cc: Only make num_threads - 1 SkPicture clones.

cc/resources/picture.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/resources/picture.h"
 
 #include <algorithm>
 #include <limits>
 #include <set>
 
@@ skipping 74 matching lines @@
     const gfx::Rect& layer_rect,
     ContentLayerClient* client,
     const SkTileGridPicture::TileGridInfo& tile_grid_info,
     bool gather_pixel_refs,
     int num_raster_threads) {
   scoped_refptr<Picture> picture = make_scoped_refptr(new Picture(layer_rect));
 
   picture->Record(client, tile_grid_info);
   if (gather_pixel_refs)
     picture->GatherPixelRefs(tile_grid_info);
-  if (num_raster_threads > 0)
-    picture->CloneForDrawing(num_raster_threads);
-
-  // This picture may be rasterized on a different thread.
-  picture->raster_thread_checker_.DetachFromThread();
+  picture->CloneForDrawing(num_raster_threads);
 
   return picture;
 }
 
 Picture::Picture(const gfx::Rect& layer_rect)
   : layer_rect_(layer_rect),
     cell_size_(layer_rect.size()) {
   // Instead of recording a trace event for object creation here, we wait for
   // the picture to be recorded in Picture::Record.
 }
@@ skipping 75 matching lines @@
     picture_(picture),
     pixel_refs_(pixel_refs),
     cell_size_(layer_rect.size()) {
 }
 
 Picture::~Picture() {
   TRACE_EVENT_OBJECT_DELETED_WITH_ID(
     TRACE_DISABLED_BY_DEFAULT("cc.debug"), "cc::Picture", this);
 }
 
-scoped_refptr<Picture> Picture::GetCloneForDrawingOnThread(
-    unsigned thread_index) const {
+Picture* Picture::GetCloneForDrawingOnThread(unsigned thread_index) {
   // SkPicture is not thread-safe to rasterize with, this returns a clone
   // to rasterize with on a specific thread.
-  CHECK_GT(clones_.size(), thread_index);
-  return clones_[thread_index];
+  CHECK_GE(clones_.size(), thread_index);
+  return thread_index == clones_.size() ? this : clones_[thread_index].get();
 }
 
 void Picture::CloneForDrawing(int num_threads) {
   TRACE_EVENT1("cc", "Picture::CloneForDrawing", "num_threads", num_threads);
 
   DCHECK(picture_);
   DCHECK(clones_.empty());
 
-  scoped_ptr<SkPicture[]> clones(new SkPicture[num_threads]);
-  picture_->clone(&clones[0], num_threads);
+  // We can re-use this picture for one raster worker thread.
+  raster_thread_checker_.DetachFromThread();
 
-  for (int i = 0; i < num_threads; i++) {
-    scoped_refptr<Picture> clone = make_scoped_refptr(
-        new Picture(skia::AdoptRef(new SkPicture(clones[i])),
-                    layer_rect_,
-                    opaque_rect_,
-                    pixel_refs_));
-    clones_.push_back(clone);
+  if (num_threads > 1) {
+    scoped_ptr<SkPicture[]> clones(new SkPicture[num_threads - 1]);
+    picture_->clone(&clones[0], num_threads - 1);
 
-    clone->EmitTraceSnapshotAlias(this);
-    clone->raster_thread_checker_.DetachFromThread();
+    for (int i = 0; i < num_threads - 1; i++) {
+      scoped_refptr<Picture> clone = make_scoped_refptr(
+          new Picture(skia::AdoptRef(new SkPicture(clones[i])),
+                      layer_rect_,
+                      opaque_rect_,
+                      pixel_refs_));
+      clones_.push_back(clone);
+
+      clone->EmitTraceSnapshotAlias(this);

[enne (OOO), 2014/02/11 22:30:45]

Do you need to emit the trace snapshot alias for the 0th picture too?

[reveman, 2014/02/11 23:40:42]

Not needed as discussed.

+      clone->raster_thread_checker_.DetachFromThread();
+    }
   }
 }
 
 void Picture::Record(ContentLayerClient* painter,
                      const SkTileGridPicture::TileGridInfo& tile_grid_info) {
   TRACE_EVENT1("cc", "Picture::Record",
                "data", AsTraceableRecordData());
 
   DCHECK(!picture_);
   DCHECK(!tile_grid_info.fTileInterval.isEmpty());
@@ skipping 272 matching lines @@
 scoped_refptr<base::debug::ConvertableToTraceFormat>
     Picture::AsTraceableRecordData() const {
   scoped_ptr<base::DictionaryValue> record_data(new base::DictionaryValue());
   record_data->Set("picture_id", TracedValue::CreateIDRef(this).release());
   record_data->SetInteger("width", layer_rect_.width());
   record_data->SetInteger("height", layer_rect_.height());
   return TracedValue::FromValue(record_data.release());
 }
 
 }  // namespace cc