@@ -196,6 +196,9 @@ }
 	if (_lookupIntValue(config, "videoSync", &fakeBool)) {
 		opts->videoSync = fakeBool;
 	}
+	if (_lookupIntValue(config, "lockAspectRatio", &fakeBool)) {
+		opts->lockAspectRatio = fakeBool;
+	}
 
 	_lookupIntValue(config, "fullscreen", &opts->fullscreen);
 	_lookupIntValue(config, "width", &opts->width);
@@ -215,6 +218,7 @@ ConfigurationSetIntValue(&config->defaultsTable, 0, "videoSync", opts->videoSync);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "fullscreen", opts->fullscreen);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "width", opts->width);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "height", opts->height);
+	ConfigurationSetIntValue(&config->defaultsTable, 0, "lockAspectRatio", opts->lockAspectRatio);
 }
 
 void GBAConfigFreeOpts(struct GBAOptions* opts) {

@@ -28,6 +28,7 @@
 	int fullscreen;
 	int width;
 	int height;
+	bool lockAspectRatio;
 
 	bool videoSync;
 	bool audioSync;

@@ -53,6 +53,8 @@ doneCurrent();
 	context()->moveToThread(m_drawThread);
 	connect(m_drawThread, SIGNAL(started()), m_painter, SLOT(start()));
 	m_drawThread->start(QThread::TimeCriticalPriority);
+
+	lockAspectRatio(m_lockAspectRatio);
 }
 
 void Display::stopDrawing() {
@@ -105,6 +107,13 @@ QMetaObject::invokeMethod(m_painter, "forceDraw", Qt::QueuedConnection);
 	}
 }
 
+void Display::lockAspectRatio(bool lock) {
+	m_lockAspectRatio = lock;
+	if (m_drawThread) {
+		QMetaObject::invokeMethod(m_painter, "lockAspectRatio", Qt::QueuedConnection, Q_ARG(bool, lock));
+	}
+}
+
 #ifdef USE_PNG
 void Display::screenshot() {
 	GBAThreadInterrupt(m_context);
@@ -131,6 +140,7 @@ }
 
 Painter::Painter(Display* parent)
 	: m_gl(parent)
+	, m_lockAspectRatio(false)
 {
 	m_size = parent->size();
 }
@@ -145,11 +155,12 @@ }
 
 void Painter::resize(const QSize& size) {
 	m_size = size;
-	m_gl->makeCurrent();
-	glViewport(0, 0, m_size.width() * m_gl->devicePixelRatio(), m_size.height() * m_gl->devicePixelRatio());
-	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
-	m_gl->swapBuffers();
-	m_gl->doneCurrent();
+	forceDraw();
+}
+
+void Painter::lockAspectRatio(bool lock) {
+	m_lockAspectRatio = lock;
+	forceDraw();
 }
 
 void Painter::start() {
@@ -181,12 +192,7 @@
 void Painter::draw() {
 	m_gl->makeCurrent();
 	if (GBASyncWaitFrameStart(&m_context->sync, m_context->frameskip)) {
-		glViewport(0, 0, m_size.width() * m_gl->devicePixelRatio(), m_size.height() * m_gl->devicePixelRatio());
-		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_backing);
-		glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
-		if (m_context->sync.videoFrameWait) {
-			glFlush();
-		}
+		performDraw();
 	}
 	GBASyncWaitFrameEnd(&m_context->sync);
 	m_gl->swapBuffers();
@@ -195,12 +201,7 @@ }
 
 void Painter::forceDraw() {
 	m_gl->makeCurrent();
-	glViewport(0, 0, m_size.width() * m_gl->devicePixelRatio(), m_size.height() * m_gl->devicePixelRatio());
-	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_backing);
-	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
-	if (m_context->sync.videoFrameWait) {
-		glFlush();
-	}
+	performDraw();
 	m_gl->swapBuffers();
 	m_gl->doneCurrent();
 }
@@ -226,3 +227,25 @@
 void Painter::unpause() {
 	m_drawTimer->start();
 }
+
+void Painter::performDraw() {
+	glViewport(0, 0, m_size.width() * m_gl->devicePixelRatio(), m_size.height() * m_gl->devicePixelRatio());
+	glClear(GL_COLOR_BUFFER_BIT);
+	int w = m_size.width() * m_gl->devicePixelRatio();
+	int h = m_size.height() * m_gl->devicePixelRatio();
+	int drawW = w;
+	int drawH = h;
+	if (m_lockAspectRatio) {
+		if (w * 2 > h * 3) {
+			drawW = h * 3 / 2;
+		} else if (w * 2 < h * 3) {
+			drawH = w * 2 / 3;
+		}
+	}
+	glViewport((w - drawW) / 2, (h - drawH) / 2, drawW, drawH);
+	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_backing);
+	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+	if (m_context->sync.videoFrameWait) {
+		glFlush();
+	}
+}

@@ -27,6 +27,7 @@ void stopDrawing();
 	void pauseDrawing();
 	void unpauseDrawing();
 	void forceDraw();
+	void lockAspectRatio(bool lock);
 #ifdef USE_PNG
 	void screenshot();
 #endif
@@ -40,6 +41,7 @@ private:
 	Painter* m_painter;
 	QThread* m_drawThread;
 	GBAThread* m_context;
+	bool m_lockAspectRatio;
 };
 
 class Painter : public QObject {
@@ -59,14 +61,18 @@ void stop();
 	void pause();
 	void unpause();
 	void resize(const QSize& size);
+	void lockAspectRatio(bool lock);
 
 private:
+	void performDraw();
+
 	QTimer* m_drawTimer;
 	GBAThread* m_context;
 	const uint32_t* m_backing;
 	GLuint m_tex;
 	QGLWidget* m_gl;
 	QSize m_size;
+	bool m_lockAspectRatio;
 };
 
 }

@@ -133,6 +133,7 @@
 	m_controller->setFrameskip(opts->frameskip);
 	m_controller->setAudioSync(opts->audioSync);
 	m_controller->setVideoSync(opts->videoSync);
+	m_display->lockAspectRatio(opts->lockAspectRatio);
 
 	if (opts->bios) {
 		m_controller->loadBIOS(opts->bios);
@@ -508,6 +509,11 @@ resizeFrame(VIDEO_HORIZONTAL_PIXELS * 4, VIDEO_VERTICAL_PIXELS * 4);
 	});
 	frameMenu->addAction(setSize);
 	addAction(frameMenu->addAction(tr("Fullscreen"), this, SLOT(toggleFullScreen()), QKeySequence("Ctrl+F")));
+
+	ConfigOption* lockAspectRatio = m_config->addOption("lockAspectRatio");
+	lockAspectRatio->addBoolean(tr("Lock aspect ratio"), avMenu);
+	lockAspectRatio->connect([this](const QVariant& value) { m_display->lockAspectRatio(value.toBool()); });
+	m_config->updateOption("lockAspectRatio");
 
 	QMenu* skipMenu = avMenu->addMenu(tr("Frame&skip"));
 	ConfigOption* skip = m_config->addOption("frameskip");