System: Redraw skins when a user session changes

Fixes issue with certain builds of Windows 7 where the skin window would appear to disappear when returning from the Windows "Switch user" screen
https://forum.rainmeter.net/viewtopic.php?t=39722#p203252

Library/Library.vcxproj

@@ -22,7 +22,7 @@
       <PrecompiledHeader>Use</PrecompiledHeader>
     </ClCompile>
     <Link>
-      <AdditionalDependencies>Bcrypt.lib;comctl32.lib;dwmapi.lib;Wininet.lib;UxTheme.lib;Winmm.lib;gdiplus.lib;Iphlpapi.lib;ws2_32.lib;PowrProf.lib;netapi32.lib;Ntdll.lib;shlwapi.lib;d3d11.lib;d2d1.lib;dwrite.lib;windowscodecs.lib;Version.lib;Imagehlp.lib;Urlmon.lib;psapi.lib;dxguid.lib;Rpcrt4.lib;wlanapi.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>Bcrypt.lib;comctl32.lib;dwmapi.lib;Wininet.lib;UxTheme.lib;Winmm.lib;gdiplus.lib;Iphlpapi.lib;ws2_32.lib;PowrProf.lib;netapi32.lib;Ntdll.lib;shlwapi.lib;d3d11.lib;d2d1.lib;dwrite.lib;windowscodecs.lib;Version.lib;Imagehlp.lib;Urlmon.lib;psapi.lib;dxguid.lib;Rpcrt4.lib;wlanapi.lib;Wtsapi32.lib;%(AdditionalDependencies)</AdditionalDependencies>
       <DelayLoadDLLs>Bcrypt.dll;dwmapi.dll;Iphlpapi.dll;Winmm.dll;Version.dll;Imagehlp.dll;Urlmon.dll;psapi.dll;wlanapi.dll;$(DelayLoadTestDLL)</DelayLoadDLLs>
       <ModuleDefinitionFile>Exports.def</ModuleDefinitionFile>
     </Link>

Library/System.cpp

@@ -13,6 +13,7 @@
 #include "MeasureNet.h"
 #include "../Common/PathUtil.h"
 #include <TlHelp32.h>
+#include <WtsApi32.h>
 
 using namespace Gdiplus;
 
@@ -88,6 +89,8 @@ void System::Initialize(HINSTANCE instance)
 		instance,
 		nullptr);
 
+	WTSRegisterSessionNotification(c_Window, NOTIFY_FOR_THIS_SESSION);
+
 	SetWindowPos(c_Window, HWND_BOTTOM, 0, 0, 0, 0, ZPOS_FLAGS);
 	SetWindowPos(c_HelperWindow, HWND_BOTTOM, 0, 0, 0, 0, ZPOS_FLAGS);
 
@@ -133,6 +136,7 @@ void System::Finalize()
 
 	if (c_Window)
 	{
+		WTSUnRegisterSessionNotification(c_Window);
 		DestroyWindow(c_Window);
 		c_Window = nullptr;
 	}
@@ -983,6 +987,18 @@ LRESULT CALLBACK System::WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lPa
 		}
 		return TRUE;
 
+	case WM_WTSSESSION_CHANGE:
+		LogDebugF(L"System: User session change detected! Session ID: 0x%08X Type: 0x%08X", lParam, wParam);
+		if (GetRainmeter().IsRedrawable())
+		{
+			std::map<std::wstring, Skin*>::const_iterator iter = GetRainmeter().GetAllSkins().begin();
+			for (; iter != GetRainmeter().GetAllSkins().end(); ++iter)
+			{
+				(*iter).second->RedrawWindow();
+			}
+		}
+		break;
+
 	default:
 		return DefWindowProc(hWnd, uMsg, wParam, lParam);
 	}