How to make a transparent and click-through window

Download demo project - 27.6 Kb

Introduction

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) CLayered.

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 WS_EX_LAYERED and WS_EX_TRANSPARENT styles.

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>, 
                public CUpdateUI<CMainDlg>,
                public CMessageFilter, 
                public CIdleHandler,
                CLayered<CMainDlg>

Then somewhere in your code, modify your window style:

// To make a visible-through window
BOOL SetLayered()

// To make a clicked-through window
BOOL SetClickThru()

And set the transparency of the window. If necessary, call:
```
BOOL MakeTransparent(int nOpacity)
```
where nOpacity describes the opacity of the layered window. 0 means the window is completely transparent, 255 means the window is opaque.

Software requirements

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.