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audio: Allow streams to change the device-side channels maps.

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Fixes #11881.
This commit is contained in:
Ryan C. Gordon 2025-01-14 16:35:04 -05:00
parent b2793a2ce2
commit 9e60a8994f
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GPG key ID: FA148B892AB48044
4 changed files with 67 additions and 10 deletions
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20
include/SDL3/SDL_audio.h
View file

@ -942,7 +942,7 @@ extern SDL_DECLSPEC void SDLCALL SDL_CloseAudioDevice(SDL_AudioDeviceID devid);
* Binding a stream to a device will set its output format for playback
* devices, and its input format for recording devices, so they match the
* device's settings. The caller is welcome to change the other end of the
* stream's format at any time.
* stream's format at any time with SDL_SetAudioStreamFormat().
*
* \param devid an audio device to bind a stream to.
* \param streams an array of audio streams to bind.
@ -1104,6 +1104,12 @@ extern SDL_DECLSPEC bool SDLCALL SDL_GetAudioStreamFormat(SDL_AudioStream *strea
* next sound file, and start putting that new data while the previous sound
* file is still queued, and everything will still play back correctly.
*
* If a stream is bound to a device, then the format of the side of the stream
* bound to a device cannot be changed (src_spec for recording devices,
* dst_spec for playback devices). Attempts to make a change to this side
* will be ignored, but this will not report an error. The other side's format
* can be changed.
*
* \param stream the stream the format is being changed.
* \param src_spec the new format of the audio input; if NULL, it is not
* changed.
@ -1298,6 +1304,11 @@ extern SDL_DECLSPEC int * SDLCALL SDL_GetAudioStreamOutputChannelMap(SDL_AudioSt
* race condition hasn't changed the format while this call is setting the
* channel map.
*
* Unlike attempting to change the stream's format, the input channel map on a
* stream bound to a recording device is permitted to change at any time; any
* data added to the stream from the device after this call will have the new
* mapping, but previously-added data will still have the prior mapping.
*
* \param stream the SDL_AudioStream to change.
* \param chmap the new channel map, NULL to reset to default.
* \param count The number of channels in the map.
@ -1349,6 +1360,13 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetAudioStreamInputChannelMap(SDL_AudioStre
* race condition hasn't changed the format while this call is setting the
* channel map.
*
* Unlike attempting to change the stream's format, the output channel map on
* a stream bound to a recording device is permitted to change at any time;
* any data added to the stream after this call will have the new mapping, but
* previously-added data will still have the prior mapping. When the channel
* map doesn't match the hardware's channel layout, SDL will convert the data
* before feeding it to the device for playback.
*
* \param stream the SDL_AudioStream to change.
* \param chmap the new channel map, NULL to reset to default.
* \param count The number of channels in the map.

38
src/audio/SDL_audio.c
View file

@ -281,6 +281,18 @@ bool SDL_AudioSpecsEqual(const SDL_AudioSpec *a, const SDL_AudioSpec *b, const i
return true;
}
bool SDL_AudioChannelMapsEqual(int channels, const int *channel_map_a, const int *channel_map_b)
{
if (channel_map_a == channel_map_b) {
return true;
} else if ((channel_map_a != NULL) != (channel_map_b != NULL)) {
return false;
} else if (channel_map_a && (SDL_memcmp(channel_map_a, channel_map_b, sizeof (*channel_map_a) * channels) != 0)) {
return false;
}
return true;
}
// Zombie device implementation...
@ -1134,7 +1146,7 @@ bool SDL_PlaybackAudioThreadIterate(SDL_AudioDevice *device)
SDL_AudioStream *stream = logdev->bound_streams;
// We should have updated this elsewhere if the format changed!
SDL_assert(SDL_AudioSpecsEqual(&stream->dst_spec, &device->spec, stream->dst_chmap, device->chmap));
SDL_assert(SDL_AudioSpecsEqual(&stream->dst_spec, &device->spec, NULL, NULL));
const int br = SDL_GetAtomicInt(&logdev->paused) ? 0 : SDL_GetAudioStreamDataAdjustGain(stream, device_buffer, buffer_size, logdev->gain);
if (br < 0) { // Probably OOM. Kill the audio device; the whole thing is likely dying soon anyhow.
@ -1143,6 +1155,12 @@ bool SDL_PlaybackAudioThreadIterate(SDL_AudioDevice *device)
} else if (br < buffer_size) {
SDL_memset(device_buffer + br, device->silence_value, buffer_size - br); // silence whatever we didn't write to.
}
// generally channel maps will line up, but if the audio stream's chmap has been explicitly changed, do a final swizzle to device layout.
if ((br > 0) && (!SDL_AudioChannelMapsEqual(device->spec.channels, stream->dst_chmap, device->chmap))) {
ConvertAudio(br / SDL_AUDIO_FRAMESIZE(device->spec), device_buffer, device->spec.format, device->spec.channels, NULL,
device_buffer, device->spec.format, device->spec.channels, device->chmap, NULL, 1.0f);
}
} else { // need to actually mix (or silence the buffer)
float *final_mix_buffer = (float *) ((device->spec.format == SDL_AUDIO_F32) ? device_buffer : device->mix_buffer);
const int needed_samples = buffer_size / SDL_AUDIO_BYTESIZE(device->spec.format);
@ -1170,7 +1188,7 @@ bool SDL_PlaybackAudioThreadIterate(SDL_AudioDevice *device)
for (SDL_AudioStream *stream = logdev->bound_streams; stream; stream = stream->next_binding) {
// We should have updated this elsewhere if the format changed!
SDL_assert(SDL_AudioSpecsEqual(&stream->dst_spec, &outspec, stream->dst_chmap, device->chmap));
SDL_assert(SDL_AudioSpecsEqual(&stream->dst_spec, &outspec, NULL, NULL));
/* this will hold a lock on `stream` while getting. We don't explicitly lock the streams
for iterating here because the binding linked list can only change while the device lock is held.
@ -1181,6 +1199,11 @@ bool SDL_PlaybackAudioThreadIterate(SDL_AudioDevice *device)
failed = true;
break;
} else if (br > 0) { // it's okay if we get less than requested, we mix what we have.
// generally channel maps will line up, but if the audio stream's chmap has been explicitly changed, do a final swizzle to device layout.
if (!SDL_AudioChannelMapsEqual(device->spec.channels, stream->dst_chmap, device->chmap)) {
ConvertAudio(br / SDL_AUDIO_FRAMESIZE(device->spec), device->work_buffer, device->spec.format, device->spec.channels, NULL,
device->work_buffer, device->spec.format, device->spec.channels, device->chmap, NULL, 1.0f);
}
MixFloat32Audio(mix_buffer, (float *) device->work_buffer, br);
}
}
@ -1303,11 +1326,20 @@ bool SDL_RecordingAudioThreadIterate(SDL_AudioDevice *device)
SDL_assert(stream->src_spec.channels == device->spec.channels);
SDL_assert(stream->src_spec.freq == device->spec.freq);
void *final_buf = output_buffer;
// generally channel maps will line up, but if the audio stream's chmap has been explicitly changed, do a final swizzle to stream layout.
if (!SDL_AudioChannelMapsEqual(device->spec.channels, stream->src_chmap, device->chmap)) {
final_buf = device->mix_buffer; // this is otherwise unused on recording devices, so it makes convenient scratch space here.
ConvertAudio(br / SDL_AUDIO_FRAMESIZE(device->spec), output_buffer, device->spec.format, device->spec.channels, NULL,
final_buf, device->spec.format, device->spec.channels, stream->src_chmap, NULL, 1.0f);
}
/* this will hold a lock on `stream` while putting. We don't explicitly lock the streams
for iterating here because the binding linked list can only change while the device lock is held.
(we _do_ lock the stream during binding/unbinding to make sure that two threads can't try to bind
the same stream to different devices at the same time, though.) */
if (!SDL_PutAudioStreamData(stream, output_buffer, br)) {
if (!SDL_PutAudioStreamData(stream, final_buf, br)) {
// oh crud, we probably ran out of memory. This is possibly an overreaction to kill the audio device, but it's likely the whole thing is going down in a moment anyhow.
failed = true;
break;

13
src/audio/SDL_audiocvt.c
View file

@ -154,7 +154,7 @@ static void SwizzleAudio(const int num_frames, void *dst, const void *src, int c
{
const int bitsize = (int) SDL_AUDIO_BITSIZE(fmt);
bool has_null_mappings = false;
bool has_null_mappings = false; // !!! FIXME: calculate this when setting the channel map instead.
for (int i = 0; i < channels; i++) {
if (map[i] == -1) {
has_null_mappings = true;
@ -257,6 +257,11 @@ void ConvertAudio(int num_frames,
const int dst_bitsize = (int) SDL_AUDIO_BITSIZE(dst_format);
const int dst_sample_frame_size = (dst_bitsize / 8) * dst_channels;
const bool chmaps_match = (src_channels == dst_channels) && SDL_AudioChannelMapsEqual(src_channels, src_map, dst_map);
if (chmaps_match) {
src_map = dst_map = NULL; // NULL both these out so we don't do any unnecessary swizzling.
}
/* Type conversion goes like this now:
- swizzle through source channel map to "standard" layout.
- byteswap to CPU native format first if necessary.
@ -635,8 +640,6 @@ bool SetAudioStreamChannelMap(SDL_AudioStream *stream, const SDL_AudioSpec *spec
// already have this map, don't allocate/copy it again.
} else if (SDL_ChannelMapIsBogus(chmap, channels)) {
result = SDL_SetError("Invalid channel mapping");
} else if ((isinput != -1) && stream->bound_device && (!!isinput == !!stream->bound_device->physical_device->recording)) {
// quietly refuse to change the format of the end currently bound to a device.
} else {
if (SDL_ChannelMapIsDefault(chmap, channels)) {
chmap = NULL; // just apply a default mapping.
@ -661,12 +664,12 @@ bool SetAudioStreamChannelMap(SDL_AudioStream *stream, const SDL_AudioSpec *spec
bool SDL_SetAudioStreamInputChannelMap(SDL_AudioStream *stream, const int *chmap, int channels)
{
return SetAudioStreamChannelMap(stream, &stream->src_spec, &stream->src_chmap, chmap, channels, true);
return SetAudioStreamChannelMap(stream, &stream->src_spec, &stream->src_chmap, chmap, channels, 1);
}
bool SDL_SetAudioStreamOutputChannelMap(SDL_AudioStream *stream, const int *chmap, int channels)
{
return SetAudioStreamChannelMap(stream, &stream->dst_spec, &stream->dst_chmap, chmap, channels, false);
return SetAudioStreamChannelMap(stream, &stream->dst_spec, &stream->dst_chmap, chmap, channels, 0);
}
int *SDL_GetAudioStreamInputChannelMap(SDL_AudioStream *stream, int *count)

6
src/audio/SDL_sysaudio.h
View file

@ -125,9 +125,13 @@ extern void ConvertAudio(int num_frames,
// Compare two SDL_AudioSpecs, return true if they match exactly.
// Using SDL_memcmp directly isn't safe, since potential padding might not be initialized.
// either channel maps can be NULL for the default (and both should be if you don't care about them).
// either channel map can be NULL for the default (and both should be if you don't care about them).
extern bool SDL_AudioSpecsEqual(const SDL_AudioSpec *a, const SDL_AudioSpec *b, const int *channel_map_a, const int *channel_map_b);
// See if two channel maps match
// either channel map can be NULL for the default (and both should be if you don't care about them).
extern bool SDL_AudioChannelMapsEqual(int channels, const int *channel_map_a, const int *channel_map_b);
// allocate+copy a channel map.
extern int *SDL_ChannelMapDup(const int *origchmap, int channels);