ScreenPanelNative: Don't try to render the framebuffer if the emulator is not actually active.

This fixes an issue where the window draws with a gray background in macOS, and is see-through on Wayland-based desktops.

src/frontend/qt_sdl/main.cpp

@@ -714,6 +714,11 @@ bool EmuThread::emuIsRunning()
     return (EmuRunning == 1);
 }
 
+bool EmuThread::emuIsActive()
+{
+    return (RunningSomething == 1);
+}
+
 
 void ScreenHandler::screenSetupLayout(int w, int h)
 {
@@ -942,6 +947,8 @@ void ScreenPanelNative::paintEvent(QPaintEvent* event)
     // fill background
     painter.fillRect(event->rect(), QColor::fromRgb(0, 0, 0));
 
+    if (emuThread->emuIsActive())
+    {
         emuThread->FrontBufferLock.lock();
         int frontbuf = emuThread->FrontBuffer;
         if (!GPU::Framebuffer[frontbuf][0] || !GPU::Framebuffer[frontbuf][1])
@@ -963,6 +970,7 @@ void ScreenPanelNative::paintEvent(QPaintEvent* event)
             painter.setTransform(screenTrans[i]);
             painter.drawImage(screenrc, screen[screenKind[i]]);
         }
+    }
 
     OSD::Update(nullptr);
     OSD::DrawNative(painter);

src/frontend/qt_sdl/main.h

@@ -59,6 +59,7 @@ public:
     void emuFrameStep();
 
     bool emuIsRunning();
+    bool emuIsActive();
 
     int FrontBuffer = 0;
     QMutex FrontBufferLock;