video_core: Allow changing background color while emulation is running

As @jroweboy stated, this is just one more atomic in VideoCore.

src/core/settings.cpp

@@ -31,6 +31,8 @@ void Apply() {
         VideoCore::g_emu_window->UpdateCurrentFramebufferLayout(layout.width, layout.height);
     }
 
+    VideoCore::g_renderer_bg_color_update_requested = true;
+
     if (Core::System::GetInstance().IsPoweredOn()) {
         Core::DSP().SetSink(values.sink_id, values.audio_device_id);
         Core::DSP().EnableStretching(values.enable_audio_stretching);

src/video_core/renderer_opengl/renderer_opengl.cpp

@@ -384,6 +384,12 @@ void RendererOpenGL::DrawSingleScreenRotated(const ScreenInfo& screen_info, floa
  * Draws the emulated screens to the emulator window.
  */
 void RendererOpenGL::DrawScreens() {
+    if (VideoCore::g_renderer_bg_color_update_requested.exchange(false)) {
+        // Update background color before drawing
+        glClearColor(Settings::values.bg_red, Settings::values.bg_green, Settings::values.bg_blue,
+                     0.0f);
+    }
+
     auto layout = render_window->GetFramebufferLayout();
     const auto& top_screen = layout.top_screen;
     const auto& bottom_screen = layout.bottom_screen;

src/video_core/video_core.cpp

@@ -22,6 +22,7 @@ std::atomic<bool> g_shader_jit_enabled;
 std::atomic<bool> g_hw_shader_enabled;
 std::atomic<bool> g_hw_shader_accurate_gs;
 std::atomic<bool> g_hw_shader_accurate_mul;
+std::atomic<bool> g_renderer_bg_color_update_requested;
 
 /// Initialize the video core
 bool Init(EmuWindow* emu_window) {

src/video_core/video_core.h

@@ -25,6 +25,7 @@ extern std::atomic<bool> g_shader_jit_enabled;
 extern std::atomic<bool> g_hw_shader_enabled;
 extern std::atomic<bool> g_hw_shader_accurate_gs;
 extern std::atomic<bool> g_hw_shader_accurate_mul;
+extern std::atomic<bool> g_renderer_bg_color_update_requested;
 
 /// Start the video core
 void Start();