Qt: Fix some Qt display driver race conditions

CHANGES

@@ -37,6 +37,7 @@ Other fixes:
  - Qt: Fix adjusting magnification in tile viewer when not fitting to window
  - FFmpeg: Improve initialization reliability and cleanup
  - Wii: Fix aspect ratio (fixes mgba.io/i/500)
+ - Qt: Fix some Qt display driver race conditions
 Misc:
  - GBA Savedata: EEPROM performance fixes
  - GBA Savedata: Automatically map 1Mbit Flash files as 1Mbit Flash

src/platform/qt/DisplayGL.cpp

@@ -37,6 +37,7 @@ DisplayGL::DisplayGL(const QGLFormat& format, QWidget* parent)
 	m_painter = new PainterGL(format.majorVersion() < 2 ? 1 : m_gl->format().majorVersion(), m_gl);
 	m_gl->setMouseTracking(true);
 	m_gl->setAttribute(Qt::WA_TransparentForMouseEvents); // This doesn't seem to work?
+	setUpdatesEnabled(false); // Prevent paint events, which can cause race conditions
 }
 
 DisplayGL::~DisplayGL() {
@@ -219,6 +220,9 @@ PainterGL::PainterGL(int majorVersion, QGLWidget* parent)
 #endif
 	m_backend->swap = [](VideoBackend* v) {
 		PainterGL* painter = static_cast<PainterGL*>(v->user);
+		if (!painter->m_gl->isVisible()) {
+			return;
+		}
 		painter->m_gl->swapBuffers();
 	};
 

src/platform/qt/DisplayGL.h

@@ -32,7 +32,7 @@ public:
 	EmptyGLWidget(const QGLFormat& format, QWidget* parent) : QGLWidget(format, parent) { setAutoBufferSwap(false); }
 
 protected:
-	void paintEvent(QPaintEvent*) override {}
+	void paintEvent(QPaintEvent* event) override { event->ignore(); }
 	void resizeEvent(QResizeEvent*) override {}
 	void mouseMoveEvent(QMouseEvent* event) override { event->ignore(); }
 };