Minimize invalidation on window position changes

DDrawCompat/CompatDirectDrawSurface.cpp

@@ -602,7 +602,7 @@ HRESULT STDMETHODCALLTYPE CompatDirectDrawSurface<TSurface>::Restore(TSurface* T
 			result = RealPrimarySurface::restore();
 			if (wasLost)
 			{
-				CompatGdi::invalidate();
+				CompatGdi::invalidate(nullptr);
 			}
 		}
 	}

DDrawCompat/CompatGdi.cpp

@@ -58,14 +58,33 @@ namespace
 		return nullptr;
 	}
 
-	BOOL CALLBACK invalidateWindow(HWND hwnd, LPARAM /*lParam*/)
+	BOOL CALLBACK invalidateWindow(HWND hwnd, LPARAM lParam)
 	{
+		if (!IsWindowVisible(hwnd))
+		{
+			return TRUE;
+		}
+
 		DWORD processId = 0;
 		GetWindowThreadProcessId(hwnd, &processId);
-		if (processId == GetCurrentProcessId())
+		if (processId != GetCurrentProcessId())
+		{
+			return TRUE;
+		}
+
+		if (lParam)
+		{
+			POINT origin = {};
+			ClientToScreen(hwnd, &origin);
+			RECT rect = *reinterpret_cast<const RECT*>(lParam);
+			OffsetRect(&rect, -origin.x, -origin.y);
+			RedrawWindow(hwnd, &rect, nullptr, RDW_ERASE | RDW_FRAME | RDW_INVALIDATE | RDW_ALLCHILDREN);
+		}
+		else
 		{
 			RedrawWindow(hwnd, nullptr, nullptr, RDW_ERASE | RDW_FRAME | RDW_INVALIDATE | RDW_ALLCHILDREN);
 		}
+
 		return TRUE;
 	}
 
@@ -237,9 +256,9 @@ namespace CompatGdi
 		}
 	}
 
-	void invalidate()
+	void invalidate(const RECT* rect)
 	{
-		EnumWindows(&invalidateWindow, 0);
+		EnumWindows(&invalidateWindow, reinterpret_cast<LPARAM>(rect));
 	}
 
 	void updatePalette()
@@ -257,7 +276,7 @@ namespace CompatGdi
 
 			if (0 != memcmp(usedPaletteEntries, g_usedPaletteEntries, sizeof(usedPaletteEntries)))
 			{
-				invalidate();
+				invalidate(nullptr);
 			}
 		}
 	}

DDrawCompat/CompatGdi.h

@@ -45,6 +45,6 @@ namespace CompatGdi
 	}
 
 	void installHooks();
-	void invalidate();
+	void invalidate(const RECT* rect);
 	void updatePalette();
 };

DDrawCompat/CompatGdiWinProc.cpp

@@ -1,5 +1,7 @@
 #define WIN32_LEAN_AND_MEAN
 
+#include <unordered_map>
+
 #include <dwmapi.h>
 #include <Windows.h>
 
@@ -12,9 +14,13 @@
 
 namespace
 {
+	std::unordered_map<HWND, RECT> g_prevWindowRect;
+
 	void disableDwmAttributes(HWND hwnd);
 	void eraseBackground(HWND hwnd, HDC dc);
 	void ncPaint(HWND hwnd);
+	void onWindowPosChanged(HWND hwnd);
+	void removeDropShadow(HWND hwnd);
 	void updateScrolledWindow(HWND hwnd);
 
 	LRESULT CALLBACK callWndRetProc(int nCode, WPARAM wParam, LPARAM lParam)
@@ -25,6 +31,12 @@ namespace
 			if (WM_CREATE == ret->message)
 			{
 				disableDwmAttributes(ret->hwnd);
+				removeDropShadow(ret->hwnd);
+			}
+			else if (WM_DESTROY == ret->message)
+			{
+				CompatGdi::GdiScopedThreadLock lock;
+				g_prevWindowRect.erase(ret->hwnd);
 			}
 			else if (WM_ERASEBKGND == ret->message)
 			{
@@ -42,7 +54,7 @@ namespace
 			}
 			else if (WM_WINDOWPOSCHANGED == ret->message)
 			{
-				CompatGdi::invalidate();
+				onWindowPosChanged(ret->hwnd);
 			}
 			else if (WM_VSCROLL == ret->message || WM_HSCROLL == ret->message)
 			{
@@ -201,6 +213,36 @@ namespace
 		}
 	}
 
+	void onWindowPosChanged(HWND hwnd)
+	{
+		CompatGdi::GdiScopedThreadLock lock;
+
+		const auto it = g_prevWindowRect.find(hwnd);
+		if (it != g_prevWindowRect.end())
+		{
+			CompatGdi::invalidate(&it->second);
+		}
+
+		if (IsWindowVisible(hwnd))
+		{
+			GetWindowRect(hwnd, it != g_prevWindowRect.end() ? &it->second : &g_prevWindowRect[hwnd]);
+			RedrawWindow(hwnd, nullptr, nullptr, RDW_ERASE | RDW_FRAME | RDW_INVALIDATE | RDW_ALLCHILDREN);
+		}
+		else if (it != g_prevWindowRect.end())
+		{
+			g_prevWindowRect.erase(it);
+		}
+	}
+
+	void removeDropShadow(HWND hwnd)
+	{
+		const auto style = GetClassLongPtr(hwnd, GCL_STYLE);
+		if (style & CS_DROPSHADOW)
+		{
+			SetClassLongPtr(hwnd, GCL_STYLE, style ^ CS_DROPSHADOW);
+		}
+	}
+
 	void updateScrolledWindow(HWND hwnd)
 	{
 		RedrawWindow(hwnd, nullptr, nullptr, RDW_ERASE | RDW_FRAME | RDW_INVALIDATE);