tesseract/ccmain/resultiterator.h

///////////////////////////////////////////////////////////////////////
// File:        resultiterator.h
// Description: Iterator for tesseract results that is capable of
//              iterating in proper reading order over Bi Directional
//              (e.g. mixed Hebrew and English) text.
// Author:      David Eger
// Created:     Fri May 27 13:58:06 PST 2011
//
// (C) Copyright 2011, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
///////////////////////////////////////////////////////////////////////

#ifndef TESSERACT_CCMAIN_RESULT_ITERATOR_H__
#define TESSERACT_CCMAIN_RESULT_ITERATOR_H__

#include "ltrresultiterator.h"
#include "genericvector.h"

class BLOB_CHOICE_IT;
class WERD_RES;
class STRING;

namespace tesseract {

class Tesseract;

class ResultIterator : public LTRResultIterator {
 public:
  static ResultIterator *StartOfParagraph(const LTRResultIterator &resit);

  // ResultIterator is copy constructible!
  // The default copy constructor works just fine for us.
  virtual ~ResultIterator() {}

  // ============= Moving around within the page ============.
  // Moves the iterator to point to the start of the page to begin an iteration.
  virtual void Begin();

  // Moves to the start of the next object at the given level in the
  // page hierarchy in the appropriate reading order and returns false if
  // the end of the page was reached.
  // NOTE that RIL_SYMBOL will skip non-text blocks, but all other
  // PageIteratorLevel level values will visit each non-text block once.
  // Think of non text blocks as containing a single para, with a single line,
  // with a single imaginary word.
  // Calls to Next with different levels may be freely intermixed.
  // This function iterates words in right-to-left scripts correctly, if
  // the appropriate language has been loaded into Tesseract.
  virtual bool Next(PageIteratorLevel level);

  // IsAtBeginningOf() returns whether we're at the logical beginning of the
  // given level.  (as opposed to ResultIterator's left-to-right top-to-bottom
  // order).  Otherwise, this acts the same as PageIterator::IsAtBeginningOf().
  // For a full description, see pageiterator.h
  virtual bool IsAtBeginningOf(PageIteratorLevel level) const;

  // Implement PageIterator's IsAtFinalElement correctly in a BiDi context.
  // For instance, IsAtFinalElement(RIL_PARA, RIL_WORD) returns whether we
  // point at the last word in a paragraph.  See PageIterator for full comment.
  virtual bool IsAtFinalElement(PageIteratorLevel level,
                                PageIteratorLevel element) const;

  // ============= Accessing data ==============.

  // Returns the null terminated UTF-8 encoded text string for the current
  // object at the given level. Use delete [] to free after use.
  virtual char* GetUTF8Text(PageIteratorLevel level) const;

  // Return whether the current paragraph's dominant reading direction
  // is left-to-right (as opposed to right-to-left).
  bool ParagraphIsLtr() const;

  // ============= Exposed only for testing =============.

  // Yields the reading order as a sequence of indices and (optional)
  // meta-marks for a set of words (given left-to-right).
  // The meta marks are passed as negative values:
  //   kMinorRunStart  Start of minor direction text.
  //   kMinorRunEnd    End of minor direction text.
  //   kComplexWord    The next indexed word contains both left-to-right and
  //                    right-to-left characters and was treated as neutral.
  //
  // For example, suppose we have five words in a text line,
  // indexed [0,1,2,3,4] from the leftmost side of the text line.
  // The following are all believable reading_orders:
  //
  // Left-to-Right (in ltr paragraph):
  //     { 0, 1, 2, 3, 4 }
  // Left-to-Right (in rtl paragraph):
  //     { kMinorRunStart, 0, 1, 2, 3, 4, kMinorRunEnd }
  // Right-to-Left (in rtl paragraph):
  //     { 4, 3, 2, 1, 0 }
  // Left-to-Right except for an RTL phrase in words 2, 3 in an ltr paragraph:
  //     { 0, 1, kMinorRunStart, 3, 2, kMinorRunEnd, 4 }
  static void CalculateTextlineOrder(
      bool paragraph_is_ltr,
      const GenericVector<StrongScriptDirection> &word_dirs,
      GenericVectorEqEq<int> *reading_order);

  static const int kMinorRunStart;
  static const int kMinorRunEnd;
  static const int kComplexWord;

 protected:
  // We presume the data associated with the given iterator will outlive us.
  // NB: This is private because it does something that is non-obvious:
  //   it resets to the beginning of the paragraph instead of staying wherever
  //   resit might have pointed.
  explicit ResultIterator(const LTRResultIterator &resit);

 private:
  // Calculates the current paragraph's dominant writing direction.
  // Typically, members should use current_paragraph_ltr_ instead.
  bool CurrentParagraphIsLtr() const;

  // Returns word indices as measured from resit->RestartRow() = index 0
  // for the reading order of words within a textline given an iterator
  // into the middle of the text line.
  // In addition to non-negative word indices, the following negative values
  // may be inserted:
  //   kMinorRunStart  Start of minor direction text.
  //   kMinorRunEnd    End of minor direction text.
  //   kComplexWord    The previous word contains both left-to-right and
  //                   right-to-left characters and was treated as neutral.
  void CalculateTextlineOrder(bool paragraph_is_ltr,
                              const LTRResultIterator &resit,
                              GenericVectorEqEq<int> *indices) const;
  // Same as above, but the caller's ssd gets filled in if ssd != NULL.
  void CalculateTextlineOrder(bool paragraph_is_ltr,
                              const LTRResultIterator &resit,
                              GenericVector<StrongScriptDirection> *ssd,
                              GenericVectorEqEq<int> *indices) const;

  // What is the index of the current word in a strict left-to-right reading
  // of the row?
  int LTRWordIndex() const;

  // Given an iterator pointing at a word, returns the logical reading order
  // of blob indices for the word.
  void CalculateBlobOrder(GenericVector<int> *blob_indices) const;

  // Precondition: current_paragraph_is_ltr_ is set.
  void MoveToLogicalStartOfTextline();

  // Precondition: current_paragraph_is_ltr_ and in_minor_direction_ are set.
  void MoveToLogicalStartOfWord();

  // Are we pointing at the final (reading order) symbol of the word?
  bool IsAtFinalSymbolOfWord() const;

  // Are we pointing at the first (reading order) symbol of the word?
  bool IsAtFirstSymbolOfWord() const;

  // Append any extra marks that should be appended to this word when printed.
  // Mostly, these are Unicode BiDi control characters.
  void AppendSuffixMarks(STRING *text) const;

  // Appends the current word in reading order to the given buffer.
  void AppendUTF8WordText(STRING *text) const;

  // Appends the text of the current text line, *assuming this iterator is
  // positioned at the beginning of the text line*  This function
  // updates the iterator to point to the first position past the text line.
  // Each textline is terminated in a single newline character.
  // If the textline ends a paragraph, it gets a second terminal newline.
  void IterateAndAppendUTF8TextlineText(STRING *text);

  // Appends the text of the current paragraph in reading order
  // to the given buffer.
  // Each textline is terminated in a single newline character, and the
  // paragraph gets an extra newline at the end.
  void AppendUTF8ParagraphText(STRING *text) const;

  // Returns whether the bidi_debug flag is set to at least min_level.
  bool BidiDebug(int min_level) const;

  bool current_paragraph_is_ltr_;

  // Is the currently pointed-at character at the beginning of
  // a minor-direction run?
  bool at_beginning_of_minor_run_;

  // Is the currently pointed-at character in a minor-direction sequence?
  bool in_minor_direction_;
};

}  // namespace tesseract.

#endif  // TESSERACT_CCMAIN_RESULT_ITERATOR_H__