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 ** This file is part of the examples of the Qt Toolkit.
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#include <QtGui>

#include "codeeditor.h"

CodeEditor::CodeEditor(QWidget* parent)
  : QPlainTextEdit(parent)
{
  lineNumberArea = new LineNumberArea(this);

  connect(this, SIGNAL(blockCountChanged(int)), this,
          SLOT(updateLineNumberAreaWidth(int)));
  connect(this, SIGNAL(updateRequest(QRect, int)), this,
          SLOT(updateLineNumberArea(QRect, int)));
  connect(this, SIGNAL(cursorPositionChanged()), this,
          SLOT(highlightCurrentLine()));

  updateLineNumberAreaWidth(0);
  highlightCurrentLine();
}

int CodeEditor::lineNumberAreaWidth()
{
  int digits = 1;
  int max = qMax(1, blockCount());
  while (max >= 10) {
    max /= 10;
    ++digits;
  }

  int space = 3 + fontMetrics().width(QLatin1Char('9')) * digits;

  return space;
}

void CodeEditor::updateLineNumberAreaWidth(int /* newBlockCount */)
{
  setViewportMargins(lineNumberAreaWidth(), 0, 0, 0);
}

void CodeEditor::updateLineNumberArea(const QRect& rect, int dy)
{
  if (dy)
    lineNumberArea->scroll(0, dy);
  else
    lineNumberArea->update(0, rect.y(), lineNumberArea->width(),
                           rect.height());

  if (rect.contains(viewport()->rect()))
    updateLineNumberAreaWidth(0);
}

void CodeEditor::resizeEvent(QResizeEvent* e)
{
  QPlainTextEdit::resizeEvent(e);

  QRect cr = contentsRect();
  lineNumberArea->setGeometry(
    QRect(cr.left(), cr.top(), lineNumberAreaWidth(), cr.height()));
}

void CodeEditor::highlightCurrentLine()
{
  QList<QTextEdit::ExtraSelection> extraSelections;

  if (!isReadOnly()) {
    QTextEdit::ExtraSelection selection;

    QColor lineColor = QColor(Qt::yellow).lighter(160);

    selection.format.setBackground(lineColor);
    selection.format.setProperty(QTextFormat::FullWidthSelection, true);
    selection.cursor = textCursor();
    selection.cursor.clearSelection();
    extraSelections.append(selection);
  }

  setExtraSelections(extraSelections);
}

void CodeEditor::lineNumberAreaPaintEvent(QPaintEvent* event)
{
  QPainter painter(lineNumberArea);
  painter.fillRect(event->rect(), Qt::lightGray);

  QTextBlock block = firstVisibleBlock();
  int blockNumber = block.blockNumber();
  int top =
    (int)blockBoundingGeometry(block).translated(contentOffset()).top();
  int bottom = top + (int)blockBoundingRect(block).height();

  while (block.isValid() && top <= event->rect().bottom()) {
    if (block.isVisible() && bottom >= event->rect().top()) {
      QString number = QString::number(blockNumber + 1);
      painter.setPen(Qt::black);
      painter.drawText(0, top, lineNumberArea->width(), fontMetrics().height(),
                       Qt::AlignRight, number);
    }

    block = block.next();
    top = bottom;
    bottom = top + (int)blockBoundingRect(block).height();
    ++blockNumber;
  }
}

#include "codeeditor.moc"