ui/gfx/selection_model.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_GFX_SELECTION_MODEL_H_
   6 #define UI_GFX_SELECTION_MODEL_H_
   7
   8 #include <string>
   9
  10 #include "ui/gfx/gfx_export.h"
  11 #include "ui/gfx/range/range.h"
  12
  13 namespace gfx {
  14
  15 // VisualCursorDirection and LogicalCursorDirection represent directions of
  16 // motion of the cursor in BiDi text. The combinations that make sense are:
  17 //
  18 //  base::i18n::TextDirection  VisualCursorDirection  LogicalCursorDirection
  19 //       LEFT_TO_RIGHT             CURSOR_LEFT           CURSOR_BACKWARD
  20 //       LEFT_TO_RIGHT             CURSOR_RIGHT          CURSOR_FORWARD
  21 //       RIGHT_TO_LEFT             CURSOR_RIGHT          CURSOR_BACKWARD
  22 //       RIGHT_TO_LEFT             CURSOR_LEFT           CURSOR_FORWARD
  23 enum VisualCursorDirection {
  24   CURSOR_LEFT,
  25   CURSOR_RIGHT
  26 };
  27 enum LogicalCursorDirection {
  28   CURSOR_BACKWARD,
  29   CURSOR_FORWARD
  30 };
  31
  32 // TODO(xji): publish bidi-editing guide line and replace the place holder.
  33 // SelectionModel is used to represent the logical selection and visual
  34 // position of cursor.
  35 //
  36 // For bi-directional text, the mapping between visual position and logical
  37 // position is not one-to-one. For example, logical text "abcDEF" where capital
  38 // letters stand for Hebrew, the visual display is "abcFED". According to the
  39 // bidi editing guide (http://bidi-editing-guideline):
  40 // 1. If pointing to the right half of the cell of a LTR character, the current
  41 // position must be set after this character and the caret must be displayed
  42 // after this character.
  43 // 2. If pointing to the right half of the cell of a RTL character, the current
  44 // position must be set before this character and the caret must be displayed
  45 // before this character.
  46 //
  47 // Pointing to the right half of 'c' and pointing to the right half of 'D' both
  48 // set the logical cursor position to 3. But the cursor displayed visually at
  49 // different places:
  50 // Pointing to the right half of 'c' displays the cursor right of 'c' as
  51 // "abc|FED".
  52 // Pointing to the right half of 'D' displays the cursor right of 'D' as
  53 // "abcFED|".
  54 // So, besides the logical selection start point and end point, we need extra
  55 // information to specify to which character the visual cursor is bound. This
  56 // is given by a "caret affinity" which is either CURSOR_BACKWARD (indicating
  57 // the trailing half of the 'c' in this case) or CURSOR_FORWARD (indicating
  58 // the leading half of the 'D').
  59 class GFX_EXPORT SelectionModel {
  60  public:
  61   // Create a default SelectionModel to be overwritten later.
  62   SelectionModel();
  63   // Create a SelectionModel representing a caret |position| without a
  64   // selection. The |affinity| is meaningful only when the caret is positioned
  65   // between bidi runs that are not visually contiguous: in that case, it
  66   // indicates the run to which the caret is attached for display purposes.
  67   SelectionModel(size_t position, LogicalCursorDirection affinity);
  68   // Create a SelectionModel representing a selection (which may be empty).
  69   // The caret position is the end of the range.
  70   SelectionModel(const Range& selection, LogicalCursorDirection affinity);
  71
  72   const Range& selection() const { return selection_; }
  73   size_t caret_pos() const { return selection_.end(); }
  74   LogicalCursorDirection caret_affinity() const { return caret_affinity_; }
  75
  76   // WARNING: Generally the selection start should not be changed without
  77   // considering the effect on the caret affinity.
  78   void set_selection_start(size_t pos) { selection_.set_start(pos); }
  79
  80   bool operator==(const SelectionModel& sel) const;
  81   bool operator!=(const SelectionModel& sel) const { return !(*this == sel); }
  82
  83   std::string ToString() const;
  84
  85  private:
  86   // Logical selection. The logical caret position is the end of the selection.
  87   Range selection_;
  88
  89   // The logical direction from the caret position (selection_.end()) to the
  90   // character it is attached to for display purposes. This matters only when
  91   // the surrounding characters are not visually contiguous, which happens only
  92   // in bidi text (and only at bidi run boundaries). The text is treated as
  93   // though it was surrounded on both sides by runs in the dominant text
  94   // direction. For example, supposing the dominant direction is LTR and the
  95   // logical text is "abcDEF", where DEF is right-to-left text, the visual
  96   // cursor will display as follows:
  97   //    caret position    CURSOR_BACKWARD affinity    CURSOR_FORWARD affinity
  98   //          0                  |abcFED                     |abcFED
  99   //          1                  a|bcFED                     a|bcFED
 100   //          2                  ab|cFED                     ab|cFED
 101   //          3                  abc|FED                     abcFED|
 102   //          4                  abcFE|D                     abcFE|D
 103   //          5                  abcF|ED                     abcF|ED
 104   //          6                  abc|FED                     abcFED|
 105   LogicalCursorDirection caret_affinity_;
 106 };
 107
 108 }  // namespace gfx
 109
 110 #endif  // UI_GFX_SELECTION_MODEL_H_