Shunts audio into its own QThread.

For the record, this was the first means I found of attempting that which actually seemed to work. A plain QThread, with something `connect`ed to its `started` signal didn't seem to work (perhaps `connect` is smart at thread confinement?), `moveToThread` didn't work on the audio output after the fact, etc.

OSBindings/Qt/ClockSignal.pro

@@ -249,6 +249,7 @@ HEADERS += \
     ../../Storage/Tape/Parsers/*.hpp \
 \
     audiobuffer.h \
+    functionthread.h \
     mainwindow.h \
     scantargetwidget.h \
     timer.h

OSBindings/Qt/audiobuffer.h

@@ -24,6 +24,7 @@ struct AudioBuffer: public QIODevice {
 	}
 
 	void setDepth(size_t depth) {
+		std::lock_guard lock(mutex);
 		buffer.resize(depth);
 	}
 
@@ -35,7 +36,7 @@ struct AudioBuffer: public QIODevice {
 		}
 
 		std::lock_guard lock(mutex);
-		if(readPointer == writePointer) return 0;
+		if(readPointer == writePointer || buffer.empty()) return 0;
 
 		const size_t dataAvailable = std::min(writePointer - readPointer, size_t(maxlen));
 		size_t bytesToCopy = dataAvailable;
@@ -66,6 +67,7 @@ struct AudioBuffer: public QIODevice {
 	// after the buffer is full will overwrite the newest data.
 	void write(const std::vector<int16_t> &source) {
 		std::lock_guard lock(mutex);
+		if(buffer.empty()) return;
 		const size_t sourceSize = source.size() * sizeof(int16_t);
 
 		size_t bytesToCopy = sourceSize;

OSBindings/Qt/functionthread.h

@@ -0,0 +1,31 @@
+#ifndef FUNCTIONTHREAD_H
+#define FUNCTIONTHREAD_H
+
+#include <QThread>
+
+/*!
+ * \brief The LambdaThread class
+ *
+ * Provides a QThread which performs a supplied lambda before kicking off its event loop.
+ *
+ * Disclaimer: this might be a crutch that reveals a misunderstanding of the Qt
+ * threading infrastructure. We'll see.
+ */
+class FunctionThread: public QThread {
+	public:
+		FunctionThread() : QThread() {}
+
+		void setFunction(const std::function<void(void)> &function) {
+			this->function = function;
+		}
+
+		void run() override {
+			function();
+			exec();
+		}
+
+	private:
+		std::function<void(void)> function;
+};
+
+#endif // FUNCTIONTHREAD_H

OSBindings/Qt/mainwindow.cpp

@@ -133,12 +133,6 @@ void MainWindow::launchMachine() {
 			ui->missingROMsBox->setVisible(false);
 			uiPhase = UIPhase::RunningMachine;
 
-			// Install user-friendly options. TODO: plus user overrides.
-//			const auto configurable = machine->configurable_device();
-//			if(configurable) {
-//				configurable->set_options(configurable->get_options());
-//			}
-
 			// Supply the scan target.
 			// TODO: in the future, hypothetically, deal with non-scan producers.
 			const auto scan_producer = machine->scan_producer();
@@ -159,19 +153,23 @@ void MainWindow::launchMachine() {
 					// are available, and — at least for now — assume a good buffer size.
 					audioIsStereo = (idealFormat.channelCount() > 1) && speaker->get_is_stereo();
 					audioIs8bit = idealFormat.sampleSize() < 16;
-					speaker->set_output_rate(idealFormat.sampleRate(), samplesPerBuffer, audioIsStereo);
-
-					// Adjust format appropriately, and create an audio output.
 					idealFormat.setChannelCount(1 + int(audioIsStereo));
 					idealFormat.setSampleSize(audioIs8bit ? 8 : 16);
-					audioOutput = std::make_unique<QAudioOutput>(idealFormat, this);
 
-					// Start the output. The additional `audioBuffer` is meant to minimise latency,
-					// believe it or not, given Qt's semantics.
+					speaker->set_output_rate(idealFormat.sampleRate(), samplesPerBuffer, audioIsStereo);
 					speaker->set_delegate(this);
-					audioOutput->setBufferSize(samplesPerBuffer * sizeof(int16_t));
-					audioOutput->start(&audioBuffer);
-					audioBuffer.setDepth(audioOutput->bufferSize());
+
+					audioThread.setFunction([this, idealFormat] {
+						// Create an audio output.
+						audioOutput = std::make_unique<QAudioOutput>(idealFormat);
+
+						// Start the output. The additional `audioBuffer` is meant to minimise latency,
+						// believe it or not, given Qt's semantics.
+						audioOutput->setBufferSize(samplesPerBuffer * sizeof(int16_t));
+						audioOutput->start(&audioBuffer);
+						audioBuffer.setDepth(audioOutput->bufferSize());
+					});
+					audioThread.start();
 				}
 			}
 
@@ -213,13 +211,6 @@ void MainWindow::launchMachine() {
 
 void MainWindow::speaker_did_complete_samples(Outputs::Speaker::Speaker *, const std::vector<int16_t> &buffer) {
 	audioBuffer.write(buffer);
-//	const char *data = reinterpret_cast<const char *>(buffer.data());
-//	size_t sizeLeft = buffer.size() * sizeof(int16_t);
-//	while(sizeLeft) {
-//		const auto bytesWritten = audioIODevice->write(data, qint64(sizeLeft));
-//		sizeLeft -= bytesWritten;
-//		data += bytesWritten;
-//	}
 }
 
 void MainWindow::dragEnterEvent(QDragEnterEvent* event) {

OSBindings/Qt/mainwindow.h

@@ -8,6 +8,7 @@
 #include "audiobuffer.h"
 #include "timer.h"
 #include "ui_mainwindow.h"
+#include "functionthread.h"
 
 #include "../../Analyser/Static/StaticAnalyser.hpp"
 #include "../../Machines/Utility/MachineForTarget.hpp"
@@ -54,6 +55,7 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 		bool audioIs8bit = false, audioIsStereo = false;
 		void speaker_did_complete_samples(Outputs::Speaker::Speaker *speaker, const std::vector<int16_t> &buffer) override;
 		AudioBuffer audioBuffer;
+		FunctionThread audioThread;
 
 		bool processEvent(QKeyEvent *);