ref: 38ea875e11a64f5c3ff50fe49bcc70676c542d82
dir: /src/Backends/Audio/SoftwareMixer.cpp/
#include "SoftwareMixer.h" #include <math.h> #include <stddef.h> #include <stdio.h> #include <stdlib.h> #include <string.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)) struct Mixer_Sound { signed char *samples; size_t frames; double position; double advance_delta; bool playing; bool looping; unsigned int frequency; float volume; float pan_l; float pan_r; float volume_l; float volume_r; struct Mixer_Sound *next; }; static Mixer_Sound *sound_list_head; static unsigned long output_frequency; static double MillibelToScale(long volume) { // Volume is in hundredths of a decibel, from 0 to -10000 volume = CLAMP(volume, -10000, 0); return pow(10.0, volume / 2000.0); } 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; sound->samples = (signed char*)malloc(length + 1); if (sound->samples == NULL) { free(sound); return NULL; } 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 = 0.0; 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; free(sound->samples); free(sound); break; } } } void Mixer_PlaySound(Mixer_Sound *sound, bool looping) { sound->playing = true; sound->looping = looping; sound->samples[sound->frames] = looping ? sound->samples[0] : 0; // For the linear interpolator } void Mixer_StopSound(Mixer_Sound *sound) { sound->playing = false; sound->position = 0.0; } void Mixer_RewindSound(Mixer_Sound *sound) { sound->position = 0.0; } void Mixer_SetSoundFrequency(Mixer_Sound *sound, unsigned int frequency) { sound->frequency = frequency; sound->advance_delta = (double)frequency / (double)output_frequency; } void Mixer_SetSoundVolume(Mixer_Sound *sound, long volume) { sound->volume = (float)MillibelToScale(volume); sound->volume_l = sound->pan_l * sound->volume; sound->volume_r = sound->pan_r * sound->volume; } void Mixer_SetSoundPan(Mixer_Sound *sound, long pan) { sound->pan_l = (float)MillibelToScale(-pan); sound->pan_r = (float)MillibelToScale(pan); sound->volume_l = sound->pan_l * sound->volume; sound->volume_r = sound->pan_r * sound->volume; } // Most CPU-intensive function in the game (2/3rd CPU time consumption in my experience), so marked with attrHot so the compiler considers it a hot spot (as it is) when optimizing ATTRIBUTE_HOT void Mixer_MixSounds(float *stream, unsigned int frames_total) { for (Mixer_Sound *sound = sound_list_head; sound != NULL; sound = sound->next) { if (sound->playing) { float *steam_pointer = stream; for (unsigned int frames_done = 0; frames_done < frames_total; ++frames_done) { const size_t position_integral = (size_t)sound->position; const float position_fractional = sound->position - position_integral; // Get two samples, and normalise them to 0-1 const float sample1 = sound->samples[position_integral] / 128.0f; const float sample2 = sound->samples[position_integral + 1] / 128.0f; // Perform linear interpolation const float interpolated_sample = sample1 + (sample2 - sample1) * position_fractional; *steam_pointer++ += interpolated_sample * sound->volume_l; *steam_pointer++ += interpolated_sample * sound->volume_r; sound->position += sound->advance_delta; if (sound->position >= sound->frames) { if (sound->looping) { sound->position = fmod(sound->position, (double)sound->frames); } else { sound->playing = false; sound->position = 0.0; break; } } } } } }