[Wayland-bugs] [Bug 727452] Wayland windows with non-trivial alpha get new content drawn over old

[gtk+ (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=727452
  gtk+ | Backend: Wayland | 3.12.x

Benjamin Otte (Company) <otte> changed:

           What    |Removed                     |Added
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                 CC|                            |otte at gnome.org

--- Comment #13 from Benjamin Otte (Company) <otte at gnome.org> 2014-04-03 00:43:43 UTC ---
That's because the behavior is specific to reusing surfaces. And in mutter and
pixman-weston, the compositor doesn't release the surface immediately so GDK
marks it as busy and falls back to the way we do it in X by using a similar
surface.

I believe regular weston releases the buffer pretty much immediately (as its
contents are uploaded to a GL texture). So GDK reuses the buffer and because it
isn't cleared, the bug happens.

I'm not sure memsetting the whole buffer is correcct for the cases where we
only redraw parts of the window. 
Also, if we wonder about performance, CAIRO_OPERATOR_CLEAR'ing its cairo
surface should be faster as cairo has optimizations for cleared surfaces.


I think the problem is that we have no definition inside GDK if begin_paint
clears the cairo surface or returns a cairo surface with undefined contents.

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