Fix obmc chroma prediction involving neighboring sub8x8 blocks' mvs

When the neighbor uses a sub8x8 partition, to predict chroma pixels in
the overlapping region, instead of averaging all mvs in the 8x8 block,
only apply those belonging to neighboring sub8x8 parts to the
corresponding sub-regions (no averaging).
The change applies to both settings w/ and w/o SUB8X8_MC experiment.

Change-Id: I033e9f218d02bc9879841b794931b575fac14f25

av1/common/reconinter.c

@@ -69,6 +69,7 @@ void build_inter_predictors(MACROBLOCKD *xd, int plane,
   struct macroblockd_plane *const pd = &xd->plane[plane];
 #if CONFIG_MOTION_VAR
   const MODE_INFO *mi = xd->mi[mi_col_offset + xd->mi_stride * mi_row_offset];
+  const int build_for_obmc = !(mi_col_offset == 0 && mi_row_offset == 0);
 #else
   const MODE_INFO *mi = xd->mi[0];
 #endif  // CONFIG_MOTION_VAR
@@ -76,7 +77,11 @@ void build_inter_predictors(MACROBLOCKD *xd, int plane,
   int ref;
 
 #if CONFIG_SUB8X8_MC
+#if CONFIG_MOTION_VAR
+  if (mi->mbmi.sb_type < BLOCK_8X8 && plane > 0 && !build_for_obmc) {
+#else
   if (mi->mbmi.sb_type < BLOCK_8X8 && plane > 0) {
+#endif  // CONFIG_MOTION_VAR
     // block size in log2
     const int b4_wl = b_width_log2_lookup[mi->mbmi.sb_type];
     const int b4_hl = b_height_log2_lookup[mi->mbmi.sb_type];
@@ -162,7 +167,12 @@ void build_inter_predictors(MACROBLOCKD *xd, int plane,
     struct buf_2d *const dst_buf = &pd->dst;
     uint8_t *const dst = dst_buf->buf + dst_buf->stride * y + x;
     const MV mv = mi->mbmi.sb_type < BLOCK_8X8
+#if CONFIG_MOTION_VAR
+                      ? (build_for_obmc ? mi->bmi[block].as_mv[ref].as_mv
+                                        : average_split_mvs(pd, mi, ref, block))
+#else
                       ? average_split_mvs(pd, mi, ref, block)
+#endif  // CONFIG_SUB8X8_MC && CONFIG_MOTION_VAR
                       : mi->mbmi.mv[ref].as_mv;
 
     // TODO(jkoleszar): This clamping is done in the incorrect place for the
@@ -526,20 +536,19 @@ void av1_build_prediction_by_above_preds(const AV1_COMMON *cm, MACROBLOCKD *xd,
         const PARTITION_TYPE bp = BLOCK_8X8 - mbmi->sb_type;
         const int have_vsplit = bp != PARTITION_HORZ;
         const int have_hsplit = bp != PARTITION_VERT;
-        const int num_4x4_w = 2 >> ((!have_vsplit) | pd->subsampling_x);
-        const int num_4x4_h = 2 >> ((!have_hsplit) | pd->subsampling_y);
-        const int pw = 8 >> (have_vsplit | pd->subsampling_x);
+        const int num_4x4_w = 2 >> (!have_vsplit);
+        const int num_4x4_h = 2 >> (!have_hsplit);
+        const int pw = 8 >> (have_vsplit + pd->subsampling_x);
         int x, y;
 
         for (y = 0; y < num_4x4_h; ++y)
           for (x = 0; x < num_4x4_w; ++x) {
-            if ((bp == PARTITION_HORZ || bp == PARTITION_SPLIT) && y == 0 &&
-                !pd->subsampling_y)
+            if ((bp == PARTITION_HORZ || bp == PARTITION_SPLIT) && y == 0)
               continue;
 
-            build_inter_predictors(xd, j, mi_col_offset, mi_row_offset,
-                                   y * 2 + x, bw, bh, 4 * x, 0, pw, bh, mi_x,
-                                   mi_y);
+            build_inter_predictors(
+                xd, j, mi_col_offset, mi_row_offset, y * 2 + x, bw, bh,
+                (4 * x) >> pd->subsampling_x, 0, pw, bh, mi_x, mi_y);
           }
       } else {
         build_inter_predictors(xd, j, mi_col_offset, mi_row_offset, 0, bw, bh,
@@ -608,20 +617,19 @@ void av1_build_prediction_by_left_preds(const AV1_COMMON *cm, MACROBLOCKD *xd,
         const PARTITION_TYPE bp = BLOCK_8X8 - mbmi->sb_type;
         const int have_vsplit = bp != PARTITION_HORZ;
         const int have_hsplit = bp != PARTITION_VERT;
-        const int num_4x4_w = 2 >> ((!have_vsplit) | pd->subsampling_x);
-        const int num_4x4_h = 2 >> ((!have_hsplit) | pd->subsampling_y);
-        const int ph = 8 >> (have_hsplit | pd->subsampling_y);
+        const int num_4x4_w = 2 >> (!have_vsplit);
+        const int num_4x4_h = 2 >> (!have_hsplit);
+        const int ph = 8 >> (have_hsplit + pd->subsampling_y);
         int x, y;
 
         for (y = 0; y < num_4x4_h; ++y)
           for (x = 0; x < num_4x4_w; ++x) {
-            if ((bp == PARTITION_VERT || bp == PARTITION_SPLIT) && x == 0 &&
-                !pd->subsampling_x)
+            if ((bp == PARTITION_VERT || bp == PARTITION_SPLIT) && x == 0)
               continue;
 
-            build_inter_predictors(xd, j, mi_col_offset, mi_row_offset,
-                                   y * 2 + x, bw, bh, 0, 4 * y, bw, ph, mi_x,
-                                   mi_y);
+            build_inter_predictors(
+                xd, j, mi_col_offset, mi_row_offset, y * 2 + x, bw, bh, 0,
+                (4 * y) >> pd->subsampling_y, bw, ph, mi_x, mi_y);
           }
       } else {
         build_inter_predictors(xd, j, mi_col_offset, mi_row_offset, 0, bw, bh,