Mac: Optimize TabView drawing.

ui/base/cocoa/three_part_image.h

Index: ui/base/cocoa/three_part_image.h
diff --git a/ui/base/cocoa/three_part_image.h b/ui/base/cocoa/three_part_image.h
new file mode 100644
index 0000000000000000000000000000000000000000..01a66911bcb6e24bbd29a0d43b1721ece942ed54
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+++ b/ui/base/cocoa/three_part_image.h
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+// 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 UI_BASE_COCOA_THREE_PART_IMAGE_H
+#define UI_BASE_COCOA_THREE_PART_IMAGE_H
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/mac/scoped_nsobject.h"
+#include "ui/base/ui_base_export.h"
+
+namespace ui {
+
+// A wrapper around NSDrawThreePartImage that caches the images.
+// The middle image is optional.
+// Vertical orientation is not currently supported.
+class UI_BASE_EXPORT ThreePartImage {
+ public:
+  // |left_id|, |middle_id|, and |right_id| are ResourceBundle image
+  // identifiers. Specify 0 for |middle_id| if there is no middle image.
+  ThreePartImage(int left_id, int middle_id, int right_id);
+  ~ThreePartImage();
+
+  // Returns the image rects if drawn in |bounds|.
+  NSRect GetLeftRect(NSRect bounds) const;
+  NSRect GetMiddleRect(NSRect bounds) const;
+  NSRect GetRightRect(NSRect bounds) const;
+
+  // Draws the three part image inside |rect|.
+  void DrawInRect(NSRect rect, NSCompositingOperation op, CGFloat alpha) const;
+
+  // Returns YES if |point| is in a non-transparent part of the images.
+  // Returns YES if |point| is inside the middle rect and there is no middle
+  // image.
+  BOOL HitTest(NSPoint point, NSRect bounds) const;
+
+ private:
+  // Returns YES if |point| is in a non-transparent part of |image|.
+  BOOL HitTestImage(NSPoint point, NSImage* image, NSRect imageRect) const;
+
+  base::scoped_nsobject<NSImage> leftImage_;
+  base::scoped_nsobject<NSImage> middleImage_;
+  base::scoped_nsobject<NSImage> rightImage_;
+  NSSize leftSize_;
+  NSSize rightSize_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreePartImage);
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_COCOA_THREE_PART_IMAGE_H