Qt: Move OpenGL proxy onto its own thread (fixes #2493)

CHANGES

@@ -18,6 +18,7 @@ Misc:
  - macOS: Add category to plist (closes mgba.io/i/2691)
  - macOS: Fix modern build with libepoxy (fixes mgba.io/i/2700)
  - Qt: Keep track of current palette preset name (fixes mgba.io/i/2680)
+ - Qt: Move OpenGL proxy onto its own thread (fixes mgba.io/i/2493)
 
 0.10.0: (2022-10-11)
 Features:

src/platform/qt/DisplayGL.cpp

@@ -175,6 +175,11 @@ DisplayGL::DisplayGL(const QSurfaceFormat& format, QWidget* parent)
 	m_drawThread.setObjectName("Painter Thread");
 	m_painter->setThread(&m_drawThread);
 
+	m_proxyThread.setObjectName("OpenGL Proxy Thread");
+	m_proxyContext = std::make_unique<QOpenGLContext>();
+	m_proxyContext->setFormat(format);
+	connect(m_painter.get(), &PainterGL::created, this, &DisplayGL::setupProxyThread);
+
 	connect(&m_drawThread, &QThread::started, m_painter.get(), &PainterGL::create);
 	connect(m_painter.get(), &PainterGL::started, this, [this] {
 		m_hasStarted = true;
@@ -189,6 +194,11 @@ DisplayGL::~DisplayGL() {
 	QMetaObject::invokeMethod(m_painter.get(), "destroy", Qt::BlockingQueuedConnection);
 	m_drawThread.exit();
 	m_drawThread.wait();
+
+	if (m_proxyThread.isRunning()) {
+		m_proxyThread.exit();
+		m_proxyThread.wait();
+	}
 }
 
 bool DisplayGL::supportsShaders() const {
@@ -209,9 +219,6 @@ void DisplayGL::startDrawing(std::shared_ptr<CoreController> controller) {
 	m_painter->setContext(controller);
 	m_painter->setMessagePainter(messagePainter());
 	m_context = controller;
-	if (videoProxy()) {
-		videoProxy()->moveToThread(&m_drawThread);
-	}
 
 	lockAspectRatio(isAspectRatioLocked());
 	lockIntegerScaling(isIntegerScalingLocked());
@@ -411,11 +418,34 @@ bool DisplayGL::shouldDisableUpdates() {
 void DisplayGL::setVideoProxy(std::shared_ptr<VideoProxy> proxy) {
 	Display::setVideoProxy(proxy);
 	if (proxy) {
-		proxy->moveToThread(&m_drawThread);
+		proxy->moveToThread(&m_proxyThread);
 	}
 	m_painter->setVideoProxy(proxy);
 }
 
+void DisplayGL::setupProxyThread() {
+	m_proxyContext->moveToThread(&m_proxyThread);
+	connect(&m_proxyThread, &QThread::started, m_proxyContext.get(), [this]() {
+		m_proxyContext->setShareContext(m_painter->shareContext());
+		m_proxyContext->create();
+		m_proxySurface.create();
+		m_proxyContext->makeCurrent(&m_proxySurface);
+#if defined(_WIN32) && defined(USE_EPOXY)
+		epoxy_handle_external_wglMakeCurrent();
+#endif
+	});
+	connect(m_painter.get(), &PainterGL::texSwapped, m_proxyContext.get(), [this]() {
+		if (!m_context->hardwareAccelerated()) {
+			return;
+		}
+		if (videoProxy()) {
+			videoProxy()->processData();
+		}
+		m_painter->updateFramebufferHandle();
+	}, Qt::BlockingQueuedConnection);
+	m_proxyThread.start();
+}
+
 int DisplayGL::framebufferHandle() {
 	return m_painter->glTex();
 }
@@ -481,9 +511,15 @@ void PainterGL::create() {
 
 #if defined(BUILD_GLES2) || defined(BUILD_GLES3)
 	if (m_supportsShaders) {
+		QOpenGLFunctions_Baseline* fn = m_gl->versionFunctions<QOpenGLFunctions_Baseline>();
 		gl2Backend = static_cast<mGLES2Context*>(malloc(sizeof(mGLES2Context)));
 		mGLES2ContextCreate(gl2Backend);
 		m_backend = &gl2Backend->d;
+		fn->glGenTextures(m_bridgeTexes.size(), m_bridgeTexes.data());
+		for (auto tex : m_bridgeTexes) {
+			m_freeTex.enqueue(tex);
+		}
+		m_bridgeTexIn = m_freeTex.dequeue();
 	}
 #endif
 
@@ -503,10 +539,10 @@ void PainterGL::create() {
 		painter->makeCurrent();
 
 #if defined(BUILD_GLES2) || defined(BUILD_GLES3)
+		mGLES2Context* gl2Backend = reinterpret_cast<mGLES2Context*>(painter->m_backend);
 		if (painter->m_widget && painter->supportsShaders()) {
 			QOpenGLFunctions_Baseline* fn = painter->m_gl->versionFunctions<QOpenGLFunctions_Baseline>();
 			fn->glFinish();
-			mGLES2Context* gl2Backend = reinterpret_cast<mGLES2Context*>(painter->m_backend);
 			painter->m_widget->setTex(painter->m_finalTex[painter->m_finalTexIdx]);
 			painter->m_finalTexIdx ^= 1;
 			gl2Backend->finalShader.tex = painter->m_finalTex[painter->m_finalTexIdx];
@@ -540,6 +576,8 @@ void PainterGL::create() {
 	m_backend->filter = false;
 	m_backend->lockAspectRatio = false;
 	m_backend->interframeBlending = false;
+
+	emit created();
 }
 
 void PainterGL::destroy() {
@@ -548,9 +586,11 @@ void PainterGL::destroy() {
 	}
 	makeCurrent();
 #if defined(BUILD_GLES2) || defined(BUILD_GLES3)
+	QOpenGLFunctions_Baseline* fn = m_gl->versionFunctions<QOpenGLFunctions_Baseline>();
 	if (m_shader.passes) {
 		mGLES2ShaderFree(&m_shader);
 	}
+	fn->glDeleteTextures(m_bridgeTexes.size(), m_bridgeTexes.data());
 #endif
 	m_backend->deinit(m_backend);
 	m_gl->doneCurrent();
@@ -636,6 +676,7 @@ void PainterGL::start() {
 	}
 #endif
 	resizeContext();
+	m_context->addFrameAction(std::bind(&PainterGL::swapTex, this));
 
 	m_buffer = nullptr;
 	m_active = true;
@@ -644,7 +685,7 @@ void PainterGL::start() {
 }
 
 void PainterGL::draw() {
-	if (!m_started || m_queue.isEmpty()) {
+	if (!m_started || (m_queue.isEmpty() && m_queueTex.isEmpty())) {
 		return;
 	}
 
@@ -671,7 +712,7 @@ void PainterGL::draw() {
 		return;
 	}
 	dequeue();
-	bool forceRedraw = !m_videoProxy;
+	bool forceRedraw = true;
 	if (!m_delayTimer.isValid()) {
 		m_delayTimer.start();
 	} else {
@@ -725,11 +766,6 @@ void PainterGL::doStop() {
 			m_videoProxy->processData();
 		}
 	}
-	if (m_videoProxy) {
-		m_videoProxy->reset();
-		m_videoProxy->moveToThread(m_window->thread());
-		m_videoProxy.reset();
-	}
 	m_backend->clear(m_backend);
 	m_backend->swap(m_backend);
 }
@@ -759,9 +795,11 @@ void PainterGL::performDraw() {
 }
 
 void PainterGL::enqueue(const uint32_t* backing) {
+	if (!backing) {
+		return;
+	}
 	QMutexLocker locker(&m_mutex);
 	uint32_t* buffer = nullptr;
-	if (backing) {
 	if (m_free.isEmpty()) {
 		buffer = m_queue.dequeue();
 	} else {
@@ -771,26 +809,46 @@ void PainterGL::enqueue(const uint32_t* backing) {
 		QSize size = m_context->screenDimensions();
 		memcpy(buffer, backing, size.width() * size.height() * BYTES_PER_PIXEL);
 	}
-	}
 	m_queue.enqueue(buffer);
 }
 
+void PainterGL::enqueue(GLuint tex) {
+	QMutexLocker locker(&m_mutex);
+	if (m_freeTex.isEmpty()) {
+		m_bridgeTexIn = m_queueTex.dequeue();
+	} else {
+		m_bridgeTexIn = m_freeTex.takeLast();
+	}
+	m_queueTex.enqueue(tex);
+}
+
 void PainterGL::dequeue() {
 	QMutexLocker locker(&m_mutex);
-	if (m_queue.isEmpty()) {
+	if (!m_queue.isEmpty()) {
-		return;
-	}
 		uint32_t* buffer = m_queue.dequeue();
 		if (m_buffer) {
 			m_free.append(m_buffer);
-		m_buffer = nullptr;
 		}
 		m_buffer = buffer;
+	}
+
+	if (!m_queueTex.isEmpty()) {
+		if (m_bridgeTexOut != std::numeric_limits<GLuint>::max()) {
+			m_freeTex.enqueue(m_bridgeTexOut);
+		}
+		m_bridgeTexOut = m_queueTex.dequeue();
+#if defined(BUILD_GLES2) || defined(BUILD_GLES3)
+		if (supportsShaders()) {
+			mGLES2Context* gl2Backend = reinterpret_cast<mGLES2Context*>(m_backend);
+			gl2Backend->tex = m_bridgeTexOut;
+		}
+#endif
+	}
 }
 
 void PainterGL::dequeueAll(bool keep) {
 	QMutexLocker locker(&m_mutex);
-	uint32_t* buffer = 0;
+	uint32_t* buffer = nullptr;
 	while (!m_queue.isEmpty()) {
 		buffer = m_queue.dequeue();
 		if (keep) {
@@ -802,6 +860,13 @@ void PainterGL::dequeueAll(bool keep) {
 			m_free.append(buffer);
 		}
 	}
+	m_queueTex.clear();
+	m_freeTex.clear();
+	for (auto tex : m_bridgeTexes) {
+		m_freeTex.enqueue(tex);
+	}
+	m_bridgeTexIn = m_freeTex.dequeue();
+	m_bridgeTexOut = std::numeric_limits<GLuint>::max();
 	if (m_buffer && !keep) {
 		m_free.append(m_buffer);
 		m_buffer = nullptr;
@@ -861,4 +926,29 @@ int PainterGL::glTex() {
 #endif
 }
 
+QOpenGLContext* PainterGL::shareContext() {
+	if (m_widget) {
+		return m_widget->context();
+	} else {
+		return m_gl.get();
+	}
+}
+
+void PainterGL::updateFramebufferHandle() {
+	QOpenGLFunctions_Baseline* fn = m_gl->versionFunctions<QOpenGLFunctions_Baseline>();
+	fn->glFinish();
+	enqueue(m_bridgeTexIn);
+	m_context->setFramebufferHandle(m_bridgeTexIn);
+}
+
+void PainterGL::swapTex() {
+	if (!m_started) {
+		return;
+	}
+
+	CoreController::Interrupter interrupter(m_context);
+	emit texSwapped();
+	m_context->addFrameAction(std::bind(&PainterGL::swapTex, this));
+}
+
 #endif

src/platform/qt/DisplayGL.h

@@ -112,6 +112,9 @@ protected:
 	virtual void paintEvent(QPaintEvent*) override { forceDraw(); }
 	virtual void resizeEvent(QResizeEvent*) override;
 
+private slots:
+	void setupProxyThread();
+
 private:
 	void resizePainter();
 	bool shouldDisableUpdates();
@@ -122,8 +125,11 @@ private:
 	bool m_hasStarted = false;
 	std::unique_ptr<PainterGL> m_painter;
 	QThread m_drawThread;
+	QThread m_proxyThread;
 	std::shared_ptr<CoreController> m_context;
 	mGLWidget* m_gl;
+	QOffscreenSurface m_proxySurface;
+	std::unique_ptr<QOpenGLContext> m_proxyContext;
 };
 
 class PainterGL : public QObject {
@@ -137,15 +143,21 @@ public:
 	void setContext(std::shared_ptr<CoreController>);
 	void setMessagePainter(MessagePainter*);
 	void enqueue(const uint32_t* backing);
+	void enqueue(GLuint tex);
 
 	void stop();
 
 	bool supportsShaders() const { return m_supportsShaders; }
 	int glTex();
 
+	QOpenGLContext* shareContext();
+
 	void setVideoProxy(std::shared_ptr<VideoProxy>);
 	void interrupt();
 
+	// Run on main thread
+	void swapTex();
+
 public slots:
 	void create();
 	void destroy();
@@ -163,13 +175,16 @@ public slots:
 	void showFrameCounter(bool enable);
 	void filter(bool filter);
 	void resizeContext();
+	void updateFramebufferHandle();
 
 	void setShaders(struct VDir*);
 	void clearShaders();
 	VideoShader* shaders();
 
 signals:
+	void created();
 	void started();
+	void texSwapped();
 
 private slots:
 	void doStop();
@@ -184,6 +199,14 @@ private:
 	QList<uint32_t*> m_free;
 	QQueue<uint32_t*> m_queue;
 	uint32_t* m_buffer = nullptr;
+
+	std::array<GLuint, 3> m_bridgeTexes;
+	QQueue<GLuint> m_freeTex;
+	QQueue<GLuint> m_queueTex;
+
+	GLuint m_bridgeTexIn = std::numeric_limits<GLuint>::max();
+	GLuint m_bridgeTexOut = std::numeric_limits<GLuint>::max();
+
 	QPainter m_painter;
 	QMutex m_mutex;
 	QWindow* m_window;