Qt: Defer texture updates until frame is drawn (fixes #1590)

CHANGES

@@ -24,6 +24,7 @@ Misc:
  - Qt: Add hex index to palette view
  - Qt: Add transformation matrix info to sprite view
  - Qt: Disable Replace ROM option when no game loaded
+ - Qt: Defer texture updates until frame is drawn (fixes mgba.io/i/1590)
 
 0.8.1: (2020-02-16)
 Emulation fixes:

src/platform/qt/DisplayGL.cpp

@@ -327,7 +327,7 @@ PainterGL::PainterGL(QWindow* surface, QOpenGLContext* parent, int forceVersion)
 	m_backend->lockAspectRatio = false;
 	m_backend->interframeBlending = false;
 
-	for (int i = 0; i < 2; ++i) {
+	for (int i = 0; i < 3; ++i) {
 		m_free.append(new uint32_t[1024 * 2048]);
 	}
 }
@@ -423,6 +423,7 @@ void PainterGL::start() {
 	}
 #endif
 
+	m_buffer = nullptr;
 	m_active = true;
 	m_started = true;
 }
@@ -490,6 +491,11 @@ void PainterGL::performDraw() {
 	m_painter.beginNativePainting();
 	float r = m_surface->devicePixelRatio();
 	m_backend->resized(m_backend, m_size.width() * r, m_size.height() * r);
+	if (m_buffer) {
+		m_backend->postFrame(m_backend, m_buffer);
+		m_free.append(m_buffer);
+		m_buffer = nullptr;
+	}
 	m_backend->drawFrame(m_backend);
 	m_painter.endNativePainting();
 	if (m_showOSD && m_messagePainter) {
@@ -520,9 +526,12 @@ void PainterGL::dequeue() {
 		return;
 	}
 	uint32_t* buffer = m_queue.dequeue();
+	if (m_buffer) {
+		m_free.append(m_buffer);
+		m_buffer = nullptr;
+	}
 	if (buffer) {
-		m_backend->postFrame(m_backend, buffer);
-		m_free.append(buffer);
+		m_buffer = buffer;
 	}
 	m_mutex.unlock();
 }
@@ -539,6 +548,10 @@ void PainterGL::dequeueAll() {
 	if (buffer) {
 		m_backend->postFrame(m_backend, buffer);
 	}
+	if (m_buffer) {
+		m_free.append(m_buffer);
+		m_buffer = nullptr;
+	}
 	m_mutex.unlock();
 }
 

src/platform/qt/DisplayGL.h

@@ -121,6 +121,7 @@ private:
 
 	QList<uint32_t*> m_free;
 	QQueue<uint32_t*> m_queue;
+	uint32_t* m_buffer;
 	QPainter m_painter;
 	QMutex m_mutex;
 	QWindow* m_surface;