cc: Use a ListContainer for DisplayItemList to reduce allocations.

cc/resources/display_item_list.cc

 // Copyright 2014 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/display_item_list.h"
 
 #include <string>
 
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/picture_debug_util.h"
 #include "cc/debug/traced_picture.h"
 #include "cc/debug/traced_value.h"
+#include "cc/resources/largest_display_item.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkDrawPictureCallback.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 #include "third_party/skia/include/utils/SkPictureUtils.h"
 #include "ui/gfx/skia_util.h"
 
 namespace cc {
 
 namespace {
 
 bool PictureTracingEnabled() {
   bool tracing_enabled;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(
     TRACE_DISABLED_BY_DEFAULT("cc.debug.picture") ","
     TRACE_DISABLED_BY_DEFAULT("devtools.timeline.picture"),
     &tracing_enabled);
   return tracing_enabled;
 }
 
+const int kDefaultNumDisplayItemsToReserve = 100;
+
 }  // namespace
 
 DisplayItemList::DisplayItemList(gfx::Rect layer_rect,
                                  bool use_cached_picture,
                                  bool retain_individual_display_items)
-    : recorder_(new SkPictureRecorder()),
+    : items_(LargestDisplayItemSize(), kDefaultNumDisplayItemsToReserve),
+      recorder_(new SkPictureRecorder()),
       use_cached_picture_(use_cached_picture),
       retain_individual_display_items_(retain_individual_display_items),
       layer_rect_(layer_rect),
       is_suitable_for_gpu_rasterization_(true),
       approximate_op_count_(0),
       picture_memory_usage_(0) {
+#if DCHECK_IS_ON()
+  needs_process_ = false;
+#endif
   if (use_cached_picture_) {
     SkRTreeFactory factory;
     recorder_.reset(new SkPictureRecorder());
     canvas_ = skia::SharePtr(recorder_->beginRecording(
         layer_rect_.width(), layer_rect_.height(), &factory));
     canvas_->translate(-layer_rect_.x(), -layer_rect_.y());
     canvas_->clipRect(gfx::RectToSkRect(layer_rect_));
   }
 }
 
 DisplayItemList::DisplayItemList(gfx::Rect layer_rect, bool use_cached_picture)
     : DisplayItemList(layer_rect,
                       use_cached_picture,
                       !use_cached_picture || PictureTracingEnabled()) {
 }
 
 scoped_refptr<DisplayItemList> DisplayItemList::Create(
     gfx::Rect layer_rect,
     bool use_cached_picture) {
   return make_scoped_refptr(
       new DisplayItemList(layer_rect, use_cached_picture));
 }
 
 DisplayItemList::~DisplayItemList() {
 }
 
 void DisplayItemList::Raster(SkCanvas* canvas,
                              SkDrawPictureCallback* callback,
                              float contents_scale) const {
+  DCHECK(ProcessAppendedItemsCalled());
   if (!use_cached_picture_) {
     canvas->save();
     canvas->scale(contents_scale, contents_scale);
-    for (size_t i = 0; i < items_.size(); ++i) {
-      items_[i]->Raster(canvas, callback);
-    }
+    for (auto* item : items_)
+      item->Raster(canvas, callback);
     canvas->restore();
   } else {
     DCHECK(picture_);
 
     canvas->save();
     canvas->scale(contents_scale, contents_scale);
     canvas->translate(layer_rect_.x(), layer_rect_.y());
     if (callback) {
       // If we have a callback, we need to call |draw()|, |drawPicture()|
       // doesn't take a callback.  This is used by |AnalysisCanvas| to early
       // out.
       picture_->playback(canvas, callback);
     } else {
       // Prefer to call |drawPicture()| on the canvas since it could place the
       // entire picture on the canvas instead of parsing the skia operations.
       canvas->drawPicture(picture_.get());
     }
     canvas->restore();
   }
 }
 
+void DisplayItemList::ProcessAppendedItems() {
+#if DCHECK_IS_ON()
+  needs_process_ = false;
+#endif
+  for (DisplayItem* item : items_) {

[ajuma, 2015/05/06 15:49:48]

With this post-processing approach, the ListContainer will need to have enough
capacity for the entire list of items even when we're not retaining individual
items. If this is a lot of memory, an alternative would be to process after
every item (or after every, say, 100 items).

+    is_suitable_for_gpu_rasterization_ &= item->IsSuitableForGpuRasterization();
+    approximate_op_count_ += item->ApproximateOpCount();
+
+    if (use_cached_picture_) {
+      DCHECK(canvas_);
+      item->Raster(canvas_.get(), NULL);
+    }
+
+    if (retain_individual_display_items_) {
+      // Warning: this double-counts SkPicture data if use_cached_picture_ is
+      // also true.
+      picture_memory_usage_ += item->PictureMemoryUsage();
+    }
+  }
+
+  if (!retain_individual_display_items_)
+    items_.clear();
+}
+
 void DisplayItemList::CreateAndCacheSkPicture() {
+  DCHECK(ProcessAppendedItemsCalled());
   // Convert to an SkPicture for faster rasterization.
   DCHECK(use_cached_picture_);
   DCHECK(!picture_);
   picture_ = skia::AdoptRef(recorder_->endRecordingAsPicture());
   DCHECK(picture_);
   picture_memory_usage_ += SkPictureUtils::ApproximateBytesUsed(picture_.get());
   recorder_.reset();
   canvas_.clear();
 }
 
-void DisplayItemList::AppendItem(scoped_ptr<DisplayItem> item) {
-  is_suitable_for_gpu_rasterization_ &= item->IsSuitableForGpuRasterization();
-  approximate_op_count_ += item->ApproximateOpCount();
-
-  if (use_cached_picture_) {
-    DCHECK(canvas_);
-    item->Raster(canvas_.get(), NULL);
-  }
-
-  if (retain_individual_display_items_) {
-    // Warning: this double-counts SkPicture data if use_cached_picture_ is also
-    // true.
-    picture_memory_usage_ += item->PictureMemoryUsage();
-    items_.push_back(item.Pass());
-  }
-}
-
 bool DisplayItemList::IsSuitableForGpuRasterization() const {
+  DCHECK(ProcessAppendedItemsCalled());
   // This is more permissive than Picture's implementation, since none of the
   // items might individually trigger a veto even though they collectively have
   // enough "bad" operations that a corresponding Picture would get vetoed.
   return is_suitable_for_gpu_rasterization_;
 }
 
 int DisplayItemList::ApproximateOpCount() const {
+  DCHECK(ProcessAppendedItemsCalled());
   return approximate_op_count_;
 }
 
 size_t DisplayItemList::PictureMemoryUsage() const {
+  DCHECK(ProcessAppendedItemsCalled());
   // We double-count in this case. Produce zero to avoid being misleading.
   if (use_cached_picture_ && retain_individual_display_items_)
     return 0;
 
   DCHECK_IMPLIES(use_cached_picture_, picture_);
   return picture_memory_usage_;
 }
 
 scoped_refptr<base::trace_event::ConvertableToTraceFormat>
 DisplayItemList::AsValue() const {
+  DCHECK(ProcessAppendedItemsCalled());
   scoped_refptr<base::trace_event::TracedValue> state =
       new base::trace_event::TracedValue();
 
   state->SetInteger("length", items_.size());
   state->BeginArray("params.items");
   for (const DisplayItem* item : items_) {
     item->AsValueInto(state.get());
   }
   state->EndArray();
   state->SetValue("params.layer_rect",
                   MathUtil::AsValue(layer_rect_).release());
 
   SkPictureRecorder recorder;
   SkCanvas* canvas =
       recorder.beginRecording(layer_rect_.width(), layer_rect_.height());
   canvas->translate(-layer_rect_.x(), -layer_rect_.y());
   canvas->clipRect(gfx::RectToSkRect(layer_rect_));
   Raster(canvas, NULL, 1.f);
   skia::RefPtr<SkPicture> picture =
       skia::AdoptRef(recorder.endRecordingAsPicture());
 
   std::string b64_picture;
   PictureDebugUtil::SerializeAsBase64(picture.get(), &b64_picture);
   state->SetString("skp64", b64_picture);
 
   return state;
 }
 
 void DisplayItemList::EmitTraceSnapshot() const {
+  DCHECK(ProcessAppendedItemsCalled());
   TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.picture") ","
       TRACE_DISABLED_BY_DEFAULT("devtools.timeline.picture"),
       "cc::DisplayItemList", this, AsValue());
 }
 
 void DisplayItemList::GatherPixelRefs(const gfx::Size& grid_cell_size) {
+  DCHECK(ProcessAppendedItemsCalled());
   // This should be only called once, and only after CreateAndCacheSkPicture.
   DCHECK(picture_);
   DCHECK(!pixel_refs_);
   pixel_refs_ = make_scoped_ptr(new PixelRefMap(grid_cell_size));
   if (!picture_->willPlayBackBitmaps())
     return;
 
   pixel_refs_->GatherPixelRefsFromPicture(picture_.get());
 }
 }  // namespace cc