[PATCH] wined3d: Use query buffer objects for occlusion queries.

[Henri Verbeet]

On 6 September 2018 at 20:37, Andrew Wesie <awesie at gmail.com> wrote:
> On Thu, Sep 6, 2018 at 9:46 AM, Henri Verbeet <hverbeet at gmail.com> wrote:
>>
>> While at least for occlusion queries this would be a very unlikely
>> result, it's not in general an invalid query result. I think ideally
>> we'd write QUERY_RESULT_AVAILABLE to the buffer object as well, but
>> based on the language in the extension spec, I don't see the
>> requirement that that should flush lifted. On the other hand, based on
>> a quick look at the Mesa source, it's not obvious to me that it
>> actually does flush. Perhaps this is ok in practice, and just an
>> oversight in the spec language.
>>
>
> We could do something closer to "Example 2" in ARB_query_buffer_object spec.
> At a high level:
>  - after glEndQuery, query on both GL_QUERY_RESULT_AVAILABLE and
> GL_QUERY_RESULT_NO_WAIT

The issue I see with that example is that I think there's a potential
race condition there, although it probably won't race in practice
because of driver internals. I.e., consider the result of the query
becoming available between retrieving QUERY_RESULT_AVAILABLE and
QUERY_RESULT_NO_WAIT. On the other hand, if we were to retrieve
QUERY_RESULT_AVAILABLE first, the application thread may read it
before we retrieve QUERY_RESULT_NO_WAIT. It may still be possible to
make it work somehow though.