[cairo] XDBE

[Keith Packard]

On Tue, 2005-11-22 at 13:03 -0800, Bill Spitzak wrote:

> Another possible better fix is that resizes should copy *into* the 
> backing buffer the current contents of the screen. Then if it 
> accidentally gets swapped back before the program finishes drawing it, 
> the user will not see any change in the undrawn areas.

Composite does this.

> I agree. It would be nice if *all* backing copies went to the same area, 
> no matter how they are created. Ignore any minor glitches (ie I think 
> the composite extension could show partially-updated backbuffer, just 
> try to avoid recompositing except when a program sends the 
> back-buffer-swap command).

Most apps that 'double buffer' do it themselves with a separate pixmap;
it's more portable, and gives reliable results. This makes solving the
DOUBLE-BUFFER case a lot less interesting.

Of course, backing store should be implemented with Composite in any
case; it's far more efficient and follows the protocol specification
correctly (unlike the existing backing store code which saves far too
much).  If we do that, we'll eliminate miles of X server code, and the
separate buffering for backing store as well.

-keith

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