libvpx: Pull from upstream

source/libvpx/vp9/encoder/vp9_lookahead.c

 /*
  *  Copyright (c) 2011 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 <assert.h>
@@ skipping 10 matching lines @@
 struct lookahead_ctx {
   unsigned int max_sz;         /* Absolute size of the queue */
   unsigned int sz;             /* Number of buffers currently in the queue */
   unsigned int read_idx;       /* Read index */
   unsigned int write_idx;      /* Write index */
   struct lookahead_entry *buf; /* Buffer list */
 };
 
 
 /* Return the buffer at the given absolute index and increment the index */
-static struct lookahead_entry * pop(struct lookahead_ctx *ctx,
-                                    unsigned int *idx) {
+static struct lookahead_entry *pop(struct lookahead_ctx *ctx,
+                                   unsigned int *idx) {
   unsigned int index = *idx;
   struct lookahead_entry *buf = ctx->buf + index;
 
   assert(index < ctx->max_sz);
   if (++index >= ctx->max_sz)
     index -= ctx->max_sz;
   *idx = index;
   return buf;
 }
 
 
 void vp9_lookahead_destroy(struct lookahead_ctx *ctx) {
   if (ctx) {
     if (ctx->buf) {
       unsigned int i;
 
       for (i = 0; i < ctx->max_sz; i++)
         vp9_free_frame_buffer(&ctx->buf[i].img);
       free(ctx->buf);
     }
     free(ctx);
   }
 }
 
 
-struct lookahead_ctx * vp9_lookahead_init(unsigned int width,
-                                          unsigned int height,
-                                          unsigned int subsampling_x,
-                                          unsigned int subsampling_y,
-                                          unsigned int depth) {
+struct lookahead_ctx *vp9_lookahead_init(unsigned int width,
+                                         unsigned int height,
+                                         unsigned int subsampling_x,
+                                         unsigned int subsampling_y,
+                                         unsigned int depth) {
   struct lookahead_ctx *ctx = NULL;
 
   // Clamp the lookahead queue depth
   depth = clamp(depth, 1, MAX_LAG_BUFFERS);
 
+  // Allocate memory to keep previous source frames available.
+  depth += MAX_PRE_FRAMES;
+
   // Allocate the lookahead structures
   ctx = calloc(1, sizeof(*ctx));
   if (ctx) {
     unsigned int i;
     ctx->max_sz = depth;
     ctx->buf = calloc(depth, sizeof(*ctx->buf));
     if (!ctx->buf)
       goto bail;
     for (i = 0; i < depth; i++)
       if (vp9_alloc_frame_buffer(&ctx->buf[i].img,
@@ skipping 11 matching lines @@
 
 int vp9_lookahead_push(struct lookahead_ctx *ctx, YV12_BUFFER_CONFIG   *src,
                        int64_t ts_start, int64_t ts_end, unsigned int flags) {
   struct lookahead_entry *buf;
 #if USE_PARTIAL_COPY
   int row, col, active_end;
   int mb_rows = (src->y_height + 15) >> 4;
   int mb_cols = (src->y_width + 15) >> 4;
 #endif
 
-  if (ctx->sz + 1 > ctx->max_sz)
+  if (ctx->sz + 1  + MAX_PRE_FRAMES > ctx->max_sz)
     return 1;
   ctx->sz++;
   buf = pop(ctx, &ctx->write_idx);
 
 #if USE_PARTIAL_COPY
   // TODO(jkoleszar): This is disabled for now, as
   // vp9_copy_and_extend_frame_with_rect is not subsampling/alpha aware.
 
   // Only do this partial copy if the following conditions are all met:
   // 1. Lookahead queue has has size of 1.
@@ skipping 42 matching lines @@
   vp9_copy_and_extend_frame(src, &buf->img);
 #endif
 
   buf->ts_start = ts_start;
   buf->ts_end = ts_end;
   buf->flags = flags;
   return 0;
 }
 
 
-struct lookahead_entry * vp9_lookahead_pop(struct lookahead_ctx *ctx,
-                                           int drain) {
+struct lookahead_entry *vp9_lookahead_pop(struct lookahead_ctx *ctx,
+                                          int drain) {
   struct lookahead_entry *buf = NULL;
 
-  if (ctx->sz && (drain || ctx->sz == ctx->max_sz)) {
+  if (ctx->sz && (drain || ctx->sz == ctx->max_sz - MAX_PRE_FRAMES)) {
     buf = pop(ctx, &ctx->read_idx);
     ctx->sz--;
   }
   return buf;
 }
 
 
-struct lookahead_entry * vp9_lookahead_peek(struct lookahead_ctx *ctx,
-                                            int index) {
+struct lookahead_entry *vp9_lookahead_peek(struct lookahead_ctx *ctx,
+                                           int index) {
   struct lookahead_entry *buf = NULL;
 
-  if (index < (int)ctx->sz) {
-    index += ctx->read_idx;
-    if (index >= (int)ctx->max_sz)
-      index -= ctx->max_sz;
-    buf = ctx->buf + index;
+  if (index >= 0) {
+    // Forward peek
+    if (index < (int)ctx->sz) {
+      index += ctx->read_idx;
+      if (index >= (int)ctx->max_sz)
+        index -= ctx->max_sz;
+      buf = ctx->buf + index;
+    }
+  } else if (index < 0) {
+    // Backward peek
+    if (-index <= MAX_PRE_FRAMES) {
+      index += ctx->read_idx;
+      if (index < 0)
+        index += ctx->max_sz;
+      buf = ctx->buf + index;
+    }
   }
+
   return buf;
 }
 
 unsigned int vp9_lookahead_depth(struct lookahead_ctx *ctx) {
   return ctx->sz;
 }