ARB/EXT_timer_query's definition of GL_TIME_ELAPSED match precisely the
subtraction of two GL_TIMESTAMP queries.
And for a lot of drivers, that's precisely how they have to implement
internally -- by emitting two hardware timestamp queries.
So, to simplify driver implementation, simply allow doing so in the state
tracker.
Eventually if no driver implements PIPE_QUERY_TIME_ELAPSED then we could
retire it.
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
José Fonseca
3160b0b9fc