cc: Do GatherPixelRefs from skia at record time

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>
+
 #include "base/base64.h"
 #include "base/debug/trace_event.h"
+#include "cc/base/util.h"
 #include "cc/debug/rendering_stats.h"
 #include "cc/layers/content_layer_client.h"
 #include "skia/ext/analysis_canvas.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkData.h"
 #include "third_party/skia/include/core/SkDrawFilter.h"
 #include "third_party/skia/include/core/SkPaint.h"
 #include "third_party/skia/include/core/SkStream.h"
 #include "third_party/skia/include/utils/SkPictureUtils.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/skia_util.h"
 
 namespace {
 // URI label for a lazily decoded SkPixelRef.
 const char kLabelLazyDecoded[] = "lazy";
+
 // Version ID; to be used in serialization.
 const int kPictureVersion = 1;
+
 // Minimum size of a decoded stream that we need.
 // 4 bytes for version, 4 * 4 for each of the 2 rects.
 const unsigned int kMinPictureSizeBytes = 36;
 
 class DisableLCDTextFilter : public SkDrawFilter {
  public:
   // SkDrawFilter interface.
   virtual bool filter(SkPaint* paint, SkDrawFilter::Type type) OVERRIDE {
     if (type != SkDrawFilter::kText_Type)
       return true;
@@ skipping 58 matching lines @@
                            opaque_rect_y,
                            opaque_rect_width,
                            opaque_rect_height);
 
   // Read the picture. This creates an empty picture on failure.
   picture_ = skia::AdoptRef(new SkPicture(&stream, success, NULL));
 }
 
 Picture::Picture(const skia::RefPtr<SkPicture>& picture,
                  gfx::Rect layer_rect,
-                 gfx::Rect opaque_rect) :
+                 gfx::Rect opaque_rect,
+                 const PixelRefMap& pixel_refs) :
     layer_rect_(layer_rect),
     opaque_rect_(opaque_rect),
-    picture_(picture) {
+    picture_(picture),
+    pixel_refs_(pixel_refs) {
 }
 
 Picture::~Picture() {
 }
 
 scoped_refptr<Picture> Picture::GetCloneForDrawingOnThread(
     unsigned thread_index) const {
   // 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];
 }
 
 void Picture::CloneForDrawing(int num_threads) {
   TRACE_EVENT1("cc", "Picture::CloneForDrawing", "num_threads", num_threads);
 
   DCHECK(picture_);
   scoped_ptr<SkPicture[]> clones(new SkPicture[num_threads]);
   picture_->clone(&clones[0], num_threads);
 
   clones_.clear();
   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_));
+                    opaque_rect_,
+                    pixel_refs_));
     clones_.push_back(clone);
   }
 }
 
 void Picture::Record(ContentLayerClient* painter,
                      RenderingStats* stats,
                      const SkTileGridPicture::TileGridInfo& tile_grid_info) {
   TRACE_EVENT2("cc", "Picture::Record",
                "width", layer_rect_.width(), "height", layer_rect_.height());
 
@@ skipping 31 matching lines @@
   if (stats) {
     stats->total_paint_time += base::TimeTicks::Now() - begin_paint_time;
     stats->total_pixels_painted +=
         layer_rect_.width() * layer_rect_.height();
   }
 
   canvas->restore();
   picture_->endRecording();
 
   opaque_rect_ = gfx::ToEnclosedRect(opaque_layer_rect);
+
+  cell_size_ = gfx::Size(
+      tile_grid_info.fTileInterval.width() +
+          2 * tile_grid_info.fMargin.width(),
+      tile_grid_info.fTileInterval.height() +
+          2 * tile_grid_info.fMargin.height());
+  DCHECK_GT(cell_size_.width(), 0);
+  DCHECK_GT(cell_size_.height(), 0);
+  GatherAllPixelRefs();
 }
 
 void Picture::Raster(
     SkCanvas* canvas,
     gfx::Rect content_rect,
     float contents_scale,
     bool enable_lcd_text) {
   TRACE_EVENT2("cc", "Picture::Raster",
                "layer width", layer_rect_.width(),
                "layer height", layer_rect_.height());
   DCHECK(picture_);
 
   DisableLCDTextFilter disable_lcd_text_filter;
 
   canvas->save();
   canvas->clipRect(gfx::RectToSkRect(content_rect));
   canvas->scale(contents_scale, contents_scale);
   canvas->translate(layer_rect_.x(), layer_rect_.y());
   // Pictures by default have LCD text enabled.
   if (!enable_lcd_text)
     canvas->setDrawFilter(&disable_lcd_text_filter);
   canvas->drawPicture(*picture_);
   canvas->restore();
 }
 
-void Picture::GatherPixelRefs(const gfx::Rect& layer_rect,
-                              std::list<skia::LazyPixelRef*>& pixel_ref_list) {
+void Picture::GatherPixelRefsFromSkia(
+    gfx::Rect query_rect,
+    std::list<skia::LazyPixelRef*>* pixel_ref_list) {
   DCHECK(picture_);
   SkData* pixel_refs = SkPictureUtils::GatherPixelRefs(
-      picture_.get(), SkRect::MakeXYWH(layer_rect.x(),
-                                       layer_rect.y(),
-                                       layer_rect.width(),
-                                       layer_rect.height()));
+      picture_.get(), SkRect::MakeXYWH(query_rect.x() - layer_rect_.x(),
+                                       query_rect.y() - layer_rect_.y(),
+                                       query_rect.width(),
+                                       query_rect.height()));
   if (!pixel_refs)
     return;
 
   void* data = const_cast<void*>(pixel_refs->data());
   if (!data) {
     pixel_refs->unref();
     return;
   }
 
   SkPixelRef** refs = reinterpret_cast<SkPixelRef**>(data);
   for (size_t i = 0; i < pixel_refs->size() / sizeof(*refs); ++i) {
     if (*refs && (*refs)->getURI() && !strncmp(
         (*refs)->getURI(), kLabelLazyDecoded, 4)) {
-      pixel_ref_list.push_back(static_cast<skia::LazyPixelRef*>(*refs));
+      pixel_ref_list->push_back(static_cast<skia::LazyPixelRef*>(*refs));
     }
     refs++;
   }
   pixel_refs->unref();
 }
 
 void Picture::AsBase64String(std::string* output) const {
   SkDynamicMemoryWStream stream;
 
   // First save the version, layer_rect_ and opaque_rect.
@@ skipping 13 matching lines @@
   picture_->serialize(&stream);
 
   // Encode the picture as base64.
   size_t serialized_size = stream.bytesWritten();
   scoped_ptr<char[]> serialized_picture(new char[serialized_size]);
   stream.copyTo(serialized_picture.get());
   base::Base64Encode(std::string(serialized_picture.get(), serialized_size),
                      output);
 }
 
+void Picture::GatherAllPixelRefs() {
+  int min_x = std::numeric_limits<int>::max();
+  int min_y = std::numeric_limits<int>::max();
+  int max_x = 0;
+  int max_y = 0;
+
+  // Capture pixel refs for this picture in a grid
+  // with cell_size_ sized cells.
+  for (int y = layer_rect_.y();
+      y < layer_rect_.bottom();
+      y += cell_size_.height()) {
+    for (int x = layer_rect_.x();
+        x < layer_rect_.right();
+        x += cell_size_.width()) {
+      gfx::Rect rect(gfx::Point(x, y), cell_size_);
+      rect.Intersect(layer_rect_);
+
+      std::list<skia::LazyPixelRef*> pixel_refs;
+      GatherPixelRefsFromSkia(rect, &pixel_refs);
+
+      // Only capture non-empty cells.
+      if (!pixel_refs.empty()) {
+        pixel_refs_[PixelRefMapKey(x, y)].swap(pixel_refs);
+        min_x = std::min(min_x, x);
+        min_y = std::min(min_y, y);
+        max_x = std::max(max_x, x);
+        max_y = std::max(max_y, y);
+      }
+    }
+  }
+
+  min_pixel_cell_ = gfx::Point(min_x, min_y);
+  max_pixel_cell_ = gfx::Point(max_x, max_y);
+}
+
+Picture::PixelRefIterator::PixelRefIterator()
+    : picture_(NULL),
+      min_point_(-1, -1),
+      max_point_(-1, -1),
+      current_x_(0),
+      current_y_(0) {
+  sentinel_list_.push_back(NULL);
+  current_list_ = &sentinel_list_;
+  current_list_iterator_ = current_list_->begin();
+}
+
+Picture::PixelRefIterator::PixelRefIterator(const PixelRefIterator& other) {

[reveman, 2013/04/24 14:10:52]

why do you need this ctor?

[vmpstr, 2013/04/24 21:11:10]

If the "other" iterator is pointing to the sentinel list, I want to ensure that
we start pointing to our sentinel list, instead of "other" sentinel list. Hence,
I have to do a different operator= (below), and a copy ctor as well.

[reveman, 2013/04/24 23:01:27]

If you use an index to iterate over each vector I think you can avoid all this
with global base::LazyInstance<std::vector<skia::LazyPixelRef*> > as sentinel
value.

+  sentinel_list_.push_back(NULL);
+  *this = other;
+}
+
+Picture::PixelRefIterator::PixelRefIterator(
+    gfx::Rect query_rect,
+    const Picture* picture)
+    : picture_(picture) {
+  gfx::Rect layer_rect = picture->layer_rect_;
+  gfx::Size cell_size = picture->cell_size_;
+
+  sentinel_list_.push_back(NULL);
+  current_list_ = &sentinel_list_;
+  current_list_iterator_ = current_list_->begin();
+
+  // We have to find a cell_size aligned point that
+  // corresponds to query_rect. First, subtract the layer origin,
+  // then ensure the point is a multiple of cell_size,
+  // and finally, add the layer origin back.
+  min_point_ = gfx::Point(
+      RoundDown(query_rect.x() - layer_rect.x(), cell_size.width())
+          + layer_rect.x(),
+      RoundDown(query_rect.y() - layer_rect.y(), cell_size.height())
+          + layer_rect.y());
+  max_point_ = gfx::Point(
+      RoundDown(query_rect.right() - layer_rect.x() - 1, cell_size.width())
+          + layer_rect.x(),
+      RoundDown(query_rect.bottom() - layer_rect.y() - 1, cell_size.height())
+          + layer_rect.y());
+
+  // Limit the points to known pixel ref boundaries.
+  min_point_ = gfx::Point(
+      std::max(min_point_.x(), picture->min_pixel_cell_.x()),
+      std::max(min_point_.y(), picture->min_pixel_cell_.y()));
+  max_point_ = gfx::Point(
+      std::min(max_point_.x(), picture->max_pixel_cell_.x()),
+      std::min(max_point_.y(), picture->max_pixel_cell_.y()));
+
+  // Make the current x be cell_size.width() less than min point, so that
+  // the first increment will point at min_point_.
+  current_x_ = min_point_.x() - cell_size.width();
+  current_y_ = min_point_.y();
+  ++(*this);
+}
+
+Picture::PixelRefIterator::~PixelRefIterator() {
+}
+
+Picture::PixelRefIterator& Picture::PixelRefIterator::operator++() {
+  ++current_list_iterator_;
+  // If we're not at the end of the list, then we have the next item.
+  if (current_list_iterator_ != current_list_->end())
+    return *this;
+
+  // If we already passed the max y, reset back to sentinel list.
+  if (current_y_ > max_point_.y()) {

[reveman, 2013/04/24 14:10:52]

is this ever true? is the loop below not already catching it?

[vmpstr, 2013/04/24 21:11:10]

This can be true. The loop below (the if) would only hit if x > max.x. If x <=
max.x, then it would go through the whole loop of looking for the pixel ref. I
think it's better (ie easier to reason about it) if we check it here.

[reveman, 2013/04/24 23:01:27]

hm, I still can't see how a valid call to operator++() can cause this to happen
as you perform the "current_y_ > max_point_.y()" check whenever you increment
current_y. It's a bug if operator++() is called after reaching the end and if
you want to protect against that you should use a DCHECK instead.

+    current_list_ = &sentinel_list_;
+    current_list_iterator_ = current_list_->begin();
+    return *this;
+  }
+
+  while (true) {
+    gfx::Size cell_size = picture_->cell_size_;
+
+    // Advance the current grid cell.
+    current_x_ += cell_size.width();
+    if (current_x_ > max_point_.x()) {
+      current_y_ += cell_size.height();
+      current_x_ = min_point_.x();
+      // Min x can be greater than max x if the query rect
+      // does not intersect the layer rect.

[reveman, 2013/04/24 14:10:52]

can this special condition be handled in the ctor instead of in every iteration
of this loop?

[vmpstr, 2013/04/24 21:11:10]

Done. I added an intersect check in the ctor.

+      if (current_y_ > max_point_.y() ||
+          current_x_ > max_point_.x()) {
+        current_list_ = &sentinel_list_;
+        current_list_iterator_ = current_list_->begin();
+        break;
+      }
+    }
+
+    // If there are no pixel refs at this grid cell, keep incrementing.
+    PixelRefMapKey key(current_x_, current_y_);
+    PixelRefMap::const_iterator iter = picture_->pixel_refs_.find(key);
+    if (iter == picture_->pixel_refs_.end())
+      continue;
+
+    // We found a non-empty list: store it and get the first pixel ref.
+    current_list_ = &iter->second;
+    current_list_iterator_ = current_list_->begin();
+    break;
+  }
+  return *this;
+}
+
+Picture::PixelRefIterator& Picture::PixelRefIterator::operator=(
+    const PixelRefIterator& other) {
+  if (this == &other)
+    return *this;
+
+  picture_ = other.picture_;
+  // If other is pointing to its sentinel list, set
+  // the iterator to point to our sentinel list.
+  if (other.current_list_ == &other.sentinel_list_) {
+    current_list_ = &sentinel_list_;
+    current_list_iterator_ = current_list_->begin();
+  } else {
+    current_list_ = other.current_list_;
+    current_list_iterator_ = other.current_list_iterator_;
+  }
+  min_point_ = other.min_point_;
+  max_point_ = other.max_point_;
+  current_x_ = other.current_x_;
+  current_y_ = other.current_y_;
+  return *this;
+}
+
 }  // namespace cc