Re: SetLayeredWindowAttributes()?

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 19 Sep 2008 14:14:42 -0400

Message-ID:

<eTAgXOoGJHA.3576@TK2MSFTNGP06.phx.gbl>

Vincent Fatica <vince@blackholespam.net> wrote:

The docs say: "once SetLayeredWindowAttributes has been called for a
layered window, subsequent UpdateLayeredWindow calls will fail until
the layering style bit is cleared and set again".

That seems pretty straightforward, but I find that I can freely make
a layered window (text with alpha, transparent background) "blink"
with code like that below and without explicitly touching the
layering style bit.

case WM_TIMER :
if ( wParam == FLASH_TIMER )
{
if ( pOSD->bToggle )
SetLayeredWindowAttributes(hWnd, CR_BACK, 0,
LWA_COLORKEY | LWA_ALPHA);
else
SetLayeredWindowAttributes(hWnd, CR_BACK, pOSD->alpha,
LWA_COLORKEY | LWA_ALPHA);
pOSD->bToggle = !pOSD->bToggle;
}

Though I haven't checked the return value,
SetLayeredWindowAttributes() does not seem to be failing.

The documentation you quoted doesn't say anything about
SetLayeredWindowAttributes failing. It promises that UpdateLayeredWindow
calls will fail. But you don't make any.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925