Make fullscreen changes better (especially under windows)

src/engine/client/backend_sdl.cpp

@@ -1168,8 +1168,16 @@ void CGraphicsBackend_SDL_OpenGL::SetWindowGrab(bool Grab)
 
 void CGraphicsBackend_SDL_OpenGL::ResizeWindow(int w, int h, int RefreshRate)
 {
+	// don't call resize events when the window is at fullscreen desktop
+	if((SDL_GetWindowFlags(m_pWindow) & SDL_WINDOW_FULLSCREEN_DESKTOP) != SDL_WINDOW_FULLSCREEN_DESKTOP)
+	{
+		// if the window is at fullscreen use SDL_SetWindowDisplayMode instead, suggested by SDL
 		if(SDL_GetWindowFlags(m_pWindow) & SDL_WINDOW_FULLSCREEN)
 		{
+#ifdef CONF_PLATFORM_WINDOWS
+			// in windows make the window windowed mode first, this prevents strange window glitches (other games probably do something similar)
+			SetWindowParams(0, 1);
+#endif
 			SDL_DisplayMode SetMode = {};
 			SDL_DisplayMode ClosestMode = {};
 			SetMode.format = 0;
@@ -1177,6 +1185,11 @@ void CGraphicsBackend_SDL_OpenGL::ResizeWindow(int w, int h, int RefreshRate)
 			SetMode.h = h;
 			SetMode.refresh_rate = RefreshRate;
 			SDL_SetWindowDisplayMode(m_pWindow, SDL_GetClosestDisplayMode(g_Config.m_GfxScreen, &SetMode, &ClosestMode));
+#ifdef CONF_PLATFORM_WINDOWS
+			// now change it back to fullscreen, this will restore the above set state, bcs SDL saves fullscreen modes appart from other video modes (as of SDL 2.0.16)
+			// see implementation of SDL_SetWindowDisplayMode
+			SetWindowParams(1, 0);
+#endif
 		}
 		else
 		{
@@ -1186,6 +1199,7 @@ void CGraphicsBackend_SDL_OpenGL::ResizeWindow(int w, int h, int RefreshRate)
 				SDL_RestoreWindow(m_pWindow);
 		}
 	}
+}
 
 void CGraphicsBackend_SDL_OpenGL::GetViewportSize(int &w, int &h)
 {

src/engine/client/graphics_threaded.cpp

@@ -2329,9 +2329,14 @@ void CGraphics_Threaded::Resize(int w, int h, int RefreshRate, bool SetWindowSiz
 	if(!ForceResizeEvent && WindowWidth() == w && WindowHeight() == h && (RefreshRate != -1 && RefreshRate == m_ScreenRefreshRate))
 		return;
 
+	// if the size is changed manually, only set the window resize, a window size changed event is triggered anyway
 	if(SetWindowSize)
+	{
 		m_pBackend->ResizeWindow(w, h, RefreshRate);
-
+	}
+	else
+	{
+		// if the size change event is triggered, set all parameters and change the viewport
 		m_pBackend->GetViewportSize(m_ScreenWidth, m_ScreenHeight);
 
 		// adjust the viewport to only allow certain aspect ratios
@@ -2365,6 +2370,7 @@ void CGraphics_Threaded::Resize(int w, int h, int RefreshRate, bool SetWindowSiz
 		for(auto &ResizeListener : m_ResizeListeners)
 			ResizeListener.m_pFunc(ResizeListener.m_pUser);
 	}
+}
 
 void CGraphics_Threaded::AddWindowResizeListener(WINDOW_RESIZE_FUNC pFunc, void *pUser)
 {

src/engine/client/input.cpp

@@ -344,7 +344,8 @@ int CInput::Update()
 				// shortcuts
 				switch(Event.window.event)
 				{
-				case SDL_WINDOWEVENT_RESIZED:
+				// listen to size changes, this includes our manual changes and the ones by the window manager
+				case SDL_WINDOWEVENT_SIZE_CHANGED:
 					Graphics()->Resize(Event.window.data1, Event.window.data2, -1);
 					break;
 				case SDL_WINDOWEVENT_FOCUS_GAINED: