Back PaintRecord with PaintOpBuffer instead of SkPicture

cc/paint/paint_op_buffer.h

+// Copyright 2017 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.
+
+#ifndef CC_PAINT_PAINT_OP_BUFFER_H_
+#define CC_PAINT_PAINT_OP_BUFFER_H_
+
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "cc/paint/paint_canvas.h"
+#include "cc/paint/paint_export.h"
+#include "cc/paint/paint_flags.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "third_party/skia/include/core/SkRect.h"
+#include "third_party/skia/include/core/SkTextBlob.h"
+
+// PaintOpBuffer is a reimplementation of SkLiteDL.
+// See: third_party/skia/src/core/SkLiteDL.h.
+
+namespace cc {
+
+class DisplayItemList;
+
+class ThreadsafeMatrix : public SkMatrix {
+ public:
+  explicit ThreadsafeMatrix(const SkMatrix& matrix) : SkMatrix(matrix) {
+    (void)getType();
+  }
+};
+
+class ThreadsafePath : public SkPath {
+ public:
+  explicit ThreadsafePath(const SkPath& path) : SkPath(path) {
+    updateBoundsCache();
+  }
+};
+
+enum class PaintOpType : uint8_t {
+  Annotate,
+  ClipPath,
+  ClipRect,
+  ClipRRect,
+  Concat,
+  DrawArc,
+  DrawCircle,
+  DrawColor,
+  DrawDisplayItemList,
+  DrawDRRect,
+  DrawImage,
+  DrawImageRect,
+  DrawIRect,
+  DrawLine,
+  DrawOval,
+  DrawPath,
+  DrawPosText,
+  DrawRecord,
+  DrawRect,
+  DrawRRect,
+  DrawText,
+  DrawTextBlob,
+  Noop,
+  Restore,
+  Rotate,
+  Save,
+  SaveLayer,
+  SaveLayerAlpha,
+  Scale,
+  SetMatrix,
+  Translate,
+  LastPaintOpType = Translate,
+};
+
+struct CC_PAINT_EXPORT PaintOp {
+  uint32_t type : 8;
+  uint32_t skip : 24;
+
+  PaintOpType GetType() const { return static_cast<PaintOpType>(type); }
+
+  void Raster(SkCanvas* canvas, const SkMatrix& original_ctm) const;
+  bool IsDrawOp() const;
+
+  // Only valid for draw ops.
+  void RasterWithAlpha(SkCanvas* canvas, uint8_t alpha) const;
+
+  int CountSlowPaths() const { return 0; }
+
+  // Returns the number of bytes used by this op in referenced sub records
+  // and display lists.  This doesn't count other objects like paths or blobs.
+  size_t AdditionalBytesUsed() const { return 0; }
+
+  static constexpr bool kIsDrawOp = false;
+  // If an op has |kHasPaintFlags| set to true, it must:
+  // (1) Provide a PaintFlags member called |flags|
+  // (2) Provide a RasterWithFlags function instead of a Raster function.
+  static constexpr bool kHasPaintFlags = false;
+  static SkRect kUnsetRect;
+};
+
+struct PaintOpWithData : PaintOp {
+  // Having data is just a helper for ops that have a varying amount of data and
+  // want a way to store that inline.  This is for ops that pass in a
+  // void* and a length.
+  explicit PaintOpWithData(size_t bytes) : bytes(bytes) {}
+
+  // Get data out by calling paint_op_data.  This can't be part of the class
+  // because it needs to know the size of the derived type.
+  size_t bytes;
+};
+
+template <typename T>
+const void* paint_op_data(const T* op) {
+  static_assert(std::is_convertible<T, PaintOpWithData>::value,
+                "T is not a PaintOpWithData");
+  // Arbitrary data for a PaintOp is stored after the PaintOp itself
+  // in the PaintOpBuffer.  Therefore, to access this data, it's
+  // pointer math to increment past the size of T.  Accessing the
+  // next op in the buffer is ((char*)op) + op->skip, with the data
+  // fitting between.
+  return op + 1;
+}
+
+template <typename T>
+void* paint_op_data(T* op) {
+  static_assert(std::is_convertible<T, PaintOpWithData>::value,
+                "T is not a PaintOpWithData");
+  return op + 1;
+}
+
+struct PaintOpWithDataArrayBase : PaintOpWithData {
+  // Helper class for static asserts in push functions.
+  using PaintOpWithData::PaintOpWithData;
+};
+
+template <typename T>
+struct PaintOpWithDataArray : PaintOpWithDataArrayBase {
+  // Paint op that has a T[count] and a char[bytes].
+  PaintOpWithDataArray(size_t bytes, size_t count)
+      : PaintOpWithDataArrayBase(bytes), count(count) {}
+  // Use paint_op_array to get array data.
+
+  size_t count;
+};
+
+template <typename M, typename T>
+const M* paint_op_array(const T* op) {
+  static_assert(std::is_convertible<T, PaintOpWithDataArrayBase>::value,
+                "T is not a PaintOpWithDataArray");
+  // See comment in paint_op_data.  Array data is stored after
+  // any void* data.  Memory layout here is: |op|data|array data|next op|
+  return SkTAddOffset<const M>(op + 1, op->bytes);
+}
+template <typename M, typename T>
+M* paint_op_array(T* op) {
+  static_assert(std::is_convertible<T, PaintOpWithDataArrayBase>::value,
+                "T is not a PaintOpWithDataArray");
+  return SkTAddOffset<M>(op + 1, op->bytes);
+}
+
+struct AnnotateOp final : PaintOp {
+  enum class AnnotationType {
+    URL,
+    LinkToDestination,
+    NamedDestination,
+  };
+
+  static constexpr PaintOpType kType = PaintOpType::Annotate;
+  AnnotateOp(PaintCanvas::AnnotationType annotation_type,
+             const SkRect& rect,
+             sk_sp<SkData> data);
+  ~AnnotateOp();
+  void Raster(SkCanvas* canvas) const;
+
+  PaintCanvas::AnnotationType annotation_type;
+  SkRect rect;
+  sk_sp<SkData> data;
+};
+
+struct ClipPathOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::ClipPath;
+  ClipPathOp(SkPath path, SkClipOp op, bool antialias)
+      : path(path), op(op), antialias(antialias) {}
+  void Raster(SkCanvas* canvas) const;
+  int CountSlowPaths() const;
+
+  ThreadsafePath path;
+  SkClipOp op;
+  bool antialias;
+};
+
+struct ClipRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::ClipRect;
+  ClipRectOp(const SkRect& rect, SkClipOp op, bool antialias)
+      : rect(rect), op(op), antialias(antialias) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkRect rect;
+  SkClipOp op;
+  bool antialias;
+};
+
+struct ClipRRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::ClipRRect;
+  ClipRRectOp(const SkRRect& rrect, SkClipOp op, bool antialias)
+      : rrect(rrect), op(op), antialias(antialias) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkRRect rrect;
+  SkClipOp op;
+  bool antialias;
+};
+
+struct ConcatOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Concat;
+  explicit ConcatOp(const SkMatrix& matrix) : matrix(matrix) {}
+  void Raster(SkCanvas* canvas) const;
+
+  ThreadsafeMatrix matrix;
+};
+
+struct DrawArcOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawArc;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawArcOp(const SkRect& oval,
+            SkScalar start_angle,
+            SkScalar sweep_angle,
+            bool use_center,
+            const PaintFlags& flags)
+      : oval(oval),
+        start_angle(start_angle),
+        sweep_angle(sweep_angle),
+        use_center(use_center),
+        flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRect oval;
+  SkScalar start_angle;
+  SkScalar sweep_angle;
+  bool use_center;
+  PaintFlags flags;
+};
+
+struct DrawCircleOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawCircle;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawCircleOp(SkScalar cx,
+               SkScalar cy,
+               SkScalar radius,
+               const PaintFlags& flags)
+      : cx(cx), cy(cy), radius(radius), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkScalar cx;
+  SkScalar cy;
+  SkScalar radius;
+  PaintFlags flags;
+};
+
+struct DrawColorOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawColor;
+  static constexpr bool kIsDrawOp = true;
+  DrawColorOp(SkColor color, SkBlendMode mode) : color(color), mode(mode) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkColor color;
+  SkBlendMode mode;
+};
+
+struct DrawDisplayItemListOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawDisplayItemList;
+  static constexpr bool kIsDrawOp = true;
+  explicit DrawDisplayItemListOp(scoped_refptr<DisplayItemList> list);
+  ~DrawDisplayItemListOp();
+  void Raster(SkCanvas* canvas) const;
+  size_t AdditionalBytesUsed() const;
+  // TODO(enne): DisplayItemList should know number of slow paths.
+
+  scoped_refptr<DisplayItemList> list;
+};
+
+struct DrawDRRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawDRRect;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawDRRectOp(const SkRRect& outer,
+               const SkRRect& inner,
+               const PaintFlags& flags)
+      : outer(outer), inner(inner), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRRect outer;
+  SkRRect inner;
+  PaintFlags flags;
+};
+
+struct DrawImageOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawImage;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawImageOp(sk_sp<const SkImage> image,
+              SkScalar left,
+              SkScalar top,
+              const PaintFlags* flags);
+  ~DrawImageOp();
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  sk_sp<const SkImage> image;
+  SkScalar left;
+  SkScalar top;
+  PaintFlags flags;
+};
+
+struct DrawImageRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawImageRect;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawImageRectOp(sk_sp<const SkImage> image,
+                  const SkRect& src,
+                  const SkRect& dst,
+                  const PaintFlags* flags,
+                  PaintCanvas::SrcRectConstraint constraint);
+  ~DrawImageRectOp();
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  sk_sp<const SkImage> image;
+  PaintFlags flags;
+  SkRect src;
+  SkRect dst;
+  PaintCanvas::SrcRectConstraint constraint;
+};
+
+struct DrawIRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawIRect;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawIRectOp(const SkIRect& rect, const PaintFlags& flags)
+      : rect(rect), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkIRect rect;
+  PaintFlags flags;
+};
+
+struct DrawLineOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawLine;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawLineOp(SkScalar x0,
+             SkScalar y0,
+             SkScalar x1,
+             SkScalar y1,
+             const PaintFlags& flags)
+      : x0(x0), y0(y0), x1(x1), y1(y1), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+  int CountSlowPaths() const;
+
+  SkScalar x0;
+  SkScalar y0;
+  SkScalar x1;
+  SkScalar y1;
+  PaintFlags flags;
+};
+
+struct DrawOvalOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawOval;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawOvalOp(const SkRect& oval, const PaintFlags& flags)
+      : oval(oval), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRect oval;
+  PaintFlags flags;
+};
+
+struct DrawPathOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawPath;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawPathOp(const SkPath& path, const PaintFlags& flags)
+      : path(path), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+  int CountSlowPaths() const;
+
+  ThreadsafePath path;
+  PaintFlags flags;
+};
+
+struct DrawPosTextOp final : PaintOpWithDataArray<SkPoint> {
+  static constexpr PaintOpType kType = PaintOpType::DrawPosText;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawPosTextOp(size_t bytes, size_t count, const PaintFlags& flags);
+  ~DrawPosTextOp();
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  PaintFlags flags;
+};
+
+struct DrawRecordOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawRecord;
+  static constexpr bool kIsDrawOp = true;
+  explicit DrawRecordOp(sk_sp<const PaintRecord> record);
+  ~DrawRecordOp();
+  void Raster(SkCanvas* canvas) const;
+  size_t AdditionalBytesUsed() const;
+
+  sk_sp<const PaintRecord> record;
+};
+
+struct DrawRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawRect;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawRectOp(const SkRect& rect, const PaintFlags& flags)
+      : rect(rect), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRect rect;
+  PaintFlags flags;
+};
+
+struct DrawRRectOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawRRect;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawRRectOp(const SkRRect& rrect, const PaintFlags& flags)
+      : rrect(rrect), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRRect rrect;
+  PaintFlags flags;
+};
+
+struct DrawTextOp final : PaintOpWithData {
+  static constexpr PaintOpType kType = PaintOpType::DrawText;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawTextOp(size_t bytes, SkScalar x, SkScalar y, const PaintFlags& flags)
+      : PaintOpWithData(bytes), x(x), y(y), flags(flags) {}
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkScalar x;
+  SkScalar y;
+  PaintFlags flags;
+};
+
+struct DrawTextBlobOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::DrawTextBlob;
+  static constexpr bool kIsDrawOp = true;
+  static constexpr bool kHasPaintFlags = true;
+  DrawTextBlobOp(sk_sp<SkTextBlob> blob,
+                 SkScalar x,
+                 SkScalar y,
+                 const PaintFlags& flags);
+  ~DrawTextBlobOp();
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  sk_sp<SkTextBlob> blob;
+  SkScalar x;
+  SkScalar y;
+  PaintFlags flags;
+};
+
+struct NoopOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Noop;
+  void Raster(SkCanvas* canvas) const {}
+};
+
+struct RestoreOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Restore;
+  void Raster(SkCanvas* canvas) const;
+};
+
+struct RotateOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Rotate;
+  explicit RotateOp(SkScalar degrees) : degrees(degrees) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkScalar degrees;
+};
+
+struct SaveOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Save;
+  void Raster(SkCanvas* canvas) const;
+};
+
+struct SaveLayerOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::SaveLayer;
+  static constexpr bool kHasPaintFlags = true;
+  SaveLayerOp(const SkRect* bounds, const PaintFlags* flags)
+      : bounds(bounds ? *bounds : kUnsetRect) {
+    if (flags)
+      this->flags = *flags;
+  }
+  void RasterWithFlags(SkCanvas* canvas, const PaintFlags& flags) const;
+
+  SkRect bounds;
+  PaintFlags flags;
+};
+
+struct SaveLayerAlphaOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::SaveLayerAlpha;
+  SaveLayerAlphaOp(const SkRect* bounds, uint8_t alpha)
+      : bounds(bounds ? *bounds : kUnsetRect), alpha(alpha) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkRect bounds;
+  uint8_t alpha;
+};
+
+struct ScaleOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Scale;
+  ScaleOp(SkScalar sx, SkScalar sy) : sx(sx), sy(sy) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkScalar sx;
+  SkScalar sy;
+};
+
+struct SetMatrixOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::SetMatrix;
+  explicit SetMatrixOp(const SkMatrix& matrix) : matrix(matrix) {}
+  // This is the only op that needs the original ctm of the SkCanvas
+  // used for raster (since SetMatrix is relative to the recording origin and
+  // shouldn't clobber the SkCanvas raster origin).
+  //
+  // TODO(enne): Find some cleaner way to do this, possibly by making
+  // all SetMatrix calls Concat??
+  void Raster(SkCanvas* canvas, const SkMatrix& original_ctm) const;
+
+  ThreadsafeMatrix matrix;
+};
+
+struct TranslateOp final : PaintOp {
+  static constexpr PaintOpType kType = PaintOpType::Translate;
+  TranslateOp(SkScalar dx, SkScalar dy) : dx(dx), dy(dy) {}
+  void Raster(SkCanvas* canvas) const;
+
+  SkScalar dx;
+  SkScalar dy;
+};
+
+using LargestPaintOp = DrawDRRectOp;
+
+class CC_PAINT_EXPORT PaintOpBuffer : public SkRefCnt {
+ public:
+  enum { kPageSize = 4096 };
+
+  PaintOpBuffer();
+  explicit PaintOpBuffer(const SkRect& cull_rect);
+  ~PaintOpBuffer() override;
+
+  void Reset();
+
+  void playback(SkCanvas* canvas) const;
+  void playback(SkCanvas* canvas, SkPicture::AbortCallback* callback) const;
+
+  // TODO(enne): These are no longer approximate.  Rename these.
+  int approximateOpCount() const { return op_count_; }
+  size_t approximateBytesUsed() const {
+    return sizeof(*this) + reserved_ + subrecord_bytes_used_;
+  }
+  int numSlowPaths() const { return num_slow_paths_; }
+
+  void Compact();

[vmpstr, 2017/04/12 21:47:12]

nit: comment

+
+  const SkRect& cullRect() const { return cull_rect_; }
+
+  PaintOp* GetFirstOp() const {
+    return reinterpret_cast<PaintOp*>(const_cast<char*>(&first_op_[0]));
+  }
+
+  template <typename T, typename... Args>
+  void push(Args&&... args) {
+    static_assert(std::is_convertible<T, PaintOp>::value, "T not a PaintOp.");
+    static_assert(!std::is_convertible<T, PaintOpWithData>::value,
+                  "Type needs to use push_with_data");
+    push_internal<T>(0, std::forward<Args>(args)...);
+  }
+
+  template <typename T, typename... Args>
+  void push_with_data(const void* data, size_t bytes, Args&&... args) {
+    static_assert(std::is_convertible<T, PaintOpWithData>::value,
+                  "T is not a PaintOpWithData");
+#if !defined(OS_CHROMEOS)
+    // TODO(enne): non-linux chromeos builds think that DrawTextOp
+    // can be converted to a PaintOpWithDataArrayBase.  OOPS.
+    static_assert(!std::is_convertible<T, PaintOpWithDataArrayBase>::value,
+                  "Type needs to use push_with_data_array");
+#endif
+    DCHECK_GE(bytes, 0u);
+    T* op = push_internal<T>(bytes, bytes, std::forward<Args>(args)...);
+    memcpy(paint_op_data(op), data, bytes);
+
+#if DCHECK_IS_ON()
+    // Double check the data fits between op and next op and doesn't clobber.
+    char* op_start = reinterpret_cast<char*>(op);
+    char* op_end = op_start + sizeof(T);
+    char* next_op = op_start + op->skip;
+    char* data_start = reinterpret_cast<char*>(paint_op_data(op));
+    char* data_end = data_start + bytes;
+    DCHECK_GE(data_start, op_end);
+    DCHECK_LT(data_start, next_op);
+    DCHECK_LE(data_end, next_op);
+#endif
+  }
+
+  template <typename T, typename M, typename... Args>
+  void push_with_data_array(const void* data,
+                            size_t bytes,
+                            const M* array,
+                            size_t count,
+                            Args&&... args) {
+    static_assert(std::is_convertible<T, PaintOpWithDataArray<M>>::value,
+                  "T is not a PaintOpWithDataArray");
+    DCHECK_GE(bytes, 0u);
+    DCHECK_GE(count, 0u);
+    size_t array_size = sizeof(M) * count;
+    size_t total_size = bytes + array_size;
+    T* op =
+        push_internal<T>(total_size, bytes, count, std::forward<Args>(args)...);
+    memcpy(paint_op_data(op), data, bytes);
+    memcpy(paint_op_array<M>(op), array, array_size);
+
+#if DCHECK_IS_ON()
+    // Double check data and array don't clobber op, next op, or each other
+    char* op_start = reinterpret_cast<char*>(op);
+    char* op_end = op_start + sizeof(T);
+    char* next_op = op_start + op->skip;
+    char* data_start = reinterpret_cast<char*>(paint_op_data(op));
+    char* data_end = data_start + bytes;
+    char* array_start = reinterpret_cast<char*>(paint_op_array<M>(op));
+    char* array_end = array_start + array_size;
+    DCHECK_GE(data_start, op_end);
+    DCHECK_LE(data_start, array_start);
+    DCHECK_GE(array_start, data_end);
+    DCHECK_LE(array_end, next_op);
+#endif
+  }
+
+  class Iterator {
+   public:
+    explicit Iterator(const PaintOpBuffer* buffer)
+        : buffer_(buffer), ptr_(buffer_->data_.get()) {}
+
+    PaintOp* operator->() const {
+      return op_idx_ ? reinterpret_cast<PaintOp*>(ptr_) : buffer_->GetFirstOp();
+    }
+    PaintOp* operator*() const { return operator->(); }
+    Iterator begin() { return Iterator(buffer_, buffer_->data_.get(), 0); }
+    Iterator end() {
+      return Iterator(buffer_, buffer_->data_.get() + buffer_->used_,
+                      buffer_->approximateOpCount());
+    }
+    bool operator!=(const Iterator& other) {
+      // Not valid to compare iterators on different buffers.
+      DCHECK_EQ(other.buffer_, buffer_);
+      return other.op_idx_ != op_idx_;
+    }
+    Iterator& operator++() {
+      if (!op_idx_++)
+        return *this;
+      PaintOp* op = **this;
+      uint32_t type = op->type;
+      CHECK_LE(type, static_cast<uint32_t>(PaintOpType::LastPaintOpType));
+      ptr_ += op->skip;
+      return *this;
+    }
+    operator bool() const { return op_idx_ < buffer_->approximateOpCount(); }
+
+    int op_idx() const { return op_idx_; }
+
+    // Return the next op without advancing the iterator, or nullptr if none.
+    PaintOp* peek1() const {
+      if (op_idx_ + 1 >= buffer_->approximateOpCount())
+        return nullptr;
+      if (!op_idx_)
+        return reinterpret_cast<PaintOp*>(ptr_);
+      return reinterpret_cast<PaintOp*>(ptr_ + (*this)->skip);
+    }
+
+    // Return the op two ops ahead without advancing the iterator, or nullptr if
+    // none.
+    PaintOp* peek2() const {
+      if (op_idx_ + 2 >= buffer_->approximateOpCount())
+        return nullptr;
+      char* next = ptr_ + reinterpret_cast<PaintOp*>(ptr_)->skip;
+      PaintOp* next_op = reinterpret_cast<PaintOp*>(next);
+      if (!op_idx_)
+        return next_op;
+      return reinterpret_cast<PaintOp*>(next + next_op->skip);
+    }
+
+   private:
+    Iterator(const PaintOpBuffer* buffer, char* ptr, int op_idx)
+        : buffer_(buffer), ptr_(ptr), op_idx_(op_idx) {}
+
+    const PaintOpBuffer* buffer_ = nullptr;
+    char* ptr_ = nullptr;
+    int op_idx_ = 0;
+  };
+
+ private:
+  template <typename T, bool HasFlags>
+  struct CountSlowPathsFromFlags {
+    static int Count(const T* op) { return 0; }
+  };
+
+  template <typename T>
+  struct CountSlowPathsFromFlags<T, true> {
+    static int Count(const T* op) { return op->flags.getPathEffect() ? 1 : 0; }
+  };
+
+  template <typename T, typename... Args>
+  T* push_internal(size_t bytes, Args&&... args) {
+    size_t skip = SkAlignPtr(sizeof(T) + bytes);
+    DCHECK_LT(skip, static_cast<size_t>(1) << 24);
+    if (used_ + skip > reserved_ || !op_count_) {
+      if (!op_count_) {
+        if (bytes) {
+          // Internal first_op buffer doesn't have room for extra data.

[vmpstr, 2017/04/12 21:47:12]

Can you fit another comment maybe higher up (or maybe around first_op_
declaration) that explains that this is an optimization for a common case of a
single item

+          // If the op wants extra bytes, then we'll just store a Noop
+          // in the first_op and proceed from there.  This seems unlikely
+          // to be a common case.
+          push<NoopOp>();
+        } else {
+          T* op = reinterpret_cast<T*>(&first_op_[0]);
+          new (op) T{std::forward<Args>(args)...};
+          op->type = static_cast<uint32_t>(T::kType);
+          op->skip = 0;
+          op_count_++;
+          return op;
+        }
+      }
+
+      static_assert(SkIsPow2(kPageSize),
+                    "This math needs updating for non-pow2.");
+      // Next greater multiple of kPageSize.
+      reserved_ = (used_ + skip + kPageSize) & ~(kPageSize - 1);
+      data_.realloc(reserved_);
+    }
+    DCHECK_LE(used_ + skip, reserved_);
+
+    T* op = reinterpret_cast<T*>(data_.get() + used_);
+    used_ += skip;
+    new (op) T(std::forward<Args>(args)...);
+    op->type = static_cast<uint32_t>(T::kType);
+    op->skip = skip;
+    op_count_++;
+
+    num_slow_paths_ += CountSlowPathsFromFlags<T, T::kHasPaintFlags>::Count(op);
+    num_slow_paths_ += op->CountSlowPaths();
+
+    subrecord_bytes_used_ += op->AdditionalBytesUsed();
+
+    return op;
+  }
+
+  char first_op_[sizeof(LargestPaintOp)];
+  SkAutoTMalloc<char> data_;
+  size_t used_ = 0;
+  size_t reserved_ = 0;
+  int op_count_ = 0;
+
+  // Record paths for veto-to-msaa for gpu raster.
+  int num_slow_paths_ = 0;
+  // Record additional bytes used by referenced sub-records and display lists.
+  size_t subrecord_bytes_used_ = 0;
+  SkRect cull_rect_;
+
+  DISALLOW_COPY_AND_ASSIGN(PaintOpBuffer);
+};
+
+}  // namespace cc
+
+#endif  // CC_PAINT_PAINT_OP_BUFFER_H_