XWindows - how capture window ?

[Micha]

ב-13/03/2010, בשעה 13:03, Valery Reznic <valery_reznic at yahoo.com>  
כתב/ה:

> OK, I found something interesting.
> It's turn out that for some reason on-screen rendering is a problem  
> too.
>
> Greatly oversimplified description of my application:
> There is a mai windows with 2 buttons ('A', and 'B')
> When buttons 'A' pressed Windows 'W' (with a lot of child windows)  
> created and shown on the screen. It's done with function 'callback_A'
>
> When I press button 'B' I want following to happened:
> 1. Window 'W" created, like it was created, when button 'A' pressed
> 2. Window 'W" content is captured.
>
> So I have callback_B like this:
> void callback_B()
> {
>    callback_A(); // create Window 'W'
>    capture_window();
> }
>

Problem is, like you stated that you to wait for all the drawing  
callbacks to finish

The best approach for such a thing is to post and event to do the  
capture that will go on the queue after the draw events and then  
process the capture in that callback

> So far so good. The only trouble is that requests sent to XServer in  
> the function callback_A have no chance to be processed before call  
> to capture_window() function, because application does not retirned  
> to it's main application loop, which process events.
> To get XServer chance to process events callback_B was modified as  
> following:
>
> void callback_B()
> {
>    callback_A(); // create Window 'W'
>    handle_events();
>    capture_window();
> }
>
> Where handle_events looks like:
> void handle_events()
> {
>   XFlush(display);
>   XSync(display, False);
>
>     while (XtAppPending(appContext))
>     {
>       XtAppProcessEvent(appContext,Mask );
>   }
> }
>
> This functions used in this application in other cases when events  
> should be handled and it's works OK.
> But in this case, Window 'W' was only partially drawn.
>
> I found workaround modifie callback_B
> void callback_B()
> {
>    callback_A(); // create Window 'W'
>    handle_events();
>
>    usleep(100000);
>    handle_events();
>
>    capture_window();
> }
>
> After some sleep and addition handle_events call Window 'W' rendered  
> on screen as expected.
>
> But I don't why first approach didn't work.
> From the XSync man page:
> --- 
> ----------------------------------------------------------------------
>       The XSync function flushes the output buffer and then waits  
> until all
>       requests have been received and processed by the X server.   
> Any errors
>       generated must be handled by the error handler.  For each  
> protocol
>       error received by Xlib, XSync calls the client application’s e 
> rror han-
>       dling routine (see section 11.8.2).  Any events generated by  
> the server
>       are enqueued into the library’s event queue.
> -------------------------------------------------------------------
> So it's looks like XSync alone should do the job.
> Obviously it was not - and it was a reason, that event_handle  
> function was written.
>
> What I did with sleep and two calls to even_handle is work, but it's  
> ugly.
> Anyone has idea why XSync alone is not enough and how I can wait to  
> all requests to be processed by XServer ?
>
> Regards,
> Valery.
>
>
> --- On Sun, 3/7/10, Nadav Har'El <nyh at math.technion.ac.il> wrote:
>
>> From: Nadav Har'El <nyh at math.technion.ac.il>
>> Subject: Re: XWindows - how capture window ?
>> To: "Erez D" <erez0001 at gmail.com>
>> Cc: "Valery Reznic" <valery_reznic at yahoo.com>, "linux-il." <linux-il at cs.huji.ac.il 
>> >
>> Date: Sunday, March 7, 2010, 10:38 AM
>> On Thu, Mar 04, 2010, Erez D wrote
>> about "Re: XWindows - how capture window ?":
>>> composite window managers (i.e. compiz, baryl) work by
>> drawing the original
>>> window off screen, then read it as a 2D picture, and
>> render it back to the
>>> screen with certain effects.
>>> So i know it is possible to grab an off screen window.
>> I do not know however
>>> how to make it off screen.
>>
>> This is done using the "Composite" extension. See
>> http://www.freedesktop.org/wiki/Software/CompositeExt
>>
>> But please note that all these "extensions", as their title
>> implies, are
>> not available in every installation of X. The "right way"
>> to use them is
>> to use them when they're available, but fall back to some
>> slower or uglier
>> alternative when they aren't.
>>
>>> There is an X Extension called XDamage, which reports
>> changes on the window
>>> so you do not have to poll it for changes. These
>> window managers use it.
>>
>> Right. http://www.freedesktop.org/wiki/Software/XDamage
>>
>>
>> -- 
>> Nadav Har'El
>>             |
>>     Sunday, Mar  7 2010, 21 Adar 5770
>> nyh at math.technion.ac.il
>>
>>    |-----------------------------------------
>> Phone +972-523-790466, ICQ 13349191 |Business jargon is the
>> art of saying
>> http://nadav.harel.org.il
>>    |nothing while appearing to say a lot.
>>
>
>
>
>
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