Environment: VC6 SP4, Win 2000/Win XP
There are many articles that demonstrate how you can use the new layering features of Windows 2000 or Windows XP to create applications that are translucent. This article adds to that and shows how you can use the same features to turn any application transparent even if you do not have sources for it.
By using this “WinTrans” application, you will be able to select any currently running application and turn it transparent by dragging and dropping the wand (icon at the top-left corner) on the title bar of that application. You can also control the transparency by using the slider. “WinTrans” has an interface very much like SPY and also demonstrates the usage of Win32 APIs to locate a window under the mouse pointer and extract details like the class associated with it, the caption of the window, and so forth.
“WinTrans” comes in handy if you want to work on a maximized window and at the same time keep a watch on some other application running in the background.
In Windows 2000 and Windows XP, a new function named
SetLayeredWindowAttributes has been added to User32.dll. To use this function, an application needs to set the
WS_EX_LAYERED (0x00080000) bit in the window style, either while creating it or later, by using the
SetWindowLong function. Once this bit is set, any application can call this function by passing a handle to a window and making either the whole window or a particular color on the window transparent. This function takes the following arguments:
HWND hWnd:Handle to the window
COLORREF col:Color to be made transparent
BYTE bAlpha:If this value is 0, the window becomes completely transparent; if it is 255, it becomes opaque
DWORD dwFlags:If this flag is 1, only the color
colis made transparent. If it is 2, the whole window becomes transparent as dictated by the
Using the Code
We begin by defining the following member variables of the main dialog class in WinTransDlg.h:
bool m_bTracking; // will be true when the mouse is
// being tracked
HWND m_hCurrWnd; // Handle to the window over which
// the mouse was last present
HCURSOR m_hCursor; // The wand cursor
We also define a function pointer that points to the
SetLayeredWindowAttributes function. This function is defined in the User32.dll.
// Global definition
typedef BOOL (WINAPI *lpfn) (HWND hWnd, COLORREF cr,
BYTE bAlpha, DWORD dwFlags);
OnInitDialog event handler for the dialog, we get the address of the
SetLayeredWindowAttributes function and store it in
g_pSetLayeredWindowAttributes. We also load the wand cursor and store the handle in
// get the function pointer for SetLayeredWindowAttributes
// in User32.dll
HMODULE hUser32 = GetModuleHandle(_T(“USER32.DLL”));
g_pSetLayeredWindowAttributes = (lpfn)GetProcAddress(hUser32,
if (g_pSetLayeredWindowAttributes == NULL)
“Layering is not supported in this version of Windows”,
// Load the wand cursor
HINSTANCE hInstResource = AfxFindResourceHandle(
m_hCursor = ::LoadCursor( hInstResource,
We then define handler for the
WM_MOUSEMOVE events. For the handler for
WM_LBUTTONDOWN, we do the following:
void CWinTransDlg::OnLButtonDown(UINT nFlags, CPoint point)
SetCapture(); // make mouse move events to
// be directed to this window
m_hCurrWnd = NULL; // Currently, no window is to be
// made transparent
m_bTracking = true; // set the tracking flag
::SetCursor(m_hCursor); // turn the mouse pointer into the
// wand cursor
For the mouse move event handler, the following code is used:
void CWinTransDlg::OnMouseMove(UINT nFlags, CPoint point)
// convert mouse coordinates to screen
// get the window at the mouse coords
m_hCurrWnd = ::WindowFromPoint(point);
// Show details of the window like class, caption, etc.
As long as the left mouse button is clicked anywhere inside the main dialog and is not released, the mouse pointer will change into the wand and the details of the window beneath the pointer will be displayed on the WinTrans dialog.
When the button is released, the event handler for
WM_LBUTTONUP is called.
void CWinTransDlg::OnLButtonUp(UINT nFlags, CPoint point)
// stop tracking the mouse
m_bTracking = false;
// If the window under the mouse is not of this application,
// we toggle its layer style flag and apply the alpha as set
// by the slider control
if (g_pSetLayeredWindowAttributes && m_hCurrWnd != m_hWnd)
GWL_EXSTYLE) ^ WS_EX_LAYERED);
::RedrawWindow(m_hCurrWnd, NULL, NULL,
RDW_ERASE | RDW_INVALIDATE |
RDW_FRAME | RDW_ALLCHILDREN);
Points of Interest
This application works correctly only when the wand is dropped on the title bar of another application or on the body of a dialog-based application. If, for example, the wand is dropped on the body of Notepad, it will not work.
To remove the transparent effect, you can simply drag-and-drop the wand again on that application. Because in
OnLButtonUp we toggle the
WS_EX_LAYERED bit, the transparency effect will also be toggled.
TransWand does not work on the command window.