AUDIO: Introduce a callback to the OPL code

Currently unused, but ready to be hooked up to various classes using it.

6 files changed, 174 insertions, 8 deletions

diff --git a/audio/fmopl.cpp b/audio/fmopl.cpp
index 3ee557366c..c9cb1040d6 100644
--- a/audio/fmopl.cpp
+++ b/audio/fmopl.cpp
@@ -22,10 +22,12 @@
 
 #include "audio/fmopl.h"
 
+#include "audio/mixer.h"
 #include "audio/softsynth/opl/dosbox.h"
 #include "audio/softsynth/opl/mame.h"
 
 #include "common/config-manager.h"
+#include "common/system.h"
 #include "common/textconsole.h"
 #include "common/translation.h"
 
@@ -171,6 +173,80 @@ OPL *Config::create(DriverId driver, OplType type) {
 	}
 }
 
+void OPL::start(TimerCallback *callback, int timerFrequency) {
+	_callback.reset(callback);
+	startCallbacks(timerFrequency);
+}
+
+void OPL::stop() {
+	stopCallbacks();
+	_callback.reset();
+}
+
 bool OPL::_hasInstance = false;
 
+EmulatedOPL::EmulatedOPL() :
+	_nextTick(0),
+	_samplesPerTick(0),
+	_baseFreq(0) {
+}
+
+EmulatedOPL::~EmulatedOPL() {
+	// Stop callbacks, just in case. If it's still playing at this
+	// point, there's probably a bigger issue, though.
+	stopCallbacks();
+}
+
+int EmulatedOPL::readBuffer(int16 *buffer, const int numSamples) {
+	const int stereoFactor = isStereo() ? 2 : 1;
+	int len = numSamples / stereoFactor;
+	int step;
+
+	do {
+		step = len;
+		if (step > (_nextTick >> FIXP_SHIFT))
+			step = (_nextTick >> FIXP_SHIFT);
+
+		generateSamples(buffer, step * stereoFactor);
+
+		_nextTick -= step << FIXP_SHIFT;
+		if (!(_nextTick >> FIXP_SHIFT)) {
+			if (_callback && _callback->isValid())
+				(*_callback)();
+
+			_nextTick += _samplesPerTick;
+		}
+
+		buffer += step * stereoFactor;
+		len -= step;
+	} while (len);
+
+	return numSamples;
+}
+
+int EmulatedOPL::getRate() const {
+	return g_system->getMixer()->getOutputRate();
+}
+
+void EmulatedOPL::startCallbacks(int timerFrequency) {
+	_baseFreq = timerFrequency;
+	assert(_baseFreq != 0);
+
+	int d = getRate() / _baseFreq;
+	int r = getRate() % _baseFreq;
+
+	// This is equivalent to (getRate() << FIXP_SHIFT) / BASE_FREQ
+	// but less prone to arithmetic overflow.
+
+	_samplesPerTick = (d << FIXP_SHIFT) + (r << FIXP_SHIFT) / _baseFreq;
+
+	// TODO: Eventually start mixer playback here
+	//g_system->getMixer()->playStream(Audio::Mixer::kPlainSoundType, _handle, this, -1, Audio::Mixer::kMaxChannelVolume, 0, DisposeAfterUse::NO, true);
+}
+
+void EmulatedOPL::stopCallbacks() {
+	// TODO: Eventually stop mixer playback here
+	//g_system->getMixer()->stopHandle(*_handle);
+}
+
 } // End of namespace OPL
diff --git a/audio/fmopl.h b/audio/fmopl.h
index aaa8edd42d..0e2e2b2dda 100644
--- a/audio/fmopl.h
+++ b/audio/fmopl.h
@@ -23,6 +23,8 @@
 #ifndef AUDIO_FMOPL_H
 #define AUDIO_FMOPL_H
 
+#include "common/func.h"
+#include "common/ptr.h"
 #include "common/scummsys.h"
 
 namespace Common {
@@ -98,6 +100,8 @@ private:
 	static const EmulatorDescription _drivers[];
 };
 
+typedef Common::Functor0<void> TimerCallback;
+
 class OPL {
 private:
 	static bool _hasInstance;
@@ -154,12 +158,83 @@ public:
 	 * So if you request 4 samples from a stereo OPL, you will get
 	 * a total of two left channel and two right channel samples.
 	 */
-	virtual void readBuffer(int16 *buffer, int length) = 0;
+	virtual int readBuffer(int16 *buffer, const int numSamples) = 0;
 
 	/**
 	 * Returns whether the setup OPL mode is stereo or not
 	 */
 	virtual bool isStereo() const = 0;
+
+	/**
+	 * Start the OPL with callbacks.
+	 */
+	void start(TimerCallback *callback, int timerFrequency = kDefaultCallbackFrequency);
+
+	/**
+	 * Stop the OPL
+	 */
+	void stop();
+
+	enum {
+		/**
+		 * The default callback frequency that start() uses
+		 */
+		kDefaultCallbackFrequency = 250
+	};
+
+protected:
+	/**
+	 * Start the callbacks.
+	 */
+	virtual void startCallbacks(int timerFrequency) = 0;
+
+	/**
+	 * Stop the callbacks.
+	 */
+	virtual void stopCallbacks() = 0;
+
+	/**
+	 * The functor for callbacks.
+	 */
+	Common::ScopedPtr<TimerCallback> _callback;
+};
+
+class EmulatedOPL : public OPL {
+public:
+	EmulatedOPL();
+	virtual ~EmulatedOPL();
+
+	// OPL API
+	int readBuffer(int16 *buffer, const int numSamples);
+
+	int getRate() const;
+
+protected:
+	// OPL API
+	void startCallbacks(int timerFrequency);
+	void stopCallbacks();
+
+	/**
+	 * Read up to 'length' samples.
+	 *
+	 * Data will be in native endianess, 16 bit per sample, signed.
+	 * For stereo OPL, buffer will be filled with interleaved
+	 * left and right channel samples, starting with a left sample.
+	 * Furthermore, the samples in the left and right are summed up.
+	 * So if you request 4 samples from a stereo OPL, you will get
+	 * a total of two left channel and two right channel samples.
+	 */
+	virtual void generateSamples(int16 *buffer, int numSamples) = 0;
+
+private:
+	int _baseFreq;
+
+	enum {
+		FIXP_SHIFT = 16
+	};
+
+	int _nextTick;
+	int _samplesPerTick;
 };
 
 } // End of namespace OPL
diff --git a/audio/softsynth/opl/dosbox.cpp b/audio/softsynth/opl/dosbox.cpp
index bcc73a9b9e..f6f17c5e3c 100644
--- a/audio/softsynth/opl/dosbox.cpp
+++ b/audio/softsynth/opl/dosbox.cpp
@@ -153,6 +153,7 @@ OPL::~OPL() {
 }
 
 void OPL::free() {
+	stopCallbacks();
 	delete _emulator;
 	_emulator = 0;
 }
@@ -176,6 +177,9 @@ bool OPL::init() {
 		_emulator->WriteReg(0x105, 1);
 	}
 
+	// FIXME: Remove this once EmulatedOPL is actually controlling playback
+	start(0);
+
 	return true;
 }
 
@@ -308,7 +312,7 @@ void OPL::dualWrite(uint8 index, uint8 reg, uint8 val) {
 	_emulator->WriteReg(fullReg, val);
 }
 
-void OPL::readBuffer(int16 *buffer, int length) {
+void OPL::generateSamples(int16 *buffer, int length) {
 	// For stereo OPL cards, we divide the sample count by 2,
 	// to match stereo AudioStream behavior.
 	if (_type != Config::kOpl2)
diff --git a/audio/softsynth/opl/dosbox.h b/audio/softsynth/opl/dosbox.h
index d3df6ba6ed..c52f06761a 100644
--- a/audio/softsynth/opl/dosbox.h
+++ b/audio/softsynth/opl/dosbox.h
@@ -69,7 +69,7 @@ namespace DBOPL {
 struct Chip;
 } // end of namespace DBOPL
 
-class OPL : public ::OPL::OPL {
+class OPL : public ::OPL::EmulatedOPL {
 private:
 	Config::OplType _type;
 	uint _rate;
@@ -95,8 +95,10 @@ public:
 
 	void writeReg(int r, int v);
 
-	void readBuffer(int16 *buffer, int length);
 	bool isStereo() const { return _type != Config::kOpl2; }
+
+protected:
+	void generateSamples(int16 *buffer, int length);
 };
 
 } // End of namespace DOSBox
diff --git a/audio/softsynth/opl/mame.cpp b/audio/softsynth/opl/mame.cpp
index 1a5810f6c8..fe23d300fa 100644
--- a/audio/softsynth/opl/mame.cpp
+++ b/audio/softsynth/opl/mame.cpp
@@ -48,15 +48,22 @@ namespace OPL {
 namespace MAME {
 
 OPL::~OPL() {
+	stopCallbacks();
 	MAME::OPLDestroy(_opl);
 	_opl = 0;
 }
 
 bool OPL::init() {
-	if (_opl)
+	if (_opl) {
+		stopCallbacks();
 		MAME::OPLDestroy(_opl);
+	}
 
 	_opl = MAME::makeAdLibOPL(g_system->getMixer()->getOutputRate());
+
+	// FIXME: Remove this once EmulatedOPL is actually controlling playback
+	start(0);
+
 	return (_opl != 0);
 }
 
@@ -76,7 +83,7 @@ void OPL::writeReg(int r, int v) {
 	MAME::OPLWriteReg(_opl, r, v);
 }
 
-void OPL::readBuffer(int16 *buffer, int length) {
+void OPL::generateSamples(int16 *buffer, int length) {
 	MAME::YM3812UpdateOne(_opl, buffer, length);
 }
 
diff --git a/audio/softsynth/opl/mame.h b/audio/softsynth/opl/mame.h
index 080cc6d171..67d80bb193 100644
--- a/audio/softsynth/opl/mame.h
+++ b/audio/softsynth/opl/mame.h
@@ -174,7 +174,7 @@ void YM3812UpdateOne(FM_OPL *OPL, int16 *buffer, int length);
 FM_OPL *makeAdLibOPL(int rate);
 
 // OPL API implementation
-class OPL : public ::OPL::OPL {
+class OPL : public ::OPL::EmulatedOPL {
 private:
 	FM_OPL *_opl;
 public:
@@ -189,8 +189,10 @@ public:
 
 	void writeReg(int r, int v);
 
-	void readBuffer(int16 *buffer, int length);
 	bool isStereo() const { return false; }
+
+protected:
+	void generateSamples(int16 *buffer, int length);
 };
 
 } // End of namespace MAME