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Optimise the Lanczos resampler some more

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This commit is contained in:
Clownacy 2020-09-03 14:28:04 +01:00
parent 9f002b6180
commit 67ee8b9829
1 changed files with 30 additions and 9 deletions
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39
src/Backends/Audio/SoftwareMixer.cpp
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@ -10,6 +10,8 @@
#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;
@ -51,10 +53,11 @@ Mixer_Sound* Mixer_CreateSound(unsigned int frequency, const unsigned char *samp
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(length);
sound->samples = (signed char*)malloc(LANCZOS_KERNEL_RADIUS - 1 + length + LANCZOS_KERNEL_RADIUS);
#else
sound->samples = (signed char*)malloc(length + 1); // +1 for the linear-interpolator
sound->samples = (signed char*)malloc(length + 1);
#endif
if (sound->samples == NULL)
@ -63,6 +66,14 @@ Mixer_Sound* Mixer_CreateSound(unsigned int frequency, const unsigned char *samp
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
@ -88,6 +99,9 @@ void Mixer_DestroySound(Mixer_Sound *sound)
if (*sound_pointer == sound)
{
*sound_pointer = sound->next;
#ifdef LANCZOS_RESAMPLER
sound->samples -= LANCZOS_KERNEL_RADIUS - 1;
#endif
free(sound->samples);
free(sound);
break;
@ -100,8 +114,17 @@ void Mixer_PlaySound(Mixer_Sound *sound, bool looping)
sound->playing = true;
sound->looping = looping;
#ifndef LANCZOS_RESAMPLER
sound->samples[sound->frames] = looping ? sound->samples[0] : 0; // For the linear interpolator
// 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
}
@ -151,13 +174,11 @@ ATTRIBUTE_HOT void Mixer_MixSounds(long *stream, size_t frames_total)
{
#ifdef LANCZOS_RESAMPLER
// Perform Lanczos resampling
const int kernel_radius = 2;
float accumulator = 0;
for (int i = -MIN(kernel_radius - 1, sound->position); i <= kernel_radius; ++i)
for (int i = -LANCZOS_KERNEL_RADIUS + 1; i <= LANCZOS_KERNEL_RADIUS; ++i)
{
const signed char input_sample = sound->samples[(sound->position + i) % sound->frames];
const signed char input_sample = sound->samples[sound->position + i];
const float kernel_input = ((float)sound->position_subsample / 0x10000) - i;
@ -168,7 +189,7 @@ ATTRIBUTE_HOT void Mixer_MixSounds(long *stream, size_t frames_total)
else
{
const float nx = 3.14159265358979323846f * kernel_input;
const float nxa = nx / kernel_radius;
const float nxa = nx / LANCZOS_KERNEL_RADIUS;
accumulator += input_sample * (sin(nx) * sin(nxa) / (nx * nxa));
}