Possible bug in Composite extension

[Owen Taylor]

On Wed, 2005-01-05 at 19:04 +0100, Amir Bukhari wrote:
> > Please read the earlier mails on this list from Søren Sandmann and
> > followups... just a straight copy doesn't work because
> > of gravity issues.
> >
> 
> I have found the thread, which discussed this issue, but I don't know if
> there is any implementation done. We use Xorg 6.8.0 with LG3D modification.

Nobody has fixed the bug yet. It's hard.

> With the bits copy I have made from the old pixmap to the new pixmap garbage
> content doesn't appear. Another thing Copy one pixmap content to another
> pixmap will not be affected with bit gravity, because bit gravity is related
> to window.

The point is that simply copying the pixmap contents over like that
doesn't
work because the code that moves bits around on the window may need to
access parts that aren't shared between the old and new pixmap.

That is, say you have southwest bit gravity and make a window smaller:

 +---------------+
 |               |             +---------+
 |               |             |         |
 |        XXXXXXX|       =>    |  XXXXXXX|
 |        XXXXXXX|             |  XXXXXXX|
 +----------------             +---------+

If you just copy when creating the new pixmap then you lose the bits
before 
the code has a chance to move the bits to the right place.

Regards,
					Owen

(It's not just gravity, border size changes also can cause problems
here.)
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