Fix the white line

Windows/MainWindow.cpp

@@ -179,7 +179,7 @@ namespace MainWindow
 
 		WNDCLASSEX wcdisp;
 		memset(&wcdisp, 0, sizeof(wcdisp));
-		// Display Window
+		// Display Window (contained in main window)
 		wcdisp.cbSize = sizeof(WNDCLASSEX);
 		wcdisp.style = CS_HREDRAW | CS_VREDRAW;
 		wcdisp.lpfnWndProc = (WNDPROC)DisplayProc;
@@ -730,6 +730,37 @@ namespace MainWindow
 		return 0;
 	}
 
+	RECT MapRectFromClientToWndCoords(HWND hwnd, const RECT & r)
+	{
+		RECT wnd_coords = r;
+
+		// map to screen
+		MapWindowPoints(hwnd, NULL, reinterpret_cast<POINT *>(&wnd_coords), 2);
+
+		RECT scr_coords;
+		GetWindowRect(hwnd, &scr_coords);
+
+		// map to window coords by substracting the window coord origin in
+		// screen coords.
+		OffsetRect(&wnd_coords, -scr_coords.left, -scr_coords.top);
+
+		return wnd_coords;
+	}
+
+	RECT GetNonclientMenuBorderRect(HWND hwnd)
+	{
+		RECT r;
+		GetClientRect(hwnd, &r);
+		r = MapRectFromClientToWndCoords(hwnd, r);
+		int y = r.top - 1;
+		return {
+			r.left,
+			y,
+			r.right,
+			y + 1
+		};
+	}
+
 	LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)	{
 		LRESULT darkResult = 0;
 		if (UAHDarkModeWndProc(hWnd, message, wParam, lParam, &darkResult)) {
@@ -759,6 +790,26 @@ namespace MainWindow
 			}
 			break;
 
+		// Hack to kill the white line underneath the menubar.
+		// From https://stackoverflow.com/questions/57177310/how-to-paint-over-white-line-between-menu-bar-and-client-area-of-window
+		case WM_NCPAINT:
+		case WM_NCACTIVATE:
+		{
+			if (!IsDarkModeEnabled() || IsIconic(hWnd)) {
+				return DefWindowProc(hWnd, message, wParam, lParam);
+			}
+
+			auto result = DefWindowProc(hWnd, message, wParam, lParam);
+			// Paint over the line with pure black. Could also try to figure out the dark theme color.
+			HDC hdc = GetWindowDC(hWnd);
+			RECT r = GetNonclientMenuBorderRect(hWnd);
+			HBRUSH red = CreateSolidBrush(RGB(0, 0, 0));
+			FillRect(hdc, &r, red);
+			DeleteObject(red);
+			ReleaseDC(hWnd, hdc);
+			return result;
+		}
+
 		case WM_GETMINMAXINFO:
 			{
 				MINMAXINFO *minmax = reinterpret_cast<MINMAXINFO *>(lParam);
@@ -814,7 +865,7 @@ namespace MainWindow
 
 		case WM_ERASEBKGND:
 			// This window is always covered by DisplayWindow. No reason to erase.
-			return 1;
+			return 0;
 
 		case WM_MOVE:
 			SavePosition();

Windows/W32Util/DarkMode.cpp

@@ -158,6 +158,9 @@ LRESULT DarkModeDlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam) {
 	return FALSE;
 }
 
+bool IsDarkModeEnabled() {
+	return g_darkModeEnabled;
+}
 
 constexpr bool CheckBuildNumber(DWORD buildNumber)
 {
@@ -182,7 +185,6 @@ void InitDarkMode()
 			HMODULE hUxtheme = LoadLibraryExW(L"uxtheme.dll", nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
 			if (hUxtheme)
 			{
-
 				_OpenNcThemeData = reinterpret_cast<fnOpenNcThemeData>(GetProcAddress(hUxtheme, MAKEINTRESOURCEA(49)));
 				_RefreshImmersiveColorPolicyState = reinterpret_cast<fnRefreshImmersiveColorPolicyState>(GetProcAddress(hUxtheme, MAKEINTRESOURCEA(104)));
 				_GetIsImmersiveColorUsingHighContrast = reinterpret_cast<fnGetIsImmersiveColorUsingHighContrast>(GetProcAddress(hUxtheme, MAKEINTRESOURCEA(106)));

Windows/W32Util/DarkMode.h

@@ -104,6 +104,7 @@ void InitDarkMode();
 bool AllowDarkModeForWindow(HWND hWnd, bool allow);
 void RefreshTitleBarThemeColor(HWND hWnd);
 bool IsColorSchemeChangeMessage(LPARAM lParam);
+bool IsDarkModeEnabled();
 
 void DarkModeInitDialog(HWND hDlg);
 LRESULT DarkModeDlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam);

Windows/W32Util/UAHMenuBar.cpp

@@ -38,7 +38,6 @@ bool UAHDarkModeWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam, L
 		}
 
 		DrawThemeBackground(g_menuTheme, pUDM->hdc, MENU_POPUPITEM, MPI_NORMAL, &rc, nullptr);
-
 		return true;
 	}
 	case WM_UAHDRAWMENUITEM: