[PATCH xserver 1/3] present: Only update screen pixmap from flip pixmap once per unflip

[Keith Packard]

Michel Dänzer <michel at daenzer.net> writes:

> From: Michel Dänzer <michel.daenzer at amd.com>
>
> present_unflip may be called several times from present_check_flip_window
> during the same unflip. We can only copy to the screen pixmap the first
> time, otherwise we may scribble over other windows. The flip pixmap
> contents don't get updated after the first time anyway.
>
> Fixes at least the following problems, which were introduced by commit
> 806470b9 ("present: Copy unflip contents back to the Screen Pixmap"):
>
> On xfwm4 without compositing, run glxgears and put its window into
> fullscreen mode to start flipping. While in fullscreen, open the xfwm4
> window menu by pressing Alt-Space. The window menu was invisible most
> of the time because it was getting scribbled over by a repeated unflip
> copy.
>
> When switching a flipping window out of fullscreen, a repeated unflip
> copy could leave artifacts of the flip pixmap on the desktop.
>
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>

Reviewed-by: Keith Packard <keithp at keithp.com>

> +    /* Update the screen pixmap with the current flip pixmap contents
> +     * Only do this the first time for a particular unflip operation, or
> +     * we'll probably scribble over other windows
> +     */
> +    if (screen->GetWindowPixmap(screen->root) == screen_priv->flip_pixmap) {
> +        present_copy_region(&pixmap->drawable, screen_priv->flip_pixmap,
> +                            NULL, 0, 0);
> +    }
> +

This removes the check for flip_pixmap && flip_window, but the
flip_pixmap check is not needed as you're checking it against the root
pixmap which is never NULL, and the check for flip_window was redundant
before as it was always set when flip_pixmap was set.

-- 
-keith
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