends/Audio/SoftwareMixer/Mixer.cpp/
#include "Mixer.h"
#include <math.h>
#include <stddef.h>
#include <stdlib.h>
#include "../../../Attributes.h"
#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define CLAMP(x, y, z) MIN(MAX((x), (y)), (z))
#define LANCZOS_KERNEL_RADIUS 2
struct Mixer_Sound
{
signed char *samples;
size_t frames;
size_t position;
unsigned short position_subsample;
unsigned long advance_delta; // 16.16 fixed-point
bool playing;
bool looping;
short volume; // 8.8 fixed-point
short pan_l; // 8.8 fixed-point
short pan_r; // 8.8 fixed-point
short volume_l; // 8.8 fixed-point
short volume_r; // 8.8 fixed-point
struct Mixer_Sound *next;
};
static Mixer_Sound *sound_list_head;
static unsigned long output_frequency;
static unsigned short MillibelToScale(long volume)
{
// Volume is in hundredths of a decibel, from 0 to -10000
volume = CLAMP(volume, -10000, 0);
return (unsigned short)(pow(10.0, volume / 2000.0) * 256.0f);
}
void Mixer_Init(unsigned long frequency)
{
output_frequency = frequency;
}
Mixer_Sound* Mixer_CreateSound(unsigned int frequency, const unsigned char *samples, size_t length)
{
Mixer_Sound *sound = (Mixer_Sound*)malloc(sizeof(Mixer_Sound));
if (sound == NULL)
return NULL;
// Both interpolators will read outside the array's bounds, so allocate some extra room
#ifdef LANCZOS_RESAMPLER
sound->samples = (signed char*)malloc(LANCZOS_KERNEL_RADIUS - 1 + length + LANCZOS_KERNEL_RADIUS);
#else
sound->samples = (signed char*)malloc(length + 1);
#endif
if (sound->samples == NULL)
{
free(sound);
return NULL;
}
#ifdef LANCZOS_RESAMPLER
// Blank samples outside the array bounds (we'll deal with the other half later)
for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS - 1; ++i)
sound->samples[i] = 0;
sound->samples += LANCZOS_KERNEL_RADIUS - 1;
#endif
for (size_t i = 0; i < length; ++i)
sound->samples[i] = samples[i] - 0x80; // Convert from unsigned 8-bit PCM to signed
sound->frames = length;
sound->playing = false;
sound->position = 0;
sound->position_subsample = 0;
Mixer_SetSoundFrequency(sound, frequency);
Mixer_SetSoundVolume(sound, 0);
Mixer_SetSoundPan(sound, 0);
sound->next = sound_list_head;
sound_list_head = sound;
return sound;
}
void Mixer_DestroySound(Mixer_Sound *sound)
{
for (Mixer_Sound **sound_pointer = &sound_list_head; *sound_pointer != NULL; sound_pointer = &(*sound_pointer)->next)
{
if (*sound_pointer == sound)
{
*sound_pointer = sound->next;
#ifdef LANCZOS_RESAMPLER
sound->samples -= LANCZOS_KERNEL_RADIUS - 1;
#endif
free(sound->samples);
free(sound);
break;
}
}
}
void Mixer_PlaySound(Mixer_Sound *sound, bool looping)
{
sound->playing = true;
sound->looping = looping;
// Fill the out-of-bounds part of the buffer with
// either blank samples or repeated samples
#ifdef LANCZOS_RESAMPLER
if (looping)
for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS; ++i)
sound->samples[sound->frames + i] = sound->samples[i];
else
for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS; ++i)
sound->samples[sound->frames + i] = 0;
#else
sound->samples[sound->frames] = looping ? sound->samples[0] : 0;
#endif
}
void Mixer_StopSound(Mixer_Sound *sound)
{
sound->playing = false;
}
void Mixer_RewindSound(Mixer_Sound *sound)
{
sound->position = 0;
sound->position_subsample = 0;
}
void Mixer_SetSoundFrequency(Mixer_Sound *sound, unsigned int frequency)
{
sound->advance_delta = (frequency << 16) / output_frequency;
}
void Mixer_SetSoundVolume(Mixer_Sound *sound, long volume)
{
sound->volume = MillibelToScale(volume);
sound->volume_l = (sound->pan_l * sound->volume) >> 8;
sound->volume_r = (sound->pan_r * sound->volume) >> 8;
}
void Mixer_SetSoundPan(Mixer_Sound *sound, long pan)
{
sound->pan_l = MillibelToScale(-pan);
sound->pan_r = MillibelToScale(pan);
sound->volume_l = (sound->pan_l * sound->volume) >> 8;
sound->volume_r = (sound->pan_r * sound->volume) >> 8;
}
// Most CPU-intensive function in the game (2/3rd CPU time consumption in my experience), so marked with ATTRIBUTE_HOT so the compiler considers it a hot spot (as it is) when optimizing
ATTRIBUTE_HOT void Mixer_MixSounds(long *stream, size_t frames_total)
{
for (Mixer_Sound *sound = sound_list_head; sound != NULL; sound = sound->next)
{
if (sound->playing)
{
long *stream_pointer = stream;
for (size_t frames_done = 0; frames_done < frames_total; ++frames_done)
{
#ifdef LANCZOS_RESAMPLER
// Perform Lanczos resampling
float output_sample = 0;
for (int i = -LANCZOS_KERNEL_RADIUS + 1; i <= LANCZOS_KERNEL_RADIUS; ++i)
{
const signed char input_sample = sound->samples[sound->position + i];
const float kernel_input = ((float)sound->position_subsample / 0x10000) - i;
if (kernel_input == 0.0f)
{
output_sample += input_sample;
}
else
{
const float nx = 3.14159265358979323846f * kernel_input;
const float nxa = nx / LANCZOS_KERNEL_RADIUS;
output_sample += input_sample * (sin(nx) * sin(nxa) / (nx * nxa));
}
}
// Mix, and apply volume
*stream_pointer++ += (short)(output_sample * sound->volume_l);
*stream_pointer++ += (short)(output_sample * sound->volume_r);
#else
// Perform linear interpolation
const unsigned char interpolation_scale = sound->position_subsample >> 8;
const signed char output_sample = (sound->samples[sound->position] * (0x100 - interpolation_scale)
+ sound->samples[sound->position + 1] * interpolation_scale) >> 8;
// Mix, and apply volume
*stream_pointer++ += output_sample * sound->volume_l;
*stream_pointer++ += output_sample * sound->volume_r;
#endif
// Increment sample
const unsigned long next_position_subsample = sound->position_subsample + sound->advance_delta;
sound->position += next_position_subsample >> 16;
sound->position_subsample = next_position_subsample & 0xFFFF;
// Stop or loop sample once it's reached its end
if (sound->position >= sound->frames)
{
if (sound->looping)
{
sound->position %= sound->frames;
}
else
{
sound->playing = false;
sound->position = 0;
sound->position_subsample = 0;
break;
}
}
}
}
}
}