透明背景

case WM_PAINT: {
		printf("HH\n");
		PAINTSTRUCT ps;
		HDC hdc = BeginPaint(hwnd, &ps);

		HBRUSH brush = CreateSolidBrush(0x10000ff); // 1表示透明
		//FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));
		FillRect(hdc, &ps.rcPaint, brush);

		EndPaint(hwnd, &ps);
		return 0;
	}

置顶

HWND mainWnd = CreateWindowEx(
		//0 && WS_EX_TOOLWINDOW | WS_EX_TOPMOST,               // Optional window styles. WS_EX_TOOLWINDOW 隐藏任务栏标签。WS_EX_TOPMOST 置于顶层。已有窗口使用SetWindowPos()修改。
		// WS_EX_TOOLWINDOW可能拖动到系统状态栏，因此置顶
		// WS_EX_TRANSPARENT 忽略消息
		WS_EX_TOPMOST | WS_EX_TRANSPARENT,
		CLASS_NAME,    

);

	SetWindowLong(mainWnd, GWL_EXSTYLE, GetWindowLong(mainWnd, GWL_EXSTYLE) | WS_EX_LAYERED);
	SetLayeredWindowAttributes(mainWnd, RGB(255, 0, 0), 0, LWA_COLORKEY); // CreateSolidBrush(0x1...启用透明
        SetLayeredWindowAttributes(mainWnd, RGB(0, 0, 0), 80, LWA_ALPHA); // 直接设置整个窗口的alpha值