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engines/adl/sound.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "common/system.h"
+
+#include "audio/mixer.h"
+
+#include "adl/sound.h"
+
+namespace Adl {
+
+// Generic PC-speaker synth
+// This produces more accurate frequencies than Audio::PCSpeaker, but only
+// does square waves.
+class Speaker {
+public:
+	Speaker(int sampleRate);
+
+	void startTone(double freq);
+	void stopTone();
+	void generateSamples(int16 *buffer, int numSamples);
+
+private:
+	int _rate;
+	frac_t _halfWaveLen, _halfWaveRem;
+	int16 _curSample;
+};
+
+Speaker::Speaker(int sampleRate) :
+		_rate(sampleRate),
+		_halfWaveLen(0),
+		_halfWaveRem(0),
+		_curSample(32767) { }
+
+void Speaker::startTone(double freq) {
+	_halfWaveLen = _halfWaveRem = doubleToFrac(_rate / freq / 2);
+
+	if (_halfWaveLen < (frac_t)FRAC_ONE) {
+		// Tone out of range at this sample rate
+		stopTone();
+	}
+}
+
+void Speaker::stopTone() {
+	_halfWaveLen = 0;
+}
+
+void Speaker::generateSamples(int16 *buffer, int numSamples) {
+	if (_halfWaveLen == 0) {
+		// Silence
+		memset(buffer, 0, numSamples * sizeof(int16));
+		return;
+	}
+
+	int offset = 0;
+
+	while (offset < numSamples) {
+		if (_halfWaveRem >= 0 && _halfWaveRem < (frac_t)FRAC_ONE) {
+			// Rising/falling edge
+			// Switch level
+			_curSample = ~_curSample;
+			// Use transition point fraction for current sample value
+			buffer[offset++] = _halfWaveRem ^ _curSample;
+			// Compute next transition point
+			_halfWaveRem += _halfWaveLen - FRAC_ONE;
+		} else {
+			// Low/high level
+			// Generate as many samples as we can
+			const int samples = MIN(numSamples - offset, (int)fracToInt(_halfWaveRem));
+			Common::fill(buffer + offset, buffer + offset + samples, _curSample);
+			offset += samples;
+
+			// Count down to level transition point
+			_halfWaveRem -= intToFrac(samples);
+		}
+	}
+}
+
+Sound::Sound(const Tones &tones) :
+		_tones(tones),
+		_toneIndex(0),
+		_samplesRem(0) {
+
+	_rate = g_system->getMixer()->getOutputRate();
+	_speaker = new Speaker(_rate);
+}
+
+Sound::~Sound() {
+	delete _speaker;
+}
+
+bool Sound::endOfData() const {
+	return _samplesRem == 0 && _toneIndex == _tones.size();
+}
+
+int Sound::readBuffer(int16 *buffer, const int numSamples) {
+	int offset = 0;
+
+	while (offset < numSamples) {
+		if (_samplesRem == 0) {
+			// Set up next tone
+
+			if (_toneIndex == _tones.size()) {
+				// No more tones
+				return offset;
+			}
+
+			if (_tones[_toneIndex].freq == 0.0)
+				_speaker->stopTone();
+			else
+				_speaker->startTone(_tones[_toneIndex].freq);
+
+			// Compute length of tone
+			_samplesRem = _rate * _tones[_toneIndex++].len / 1000;
+		}
+
+		// Generate as many samples as we can
+		const int samples = MIN(numSamples - offset, _samplesRem);
+		_speaker->generateSamples(buffer + offset, samples);
+
+		_samplesRem -= samples;
+		offset += samples;
+	}
+
+	return numSamples;
+}
+
+} // End of namespace Adl