Function SplitText

libs/drape_frontend/text_layout.cpp:138–195

Scan longer shaped glyphs, and try to split them into two strings if a space glyph is present. NOTE: Works only for LTR texts. Implementation should be mirrored for RTL.

// Scan longer shaped glyphs, and try to split them into two strings if a space glyph is present.
// NOTE: Works only for LTR texts. Implementation should be mirrored for RTL.
buffer_vector<LineMetrics, 2> SplitText(bool forceNoWrap, float textScale, dp::GlyphFontAndId space,
                                        dp::text::TextMetrics const & str)
{
  // Add the whole line by default.
  buffer_vector<LineMetrics, 2> lines{
      {str.m_glyphs.size(), textScale * str.m_lineWidthInPixels, textScale * str.m_maxLineHeightInPixels}};

  size_t const count = str.m_glyphs.size();
  if (forceNoWrap || count <= 15)
    return lines;

  auto const begin = str.m_glyphs.begin();
  auto const end = str.m_glyphs.end();

  // Naive split on two parts using spaces as delimiters.
  // Doesn't take into an account the width of glyphs/string.
  auto const iMiddle = begin + count / 2;

  auto const isSpaceGlyph = [space](auto const & metrics) { return metrics.m_key == space; };
  // Find next delimiter after middle [m, e)
  auto iNext = std::find_if(iMiddle, end, isSpaceGlyph);

  // Find last delimiter before middle [b, m)
  auto iPrev = std::find_if(std::reverse_iterator(iMiddle), std::reverse_iterator(begin), isSpaceGlyph).base();
  // Don't split like this:
  //     xxxx
  // xxxxxxxxxxxx
  if (4 * (iPrev - begin) <= static_cast<long>(count))
    iPrev = end;
  else
    --iPrev;

  // Get the closest space to the middle.
  if (iNext == end || (iPrev != end && iMiddle - iPrev < iNext - iMiddle))
    iNext = iPrev;

  if (iNext == end)
    return lines;

  // Split string (actually, glyphs) into 2 parts.
  ASSERT(iNext != begin, ());
  ASSERT(space == iNext->m_key, ());

  auto const spaceIndex = iNext;
  auto const afterSpace = iNext + 1;
  ASSERT(afterSpace != end, ());

  lines.push_back(LineMetrics{
      count,
      textScale * std::accumulate(afterSpace, end, 0, [](auto acc, auto const & m) { return m.m_xAdvance + acc; }),
      textScale * str.m_maxLineHeightInPixels});

  // Update the first line too.
  lines[0].m_nextLineStartIndex = afterSpace - begin;
  auto const spaceWidth = textScale * spaceIndex->m_xAdvance;
  lines[0].m_scaledLength -= lines[1].m_scaledLength + spaceWidth;
  return lines;
}