Re: minor fix for GdkPixbuf

[Ramiro Estrugo <ramiro fateware com>]

Tim Janik wrote:
> 
> erk. ok two things:
> 1) if you grab the server, mention it in the docu because that makes things
>    slow and people shouldn't use it in a loop. (though it's probably the
>    right way to do things)
> 2) deskguide won't be able to use it for snap-shooting with server grabs.
>    however, i don't see deskguide as enough for a reason to destabelize
>    gdk's common code path, so i'd apprechiate any pointers as to what you
>    improved over deskguide's shooting code, in order to back-merge these
>    things.
> 
>

This is what I had to do with the current gdk_pixbuf_get_from_drawable()
to get it to always work - in a loop amongst other extreme conditions:

http://cvs.gnome.org/lxr/source/eel/eel/eel-gdk-pixbuf-extensions.c#1350

This is evil stuff.  I have some test programs that trigger the race
conditions.  As explained in the code above, I do 2  things to make it
work.  1) handle the X protocol errors and 2) prevent gdk-pixbuf from
doing "smart" clipping - by  "pretending" the GdkWindow is a GdkPixmap,
for which there is not geometry clipping.  This second hack prevents one
type  of race condition, but triggers criticals in
gdk_pixbuf_get_from_drawable().

I tried changing it to grab/ungrab the server before and after.  The
performance change is something you can probably mesure, but not
something you can feel.  However, I still see the x protocol errors
(BadMatch)

I dunno if this is something feasable or not, but one thing you might
consider is having 2 versions of the capture  function.  One that does
"smart" clipping, grabs/ungrabs the servers and is documented to be
slow.  And, another one  doesnt do any smart stuff.  I agree this
complicates the API and can be confusing.  The reason why I did things
in  this hacky way was to reuse the gdk-pixbuf conversion functions. 
Otherwise it would have been simpler to use straight  xlib.

Since gtk widgets are now double buffered, this whole hacky mess might
be moot anyway. 

-re