film_grain: implement film grain synthesis

This is using a slightly adapted version of my GPU-based algorithm. The
major difference to the algorithm suggested by the spec (and implemented
in libaom) is that instead of using a line buffer to hold the previous
row's film grain blocks, we compute each row/block fully independently.

This opens up the door to exploit parallelism in the future, since we
don't have any left->right or top->down dependency except for the PRNG
state. (Which we could pre-compute for a massively parallel / GPU
implementation)

That being said, it's probably somewhat slower than using a line buffer
for the serial / single CPU case, although most likely not by much
(since the areas with the most redundant work get progressively smaller,
down to a single 2x2 square for the worst case).

1 files changed, 1 insertions, 0 deletions

diff --git a/include/dav1d/dav1d.h b/include/dav1d/dav1d.h
index 7179e6c..5bf7a2b 100644
--- a/include/dav1d/dav1d.h
+++ b/include/dav1d/dav1d.h
@@ -45,6 +45,7 @@ typedef struct Dav1dSettings {
     int n_frame_threads;
     int n_tile_threads;
     Dav1dPicAllocator allocator;
+    int apply_grain;
 } Dav1dSettings;
 
 /**