Stoitcho
Thu Feb 26 14:30:43 CST 2004
Hi folks,
Yes, that is what I found. I hadn't seen the flickering before because my
form was too small.
However, this is true. The flickering occures when the underlaying window is
switched to "layered mode". Actually it flickers even if you set alpha to
255 (fully opaque).
Switching to layered mode involves three steps.
1. Checking the os version - it has to be NT 5 or latter
2. Set WS_EX_LAYERED window style
3. SetWindowLayeredAttributes this method is not defined in user32.dll for
versions before Win2k that's why first step is necessary.
When a Windows Forms control is created it is not a layered window. And it
switches to this mode when set the opacity to some value less then 1.
So my solution is to switch to layered mode in some early stage of the form
life. As soon as the form is created before to become visible. Otherwise
we'll see the flickering.
Javier is completely correct that the layered window has to be fully
redrawn. But it goes only when the window (form) resizes. You can still
invalidate some portions of the form and it will works how ot supposed to
work.
Layered window could even show better performance in some situations.
How internaly layered windows work is all painting is redirected to
off-screen buffer and when the painting's done alpha blending is applied to
the resulting picture and the result is drawn on the screen. This of course
is done internaly in windows and it uses the video card hardware support for
alpha blending if it has any.
Becuse all winodw is double buffered Windows doesn't send WM_PAINT when the
form is moved for example or when some part of the form is uncovered. In
such cases Windows uses double buffered image.
When children control is moved on the form it updates as much as it is
necessary. So the performance hit is not so big.
Anyway, my first solution that I was planning to post involved P\Invoke and
calling all API functions necessary to switch to "layered mode", but then I
found that if one set Opacity to value less then 1 and then return it back
to 1 the form class doesn't switch to the "normal mode" and leave the window
layered.
So the easiest way to get rid if this flickering is by overriding
OnControlCreated method and adding the following two lines:
this.Opacity = 0.9;
this.Opacity = 1;
No more flickering.
--
HTH
B\rgds
100
"Javier Campos" <jcl.remove.this@vmslabs.andthis.com> wrote in message
news:e3yxcvJ$DHA.2180@TK2MSFTNGP09.phx.gbl...
> The problem comes when the window is converted internally from a standard
> window to a layered window (when alpha is not 100%). That causes a window
> repainting depending on your videocard drivers. to correct this and make
it
> work for all computers, just make alpha "almost-opaque" from the start, so
> the window will be a layered window all the time. That'll make the
updating
> of the window slow if it's too big (layered windows need to be updated
> completely, and won't allow invalidating regions, like standard windows
do),
> but it'll definitely do the trick and prevent the flickering from
happening.
>
> Hope this helps,
>
> Javier Campos
>
> "mdjhome@invalid.com" <anonymous@discussions.microsoft.com> escribió en el
> mensaje news:EC30139B-9886-4E5B-935B-77D98044F1DE@microsoft.com...
> > Greetings,
> >
> > Having a bit of a problem with a fade out on a form. I'm using a timer
> which is enabled via a button and then this timer tick then takes the
> opacity down to nothing and then eventually closing the application.
> >
> > However, what is happening is that when the button is clicked that
enables
> the timer and thus the first tick, the form goes all black and then then
> repaints to the original form and fades out smoothly. I'm sure that this
> does not occur on the button click event, as I've put the thread to sleep
at
> this point, and verified that it happens upon the first firing of the tick
> event.
> >
> > Here's what I've noticed, this is much worse on forms with many
controls,
> it actually appears if the form rolls into the center leaving the black
> background for just an instant before proceeding normally. Although this
> "rolling" may be an optical illusion.
> >
> > Would appreciate if anyone can assist with getting rid of the
> flicker..........argh... probably something stupid....
> >
> > Private Sub timerFade_Tick(ByVal sender As Object, ByVal e As
> System.EventArgs) Handles timerFade.Tick
> > If Me.Opacity <= 0 Then
> > Me.Close()
> > Else
> > Me.Opacity = Me.Opacity - 0.05
> > End If
> > End Sub
>
>