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

[Thomas Hellstrom]

On 09/18/2017 12:43 PM, Eric Anholt wrote:
> 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.

Given that this is actually what's happening (Keithp thinks that's not 
really the case), I think
finding and changing all potentially affected piglit tests is really not 
worth the effort.

/Thomas