New Motion Reference Search

Alternative strategy for finding a list of candidate motion
vectors to use as reference values in mv coding and as
nearest and near.

Sort by sad in vp8_find_best_ref_mvs() rather than just
pick the best. Allow 0,0 as a best ref option but not a
nearest or near unless there are no alternatives.

Encode/Decode verified on at least some clips.

Some commented out experimental and stats code still in place.

Gain over existing code averages about 1% on derf (alll metrics)
with improvement on all clips. Other test results pending.

The entropy coding of the mode (nearest/near etc) still
depends upon and requires the old "findnear" code so
this needs looking at and may provide room for further gains.

Change-Id: I871d7cba1d1c379c4bad9bcccce1fb19c46b8247

1 files changed, 303 insertions, 0 deletions

diff --git a/vp8/common/mvref_common.c b/vp8/common/mvref_common.c
new file mode 100644
index 000000000..1c345dba5
--- /dev/null
+++ b/vp8/common/mvref_common.c
@@ -0,0 +1,303 @@
+/*
+ *  Copyright (c) 2012 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "mvref_common.h"
+
+#if CONFIG_NEW_MVREF
+
+#define MVREF_NEIGHBOURS 8
+static int mv_ref_search[MVREF_NEIGHBOURS][2] =
+  { {0,-1},{-1,0},{-1,-1},{0,-2},{-2,0},{-1,-2},{-2,-1},{-2,-2} };
+static int ref_distance_weight[MVREF_NEIGHBOURS] =
+  { 3,3,2,1,1,1,1,1 };
+  //{ 4,4,2,1,1,1,1,1 };
+
+// clamp_mv
+#define MV_BORDER (16 << 3) // Allow 16 pels in 1/8th pel units
+static void clamp_mv(const MACROBLOCKD *xd, int_mv *mv) {
+
+  if (mv->as_mv.col < (xd->mb_to_left_edge - MV_BORDER))
+    mv->as_mv.col = xd->mb_to_left_edge - MV_BORDER;
+  else if (mv->as_mv.col > xd->mb_to_right_edge + MV_BORDER)
+    mv->as_mv.col = xd->mb_to_right_edge + MV_BORDER;
+
+  if (mv->as_mv.row < (xd->mb_to_top_edge - MV_BORDER))
+    mv->as_mv.row = xd->mb_to_top_edge - MV_BORDER;
+  else if (mv->as_mv.row > xd->mb_to_bottom_edge + MV_BORDER)
+    mv->as_mv.row = xd->mb_to_bottom_edge + MV_BORDER;
+}
+
+// Code for selecting / building and entropy coding a motion vector reference
+// Returns a seperation value for two vectors.
+// This is taken as the sum of the abs x and y difference.
+unsigned int mv_distance(int_mv *mv1, int_mv *mv2) {
+  return (abs(mv1->as_mv.row - mv2->as_mv.row) +
+          abs(mv1->as_mv.col - mv2->as_mv.col));
+}
+
+// Gets a best matching candidate refenence motion vector
+// from the given mode info structure (if available)
+int get_candidate_mvref(
+  const MODE_INFO *candidate_mi,
+  MV_REFERENCE_FRAME ref_frame,
+  MV_REFERENCE_FRAME *candidate_ref_frame,
+  int_mv *candidate_mv
+) {
+
+  int ret_val = FALSE;
+
+  if (ref_frame == candidate_mi->mbmi.ref_frame) {
+    candidate_mv->as_int = candidate_mi->mbmi.mv[FIRST_REF].as_int;
+    *candidate_ref_frame = ref_frame;
+    ret_val = TRUE;
+
+  } else if (ref_frame == candidate_mi->mbmi.second_ref_frame) {
+    candidate_mv->as_int = candidate_mi->mbmi.mv[SECOND_REF].as_int;
+    *candidate_ref_frame = ref_frame;
+    ret_val = TRUE;
+
+  } else if (candidate_mi->mbmi.ref_frame != INTRA_FRAME) {
+    candidate_mv->as_int = candidate_mi->mbmi.mv[FIRST_REF].as_int;
+    *candidate_ref_frame = candidate_mi->mbmi.ref_frame;
+    ret_val = TRUE;
+
+  } else if (candidate_mi->mbmi.second_ref_frame != INTRA_FRAME) {
+    candidate_mv->as_int = candidate_mi->mbmi.mv[SECOND_REF].as_int;
+    *candidate_ref_frame = candidate_mi->mbmi.second_ref_frame;
+    ret_val = TRUE;
+  }
+
+  return ret_val;
+}
+
+// Performs mv adjustment based on reference frame and clamps the MV
+// if it goes off the edge of the buffer.
+void scale_mv(
+  MACROBLOCKD *xd,
+  MV_REFERENCE_FRAME this_ref_frame,
+  MV_REFERENCE_FRAME candidate_ref_frame,
+  int_mv *candidate_mv,
+  int *ref_sign_bias
+) {
+
+  if (candidate_ref_frame != this_ref_frame) {
+
+    //int frame_distances[MAX_REF_FRAMES];
+    //int last_distance = 1;
+    //int gf_distance = xd->frames_since_golden;
+    //int arf_distance = xd->frames_till_alt_ref_frame;
+
+    // Sign inversion where appropriate.
+    if (ref_sign_bias[candidate_ref_frame] != ref_sign_bias[this_ref_frame]) {
+      candidate_mv->as_mv.row = -candidate_mv->as_mv.row;
+      candidate_mv->as_mv.col = -candidate_mv->as_mv.col;
+    }
+
+    // Scale based on frame distance if the reference frames not the same.
+    /*frame_distances[INTRA_FRAME] = 1;   // should never be used
+    frame_distances[LAST_FRAME] = 1;
+    frame_distances[GOLDEN_FRAME] =
+      (xd->frames_since_golden) ? xd->frames_since_golden : 1;
+    frame_distances[ALTREF_FRAME] =
+      (xd->frames_till_alt_ref_frame) ? xd->frames_till_alt_ref_frame : 1;
+
+    if (frame_distances[this_ref_frame] &&
+        frame_distances[candidate_ref_frame]) {
+      candidate_mv->as_mv.row =
+        (short)(((int)(candidate_mv->as_mv.row) *
+                 frame_distances[this_ref_frame]) /
+                frame_distances[candidate_ref_frame]);
+
+      candidate_mv->as_mv.col =
+        (short)(((int)(candidate_mv->as_mv.col) *
+                 frame_distances[this_ref_frame]) /
+                frame_distances[candidate_ref_frame]);
+    }
+    */
+  }
+
+  // Clamp the MV so it does not point out of the frame buffer
+  clamp_mv(xd, candidate_mv);
+}
+
+// Adds a new candidate reference vector to the list if indeed it is new.
+// If it is not new then the score of the existing candidate that it matches
+// is increased and the list is resorted.
+void addmv_and_shuffle(
+  int_mv *mv_list,
+  int *mv_scores,
+  int *index,
+  int_mv candidate_mv,
+  int weight
+) {
+
+  int i = *index;
+  int duplicate_found = FALSE;
+
+  // Check for duplicates. If there is one increment its score.
+  while (i > 0) {
+    i--;
+    if (candidate_mv.as_int == mv_list[i].as_int) {
+      duplicate_found = TRUE;
+      mv_scores[i] += weight;
+      break;
+    }
+  }
+
+  // If no duplicate was found add the new vector and give it a weight
+  if (!duplicate_found) {
+    mv_list[*index].as_int = candidate_mv.as_int;
+    mv_scores[*index] = weight;
+    i = *index;
+    (*index)++;
+  }
+
+  // Reshuffle the list so that highest scoring mvs at the top.
+  while (i > 0) {
+    if (mv_scores[i] > mv_scores[i-1]) {
+      int tmp_score = mv_scores[i-1];
+      int_mv tmp_mv = mv_list[i-1];
+
+      mv_scores[i-1] = mv_scores[i];
+      mv_list[i-1] = mv_list[i];
+      mv_scores[i] = tmp_score;
+      mv_list[i] = tmp_mv;
+      i--;
+    } else
+      break;
+  }
+}
+
+
+// Measure the distance of each reference candidate from the actual
+// residual vector and return the nearest
+unsigned int pick_best_mv_ref( int_mv target_mv,
+                               int_mv * mv_ref_list,
+                               int_mv * best_ref ) {
+
+  int i;
+  int best_index = 0;
+  unsigned int distance, distance2;
+
+  distance = mv_distance(&target_mv, &mv_ref_list[0]);
+
+  for (i = 1; i < MAX_MV_REFS; ++i ) {
+    distance2 =
+      mv_distance(&target_mv, &mv_ref_list[i]);
+    if (distance2 < distance) {
+      distance = distance2;
+      best_index = i;
+    }
+  }
+
+  (*best_ref).as_int = mv_ref_list[best_index].as_int;
+
+  return best_index;
+}
+
+// This function searches the neighbourhood of a given MB/SB and populates a
+// list of candidate reference vectors.
+//
+void find_mv_refs(
+  MACROBLOCKD *xd,
+  MODE_INFO *here,
+  MODE_INFO *lf_here,
+  MV_REFERENCE_FRAME ref_frame,
+  int_mv *mv_ref_list,
+  int *ref_sign_bias
+) {
+
+  int i;
+  MODE_INFO *candidate_mi;
+  int_mv candidate_mvs[MAX_MV_REFS];
+  int_mv c_refmv;
+  MV_REFERENCE_FRAME c_ref_frame;
+  int candidate_scores[MAX_MV_REFS];
+  int index = 0;
+  int ref_weight = 0;
+  int valid_mv_ref;
+
+  // Blank the reference vector lists and other local structures.
+  vpx_memset(mv_ref_list, 0, sizeof(int_mv) * MAX_MV_REFS);
+  vpx_memset(candidate_mvs, 0, sizeof(int_mv) * MAX_MV_REFS);
+  vpx_memset(candidate_scores, 0, sizeof(candidate_scores));
+
+  // Populate a list with candidate reference vectors from the
+  // spatial neighbours.
+  for (i = 0; i < 2; ++i) {
+    if (((mv_ref_search[i][0] << 7) >= xd->mb_to_left_edge) &&
+        ((mv_ref_search[i][1] << 7) >= xd->mb_to_top_edge)) {
+
+      candidate_mi = here + mv_ref_search[i][0] +
+                     (mv_ref_search[i][1] * xd->mode_info_stride);
+
+      valid_mv_ref = get_candidate_mvref(candidate_mi, ref_frame,
+                                         &c_ref_frame, &c_refmv);
+
+      if (valid_mv_ref) {
+          scale_mv(xd, ref_frame, c_ref_frame, &c_refmv, ref_sign_bias );
+          ref_weight = ref_distance_weight[i] +
+                       ((c_ref_frame == ref_frame) << 3);
+
+          addmv_and_shuffle(candidate_mvs, candidate_scores,
+                            &index, c_refmv, ref_weight);
+      }
+    }
+  }
+
+  // Look at the corresponding vector in the last frame
+  candidate_mi = lf_here;
+  valid_mv_ref = get_candidate_mvref(candidate_mi, ref_frame,
+                                     &c_ref_frame, &c_refmv);
+  if (valid_mv_ref) {
+    scale_mv(xd, ref_frame, c_ref_frame, &c_refmv, ref_sign_bias );
+    ref_weight = 2 + ((c_ref_frame == ref_frame) << 3);
+    addmv_and_shuffle(candidate_mvs, candidate_scores,
+                      &index, c_refmv, ref_weight);
+  }
+
+  // Populate a list with candidate reference vectors from the
+  // spatial neighbours.
+  for (i = 2; i < MVREF_NEIGHBOURS; ++i) {
+    if (((mv_ref_search[i][0] << 7) >= xd->mb_to_left_edge) &&
+        ((mv_ref_search[i][1] << 7) >= xd->mb_to_top_edge)) {
+
+      candidate_mi = here + mv_ref_search[i][0] +
+                     (mv_ref_search[i][1] * xd->mode_info_stride);
+
+      valid_mv_ref = get_candidate_mvref(candidate_mi, ref_frame,
+                                         &c_ref_frame, &c_refmv);
+
+      if (valid_mv_ref) {
+          scale_mv(xd, ref_frame, c_ref_frame, &c_refmv, ref_sign_bias );
+          ref_weight = ref_distance_weight[i] +
+                       ((c_ref_frame == ref_frame) << 3);
+
+          addmv_and_shuffle(candidate_mvs, candidate_scores,
+                            &index, c_refmv, ref_weight);
+      }
+    }
+  }
+
+  // 0,0 is always a valid reference.
+  for (i = 0; i < index; ++i)
+    if (candidate_mvs[i].as_int == 0)
+      break;
+  if (i == index) {
+    c_refmv.as_int = 0;
+    addmv_and_shuffle(candidate_mvs, candidate_scores,
+                      &index, c_refmv, 1);
+  }
+
+  // Copy over the candidate list.
+  vpx_memcpy(mv_ref_list, candidate_mvs, sizeof(candidate_mvs));
+}
+
+#endif