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audio: Allow channel maps to specify -1 to mute a channel.

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Fixes #11373.
This commit is contained in:
Ryan C. Gordon
2024-11-20 23:34:28 -05:00
parent 3303e9843f
commit f5ad66ef4b
2 changed files with 62 additions and 23 deletions
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22
include/SDL3/SDL_audio.h
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@@ -1189,8 +1189,12 @@ extern SDL_DECLSPEC int * SDLCALL SDL_GetAudioStreamOutputChannelMap(SDL_AudioSt
* channel that it should be remapped to. To reverse a stereo signal's left
* and right values, you'd have an array of `{ 1, 0 }`. It is legal to remap
* multiple channels to the same thing, so `{ 1, 1 }` would duplicate the
* right channel to both channels of a stereo signal. You cannot change the
* number of channels through a channel map, just reorder them.
* right channel to both channels of a stereo signal. An element in the
* channel map set to -1 instead of a valid channel will mute that channel,
* setting it to a silence value.
*
* You cannot change the number of channels through a channel map, just
* reorder/mute them.
*
* Data that was previously queued in the stream will still be operated on in
* the order that was current when it was added, which is to say you can put
@@ -1206,7 +1210,7 @@ extern SDL_DECLSPEC int * SDLCALL SDL_GetAudioStreamOutputChannelMap(SDL_AudioSt
*
* If `count` is not equal to the current number of channels in the audio
* stream's format, this will fail. This is a safety measure to make sure a a
* race condition hasn't changed the format while you this call is setting the
* race condition hasn't changed the format while this call is setting the
* channel map.
*
* \param stream the SDL_AudioStream to change.
@@ -1235,12 +1239,16 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetAudioStreamInputChannelMap(SDL_AudioStre
* The output channel map reorders data that leaving a stream via
* SDL_GetAudioStreamData.
*
* Each item in the array represents an output channel, and its value is the
* Each item in the array represents an input channel, and its value is the
* channel that it should be remapped to. To reverse a stereo signal's left
* and right values, you'd have an array of `{ 1, 0 }`. It is legal to remap
* multiple channels to the same thing, so `{ 1, 1 }` would duplicate the
* right channel to both channels of a stereo signal. You cannot change the
* number of channels through a channel map, just reorder them.
* right channel to both channels of a stereo signal. An element in the
* channel map set to -1 instead of a valid channel will mute that channel,
* setting it to a silence value.
*
* You cannot change the number of channels through a channel map, just
* reorder/mute them.
*
* The output channel map can be changed at any time, as output remapping is
* applied during SDL_GetAudioStreamData.
@@ -1253,7 +1261,7 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetAudioStreamInputChannelMap(SDL_AudioStre
*
* If `count` is not equal to the current number of channels in the audio
* stream's format, this will fail. This is a safety measure to make sure a a
* race condition hasn't changed the format while you this call is setting the
* race condition hasn't changed the format while this call is setting the
* channel map.
*
* \param stream the SDL_AudioStream to change.

63
src/audio/SDL_audiocvt.c
View File

@@ -129,7 +129,7 @@ bool SDL_ChannelMapIsBogus(const int *chmap, int channels)
if (chmap) {
for (int i = 0; i < channels; i++) {
const int mapping = chmap[i];
if ((mapping < 0) || (mapping >= channels)) {
if ((mapping < -1) || (mapping >= channels)) {
return true;
}
}
@@ -150,27 +150,60 @@ bool SDL_ChannelMapIsDefault(const int *chmap, int channels)
}
// Swizzle audio channels. src and dst can be the same pointer. It does not change the buffer size.
static void SwizzleAudio(const int num_frames, void *dst, const void *src, int channels, const int *map, int bitsize)
static void SwizzleAudio(const int num_frames, void *dst, const void *src, int channels, const int *map, SDL_AudioFormat fmt)
{
const int bitsize = (int) SDL_AUDIO_BITSIZE(fmt);
bool has_null_mappings = false;
for (int i = 0; i < channels; i++) {
if (map[i] == -1) {
has_null_mappings = true;
break;
}
}
#define CHANNEL_SWIZZLE(bits) { \
Uint##bits *tdst = (Uint##bits *) dst; /* treat as UintX; we only care about moving bits and not the type here. */ \
const Uint##bits *tsrc = (const Uint##bits *) src; \
if (src != dst) { /* don't need to copy to a temporary frame first. */ \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
tdst[ch] = tsrc[map[ch]]; \
if (has_null_mappings) { \
const Uint##bits silence = (Uint##bits) SDL_GetSilenceValueForFormat(fmt); \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
const int m = map[ch]; \
tdst[ch] = (m == -1) ? silence : tsrc[m]; \
} \
} \
} else { \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
tdst[ch] = tsrc[map[ch]]; \
} \
} \
} \
} else { \
bool isstack; \
Uint##bits *tmp = (Uint##bits *) SDL_small_alloc(int, channels, &isstack); /* !!! FIXME: allocate this when setting the channel map instead. */ \
if (tmp) { \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
tmp[ch] = tsrc[map[ch]]; \
if (has_null_mappings) { \
const Uint##bits silence = (Uint##bits) SDL_GetSilenceValueForFormat(fmt); \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
const int m = map[ch]; \
tmp[ch] = (m == -1) ? silence : tsrc[m]; \
} \
for (int ch = 0; ch < channels; ch++) { \
tdst[ch] = tmp[ch]; \
} \
} \
for (int ch = 0; ch < channels; ch++) { \
tdst[ch] = tmp[ch]; \
} else { \
for (int i = 0; i < num_frames; i++, tsrc += channels, tdst += channels) { \
for (int ch = 0; ch < channels; ch++) { \
tmp[ch] = tsrc[map[ch]]; \
} \
for (int ch = 0; ch < channels; ch++) { \
tdst[ch] = tmp[ch]; \
} \
} \
} \
SDL_small_free(tmp, isstack); \
@@ -221,9 +254,7 @@ void ConvertAudio(int num_frames,
SDL_Log("SDL_AUDIO_CONVERT: Convert format %04x->%04x, channels %u->%u", src_format, dst_format, src_channels, dst_channels);
#endif
const int src_bitsize = (int) SDL_AUDIO_BITSIZE(src_format);
const int dst_bitsize = (int) SDL_AUDIO_BITSIZE(dst_format);
const int dst_sample_frame_size = (dst_bitsize / 8) * dst_channels;
/* Type conversion goes like this now:
@@ -245,7 +276,7 @@ void ConvertAudio(int num_frames,
// swizzle input to "standard" format if necessary.
if (src_map) {
void* buf = scratch ? scratch : dst; // use scratch if available, since it has to be big enough to hold src, unless it's NULL, then dst has to be.
SwizzleAudio(num_frames, buf, src, src_channels, src_map, src_bitsize);
SwizzleAudio(num_frames, buf, src, src_channels, src_map, src_format);
src = buf;
}
@@ -254,7 +285,7 @@ void ConvertAudio(int num_frames,
if (src_format == dst_format) {
// nothing to do, we're already in the right format, just copy it over if necessary.
if (dst_map) {
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_bitsize);
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_format);
} else if (src != dst) {
SDL_memcpy(dst, src, num_frames * dst_sample_frame_size);
}
@@ -264,7 +295,7 @@ void ConvertAudio(int num_frames,
// just a byteswap needed?
if ((src_format ^ dst_format) == SDL_AUDIO_MASK_BIG_ENDIAN) {
if (dst_map) { // do this first, in case we duplicate channels, we can avoid an extra copy if src != dst.
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_bitsize);
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_format);
src = dst;
}
ConvertAudioSwapEndian(dst, src, num_frames * dst_channels, dst_bitsize);
@@ -348,7 +379,7 @@ void ConvertAudio(int num_frames,
SDL_assert(src == dst); // if we got here, we _had_ to have done _something_. Otherwise, we should have memcpy'd!
if (dst_map) {
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_bitsize);
SwizzleAudio(num_frames, dst, src, dst_channels, dst_map, dst_format);
}
}