[Mesa-dev] [PATCH] st/dri: Add an option to always request a front buffer from the loader

[Eric Anholt]

Thomas Hellstrom <thellstrom at vmware.com> writes:

> When an application decides to read from the front buffer of a window,
> typically a fake front is created and initialized with the real front window
> contents. However, if there was a window manager reparenting operation between
> the last swapbuffer and the read the real front window contents would be
> invalid. This hurts piglit applications that read from the front.
>
> So add an option to always request a front buffer from the dri loader. This
> makes the fake front initialization typically happen before any drawing- or
> swapbuffer operations take place and, as a result, piglit results from tests
> that read from the frontbuffer become robust with dri3.
> While there is a memory usage overhead with this option enabled, the
> performance overhead with dri3 should be minimal.
>
> With dri2 the situation is different and require more work.

Instead of hacking the GL driver to have a special path for these tests,
could we make those piglit tests loop and try again when they get a
failure but have an expose event pending?  That should work for everyone
and handle the race properly.
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