Unify [get_/skip_]samples, adding a third option for in-place mixing.

Components/6560/6560.cpp

@@ -19,6 +19,7 @@ AudioGenerator::AudioGenerator(Concurrency::AsyncTaskQueue<false> &audio_queue)
 void AudioGenerator::set_volume(uint8_t volume) {
 	audio_queue_.enqueue([this, volume]() {
 		volume_ = int16_t(volume) * range_multiplier_;
+		dc_offset_ = volume_ >> 4;
 	});
 }
 
@@ -105,7 +106,8 @@ static uint8_t noise_pattern[] = {
 // testing against 0x80. The effect should be the same: loading with 0x7f means an output update every cycle, loading with 0x7e
 // means every second cycle, etc.
 
-void AudioGenerator::get_samples(std::size_t number_of_samples, int16_t *target) {
+template <Outputs::Speaker::Action action>
+void AudioGenerator::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	for(unsigned int c = 0; c < number_of_samples; ++c) {
 		update(0, 2, shift);
 		update(1, 1, shift);
@@ -114,23 +116,22 @@ void AudioGenerator::get_samples(std::size_t number_of_samples, int16_t *target)
 
 		// this sums the output of all three sounds channels plus a DC offset for volume;
 		// TODO: what's the real ratio of this stuff?
-		target[c] = int16_t(
+		const int16_t sample =
 			(shift_registers_[0]&1) +
 			(shift_registers_[1]&1) +
 			(shift_registers_[2]&1) +
-			((noise_pattern[shift_registers_[3] >> 3] >> (shift_registers_[3]&7))&(control_registers_[3] >> 7)&1)
-		) * volume_ + (volume_ >> 4);
-	}
-}
+			((noise_pattern[shift_registers_[3] >> 3] >> (shift_registers_[3]&7))&(control_registers_[3] >> 7)&1);
 
-void AudioGenerator::skip_samples(std::size_t number_of_samples) {
-	for(unsigned int c = 0; c < number_of_samples; ++c) {
-		update(0, 2, shift);
-		update(1, 1, shift);
-		update(2, 0, shift);
-		update(3, 1, increment);
+		Outputs::Speaker::apply<action>(
+			target[c],
+			Outputs::Speaker::MonoSample(
+				sample * volume_ + dc_offset_
+			));
 	}
 }
+template void AudioGenerator::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void AudioGenerator::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void AudioGenerator::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
 void AudioGenerator::set_sample_volume_range(std::int16_t range) {
 	range_multiplier_ = int16_t(range / 64);

Components/6560/6560.hpp

@@ -25,8 +25,8 @@ class AudioGenerator: public Outputs::Speaker::BufferSource<AudioGenerator, fals
 		void set_control(int channel, uint8_t value);
 
 		// For ::SampleSource.
-		void get_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
-		void skip_samples(std::size_t number_of_samples);
+		template <Outputs::Speaker::Action action>
+			void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
 
 	private:
@@ -36,6 +36,7 @@ class AudioGenerator: public Outputs::Speaker::BufferSource<AudioGenerator, fals
 		unsigned int shift_registers_[4] = {0, 0, 0, 0};
 		uint8_t control_registers_[4] = {0, 0, 0, 0};
 		int16_t volume_ = 0;
+		int16_t dc_offset_ = 0;
 		int16_t range_multiplier_ = 1;
 };
 

Components/AY38910/AY38910.cpp

@@ -102,7 +102,8 @@ template <bool is_stereo> void AY38910<is_stereo>::set_output_mixing(float a_lef
 }
 
 template <bool is_stereo>
-void AY38910<is_stereo>::get_samples(
+template <Outputs::Speaker::Action action>
+void AY38910<is_stereo>::apply_samples(
 	std::size_t number_of_samples,
 	typename Outputs::Speaker::SampleT<is_stereo>::type *target
 ) {
@@ -117,7 +118,7 @@ void AY38910<is_stereo>::get_samples(
 
 	std::size_t c = 0;
 	while((master_divider_&3) && c < number_of_samples) {
-		target[c] = output_volume_;
+		Outputs::Speaker::apply<action>(target[c], output_volume_);
 		master_divider_++;
 		c++;
 	}
@@ -159,7 +160,7 @@ void AY38910<is_stereo>::get_samples(
 		evaluate_output_volume();
 
 		for(int ic = 0; ic < 4 && c < number_of_samples; ic++) {
-			target[c] = output_volume_;
+			Outputs::Speaker::apply<action>(target[c], output_volume_);
 			c++;
 			master_divider_++;
 		}
@@ -168,6 +169,13 @@ void AY38910<is_stereo>::get_samples(
 	master_divider_ &= 3;
 }
 
+template void AY38910<false>::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, typename Outputs::Speaker::SampleT<false>::type *);
+template void AY38910<false>::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, typename Outputs::Speaker::SampleT<false>::type *);
+template void AY38910<false>::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, typename Outputs::Speaker::SampleT<false>::type *);
+template void AY38910<true>::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, typename Outputs::Speaker::SampleT<true>::type *);
+template void AY38910<true>::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, typename Outputs::Speaker::SampleT<true>::type *);
+template void AY38910<true>::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, typename Outputs::Speaker::SampleT<true>::type *);
+
 template <bool is_stereo> void AY38910<is_stereo>::evaluate_output_volume() {
 	int envelope_volume = envelope_shapes_[output_registers_[13]][envelope_position_ | envelope_position_mask_];
 

Components/AY38910/AY38910.hpp

@@ -105,8 +105,9 @@ template <bool stereo> class AY38910: public ::Outputs::Speaker::BufferSource<AY
 		*/
 		void set_output_mixing(float a_left, float b_left, float c_left, float a_right = 1.0, float b_right = 1.0, float c_right = 1.0);
 
-		// to satisfy ::Outputs::Speaker (included via ::Outputs::Filter.
-		void get_samples(std::size_t number_of_samples, typename Outputs::Speaker::SampleT<stereo>::type *target);
+		// Buffer generation.
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, typename Outputs::Speaker::SampleT<stereo>::type *target);
 		bool is_zero_level() const;
 		void set_sample_volume_range(std::int16_t range);
 

Components/AudioToggle/AudioToggle.cpp

@@ -15,17 +15,11 @@ using namespace Audio;
 Audio::Toggle::Toggle(Concurrency::AsyncTaskQueue<false> &audio_queue) :
 	audio_queue_(audio_queue) {}
 
-void Toggle::get_samples(std::size_t number_of_samples, std::int16_t *target) {
-	std::fill(target, target + number_of_samples, level_);
-}
-
 void Toggle::set_sample_volume_range(std::int16_t range) {
 	volume_ = range;
 	level_ = level_active_ ? volume_ : 0;
 }
 
-void Toggle::skip_samples(std::size_t) {}
-
 void Toggle::set_output(bool enabled) {
 	if(is_enabled_ == enabled) return;
 	is_enabled_ = enabled;

Components/AudioToggle/AudioToggle.hpp

@@ -20,9 +20,11 @@ class Toggle: public Outputs::Speaker::BufferSource<Toggle, false> {
 	public:
 		Toggle(Concurrency::AsyncTaskQueue<false> &audio_queue);
 
-		void get_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
+			Outputs::Speaker::fill<action>(target, target + number_of_samples, level_);
+		}
 		void set_sample_volume_range(std::int16_t range);
-		void skip_samples(const std::size_t number_of_samples);
 
 		void set_output(bool enabled);
 		bool get_output() const;

Components/KonamiSCC/KonamiSCC.cpp

@@ -19,15 +19,16 @@ bool SCC::is_zero_level() const {
 	return !(channel_enable_ & 0x1f);
 }
 
-void SCC::get_samples(std::size_t number_of_samples, std::int16_t *target) {
+template <Outputs::Speaker::Action action>
+void SCC::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	if(is_zero_level()) {
-		std::memset(target, 0, sizeof(std::int16_t) * number_of_samples);
+		Outputs::Speaker::fill<action>(target, target + number_of_samples, Outputs::Speaker::MonoSample());
 		return;
 	}
 
 	std::size_t c = 0;
 	while((master_divider_&7) && c < number_of_samples) {
-		target[c] = transient_output_level_;
+		Outputs::Speaker::apply<action>(target[c], transient_output_level_);
 		master_divider_++;
 		c++;
 	}
@@ -44,12 +45,15 @@ void SCC::get_samples(std::size_t number_of_samples, std::int16_t *target) {
 		evaluate_output_volume();
 
 		for(int ic = 0; ic < 8 && c < number_of_samples; ++ic) {
-			target[c] = transient_output_level_;
+			Outputs::Speaker::apply<action>(target[c], transient_output_level_);
 			c++;
 			master_divider_++;
 		}
 	}
 }
+template void SCC::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SCC::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SCC::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
 void SCC::write(uint16_t address, uint8_t value) {
 	address &= 0xff;
@@ -111,5 +115,3 @@ uint8_t SCC::read(uint16_t address) {
 	}
 	return 0xff;
 }
-
-

Components/KonamiSCC/KonamiSCC.hpp

@@ -29,7 +29,8 @@ class SCC: public ::Outputs::Speaker::BufferSource<SCC, false> {
 		bool is_zero_level() const;
 
 		/// As per ::SampleSource; provides audio output.
-		void get_samples(std::size_t number_of_samples, std::int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
 
 		/// Writes to the SCC.
@@ -44,7 +45,7 @@ class SCC: public ::Outputs::Speaker::BufferSource<SCC, false> {
 		// State from here on down is accessed ony from the audio thread.
 		int master_divider_ = 0;
 		std::int16_t master_volume_ = 0;
-		int16_t transient_output_level_ = 0;
+		Outputs::Speaker::MonoSample transient_output_level_ = 0;
 
 		struct Channel {
 			int period = 0;

Components/OPx/OPLL.cpp

@@ -278,7 +278,8 @@ void OPLL::set_sample_volume_range(std::int16_t range) {
 	total_volume_ = range;
 }
 
-void OPLL::get_samples(std::size_t number_of_samples, std::int16_t *target) {
+template <Outputs::Speaker::Action action>
+void OPLL::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	// Both the OPLL and the OPL2 divide the input clock by 72 to get the base tick frequency;
 	// unlike the OPL2 the OPLL time-divides the output for 'mixing'.
 
@@ -289,12 +290,16 @@ void OPLL::get_samples(std::size_t number_of_samples, std::int16_t *target) {
 	while(number_of_samples--) {
 		if(!audio_offset_) update_all_channels();
 
-		*target = output_levels_[audio_offset_ / channel_output_period];
+		Outputs::Speaker::apply<action>(*target, output_levels_[audio_offset_ / channel_output_period]);
 		++target;
 		audio_offset_ = (audio_offset_ + 1) % update_period;
 	}
 }
 
+template void OPLL::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void OPLL::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void OPLL::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
+
 void OPLL::update_all_channels() {
 	oscillator_.update();
 

Components/OPx/OPLL.hpp

@@ -25,7 +25,8 @@ class OPLL: public OPLBase<OPLL, false> {
 		OPLL(Concurrency::AsyncTaskQueue<false> &task_queue, int audio_divider = 1, bool is_vrc7 = false);
 
 		/// As per ::SampleSource; provides audio output.
-		void get_samples(std::size_t number_of_samples, std::int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
 
 		// The OPLL is generally 'half' as loud as it's told to be. This won't strictly be true in

Components/SN76489/SN76489.cpp

@@ -99,10 +99,11 @@ void SN76489::evaluate_output_volume() {
 	);
 }
 
-void SN76489::get_samples(std::size_t number_of_samples, std::int16_t *target) {
+template <Outputs::Speaker::Action action>
+void SN76489::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	std::size_t c = 0;
 	while((master_divider_& (master_divider_period_ - 1)) && c < number_of_samples) {
-		target[c] = output_volume_;
+		Outputs::Speaker::apply<action>(target[c], output_volume_);
 		master_divider_++;
 		c++;
 	}
@@ -151,7 +152,7 @@ void SN76489::get_samples(std::size_t number_of_samples, std::int16_t *target) {
 		evaluate_output_volume();
 
 		for(int ic = 0; ic < master_divider_period_ && c < number_of_samples; ++ic) {
-			target[c] = output_volume_;
+			Outputs::Speaker::apply<action>(target[c], output_volume_);
 			c++;
 			master_divider_++;
 		}
@@ -159,3 +160,6 @@ void SN76489::get_samples(std::size_t number_of_samples, std::int16_t *target) {
 
 	master_divider_ &= (master_divider_period_ - 1);
 }
+template void SN76489::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SN76489::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SN76489::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);

Components/SN76489/SN76489.hpp

@@ -28,7 +28,8 @@ class SN76489: public Outputs::Speaker::BufferSource<SN76489, false> {
 		void write(uint8_t value);
 
 		// As per SampleSource.
-		void get_samples(std::size_t number_of_samples, std::int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		bool is_zero_level() const;
 		void set_sample_volume_range(std::int16_t range);
 

Machines/Apple/AppleIIgs/Sound.cpp

@@ -159,29 +159,34 @@ void GLU::run_for(Cycles cycles) {
 	pending_store_write_time_ += cycles.as<uint32_t>();
 }
 
-void GLU::get_samples(std::size_t number_of_samples, std::int16_t *target) {
+template <Outputs::Speaker::Action action>
+void GLU::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	// Update remote state, generating audio.
-	generate_audio(number_of_samples, target);
+	generate_audio<action>(number_of_samples, target);
 }
+template void GLU::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void GLU::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void GLU::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
-void GLU::skip_samples(const std::size_t number_of_samples) {
-	// Update remote state, without generating audio.
-	skip_audio(remote_, number_of_samples);
 
-	// Apply any pending stores.
-	std::atomic_thread_fence(std::memory_order::memory_order_acquire);
-	const uint32_t final_time = pending_store_read_time_ + uint32_t(number_of_samples);
-	while(true) {
-		auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
-		if(!next_store.enabled) break;
-		if(next_store.time >= final_time) break;
-		remote_.ram_[next_store.address] = next_store.value;
-		next_store.enabled = false;
-		pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);
-
-		pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
-	}
-}
+//void GLU::skip_samples(const std::size_t number_of_samples) {
+//	// Update remote state, without generating audio.
+//	skip_audio(remote_, number_of_samples);
+//
+//	// Apply any pending stores.
+//	std::atomic_thread_fence(std::memory_order::memory_order_acquire);
+//	const uint32_t final_time = pending_store_read_time_ + uint32_t(number_of_samples);
+//	while(true) {
+//		auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
+//		if(!next_store.enabled) break;
+//		if(next_store.time >= final_time) break;
+//		remote_.ram_[next_store.address] = next_store.value;
+//		next_store.enabled = false;
+//		pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);
+//
+//		pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
+//	}
+//}
 
 void GLU::set_sample_volume_range(std::int16_t range) {
 	output_range_ = range;
@@ -256,7 +261,8 @@ void GLU::skip_audio(EnsoniqState &state, size_t number_of_samples) {
 	}
 }
 
-void GLU::generate_audio(size_t number_of_samples, std::int16_t *target) {
+template <Outputs::Speaker::Action action>
+void GLU::generate_audio(size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
 	uint8_t next_amplitude = 255;
 	for(size_t sample = 0; sample < number_of_samples; sample++) {
@@ -325,7 +331,12 @@ void GLU::generate_audio(size_t number_of_samples, std::int16_t *target) {
 
 		// Maximum total output was 32 channels times a 16-bit range. Map that down.
 		// TODO: dynamic total volume?
-		target[sample] = (output * output_range_) >> 20;
+		Outputs::Speaker::apply<action>(
+			target[sample],
+			Outputs::Speaker::MonoSample(
+				(output * output_range_) >> 20
+			)
+		);
 
 		// Apply any RAM writes that interleave here.
 		++pending_store_read_time_;

Machines/Apple/AppleIIgs/Sound.hpp

@@ -34,9 +34,9 @@ class GLU: public Outputs::Speaker::BufferSource<GLU, false> {	// TODO: isn't th
 		bool get_interrupt_line();
 
 		// SampleSource.
-		void get_samples(std::size_t number_of_samples, std::int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
-		void skip_samples(const std::size_t number_of_samples);
 
 	private:
 		Concurrency::AsyncTaskQueue<false> &audio_queue_;
@@ -94,7 +94,8 @@ class GLU: public Outputs::Speaker::BufferSource<GLU, false> {	// TODO: isn't th
 
 		// Functions to update an EnsoniqState; these don't belong to the state itself
 		// because they also access the pending stores (inter alia).
-		void generate_audio(size_t number_of_samples, std::int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void generate_audio(size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void skip_audio(EnsoniqState &state, size_t number_of_samples);
 
 		// Audio-thread state.

Machines/Apple/Macintosh/Audio.cpp

@@ -71,7 +71,8 @@ void Audio::set_volume_multiplier() {
 	volume_multiplier_ = int16_t(output_volume_ * volume_ * enabled_mask_);
 }
 
-void Audio::get_samples(std::size_t number_of_samples, int16_t *target) {
+template <Outputs::Speaker::Action action>
+void Audio::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	// TODO: the implementation below acts as if the hardware uses pulse-amplitude modulation;
 	// in fact it uses pulse-width modulation. But the scale for pulses isn't specified, so
 	// that's something to return to.
@@ -82,7 +83,7 @@ void Audio::get_samples(std::size_t number_of_samples, int16_t *target) {
 
 		// Determine the output level, and output that many samples.
 		const int16_t output_level = volume_multiplier_ * (int16_t(sample_queue_.buffer[sample_queue_.read_pointer].load(std::memory_order::memory_order_relaxed)) - 128);
-		std::fill(target, target + cycles_left_in_sample, output_level);
+		Outputs::Speaker::fill<action>(target, target + cycles_left_in_sample, output_level);
 		target += cycles_left_in_sample;
 
 		// Advance the sample pointer.
@@ -94,3 +95,6 @@ void Audio::get_samples(std::size_t number_of_samples, int16_t *target) {
 		number_of_samples -= cycles_left_in_sample;
 	}
 }
+template void Audio::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void Audio::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void Audio::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);

Machines/Apple/Macintosh/Audio.hpp

@@ -50,7 +50,8 @@ class Audio: public ::Outputs::Speaker::BufferSource<Audio, false> {
 		void set_enabled(bool on);
 
 		// to satisfy ::Outputs::Speaker (included via ::Outputs::Filter.
-		void get_samples(std::size_t number_of_samples, int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		bool is_zero_level() const;
 		void set_sample_volume_range(std::int16_t range);
 

Machines/Atari/2600/TIASound.cpp

@@ -40,9 +40,10 @@ void Atari2600::TIASound::set_control(int channel, uint8_t control) {
 #define advance_poly5(c) poly5_counter_[channel] = (poly5_counter_[channel] >> 1) | (((poly5_counter_[channel] << 4) ^ (poly5_counter_[channel] << 2))&0x010)
 #define advance_poly9(c) poly9_counter_[channel] = (poly9_counter_[channel] >> 1) | (((poly9_counter_[channel] << 4) ^ (poly9_counter_[channel] << 8))&0x100)
 
-void Atari2600::TIASound::get_samples(std::size_t number_of_samples, int16_t *target) {
+template <Outputs::Speaker::Action action>
+void Atari2600::TIASound::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
 	for(unsigned int c = 0; c < number_of_samples; c++) {
-		target[c] = 0;
+		Outputs::Speaker::MonoSample output = 0;
 		for(int channel = 0; channel < 2; channel++) {
 			divider_counter_[channel] ++;
 			int divider_value = divider_counter_[channel] / (38 / CPUTicksPerAudioTick);
@@ -119,10 +120,14 @@ void Atari2600::TIASound::get_samples(std::size_t number_of_samples, int16_t *ta
 				break;
 			}
 
-			target[c] += (volume_[channel] * per_channel_volume_ * level) >> 4;
+			output += (volume_[channel] * per_channel_volume_ * level) >> 4;
 		}
+		Outputs::Speaker::apply<action>(target[c], output);
 	}
 }
+template void Atari2600::TIASound::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void Atari2600::TIASound::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void Atari2600::TIASound::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
 void Atari2600::TIASound::set_sample_volume_range(std::int16_t range) {
 	per_channel_volume_ = range / 2;

Machines/Atari/2600/TIASound.hpp

@@ -26,7 +26,8 @@ class TIASound: public Outputs::Speaker::BufferSource<TIASound, false> {
 		void set_control(int channel, uint8_t control);
 
 		// To satisfy ::SampleSource.
-		void get_samples(std::size_t number_of_samples, int16_t *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
 
 	private:

Machines/Electron/SoundGenerator.cpp

@@ -19,21 +19,26 @@ void SoundGenerator::set_sample_volume_range(std::int16_t range) {
 	volume_ = unsigned(range / 2);
 }
 
-void SoundGenerator::get_samples(std::size_t number_of_samples, int16_t *target) {
+template <Outputs::Speaker::Action action>
+void SoundGenerator::apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
+	if constexpr (action == Outputs::Speaker::Action::Ignore) {
+		counter_ = (counter_ + number_of_samples) % ((divider_+1) * 2);
+		return;
+	}
+
 	if(is_enabled_) {
 		while(number_of_samples--) {
-			*target = int16_t((counter_ / (divider_+1)) * volume_);
+			Outputs::Speaker::apply<action>(*target, Outputs::Speaker::MonoSample((counter_ / (divider_+1)) * volume_));
 			target++;
 			counter_ = (counter_ + 1) % ((divider_+1) * 2);
 		}
 	} else {
-		std::memset(target, 0, sizeof(int16_t) * number_of_samples);
+		Outputs::Speaker::fill<action>(target, target + number_of_samples, Outputs::Speaker::MonoSample(0));
 	}
 }
-
-void SoundGenerator::skip_samples(std::size_t number_of_samples) {
-	counter_ = (counter_ + number_of_samples) % ((divider_+1) * 2);
-}
+template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
+template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
 void SoundGenerator::set_divider(uint8_t divider) {
 	audio_queue_.enqueue([this, divider]() {

Machines/Electron/SoundGenerator.hpp

@@ -24,8 +24,8 @@ class SoundGenerator: public ::Outputs::Speaker::BufferSource<SoundGenerator, fa
 		static constexpr unsigned int clock_rate_divider = 8;
 
 		// To satisfy ::SampleSource.
-		void get_samples(std::size_t number_of_samples, int16_t *target);
-		void skip_samples(std::size_t number_of_samples);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
 		void set_sample_volume_range(std::int16_t range);
 
 	private:

Machines/Enterprise/Dave.cpp

@@ -99,7 +99,8 @@ void Audio::update_channel(int c) {
 	channels_[c].output |= output;
 }
 
-void Audio::get_samples(std::size_t number_of_samples, Outputs::Speaker::StereoSample *target) {
+template <Outputs::Speaker::Action action>
+void Audio::apply_samples(std::size_t number_of_samples, Outputs::Speaker::StereoSample *target) {
 	Outputs::Speaker::StereoSample output_level;
 
 	size_t c = 0;
@@ -130,7 +131,7 @@ void Audio::get_samples(std::size_t number_of_samples, Outputs::Speaker::StereoS
 
 		while(global_divider_ && c < number_of_samples) {
 			--global_divider_;
-			target[c] = output_level;
+			Outputs::Speaker::apply<action>(target[c], output_level);
 			++c;
 		}
 		global_divider_ = global_divider_reload_;
@@ -203,6 +204,9 @@ void Audio::get_samples(std::size_t number_of_samples, Outputs::Speaker::StereoS
 		}
 	}
 }
+template void Audio::apply_samples<Outputs::Speaker::Action::Mix>(std::size_t, Outputs::Speaker::StereoSample *);
+template void Audio::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::StereoSample *);
+template void Audio::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::StereoSample *);
 
 // MARK: - Interrupt source
 

Machines/Enterprise/Dave.hpp

@@ -37,7 +37,8 @@ class Audio: public Outputs::Speaker::BufferSource<Audio, true> {
 
 		// MARK: - SampleSource.
 		void set_sample_volume_range(int16_t range);
-		void get_samples(std::size_t number_of_samples, Outputs::Speaker::StereoSample *target);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::StereoSample *target);
 
 	private:
 		Concurrency::AsyncTaskQueue<false> &audio_queue_;

OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme

@@ -62,7 +62,7 @@
       </Testables>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Release"
+      buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       enableASanStackUseAfterReturn = "YES"

Outputs/Speaker/Implementation/BufferSource.hpp

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <algorithm>
 #include <array>
 #include <cstddef>
 #include <cstdint>
@@ -16,6 +17,38 @@
 
 namespace Outputs::Speaker {
 
+enum class Action {
+	/// New values should be _stored_ to the sample buffer.
+	Store,
+	/// New values should be _added_ to the sample buffer.
+	Mix,
+	/// New values shouldn't be stored; the source can skip generation of them if desired.
+	Ignore,
+};
+
+template <Action action, typename SampleT> void apply(SampleT &lhs, SampleT rhs) {
+	switch(action) {
+		case Action::Mix:	lhs += rhs;	break;
+		case Action::Store:	lhs = rhs;	break;
+		case Action::Ignore:			break;
+	}
+}
+
+template <Action action, typename IteratorT, typename SampleT> void fill(IteratorT begin, IteratorT end, SampleT value) {
+	switch(action) {
+		case Action::Mix:
+			while(begin != end) {
+				apply<action>(*begin, value);
+				++begin;
+			}
+		break;
+		case Action::Store:
+			std::fill(begin, end, value);
+		break;
+		case Action::Ignore:	break;
+	}
+}
+
 /*!
 	A sample source is something that can provide a stream of audio.
 	This optional base class provides the interface expected to be exposed
@@ -30,20 +63,11 @@ class BufferSource {
 		static constexpr bool is_stereo = stereo;
 
 		/*!
-			Should write the next @c number_of_samples to @c target.
+			Should 'apply' the next @c number_of_samples to @c target ; application means applying @c action which can be achieved either via the
+			helper functions above — @c apply and @c fill — or by semantic inspection (primarily, if an obvious quick route for @c Action::Ignore is available)
 		*/
-		void get_samples([[maybe_unused]] std::size_t number_of_samples, [[maybe_unused]] typename SampleT<stereo>::type *target) {}
-
-		/*!
-			Should skip the next @c number_of_samples. Subclasses of this SampleSource
-			need not implement this if it would no more efficient to do so than it is
-			merely to call get_samples and throw the result away, as per the default
-			implementation below.
-		*/
-		void skip_samples(std::size_t number_of_samples) {
-			typename SampleT<stereo>::type scratch_pad[number_of_samples];
-			get_samples(number_of_samples, scratch_pad);
-		}
+		template <Action action>
+		void apply_samples([[maybe_unused]] std::size_t number_of_samples, [[maybe_unused]] typename SampleT<stereo>::type *target) {}
 
 		/*!
 			@returns @c true if it is trivially true that a call to get_samples would just
@@ -75,13 +99,15 @@ class BufferSource {
 template <typename SourceT, bool stereo, int divider = 1>
 struct SampleSource: public BufferSource<SourceT, stereo> {
 	public:
-		void get_samples(std::size_t number_of_samples, typename SampleT<stereo>::type *target) {
+		template <bool mix>
+		void apply_samples(std::size_t number_of_samples, typename SampleT<stereo>::type *target) {
 			const auto &source = *static_cast<SourceT *>(this);
 
 			if constexpr (divider == 1) {
 				while(number_of_samples--) {
-					*target = source.level();
+					apply<mix>(*target, source.level());
 					++target;
+					source.advance();
 				}
 			} else {
 				std::size_t c = 0;
@@ -89,7 +115,7 @@ struct SampleSource: public BufferSource<SourceT, stereo> {
 				// Fill in the tail of any partially-captured level.
 				auto level = source.level();
 				while(c < number_of_samples && master_divider_ != divider) {
-					target[c] = level;
+					apply<mix>(target[c], level);
 					++c;
 					++master_divider_;
 				}
@@ -98,7 +124,7 @@ struct SampleSource: public BufferSource<SourceT, stereo> {
 				// Provide all full levels.
 				int whole_steps = (number_of_samples - c) / divider;
 				while(whole_steps--) {
-					std::fill(&target[c], &target[c + divider], source.level());
+					fill<mix>(&target[c], &target[c + divider], source.level());
 					c += divider;
 					source.advance();
 				}
@@ -106,31 +132,7 @@ struct SampleSource: public BufferSource<SourceT, stereo> {
 				// Provide the head of a further partial capture.
 				level = source.level();
 				master_divider_ = number_of_samples - c;
-				std::fill(&target[c], &target[number_of_samples], source.level());
-			}
-		}
-
-		void skip_samples(std::size_t number_of_samples) {
-			const auto &source = *static_cast<SourceT *>(this);
-
-			if constexpr (&SourceT::advance == &SampleSource::advance) {
-				return;
-			}
-
-			if constexpr (divider == 1) {
-				while(--number_of_samples) {
-					source.advance();
-				}
-			} else {
-				if(number_of_samples >= divider - master_divider_) {
-					source.advance();
-					number_of_samples -= (divider - master_divider_);
-				}
-				while(number_of_samples > divider) {
-					advance();
-					number_of_samples -= divider;
-				}
-				master_divider_ = number_of_samples;
+				fill<mix>(&target[c], &target[number_of_samples], source.level());
 			}
 		}
 

Outputs/Speaker/Implementation/CompoundSource.hpp

@@ -49,14 +49,13 @@ template <typename... T> class CompoundSource:
 	private:
 		template <typename... S> class CompoundSourceHolder {
 			public:
-				template <bool output_stereo>
-				void get_samples(std::size_t number_of_samples, typename SampleT<output_stereo>::type *target) {
+				template <Outputs::Speaker::Action action, bool output_stereo>
+				void apply_samples(std::size_t number_of_samples, typename SampleT<output_stereo>::type *target) {
 					// Default-construct all samples, to fill with silence.
-					std::fill(target, target + number_of_samples, typename SampleT<output_stereo>::type());
+					Outputs::Speaker::fill<action>(target, target + number_of_samples, typename SampleT<output_stereo>::type());
 				}
 
 				void set_scaled_volume_range(int16_t, double *, double) {}
-				void skip_samples(const std::size_t) {}
 
 				static constexpr std::size_t size() {
 					return 0;
@@ -75,8 +74,8 @@ template <typename... T> class CompoundSource:
 
 				static constexpr bool is_stereo = S::is_stereo || CompoundSourceHolder<R...>::is_stereo;
 
-				template <bool output_stereo>
-				void get_samples(std::size_t number_of_samples, typename ::Outputs::Speaker::SampleT<output_stereo>::type *target) {
+				template <Outputs::Speaker::Action action, bool output_stereo>
+				void apply_samples(std::size_t number_of_samples, typename ::Outputs::Speaker::SampleT<output_stereo>::type *target) {
 
 					// If this is the step at which a mono-to-stereo adaptation happens, apply it.
 					if constexpr (output_stereo && !S::is_stereo) {
@@ -87,40 +86,26 @@ template <typename... T> class CompoundSource:
 						}
 
 						// Populate the conversion buffer with this source and all below.
-						get_samples<false>(number_of_samples, conversion_source_.data());
+						apply_samples<Action::Store, false>(number_of_samples, conversion_source_.data());
 
 						// Map up and return.
 						for(std::size_t c = 0; c < number_of_samples; c++) {
-							target[c].left = target[c].right = conversion_source_[c];
+							Outputs::Speaker::apply<action>(target[c].left, StereoSample(conversion_source_[c]));
 						}
 						return;
 					}
 
 					// Get the rest of the output.
-					next_source_.template get_samples<output_stereo>(number_of_samples, target);
+					next_source_.template apply_samples<action, output_stereo>(number_of_samples, target);
 
 					if(source_.is_zero_level()) {
 						// This component is currently outputting silence; therefore don't add anything to the output
 						// audio — just pass the call onward.
-						source_.skip_samples(number_of_samples);
 						return;
 					}
 
-					// Get this component's output.
-					typename SampleT<output_stereo>::type local_samples[number_of_samples];
-					source_.get_samples(number_of_samples, local_samples);
-
-					// Merge it in.
-					while(number_of_samples--) {
-						target[number_of_samples] += local_samples[number_of_samples];
-					}
-
-					// TODO: accelerate above?
-				}
-
-				void skip_samples(const std::size_t number_of_samples) {
-					source_.skip_samples(number_of_samples);
-					next_source_.skip_samples(number_of_samples);
+					// Add in this component's output.
+					source_.template apply_samples<Action::Mix>(number_of_samples, target);
 				}
 
 				void set_scaled_volume_range(int16_t range, double *volumes, double scale) {
@@ -157,12 +142,9 @@ template <typename... T> class CompoundSource:
 			}
 		}
 
-		void get_samples(std::size_t number_of_samples, Sample *target) {
-			source_holder_.template get_samples<::Outputs::Speaker::is_stereo<T...>()>(number_of_samples, target);
-		}
-
-		void skip_samples(const std::size_t number_of_samples) {
-			source_holder_.skip_samples(number_of_samples);
+		template <Outputs::Speaker::Action action>
+		void apply_samples(std::size_t number_of_samples, Sample *target) {
+			source_holder_.template apply_samples<action, ::Outputs::Speaker::is_stereo<T...>()>(number_of_samples, target);
 		}
 
 		/*!

Outputs/Speaker/Implementation/LowpassSpeaker.hpp

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include "BufferSource.hpp"
 #include "../Speaker.hpp"
 #include "../../../SignalProcessing/FIRFilter.hpp"
 #include "../../../ClockReceiver/ClockReceiver.hpp"
@@ -396,7 +397,7 @@ template <typename SampleSource> class PullLowpass: public LowpassBase<PullLowpa
 		SampleSource &sample_source_;
 
 		void skip_samples(size_t count) {
-			sample_source_.skip_samples(count);
+			sample_source_.template apply_samples<Action::Ignore>(count, nullptr);
 		}
 
 		int get_scale() {
@@ -406,9 +407,9 @@ template <typename SampleSource> class PullLowpass: public LowpassBase<PullLowpa
 		void get_samples(size_t length, int16_t *target) {
 			if constexpr (SampleSource::is_stereo) {
 				StereoSample *const stereo_target = reinterpret_cast<StereoSample *>(target);
-				sample_source_.get_samples(length, stereo_target);
+				sample_source_.template apply_samples<Action::Store>(length, stereo_target);
 			} else {
-				sample_source_.get_samples(length, target);
+				sample_source_.template apply_samples<Action::Store>(length, target);
 			}
 		}
 };

Outputs/Speaker/Speaker.hpp

@@ -27,6 +27,9 @@ struct StereoSample {
 		left = rhs.left;
 		right = rhs.right;
 	}
+	StereoSample(MonoSample value) {
+		left = right = value;
+	}
 
 	StereoSample &operator +=(const StereoSample &rhs) {
 		left += rhs.left;