vp10: allow MV refs to point outside visible image.

In VP9, the ref MV had to point to a block that itself fully resided
within the visible image, i.e. all borders of the image had to be
within the visible borders of the coded frame. This is somewhat
illogical, and had obscure side effects, e.g. clamping of fairly
reasonable motion vectors such as 0,0 were clipped to negative values
if the block was overhanging on frame edges (such as the last rows
on 1080p content), which makes no sense whatsoever.

Instead, relax clamping constraints such that the ref MVs are allowed
to point to blocks exactly outside the visible edges in both Y as well
as UV planes, including the 8tap filter edges (that's why the offset is
8 pixels + block size).

See issue 1037.

Change-Id: I2683eb2a18b24955e4dcce36c2940aa2ba3a1061

vp10/common/mvref_common.c

@@ -27,6 +27,8 @@ static void find_mv_refs_idx(const VP10_COMMON *cm, const MACROBLOCKD *xd,
   const MV_REF *const  prev_frame_mvs = cm->use_prev_frame_mvs ?
       cm->prev_frame->mvs + mi_row * cm->mi_cols + mi_col : NULL;
   const TileInfo *const tile = &xd->tile;
+  const int bw = num_8x8_blocks_wide_lookup[mi->mbmi.sb_type] << 3;
+  const int bh = num_8x8_blocks_high_lookup[mi->mbmi.sb_type] << 3;
 
   // Blank the reference vector list
   memset(mv_ref_list, 0, sizeof(*mv_ref_list) * MAX_MV_REF_CANDIDATES);
@@ -145,7 +147,7 @@ static void find_mv_refs_idx(const VP10_COMMON *cm, const MACROBLOCKD *xd,
 
   // Clamp vectors
   for (i = 0; i < MAX_MV_REF_CANDIDATES; ++i)
-    clamp_mv_ref(&mv_ref_list[i].as_mv, xd);
+    clamp_mv_ref(&mv_ref_list[i].as_mv, bw, bh, xd);
 }
 
 void vp10_find_mv_refs(const VP10_COMMON *cm, const MACROBLOCKD *xd,

vp10/common/mvref_common.h

@@ -119,13 +119,26 @@ static const int idx_n_column_to_subblock[4][2] = {
 };
 
 // clamp_mv_ref
+#if CONFIG_MISC_FIXES
+#define MV_BORDER (8 << 3)  // Allow 8 pels in 1/8th pel units
+#else
 #define MV_BORDER (16 << 3)  // Allow 16 pels in 1/8th pel units
+#endif
 
-static INLINE void clamp_mv_ref(MV *mv, const MACROBLOCKD *xd) {
+static INLINE void clamp_mv_ref(MV *mv, int bw, int bh, const MACROBLOCKD *xd) {
+#if CONFIG_MISC_FIXES
+  clamp_mv(mv, xd->mb_to_left_edge - bw * 8 - MV_BORDER,
+               xd->mb_to_right_edge + bw * 8 + MV_BORDER,
+               xd->mb_to_top_edge - bh * 8 - MV_BORDER,
+               xd->mb_to_bottom_edge + bh * 8 + MV_BORDER);
+#else
+  (void) bw;
+  (void) bh;
   clamp_mv(mv, xd->mb_to_left_edge - MV_BORDER,
                xd->mb_to_right_edge + MV_BORDER,
                xd->mb_to_top_edge - MV_BORDER,
                xd->mb_to_bottom_edge + MV_BORDER);
+#endif
 }
 
 // This function returns either the appropriate sub block or block's mv