Added files missing from 2 commits earlier

Some new files were accidentally left out of a previous commit:
"Revamping GDI interworking - Part 2" 1999d1c56ef4af2b173764a0dffff0c270357628

The missing files are now added.

DDrawCompat/CompatGdiCaret.h

@@ -0,0 +1,6 @@
+#pragma once
+
+namespace CompatGdiCaret
+{
+	void installHooks();
+}

DDrawCompat/CompatGdiWinProc.cpp

@@ -0,0 +1,61 @@
+#define WIN32_LEAN_AND_MEAN
+
+#include <Windows.h>
+
+#include "CompatGdi.h"
+#include "CompatGdiDc.h"
+#include "CompatGdiWinProc.h"
+#include "DDrawLog.h"
+
+namespace
+{
+	void eraseBackground(HWND hwnd, HDC dc);
+
+	LRESULT CALLBACK callWndRetProc(int nCode, WPARAM wParam, LPARAM lParam)
+	{
+		if (HC_ACTION == nCode)
+		{
+			auto ret = reinterpret_cast<CWPRETSTRUCT*>(lParam);
+			if (WM_ERASEBKGND == ret->message)
+			{
+				if (0 != ret->lResult)
+				{
+					eraseBackground(ret->hwnd, reinterpret_cast<HDC>(ret->wParam));
+				}
+			}
+			else if (WM_WINDOWPOSCHANGED == ret->message)
+			{
+				CompatGdi::invalidate();
+			}
+			else if (WM_VSCROLL == ret->message || WM_HSCROLL == ret->message)
+			{
+				InvalidateRect(ret->hwnd, nullptr, TRUE);
+			}
+		}
+
+		return CallNextHookEx(nullptr, nCode, wParam, lParam);
+	}
+
+	void eraseBackground(HWND hwnd, HDC dc)
+	{
+		if (CompatGdi::beginGdiRendering())
+		{
+			HDC compatDc = CompatGdiDc::getDc(dc);
+			if (compatDc)
+			{
+				SendMessage(hwnd, WM_ERASEBKGND, reinterpret_cast<WPARAM>(compatDc), 0);
+				CompatGdiDc::releaseDc(dc);
+			}
+			CompatGdi::endGdiRendering();
+		}
+	}
+}
+
+namespace CompatGdiWinProc
+{
+	void installHooks()
+	{
+		const DWORD threadId = GetCurrentThreadId();
+		SetWindowsHookEx(WH_CALLWNDPROCRET, callWndRetProc, nullptr, threadId);
+	}
+}

DDrawCompat/CompatGdiWinProc.h

@@ -0,0 +1,6 @@
+#pragma once
+
+namespace CompatGdiWinProc
+{
+	void installHooks();
+}