public void UpdateBackgroundGraphics(byte opacity)
{
POINT dstPos = new POINT(Left, Top);
SIZE dstSize = new SIZE(Width, Height);
POINT srcPos = POINT.Empty;
BLENDFUNCTION blend = new BLENDFUNCTION(BlendOp.AC_SRC_OVER, opacity, AlphaFormat.AC_SRC_ALPHA);
if (!NativeMethods.UpdateLayeredWindow(new HandleRef(this, Handle), new HandleRef(this, hdcScreen), ref dstPos, ref dstSize,
new HandleRef(this, hdcBackground), ref srcPos, new COLORREF(), ref blend, UlwFlags.ULW_ALPHA))
throw new Win32Exception();
}
public static extern bool UpdateLayeredWindow(HandleRef hwnd, HandleRef hdcDst, [In] ref POINT pptDst, [In] ref SIZE psize,
HandleRef hdcSrc, [In] ref POINT pptSrc, COLORREF crKey, [In] ref BLENDFUNCTION pblend, UlwFlags dwFlags);
