Creates AXPosition to uniquely identify a position in the accessibility tree

ui/accessibility/ax_position.h

Index: ui/accessibility/ax_position.h
diff --git a/ui/accessibility/ax_position.h b/ui/accessibility/ax_position.h
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+// Copyright 2016 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_ACCESSIBILITY_AX_POSITION_H_
+#define UI_ACCESSIBILITY_AX_POSITION_H_
+
+#include <vector>
+
+#include "ui/accessibility/ax_node.h"
+
+namespace ui {
+
+// A position in the |AXTree|.
+// It could either indicate a non-textual node in the accessibility tree, or a
+// text node and a character offset.
+//
+// This class is copiable.
+class AX_EXPORT AXPosition {

[dmazzoni, 2016/08/24 05:46:59]

Do you want this class to handle embedded object characters? It seems like you
probably want to build that into the class to make implementing a lot of Windows
functions easier

+ public:
+  static AXPosition CreateNullPosition();
+  static AXPosition CreateTreePosition(AXNode* anchor);

[dmazzoni, 2016/08/24 05:46:59]

Should probably pass the tree in

+  static AXPosition CreateTextPosition(AXNode* anchor, int offset = 0);
+
+  virtual ~AXPosition();
+
+  static AXPosition CommonAncestor(const AXPosition& first, const AXPosition& second);
+
+  AXNode* get_anchor() const { return anchor_; }
+  int get_offset() const { return offset_; }
+
+  bool IsNullPosition() const { return !anchor_; }
+  bool IsTreePosition() const { return type_ == AXPositionType::TreePosition; }
+  bool IsTextPosition() const { return type_ == AXPositionType::TextPosition; }
+
+  // Only meaningful for text positions.
+  bool AtStartOfAnchor() const;
+  bool AtEndOfAnchor() const;
+
+  bool operator<(const AXPosition& position) const;
+  bool operator<=(const AXPosition& position) const;
+  bool operator>(const AXPosition& position) const;
+  bool operator>=(const AXPosition& position) const;
+
+  // The following two methods allow the creation of text positions that are
+  // equivalent to other positions, not necessarily text ones.
+  AXPosition ToLeafTextPosition() const;

[dmazzoni, 2016/08/24 05:46:59]

Could you define these two more clearly?

+  AXPosition ToTextPositionInAnchor(const AXNode* anchor) const;
+
+  // Returns a text position representing the first character in the current
+  // anchor.
+  AXPosition GetPositionAtStartOfAnchor() const;
+  // Returns a position representing one past the last character in the current
+  // anchor.
+  AXPosition GetPositionAtEndOfAnchor() const;
+
+  // Following methods work across anchors.
+
+  AXPosition GetNextCharacterPosition() const;
+  AXPosition GetPreviousCharacterPosition() const;
+
+  AXPosition GetNextWordStartPosition() const;

[dmazzoni, 2016/08/24 05:46:58]

It might be better to just have a single function Find() that takes a direction
(next, previous), and a granularity (character, word, sentence, paragraph, line)

+  AXPosition GetPreviousWordStartPosition() const;
+  AXPosition GetNextWordEndPosition() const;
+  AXPosition GetPreviousWordEndPosition() const;
+
+  AXPosition GetNextSentenceStartPosition() const;
+  AXPosition GetPreviousSentenceStartPosition() const;
+  AXPosition GetNextSentenceEndPosition() const;
+  AXPosition GetPreviousSentenceEndPosition() const;
+
+  AXPosition GetNextParagraphStartPosition() const;
+  AXPosition GetPreviousParagraphStartPosition() const;
+  AXPosition GetNextParagraphEndPosition() const;
+  AXPosition GetPreviousParagraphEndPosition() const;

[dmazzoni, 2016/08/24 05:46:59]

I'm not sure para is as interesting, but line should probably be included

+
+ protected:
+  virtual int AnchorChildCount() const = 0;
+  virtual AXPosition GetChildPositionAt(int index) const = 0;
+  virtual AXPosition GetParentPosition() const = 0;
+  virtual int AnchorIndexInParent() const = 0;
+  // Uses depth-first pre-order traversal.
+  virtual AXPosition GetNextAnchorPosition() const;
+  // Uses depth-first pre-order traversal.
+  virtual AXPosition GetPreviousAnchorPosition() const = 0;
+  virtual int MaxOffset() const = 0;
+
+  virtual std::vector<int> GetWordStartOffsets() = 0;

[dmazzoni, 2016/08/24 05:46:59]

I'm not sure these need to be abstract. You can get them from node->data().

I think what might need to be abstract is something like IsLeafNode(), because
BrowserAccessibility might have its own logic there.

+  virtual std::vector<int> GetWordEndOffsets() = 0;
+  virtual std::vector<int> GetParagraphStartOffsets() = 0;
+  virtual std::vector<int> GetParagraphEndOffsets() = 0;
+
+ private:
+  // Defines the type of position in the accessibility tree.
+  enum class AXPositionType {
+    TreePosition,
+    TextPosition
+  };
+
+  AXPosition(AXNode* anchor, int offset, AXPositionType type);
+
+  AXNode* anchor_;

[dmazzoni, 2016/08/24 05:46:59]

You probably need to store the AXTree here, since AXNode doesn't store its tree.

+  int offset_;
+  AXPositionType type_;

[dmazzoni, 2016/08/24 05:46:58]

I think this class needs to store the affinity. We need a way to distinguish
between the end of the previous line and the start of the next line.

+};
+
+bool operator==(const AXPosition& first, const AXPosition& second);
+bool operator!=(const AXPosition& first, const AXPosition& second);
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_POSITION_H_