Rewrite nine piece image painting code

Source/core/paint/NinePieceImageGrid.h

+// Copyright 2015 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 NinePieceImageGrid_h
+#define NinePieceImageGrid_h
+
+#include "platform/geometry/FloatRect.h"
+#include "platform/geometry/FloatSize.h"
+#include "platform/geometry/IntRect.h"
+#include "platform/geometry/IntSize.h"
+#include "platform/graphics/Image.h"
+#include "platform/heap/Heap.h"
+
+namespace blink {
+
+class IntRectOutsets;
+class NinePieceImage;
+
+enum NinePiece {
+    MinPiece = 0,
+    TopLeftPiece = MinPiece,
+    BottomLeftPiece,
+    LeftPiece,
+    TopRightPiece,
+    BottomRightPiece,
+    RightPiece,
+    TopPiece,
+    BottomPiece,
+    MiddlePiece,
+    MaxPiece
+};
+
+inline NinePiece& operator++(NinePiece& piece)
+{
+    piece = static_cast<NinePiece>(static_cast<int>(piece) + 1);
+    return piece;
+}
+
+// The NinePieceImageGrid class is responsible for computing drawing information for the nine piece image.
+//
+// http://dev.w3.org/csswg/css-backgrounds-3/#border-image-process
+//
+// Given an image, a set of slices and a border area:
+//
+//       |         |
+//   +---+---------+---+          +------------------+
+//   | 1 |    7    | 4 |          |      border      |
+// --+---+---------+---+---       |  +------------+  |
+//   |   |         |   |          |  |            |  |
+//   | 3 |    9    | 6 |          |  |    css     |  |
+//   |   |  image  |   |          |  |    box     |  |
+//   |   |         |   |          |  |            |  |
+// --+---+---------+---+---       |  |            |  |
+//   | 2 |    8    | 5 |          |  +------------+  |
+//   +---+---------+---+          |                  |
+//       |         |              +------------------+
+//
+// it generates drawing information for the nine border pieces.
+class NinePieceImageGrid {
+    STACK_ALLOCATED();
+
+public:
+    NinePieceImageGrid(const NinePieceImage&, IntSize imageSize, IntRect borderImageArea,
+        const IntRectOutsets& borderWidths);
+
+    struct NinePieceDrawInfo {
+        bool isDrawable;
+        bool isCornerPiece;
+        FloatRect destination;
+        FloatRect source;
+
+        // tileScale and tileRule are only useful for non-corners, i.e. edge and center pieces.
+        FloatSize tileScale;
+        struct {
+            Image::TileRule horizontal;
+            Image::TileRule vertical;
+        } tileRule;
+    };
+    NinePieceDrawInfo getNinePieceDrawInfo(NinePiece) const;
+
+    struct Edge {
+        bool isDrawable() const { return slice > 0 && width > 0; }
+        float scale() const { return isDrawable() ? (float)width / slice : 1; }
+        int slice;
+        int width;
+    };
+
+private:
+    void setDrawInfoCorner(NinePieceDrawInfo&, NinePiece) const;
+    void setDrawInfoEdge(NinePieceDrawInfo&, NinePiece) const;
+    void setDrawInfoMiddle(NinePieceDrawInfo&) const;
+
+    IntRect m_borderImageArea;
+    IntSize m_imageSize;
+    Image::TileRule m_horizontalTileRule;
+    Image::TileRule m_verticalTileRule;
+    bool m_fill;
+
+    Edge m_top;
+    Edge m_right;
+    Edge m_bottom;
+    Edge m_left;
+};
+
+} // namespace blink
+
+#endif // NinePieceImageGrid_h