Fix the sub8x8 block inter prediction with scaled reference frame

Sync the encoder's buffer offset calculation for sub8x8 block motion
compensated prediction with scaled reference frame to match the
decoder's behavior. This resolves an enc/dec mismatch issue when
sub8x8 inter mode with scaled is turned on.

Change-Id: I4bab3672b007a5ae0c992f8a701341892d2458b0

diff --git a/vp9/common/vp9_reconinter.c b/vp9/common/vp9_reconinter.c
index f83f8257aa71ec2ad2e54ab34fd5bd227bd30a73..d8c14ecc818bec4833a90f7bc89ef78c576f61b8 100644 (file)
--- a/vp9/common/vp9_reconinter.c
+++ b/vp9/common/vp9_reconinter.c
@@ -187,7 +187,19 @@ static void build_inter_predictors(MACROBLOCKD *xd, int plane, int block,
     const int is_scaled = vp9_is_scaled(sf);
 
     if (is_scaled) {
-      pre = pre_buf->buf + scaled_buffer_offset(x, y, pre_buf->stride, sf);
+      // Co-ordinate of containing block to pixel precision.
+      const int x_start = (-xd->mb_to_left_edge >> (3 + pd->subsampling_x));
+      const int y_start = (-xd->mb_to_top_edge >> (3 + pd->subsampling_y));
+      if (plane == 0)
+        pre_buf->buf = xd->block_refs[ref]->buf->y_buffer;
+      else if (plane == 1)
+        pre_buf->buf = xd->block_refs[ref]->buf->u_buffer;
+      else
+        pre_buf->buf = xd->block_refs[ref]->buf->v_buffer;
+
+      pre_buf->buf += scaled_buffer_offset(x_start + x, y_start + y,
+                                           pre_buf->stride, sf);
+      pre = pre_buf->buf;
       scaled_mv = vp9_scale_mv(&mv_q4, mi_x + x, mi_y + y, sf);
       xs = sf->x_step_q4;
       ys = sf->y_step_q4;