vp8: Modify to use closest reference in zero_mv bias.

Modify zero_mv bias condition to include check that "closest" reference is last_frame.
This is needed for temporal layers, where the last_frame is not always the closest reference.
Also, constain zeromv_count to be for last_frame reference.

Change-Id: I7af54a809ebf01ef43b9933c9d4095b6cb189390

vp8/encoder/onyx_if.c

diff --git a/vp8/encoder/onyx_if.c b/vp8/encoder/onyx_if.c
index 7140f2f..f5080b2 100644
--- a/vp8/encoder/onyx_if.c
+++ b/vp8/encoder/onyx_if.c
@@ -3150,10 +3150,8 @@
 
         cm->alt_fb_idx = cm->gld_fb_idx = cm->new_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
         cpi->current_ref_frames[GOLDEN_FRAME] = cm->current_video_frame;
         cpi->current_ref_frames[ALTREF_FRAME] = cm->current_video_frame;
-#endif
     }
     else    /* For non key frames */
     {
@@ -3165,9 +3163,7 @@
             cm->yv12_fb[cm->alt_fb_idx].flags &= ~VP8_ALTR_FRAME;
             cm->alt_fb_idx = cm->new_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
             cpi->current_ref_frames[ALTREF_FRAME] = cm->current_video_frame;
-#endif
         }
         else if (cm->copy_buffer_to_arf)
         {
@@ -3181,10 +3177,8 @@
                     yv12_fb[cm->alt_fb_idx].flags &= ~VP8_ALTR_FRAME;
                     cm->alt_fb_idx = cm->lst_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
                     cpi->current_ref_frames[ALTREF_FRAME] =
                         cpi->current_ref_frames[LAST_FRAME];
-#endif
                 }
             }
             else /* if (cm->copy_buffer_to_arf == 2) */
@@ -3195,10 +3189,8 @@
                     yv12_fb[cm->alt_fb_idx].flags &= ~VP8_ALTR_FRAME;
                     cm->alt_fb_idx = cm->gld_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
                     cpi->current_ref_frames[ALTREF_FRAME] =
                         cpi->current_ref_frames[GOLDEN_FRAME];
-#endif
                 }
             }
         }
@@ -3211,9 +3203,7 @@
             cm->yv12_fb[cm->gld_fb_idx].flags &= ~VP8_GOLD_FRAME;
             cm->gld_fb_idx = cm->new_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
             cpi->current_ref_frames[GOLDEN_FRAME] = cm->current_video_frame;
-#endif
         }
         else if (cm->copy_buffer_to_gf)
         {
@@ -3227,10 +3217,8 @@
                     yv12_fb[cm->gld_fb_idx].flags &= ~VP8_GOLD_FRAME;
                     cm->gld_fb_idx = cm->lst_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
                     cpi->current_ref_frames[GOLDEN_FRAME] =
                         cpi->current_ref_frames[LAST_FRAME];
-#endif
                 }
             }
             else /* if (cm->copy_buffer_to_gf == 2) */
@@ -3241,10 +3229,8 @@
                     yv12_fb[cm->gld_fb_idx].flags &= ~VP8_GOLD_FRAME;
                     cm->gld_fb_idx = cm->alt_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
                     cpi->current_ref_frames[GOLDEN_FRAME] =
                         cpi->current_ref_frames[ALTREF_FRAME];
-#endif
                 }
             }
         }
@@ -3256,9 +3242,7 @@
         cm->yv12_fb[cm->lst_fb_idx].flags &= ~VP8_LAST_FRAME;
         cm->lst_fb_idx = cm->new_fb_idx;
 
-#if CONFIG_MULTI_RES_ENCODING
         cpi->current_ref_frames[LAST_FRAME] = cm->current_video_frame;
-#endif
     }
 
 #if CONFIG_TEMPORAL_DENOISING
@@ -3494,6 +3478,31 @@
     }
 #endif
 
+    // Find the reference frame closest to the current frame.
+    cpi->closest_reference_frame = LAST_FRAME;
+    if (cm->frame_type != KEY_FRAME) {
+      int i;
+      MV_REFERENCE_FRAME closest_ref = INTRA_FRAME;
+      if (cpi->ref_frame_flags & VP8_LAST_FRAME) {
+        closest_ref = LAST_FRAME;
+      } else if (cpi->ref_frame_flags & VP8_GOLD_FRAME) {
+        closest_ref = GOLDEN_FRAME;
+      } else if (cpi->ref_frame_flags & VP8_ALTR_FRAME) {
+        closest_ref = ALTREF_FRAME;
+      }
+      for (i = 1; i <= 3; i++) {
+        vpx_ref_frame_type_t ref_frame_type = (vpx_ref_frame_type_t)
+            ((i == 3) ? 4 : i);
+        if (cpi->ref_frame_flags & ref_frame_type) {
+          if ((cm->current_video_frame - cpi->current_ref_frames[i]) <
+            (cm->current_video_frame - cpi->current_ref_frames[closest_ref])) {
+            closest_ref = i;
+          }
+        }
+      }
+      cpi->closest_reference_frame = closest_ref;
+    }
+
     /* Set various flags etc to special state if it is a key frame */
     if (cm->frame_type == KEY_FRAME)
     {
@@ -4420,7 +4429,8 @@
             {
                 for (mb_col = 0; mb_col < cm->mb_cols; mb_col ++)
                 {
-                    if(tmp->mbmi.mode == ZEROMV)
+                    if (tmp->mbmi.mode == ZEROMV &&
+                       tmp->mbmi.ref_frame == LAST_FRAME)
                         cpi->zeromv_count++;
                     tmp++;
                 }

vp8/encoder/onyx_int.h

diff --git a/vp8/encoder/onyx_int.h b/vp8/encoder/onyx_int.h
index 7a8baca..f0424e6 100644
--- a/vp8/encoder/onyx_int.h
+++ b/vp8/encoder/onyx_int.h
@@ -684,9 +684,10 @@
     int    mr_low_res_mb_cols;
     /* Indicate if lower-res mv info is available */
     unsigned char  mr_low_res_mv_avail;
+#endif
     /* The frame number of each reference frames */
     unsigned int current_ref_frames[MAX_REF_FRAMES];
-#endif
+    MV_REFERENCE_FRAME closest_reference_frame;
 
     struct rd_costs_struct
     {

vp8/encoder/pickinter.c

diff --git a/vp8/encoder/pickinter.c b/vp8/encoder/pickinter.c
index d0ad721..8dd1881 100644
--- a/vp8/encoder/pickinter.c
+++ b/vp8/encoder/pickinter.c
@@ -505,16 +505,11 @@
 
     this_rd = RDCOST(x->rdmult, x->rddiv, rate2, *distortion2);
 
-    /* Adjust rd to bias to ZEROMV */
-    if(this_mode == ZEROMV)
+    // Adjust rd for ZEROMV and LAST, if LAST is the closest reference frame.
+    if (this_mode == ZEROMV &&
+        x->e_mbd.mode_info_context->mbmi.ref_frame == LAST_FRAME &&
+        cpi->closest_reference_frame == LAST_FRAME)
     {
-        /* Bias to ZEROMV on LAST_FRAME reference when it is available. */
-        if ((cpi->ref_frame_flags & VP8_LAST_FRAME &
-            cpi->common.refresh_last_frame)
-            && x->e_mbd.mode_info_context->mbmi.ref_frame != LAST_FRAME)
-            rd_adj = 100;
-
-        // rd_adj <= 100
         this_rd = ((int64_t)this_rd) * rd_adj / 100;
     }