SDLSoundDriver.cc

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#include "SDLSoundDriver.hh"
#include "Mixer.hh"
#include "Reactor.hh"
#include "MSXMixer.hh"
#include "MSXMotherBoard.hh"
#include "RealTime.hh"
#include "GlobalSettings.hh"
#include "ThrottleManager.hh"
#include "MSXException.hh"
#include "Timer.hh"
#include "narrow.hh"
#include <algorithm>
#include <bit>
#include <cassert>
 
namespace openmsx {
 
SDLSoundDriver::SDLSoundDriver(Reactor& reactor_,
                               unsigned wantedFreq, unsigned wantedSamples)
        : reactor(reactor_)
{
        SDL_AudioSpec desired;
        desired.freq     = narrow<int>(wantedFreq);
        desired.samples  = std::bit_ceil(wantedSamples);
        desired.channels = 2; // stereo
        desired.format   = AUDIO_F32SYS;
        desired.callback = audioCallbackHelper; // must be a static method
        desired.userdata = this;
 
        SDL_AudioSpec obtained;
        deviceID = SDL_OpenAudioDevice(nullptr, SDL_FALSE, &desired, &obtained,
                                       SDL_AUDIO_ALLOW_FREQUENCY_CHANGE);
        if (!deviceID) {
                throw MSXException("Unable to open SDL audio: ", SDL_GetError());
        }
 
        frequency = obtained.freq;
        fragmentSize = obtained.samples;
 
        mixBufferSize = 3 * (obtained.size / sizeof(StereoFloat)) + 1;
        mixBuffer.resize(mixBufferSize);
        reInit();
}
 
SDLSoundDriver::~SDLSoundDriver()
{
        SDL_CloseAudioDevice(deviceID);
}
 
void SDLSoundDriver::reInit()
{
        SDL_LockAudioDevice(deviceID);
        readIdx  = 0;
        writeIdx = 0;
        SDL_UnlockAudioDevice(deviceID);
}
 
void SDLSoundDriver::mute()
{
        if (!muted) {
                muted = true;
                SDL_PauseAudioDevice(deviceID, 1);
        }
}
 
void SDLSoundDriver::unmute()
{
        if (muted) {
                muted = false;
                reInit();
                SDL_PauseAudioDevice(deviceID, 0);
        }
}
 
unsigned SDLSoundDriver::getFrequency() const
{
        return frequency;
}
 
unsigned SDLSoundDriver::getSamples() const
{
        return fragmentSize;
}
 
void SDLSoundDriver::audioCallbackHelper(void* userdata, uint8_t* strm, int len)
{
        assert((len & 7) == 0); // stereo, 32 bit float
        static_cast<SDLSoundDriver*>(userdata)->
                audioCallback(std::span{reinterpret_cast<StereoFloat*>(strm),
                                        len / (2 * sizeof(float))});
}
 
unsigned SDLSoundDriver::getBufferFilled() const
{
        int result = narrow_cast<int>(writeIdx - readIdx);
        if (result < 0) result += narrow<int>(mixBufferSize);
        assert((0 <= result) && (narrow<unsigned>(result) < mixBufferSize));
        return result;
}
 
unsigned SDLSoundDriver::getBufferFree() const
{
        // we can't distinguish completely filled from completely empty
        // (in both cases readIx would be equal to writeIdx), so instead
        // we define full as '(writeIdx + 1) == readIdx'.
        unsigned result = mixBufferSize - 1 - getBufferFilled();
        assert(narrow_cast<int>(result) >= 0);
        assert(result < mixBufferSize);
        return result;
}
 
void SDLSoundDriver::audioCallback(std::span<StereoFloat> stream)
{
        auto len = stream.size();
 
        size_t available = getBufferFilled();
        auto num = narrow<unsigned>(std::min(len, available));
        if ((readIdx + num) < mixBufferSize) {
                ranges::copy(std::span{&mixBuffer[readIdx], num}, stream);
                readIdx += num;
        } else {
                unsigned len1 = mixBufferSize - readIdx;
                ranges::copy(std::span{&mixBuffer[readIdx], len1}, stream);
                unsigned len2 = num - len1;
                ranges::copy(std::span{&mixBuffer[0], len2}, stream.subspan(len1));
                readIdx = len2;
        }
        auto missing = narrow_cast<ptrdiff_t>(len - available);
        if (missing > 0) {
                // buffer underrun
                ranges::fill(subspan(stream, available, missing), StereoFloat{});
        }
}
 
void SDLSoundDriver::uploadBuffer(std::span<const StereoFloat> buffer)
{
        SDL_LockAudioDevice(deviceID);
        unsigned free = getBufferFree();
        if (buffer.size() > free) {
                auto* board = reactor.getMotherBoard();
                if (board && !board->getMSXMixer().isSynchronousMode() && // when not recording
                    reactor.getGlobalSettings().getThrottleManager().isThrottled()) {
                        do {
                                SDL_UnlockAudioDevice(deviceID);
                                Timer::sleep(5000); // 5ms
                                SDL_LockAudioDevice(deviceID);
                                board->getRealTime().resync();
                                free = getBufferFree();
                        } while (buffer.size() > free);
                } else {
                        // drop excess samples
                        buffer = buffer.subspan(0, free);
                }
        }
        assert(buffer.size() <= free);
        if ((writeIdx + buffer.size()) < mixBufferSize) {
                ranges::copy(buffer, &mixBuffer[writeIdx]);
                writeIdx += narrow<unsigned>(buffer.size());
        } else {
                unsigned len1 = mixBufferSize - writeIdx;
                ranges::copy(buffer.subspan(0, len1), &mixBuffer[writeIdx]);
                unsigned len2 = narrow<unsigned>(buffer.size()) - len1;
                ranges::copy(buffer.subspan(len1, len2), &mixBuffer[0]);
                writeIdx = len2;
        }
 
        SDL_UnlockAudioDevice(deviceID);
}
 
} // namespace openmsx