public static void UpdateLayeredWindowHelper(Control control, Bitmap bmp)
{
IntPtr dC = Win32.GetDC(IntPtr.Zero);
Win32.Point point = new Win32.Point(control.Left, control.Top);
Win32.Size size = new Win32.Size(bmp.Width, bmp.Height);
IntPtr intPtr = Win32.CreateCompatibleDC(IntPtr.Zero);
IntPtr hbitmap = bmp.GetHbitmap(Color.Black);
Win32.SelectObject(intPtr, hbitmap);
Win32.Point point2 = new Win32.Point(0, 0);
Win32.BlendFunction blendFunction = default(Win32.BlendFunction);
blendFunction.BlendOp = 0;
blendFunction.BlendFlags = 0;
blendFunction.SourceConstantAlpha = 255;
blendFunction.AlphaFormat = 1;
Win32.UpdateLayeredWindow(control.Handle, dC, ref point, ref size, intPtr, ref point2, 0, ref blendFunction, 2);
Win32.DeleteObject(hbitmap);
Win32.DeleteDC(intPtr);
Win32.ReleaseDC(IntPtr.Zero, dC);
}
public static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Win32.Point pptDst, ref Win32.Size psize, IntPtr hdcSrc, ref Win32.Point pptSrc, int crKey, ref Win32.BlendFunction pblend, int dwFlags);
