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alsa: Map 7.1 audio channels to match what Windows and macOS expect. 

This matches what we did a long time ago for 5.1 audio.

Fixes #55.

(FIFTY FIVE. Bug reported 15 years, 3 months, and 11 days ago! lol)
This commit is contained in:
Ryan C. Gordon 2021-09-21 16:41:29 -04:00
parent 9886d897e2
commit ce11caa80f
No known key found for this signature in database
GPG Key ID: FA148B892AB48044
1 changed files with 54 additions and 14 deletions
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68
src/audio/alsa/SDL_alsa_audio.c
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@ -289,12 +289,46 @@ static void swizzle_alsa_channels_6_##T(void *buffer, const Uint32 bufferlen) {
} \
}
SWIZ6(Uint64)
SWIZ6(Uint32)
SWIZ6(Uint16)
SWIZ6(Uint8)
/* !!! FIXME: is there a channel swizzler in alsalib instead? */
/* !!! FIXME: this screams for a SIMD shuffle operation. */
/*
* https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/mapping-stream-formats-to-speaker-configurations
* For Linux ALSA, this appears to be FL-FR-RL-RR-C-LFE-SL-SR
* and for Windows DirectX [and CoreAudio], this is FL-FR-C-LFE-SL-SR-RL-RR"
*/
#define SWIZ8(T) \
static void swizzle_alsa_channels_8_##T(void *buffer, const Uint32 bufferlen) { \
T *ptr = (T *) buffer; \
Uint32 i; \
for (i = 0; i < bufferlen; i++, ptr += 6) { \
const T center = ptr[2]; \
const T subwoofer = ptr[3]; \
const T side_left = ptr[4]; \
const T side_right = ptr[5]; \
const T rear_left = ptr[6]; \
const T rear_right = ptr[7]; \
ptr[2] = rear_left; \
ptr[3] = rear_right; \
ptr[4] = center; \
ptr[5] = subwoofer; \
ptr[6] = side_left; \
ptr[7] = side_right; \
} \
}
#define CHANNEL_SWIZZLE(x) \
x(Uint64) \
x(Uint32) \
x(Uint16) \
x(Uint8)
CHANNEL_SWIZZLE(SWIZ6)
CHANNEL_SWIZZLE(SWIZ8)
#undef CHANNEL_SWIZZLE
#undef SWIZ6
#undef SWIZ8
/*
@ -304,17 +338,23 @@ SWIZ6(Uint8)
static void
swizzle_alsa_channels(_THIS, void *buffer, Uint32 bufferlen)
{
if (this->spec.channels == 6) {
switch (SDL_AUDIO_BITSIZE(this->spec.format)) {
case 8: swizzle_alsa_channels_6_Uint8(buffer, bufferlen); break;
case 16: swizzle_alsa_channels_6_Uint16(buffer, bufferlen); break;
case 32: swizzle_alsa_channels_6_Uint32(buffer, bufferlen); break;
case 64: swizzle_alsa_channels_6_Uint64(buffer, bufferlen); break;
default: SDL_assert(!"unhandled bitsize"); break;
}
}
switch (this->spec.channels) {
#define CHANSWIZ(chans) \
case chans: \
switch ((this->spec.format & (0xFF))) { \
case 8: swizzle_alsa_channels_##chans##_Uint8(buffer, bufferlen); break; \
case 16: swizzle_alsa_channels_##chans##_Uint16(buffer, bufferlen); break; \
case 32: swizzle_alsa_channels_##chans##_Uint32(buffer, bufferlen); break; \
case 64: swizzle_alsa_channels_##chans##_Uint64(buffer, bufferlen); break; \
default: SDL_assert(!"unhandled bitsize"); break; \
} \
return;
/* !!! FIXME: update this for 7.1 if needed, later. */
CHANSWIZ(6);
CHANSWIZ(8);
#undef CHANSWIZ
default: break;
}
}
#ifdef SND_CHMAP_API_VERSION