In the December 2005 column of the MSDN magazine Paul DiLascia explained how to create a so called "layered" window which is transparent and passes mouse events through itself. It turned out an easy thing to do and I wrote a WTL class that I called (surprisingly)
One remark though - code presented here will work only on Windows 2000 and higher.
To create a visible-through (layered) window, we need to set the extended style
WS_EX_LAYERED, and to make the window clicked-through, we need the
WS_EX_TRANSPARENT extended style. This is done with the
SetWindowLong() API function or the
ModifyStyleEx() function of the
CWindow class. Then, we can use the
SetLayeredWindowAttributes() API function to set the opacity and transparency of a layered window. To reverse the transparency, remove the
But let me warn you that setting the
WS_EX_TRANSPARENT attribute affects the entire window: the user can't close the window using the 'x' button, select it with the mouse, or select any controls on the window. The application can still close the window programmatically. Microsoft recommends using the
WS_EX_TRANSPARENT style for modal windows that have a short life.
Using the code
- Derive your class from
CLayered, like so:
class CMainDlg : public CDialogImpl<CMainDlg>,
- Then somewhere in your code, modify your window style:
- And set the transparency of the window. If necessary, call:
BOOL MakeTransparent(int nOpacity)
nOpacity describes the opacity of the layered window. 0 means the window is completely transparent, 255 means the window is opaque.
- Minimum operating system required - Windows 2000.
- Demo project was created with Visual Studio 2005, but it does not contain any VS2005 specific features so it would not be a problem to re-create it on a different version of the Visual Studio - just create an empty WTL project and add all the source files.
- Demo project was tested on Windows XP Pro SP2.
- November 20, 2005 - initial release.