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audio/rate.h

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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/>.
+ *
+ */
+
+#ifndef AUDIO_RATE_H
+#define AUDIO_RATE_H
+
+#include "common/frac.h"
+
+namespace Audio {
+/**
+ * @defgroup audio_rate Sample rate
+ * @ingroup audio
+ *
+ * @brief API for managing sound sample rate.
+ * @{
+ */
+
+class AudioStream;
+
+typedef int16 st_sample_t;
+typedef uint16 st_volume_t;
+typedef uint32 st_size_t;
+typedef uint32 st_rate_t;
+
+/* Minimum and maximum values a sample can hold. */
+enum {
+	ST_SAMPLE_MAX = 0x7fffL,
+	ST_SAMPLE_MIN = (-ST_SAMPLE_MAX - 1L)
+};
+
+static inline void clampedAdd(int16& a, int b) {
+	int val;
+#ifdef OUTPUT_UNSIGNED_AUDIO
+	val = (a ^ 0x8000) + b;
+#else
+	val = a + b;
+#endif
+
+	if (val > ST_SAMPLE_MAX)
+		val = ST_SAMPLE_MAX;
+	else if (val < ST_SAMPLE_MIN)
+		val = ST_SAMPLE_MIN;
+
+#ifdef OUTPUT_UNSIGNED_AUDIO
+	a = ((int16)val) ^ 0x8000;
+#else
+	a = val;
+#endif
+}
+
+/**
+ * Helper class that handles resampling an AudioStream between an input and output
+ * sample rate. Its regular use case is upsampling from the native stream rate
+ * to the one used by the sound mixer. However, the input/output rates can be
+ * manually adjusted to change playback speed and produce sound effects.
+*/
+class RateConverter {
+public:
+	RateConverter() {}
+	virtual ~RateConverter() {}
+
+	/**
+	 * Convert the provided AudioStream to the target sample rate.
+	 * 
+	 * @param input			The AudioStream to read data from.
+	 * @param outBuffer		The buffer that the resampled audio will be written to. Must have size of at least @p numSamples.
+	 * @param numSamples	The desired number of samples to be written into the buffer.
+	 * @param vol_l			Volume for left channel.
+	 * @param vol_r			Volume for right channel.
+	 * 
+	 * @return Number of sample pairs written into the buffer.
+	 */
+	virtual int convert(AudioStream &input, st_sample_t *outBuffer, st_size_t numSamples, st_volume_t vol_l, st_volume_t vol_r) = 0;
+
+	virtual void setInputRate(st_rate_t inputRate) = 0;
+	virtual void setOutputRate(st_rate_t outputRate) = 0;
+
+	virtual st_rate_t getInputRate() const = 0;
+	virtual st_rate_t getOutputRate() const = 0;
+
+	/**
+	 * Does the internal buffer still have some leftover data?
+	 * 
+	 * @return True if we need to drain, false otherwise
+	 */
+	virtual bool needsDraining() const = 0;
+};
+
+RateConverter *makeRateConverter(st_rate_t inRate, st_rate_t outRate, bool inStereo, bool outStereo, bool reverseStereo);
+
+/** @} */
+} // End of namespace Audio
+
+#endif