Guarantees of order of X events vs requests

[Maarten Maathuis]

On Wed, Oct 20, 2010 at 11:34 AM, Eirik Byrkjeflot Anonsen
<eirik at opera.com> wrote:
> What guarantees does X give when it comes to the order of events
> generated in relation to processing of the requests sent by the client?
>
> (Also, of course: To which degree does various implementations of X
> actually fulfill these guarantees?)
>
>
> Some specific questions:
>
> X events have a "serial" value.  I expect that any event delivered by X
> will reflect the state after the request number "serial" (and all
> preceding requests) have been processed.  Is this correct?
>
> Can I also assume that the X event will reflect the state before any
> requests with a later serial number is processed?
>
> (And I assume that "serial" is monotonically increasing, except on
> wrap-arounds...)

I think the ordering is kept for obvious reasons, but you don't know
when you'll see the result.

>
>
>
> Context:
>
> Given an application that frequently performs a sequence of XCopyArea()
> calls on the contents of a window.  When this application receives
> Expose events or GraphicsExpose events, it is necessary for the
> application to know exactly which XCopyArea calls have taken effect to
> be able to correctly calculate which area of the window has become
> invalid.

I think you are supposed to draw the entire area that is exposed. If
that is too costly, maybe render to a backbuffer and copy to the
window.

Just my two cents.

>
>
> eirik
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