Refactors RenderWidget to extract a PaintAggregator class....

chrome/renderer/paint_aggregator.h

+// Copyright (c) 2009 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 CHROME_RENDERER_PAINT_AGGREGATOR_H_
+#define CHROME_RENDERER_PAINT_AGGREGATOR_H_
+
+#include "base/gfx/rect.h"
+
+// This class is responsible for aggregating multiple invalidation and scroll
+// commands to produce a single scroll and repaint.
+class PaintAggregator {
+ public:
+
+  // This structure describes an aggregation of InvalidateRect and ScrollRect
+  // calls.  If |scroll_rect| is non-empty, then that rect should be scrolled
+  // by the amount specified by |scroll_delta|.  If |paint_rect| is non-empty,
+  // then that rect should be repainted.  If |scroll_rect| and |paint_rect| are
+  // non-empty, then scrolling should be performed before repainting.
+  // |scroll_delta| can only specify scrolling in one direction (i.e., the x
+  // and y members cannot both be non-zero).
+  struct PendingUpdate {
+    gfx::Point scroll_delta;
+    gfx::Rect scroll_rect;
+    gfx::Rect paint_rect;
+
+    // Returns the rect damaged by scrolling within |scroll_rect| by
+    // |scroll_delta|.  This rect must be repainted.
+    gfx::Rect GetScrollDamage() const;
+  };
+
+  // There is a PendingUpdate if InvalidateRect or ScrollRect were called and
+  // ClearPendingUpdate was not called.
+  bool HasPendingUpdate() const;
+  void ClearPendingUpdate();
+
+  const PendingUpdate& GetPendingUpdate() const { return update_; }
+
+  // The given rect should be repainted.
+  void InvalidateRect(const gfx::Rect& rect);
+
+  // The given rect should be scrolled by the given amounts.
+  void ScrollRect(int dx, int dy, const gfx::Rect& clip_rect);
+
+ private:
+  PendingUpdate update_;
+};
+
+#endif  // CHROME_RENDERER_PAINT_AGGREGATOR_H_