Commit ce11caa80f026f615afbc7c6700638a3552cc122
2021-09-21T16:41:29
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)
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diff --git a/src/audio/alsa/SDL_alsa_audio.c b/src/audio/alsa/SDL_alsa_audio.c
index d343efc..1ab7299 100644
--- a/src/audio/alsa/SDL_alsa_audio.c
+++ b/src/audio/alsa/SDL_alsa_audio.c
@@ -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