cc: Consider visible rect for update tile priority early out.

cc/layers/picture_layer_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/picture_layer_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <set>
 
@@ skipping 476 matching lines @@
 
   UpdateTilePriorities(occlusion_in_content_space);
 }
 
 void PictureLayerImpl::UpdateTilePriorities(
     const Occlusion& occlusion_in_content_space) {
   DCHECK(!pile_->is_solid_color() || !tilings_->num_tilings());
 
   TRACE_EVENT0("cc", "PictureLayerImpl::UpdateTilePriorities");
 
-  double current_frame_time_in_seconds =
-      (layer_tree_impl()->CurrentBeginFrameArgs().frame_time -
-       base::TimeTicks()).InSecondsF();

[mithro-old, 2014/10/27 13:20:36]

Just a FYI, these lines will totally not do what you expect if called at the
wrong time. It's unclear to me when exactly this function is called, so I'm not
sure if that is possible?

When not in the background, the value of CurrentBeginFrameArgs is set in
WillBeginImplFrame and cleared by calling
ResetCurrentBeginFrameArgsForNextFrame.

When in the background this happens in the
LayerTreeHostImplTimeSourceAdapter::OnTimerTick() method.

When outside of the period between Update and Reset calls the
CurrentBeginFrameArgs method just returns Now().

All the above is kind of seriously horrible and really needs to be fixed. To
make matters even more confusing, this value won't match the the last vsync
value as it's overridden to now to preserve monotonicity guarantees caused by
returning Now() at other times! :(

Does the "NeedsUpdateForFrameAtTime" method depend on the frame time being
useful, or does it just need a monotonic increasing value?

-
-  bool tiling_needs_update = false;
-  for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
-    if (tilings_->tiling_at(i)->NeedsUpdateForFrameAtTime(
-            current_frame_time_in_seconds)) {
-      tiling_needs_update = true;
-      break;
-    }
-  }
-  if (!tiling_needs_update)
-    return;
-
   gfx::Rect viewport_rect_in_layer_space =
       GetViewportForTilePriorityInContentSpace();
   WhichTree tree =
       layer_tree_impl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
   bool can_require_tiles_for_activation =
       !only_used_low_res_last_append_quads_ || RequiresHighResToDraw() ||
       !layer_tree_impl()->SmoothnessTakesPriority();
   for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
     PictureLayerTiling* tiling = tilings_->tiling_at(i);
 
@@ skipping 1163 matching lines @@
       PictureLayerTilingSet::TilingRange tiling_range = CurrentTilingRange();
       size_t current_tiling_range_offset = current_tiling_ - tiling_range.start;
       return tiling_range.end - 1 - current_tiling_range_offset;
     }
   }
   NOTREACHED();
   return 0;
 }
 
 }  // namespace cc