C# Signature:

[DllImport("user32.dll"), ExactSpelling = true, SetLastError = true)]
static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst,
   ref POINT pptDst, ref SIZE psize, IntPtr hdcSrc, ref POINT pptSrc, uint crKey,
   [In] ref BLENDFUNCTION pblend, uint dwFlags);

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

This blog entry by Mike Swanson includes a downloadable sample called AlphaWindow that calls UpdateLayeredWindow from Windows Forms for a cool alpha blended effect.

http://blogs.msdn.com/mswanson/archive/2005/07/07/436618.aspx

Alternative Managed API:

Do you know one? Please contribute it!