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◆ main openmsx / src / cassette / WavImage.cc
4.3 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#include "WavImage.hh"
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#include "File.hh"
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#include "FilePool.hh"
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#include "Filename.hh"
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#include "Math.hh"
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#include "narrow.hh"
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#include "xrange.hh"
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#include <algorithm>
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#include <array>
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#include <cassert>
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#include <map>
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namespace openmsx {
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// DC-removal filter
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//   y(n) = x(n) - x(n-1) + R * y(n-1)
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// see comments in MSXMixer.cc for more details
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class DCFilter {
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public:
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	void setFreq(unsigned sampleFreq) {
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		const float cutOffFreq = 800.0f; // trial-and-error
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		R = 1.0f - ((float(2 * Math::pi) * cutOffFreq) / narrow_cast<float>(sampleFreq));
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	}
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	[[nodiscard]] int16_t operator()(int16_t x) {
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		float t1 = R * t0 + narrow_cast<float>(x);
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		auto y = Math::clipToInt16(narrow_cast<int>(t1 - t0));
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		t0 = t1;
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		return y;
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	}
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private:
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	float R = 0.0f;
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	float t0 = 0.0f;
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};
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class WavImageCache
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{
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public:
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	struct WavInfo {
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		WavData wav;
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		Sha1Sum sum;
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	};
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	WavImageCache(const WavImageCache&) = delete;
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	WavImageCache(WavImageCache&&) = delete;
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	WavImageCache& operator=(const WavImageCache&) = delete;
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	WavImageCache& operator=(WavImageCache&&) = delete;
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	static WavImageCache& instance();
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	const WavInfo& get(const std::string& filename, FilePool& filePool);
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	void release(const WavData* wav);
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private:
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	WavImageCache() = default;
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	~WavImageCache();
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	// typically contains very few elements, but values need stable addresses
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	struct Entry {
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		unsigned refCount = 0;
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		WavInfo info;
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	};
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	std::map<std::string, Entry, std::less<>> cache;
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};
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WavImageCache::~WavImageCache()
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{
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	assert(cache.empty());
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}
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WavImageCache& WavImageCache::instance()
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{
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	static WavImageCache wavImageCache;
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	return wavImageCache;
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}
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const WavImageCache::WavInfo& WavImageCache::get(const std::string& filename, FilePool& filePool)
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{
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	// Reading file or parsing as .wav may throw, so only create cache
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	// entry after all went well.
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	auto it = cache.find(filename);
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	if (it == cache.end()) {
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		File file(filename);
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		Entry entry;
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		entry.info.sum = filePool.getSha1Sum(file, filename);
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		entry.info.wav = WavData(std::move(file), DCFilter{});
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		it = cache.try_emplace(filename, std::move(entry)).first;
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	}
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	auto& entry = it->second;
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	++entry.refCount;
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	return entry.info;
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}
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void WavImageCache::release(const WavData* wav)
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{
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	// cache contains very few entries, so linear search is ok
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	auto it = std::ranges::find(cache, wav, [](auto& pr) { return &pr.second.info.wav; });
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	assert(it != end(cache));
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	auto& entry = it->second;
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	--entry.refCount; // decrease reference count
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	if (entry.refCount == 0) {
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		cache.erase(it);
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	}
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}
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WavImage::WavImage(const Filename& filename, FilePool& filePool)
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{
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	const auto& entry = WavImageCache::instance().get(filename.getResolved(), filePool);
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	wav = &entry.wav;
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	setSha1Sum(entry.sum);
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	clock.setFreq(wav->getFreq());
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	// Note: type detection not implemented yet for WAV images
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	setFirstFileType(FileType::UNKNOWN, filename);
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}
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WavImage::~WavImage()
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{
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	WavImageCache::instance().release(wav);
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}
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int16_t WavImage::getSampleAt(EmuTime time) const
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{
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	// The WAV file is typically sampled at 44kHz, but the MSX may sample
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	// the signal at arbitrary moments in time. Initially we would simply
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	// returned the closest older sample point (sample-and-hold
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	// resampling). Now we perform cubic interpolation between the 4
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	// surrounding sample points. Presumably this results in more accurately
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	// timed zero-crossings of the signal.
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	//
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	// Thanks to 'p_gimeno' for figuring out that cubic resampling makes
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	// the tape "Ingrid's back" sha1:9493e8851e9f173b67670a9a3de4645918ef436f
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	// work in openMSX (with sample-and-hold it didn't work).
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	auto [sample, x] = clock.getTicksTillAsIntFloat(time);
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	std::array<float, 4> p = {
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		float(wav->getSample(sample - 1)), // intentional: underflow wraps to UINT_MAX
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		float(wav->getSample(sample + 0)),
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		float(wav->getSample(sample + 1)),
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		float(wav->getSample(sample + 2))
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	};
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	return Math::clipToInt16(int(Math::cubicHermite(p, x)));
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}
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EmuTime WavImage::getEndTime() const
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{
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	DynamicClock clk(clock);
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	clk += wav->getSize();
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	return clk.getTime();
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}
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unsigned WavImage::getFrequency() const
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{
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	return clock.getFreq();
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}
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void WavImage::fillBuffer(unsigned pos, std::span<float*, 1> bufs, unsigned num) const
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{
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	if (pos < wav->getSize()) {
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		for (auto i : xrange(num)) {
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			bufs[0][i] = wav->getSample(pos + i);
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		}
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	} else {
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		bufs[0] = nullptr;
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	}
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}
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float WavImage::getAmplificationFactorImpl() const
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{
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	return 1.0f / 32768;
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}
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} // namespace openmsx