When quitting/restarting client clear screen and render message

When quitting or restarting the client, clear the screen and render a message "Quitting. Please wait…" or "Restarting. Please wait…" respectively.

Previously the last frame would keep getting shown while the client is busy with cleanup tasks. Rendering a final message before the client window stops being updated provides a cleaner user experience.

src/game/client/gameclient.cpp

@@ -915,6 +915,8 @@ void CGameClient::OnStateChange(int NewState, int OldState)
 
 void CGameClient::OnShutdown()
 {
+	RenderShutdownMessage();
+
 	for(auto &pComponent : m_vpAll)
 		pComponent->OnShutdown();
 }
@@ -972,6 +974,25 @@ void CGameClient::OnLanguageChange()
 	UI()->OnLanguageChange();
 }
 
+void CGameClient::RenderShutdownMessage()
+{
+	const char *pMessage = nullptr;
+	if(Client()->State() == IClient::STATE_QUITTING)
+		pMessage = Localize("Quitting. Please wait…");
+	else if(Client()->State() == IClient::STATE_RESTARTING)
+		pMessage = Localize("Restarting. Please wait…");
+	else
+		dbg_assert(false, "Invalid client state for quitting message");
+
+	// This function only gets called after the render loop has already terminated, so we have to call Swap manually.
+	Graphics()->Clear(0.0f, 0.0f, 0.0f);
+	UI()->MapScreen();
+	TextRender()->TextColor(TextRender()->DefaultTextColor());
+	UI()->DoLabel(UI()->Screen(), pMessage, 16.0f, TEXTALIGN_MC);
+	Graphics()->Swap();
+	Graphics()->Clear(0.0f, 0.0f, 0.0f);
+}
+
 void CGameClient::OnRconType(bool UsernameReq)
 {
 	m_GameConsole.RequireUsername(UsernameReq);

src/game/client/gameclient.h

@@ -489,6 +489,8 @@ public:
 
 	void OnLanguageChange();
 
+	void RenderShutdownMessage();
+
 	const char *GetItemName(int Type) const override;
 	const char *Version() const override;
 	const char *NetVersion() const override;