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+// Copyright (c) 2011 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 PPAPI_CPP_PAINT_AGGREGATOR_H_
+#define PPAPI_CPP_PAINT_AGGREGATOR_H_
+
+#include <stddef.h>
+#include <vector>
+
+#include "ppapi/cpp/point.h"
+#include "ppapi/cpp/rect.h"
+
+/// @file
+/// This file defines the API to aggregate multiple invalidation and scroll
+/// commands to produce a scroll and repaint sequence.
+namespace pp {
+
+/// This class is responsible for aggregating multiple invalidation and scroll
+/// commands to produce a scroll and repaint sequence. You can use this manually
+/// to track your updates, but most applications will use the PaintManager to
+/// additionally handle the necessary callbacks on top of the PaintAggregator
+/// functionality.
+///
+/// Refer to <code>http://code.google.com/p/ppapi/wiki/2DPaintingModel</code>
+/// for further information.
+class PaintAggregator {
+ public:
+  struct PaintUpdate {
+    /// Default constructor for creating an is_null() <code>PaintUpdate</code>
+    /// object.
+    PaintUpdate();
+
+    /// Destructor.
+    ~PaintUpdate();
+
+    /// True if there is a scroll applied. This indicates that the scroll delta
+    /// and scroll_rect are nonzero (just as a convenience).
+    bool has_scroll;
+
+    /// The amount to scroll by. Either the X or Y may be nonzero to indicate a
+    /// scroll in that direction, but there will never be a scroll in both
+    /// directions at the same time (this will be converted to a paint of the
+    /// region instead).
+    ///
+    /// If there is no scroll, this will be (0, 0).
+    Point scroll_delta;
+
+    /// The rectangle that should be scrolled by the scroll_delta. If there is
+    /// no scroll, this will be (0, 0, 0, 0). We only track one scroll command
+    /// at once. If there are multiple ones, they will be converted to
+    /// invalidates.
+    Rect scroll_rect;
+
+    /// A list of all the individual dirty rectangles. This is an aggregated
+    /// list of all invalidate calls. Different rectangles may be unified to
+    /// produce a minimal list with no overlap that is more efficient to paint.
+    /// This list also contains the region exposed by any scroll command.
+    std::vector<Rect> paint_rects;
+
+    /// The union of all paint_rects.
+    Rect paint_bounds;
+  };
+
+  /// Default constructor.
+  PaintAggregator();
+
+  /// Setter function setting the max ratio of paint rect area to scroll rect
+  /// area that we will tolerate before downgrading the scroll into a repaint.
+  ///
+  /// If the combined area of paint rects contained within the scroll
+  /// rect grows too large, then we might as well just treat
+  /// the scroll rect as a paint rect.
+  ///
+  /// @param[in] area The max ratio of paint rect area to scroll rect area that
+  /// we will tolerate before downgrading the scroll into a repaint.
+  void set_max_redundant_paint_to_scroll_area(float area) {
+    max_redundant_paint_to_scroll_area_ = area;
+  }
+
+  /// Setter function for setting the maximum number of paint rects. If we
+  /// exceed this limit, then we'll start combining paint rects (see
+  /// CombinePaintRects). This limiting can be important since there is
+  /// typically some overhead in deciding what to paint. If your module is fast
+  /// at doing these computations, raise this threshold, if your module is
+  /// slow, lower it (probably requires some tuning to find the right value).
+  ///
+  /// @param[in] max_rects The maximum number of paint rects.
+  void set_max_paint_rects(size_t max_rects) {
+    max_paint_rects_ = max_rects;
+  }
+
+  /// This function determines if there is a pending update. There is a
+  /// PendingUpdate if InvalidateRect or ScrollRect were called and
+  /// ClearPendingUpdate was not called.
+  ///
+  /// @return true if there is a pending update, otherwise false.
+  bool HasPendingUpdate() const;
+
+  /// This function clears a pending update.
+  void ClearPendingUpdate();
+
+  /// This function gets a pending update.
+  ///
+  /// @return A PaintUpdate containing the pending update.
+  PaintUpdate GetPendingUpdate() const;
+
+  /// This function invalidates the rect so it will be repainted.
+  ///
+  /// @param[in] rect A rect to be repainted.
+  void InvalidateRect(const Rect& rect);
+
+  /// This function adds a pending scroll update.
+  ///
+  /// @param[in] clip_rect The rect to scroll.
+  /// @param[in] amount A Point amount to scroll <code>rect</code>.
+  void ScrollRect(const Rect& clip_rect, const Point& amount);
+
+ private:
+  // This structure is an internal version of PaintUpdate. It's different in
+  // two respects:
+  //
+  //  - The scroll damange (area exposed by the scroll operation, if any) is
+  //    maintained separately from the dirty rects generated by calling
+  //    InvalidateRect. We need to know this distinction for some operations.
+  //
+  //  - The paint bounds union is computed on the fly so we don't have to keep
+  //    a rectangle up-to-date as we do different operations.
+  class InternalPaintUpdate {
+   public:
+    InternalPaintUpdate();
+    ~InternalPaintUpdate();
+
+    // Computes the rect damaged by scrolling within |scroll_rect| by
+    // |scroll_delta|. This rect must be repainted. It is not included in
+    // paint_rects or in the rect returned by GetPaintBounds.
+    Rect GetScrollDamage() const;
+
+    // Returns the smallest rect containing all paint rects, not including the
+    // scroll damage rect.
+    Rect GetPaintBounds() const;
+
+    Point scroll_delta;
+    Rect scroll_rect;
+
+    // Does not include the scroll damage rect.
+    std::vector<Rect> paint_rects;
+  };
+
+  Rect ScrollPaintRect(const Rect& paint_rect, const Point& amount) const;
+  bool ShouldInvalidateScrollRect(const Rect& rect) const;
+  void InvalidateScrollRect();
+  void CombinePaintRects();
+
+  InternalPaintUpdate update_;
+
+  // If the combined area of paint rects contained within the scroll rect grows
+  // too large, then we might as well just treat the scroll rect as a paint
+  // rect. This constant sets the max ratio of paint rect area to scroll rect
+  // area that we will tolerate before downgrading the scroll into a repaint.
+  float max_redundant_paint_to_scroll_area_;
+
+  // The maximum number of paint rects. If we exceed this limit, then we'll
+  // start combining paint rects (see CombinePaintRects). This limiting can be
+  // important since there is typically some overhead in deciding what to
+  // paint. If your plugin is fast at doing these computations, raise this
+  // threshold, if your plugin is slow, lower it (probably requires some
+  // tuning to find the right value).
+  size_t max_paint_rects_;
+};
+
+}  // namespace pp
+
+#endif  // PPAPI_CPP_PAINT_AGGREGATOR_H_