til_threads: propagate threaded til_fb_fragment.zeroed

Currently when a threaded renderer performed
til_fb_fragment_zero() in render_fragment() vs. prepare_frame(),
the til_fb_fragment.zeroed maintenance would stay isolated to the
ephemeral fragment generated by the fragmenter.

With this commit, when all ephemeral fragments rendered in a
threaded fashion for a given frame returned a set .zeroed member,
the outer frame's .zeroed member gets set.

This should enable proper threaded zeroing of the frame in
render_fragment().

Note that since it's careful to actually count the number of
zeroed ephemeral subfragments and only propagates when that count
matches the number of subfragments rendered in the entire frame,
it's also supported to use til_fb_fragment_zero() conditionally
on just some fragments while not zeroing others and the entire
frame will not get its .zeroed member set.  Imagine a renderer
which randomly zeroes out some fragments, while drawing into
others, this will be honored as a non-zeroed frame on the whole.

0 files changed, 0 insertions, 0 deletions