Questions about XPresent

[Po Lu]

Michel Dänzer <michel.daenzer at mailbox.org> writes:

> You don't need to do anything special. The effect of PresentPixmap is
> essentially the same as XCopyArea as far as the destination window
> contents are concerned, regardless of how the presentation is
> effectively performed.

Thanks.

> The problem with this is that there's no explicit transfer of
> ownership of the window pixmap between the compositor and other
> entities. So the compositor may end up reading from a stale window
> pixmap after another presentation has already flipped in a new pixmap,
> and the client may already be drawing a new frame to the pixmap used
> by the compositor, resulting in visual artifacts.

If the compositor issues a Composite request, then by the time the
request arrives on the X server, won't the pixmap resource point to the
data of the pixmap that is currently busy?  Or are you saying that the X
server keeps references to pixmap data that it has sent IdleNotify
events for, and may use those pixmaps in response to a future request
from the compositor?

Thanks.