Re: [perl-win32-gui-users] Solution: flicker in Win32::GUI

[Steve P. <st...@ba...>]

Hi Jez,

What you said about WM_ERASEBKGND is true, but the results are similar to
setting WS_CLIPCHILDREN. If you block WM_ERASEBKGND messages in the
NEM_WindowMsgLoop function in GUI_MessageLoops.cpp by adding something like:

if(uMsg == WM_ERASEBKGND) return (LRESULT)1;

You get huuuge amounts of streaking whenever anything is painted (obviously,
because the background-erase is there so that this doesnt happen).

That link is interesting, I'll give it a try.

Thanks,

Steve

----- Original Message ----- 
From: "Jeremy White" <jez...@ho...>
To: <st...@ba...>; <per...@li...>
Sent: Sunday, November 16, 2003 5:16 PM
Subject: Re: [perl-win32-gui-users] Solution: flicker in Win32::GUI


> >From: "Steve Pick" <st...@ba...>
> >I've recently been looking into the flickering resize in win32::gui. The
> >most compatible solution to this I've found is extremely (and very
> >annoyingly) simple. Just add the style WS_CLIPCHILDREN to your window or
> >dialog box.
>
> Steve,
>
> I've just tried this and it works...Well, sort of:) On XP, any window
behind
> the window being resized tear as they are redrawn. Also, for some reason
> there seems to be a delay in some of the events to any window with
> WS_CLIPCHILDREN set (!?). In my case, it means I can't use WS_CLIPCHILDREN
> which is a shame since the application looks and feels so *much* better
> without the flicker.
>
> Doing a little searching I came across this page
> http://www.catch22.org.uk/tuts/flicker.asp
>
> ===========
> WM_ERASEBKGND
> The prime suspect is usually the WM_ERASEBKGND message. This message is
sent
> to a window when it's background needs to be erased. This happens because
> windows are usually painted using a 2-stage process:
>
> WM_ERASEBKGND: Clear the background
> WM_PAINT: Draw the contents on top
>
> ....
>
> Right then, how do we avoid erasing the background of a window? There are
> two methods.
>
> Set the window's background brush to NULL. (Set the hbrBackground member
of
> the WNDCLASS structure to zero when you register the window class).
> Return non-zero in the WM_ERASEBKGND message handler.
> Any one of these will steps will prevent the WM_ERASEBKGND message from
> clearing the window. The last option is usually easiest to implement:
>
> case WM_ERASEBKGND:
>     return 1;
> It is also possible to prevent WM_ERASEBKGND when you invalidate and
update
> a window. The InvalidateRect API call's last parameter specifies whether
or
> not a portion of a window is to have it's background erased when it is
next
> redrawn. Specifying FALSE for this paramter prevents WM_ERASEBKGND from
> being sent when the window is redrawn.
>
> InvalidateRect(hwnd, &rect, FALSE);
>
> ============
>
> I've no idea how to write a message handler for WM_ERASEBKGND - any ideas?
> I've played with InvalidateRect in the past but didn't get anywhere fast.
>
> >I tried to implement double-buffering in GUI.xs (I was working with
0.0.558
> >at the time) but frankly I failed.
>
> Have a look at some of the code in this page:
>
> http://www.codeproject.com/gdi/flickerfree.asp
>
> "This article presents a class called CMemDC that encapsulates most of the
> issues associated with writing to off-screen buffers. Adding CMemDC to an
> existing application or MFC Active X control is nearly trivial.
>
> Modifying an MFC Application to use CMemDC
> Add the file memdc.h in your project.
> Add the line #include "memdc.h" to stdafx.h.
> Add a windows message handler for WM_ERASEBKGND. "
>
> Would it be hard to incorporate it into GUI.xs somehow? The code is
> opensource.
>
> Cheers,
>
> jez.
>
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