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# highlighter.cpp Example File
richtext/syntaxhighlighter/highlighter.cpp

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        #include <QtGui>

        #include "highlighter.h"

        Highlighter::Highlighter(QObject *parent)
            : QObject(parent)
        {
        }

        void Highlighter::addToDocument(QTextDocument *doc)
        {
            connect(doc, SIGNAL(contentsChange(int, int, int)),
                    this, SLOT(highlight(int, int, int)));
        }

        void Highlighter::addMapping(const QString &pattern,
                                     const QTextCharFormat &format)
        {
            mappings[pattern] = format;
        }

        void Highlighter::highlight(int position, int removed, int added)
        {
            QTextDocument *doc = qobject_cast<QTextDocument *>(sender());

            QTextBlock block = doc->findBlock(position);
            if (!block.isValid())
                return;

            QTextBlock endBlock;
            if (added > removed)
                endBlock = doc->findBlock(position + added);
            else
                endBlock = block;

            while (block.isValid() && !(endBlock < block)) {
                highlightBlock(block);
                block = block.next();
            }
        }

        void Highlighter::highlightBlock(QTextBlock block)
        {
            QTextLayout *layout = block.layout();
            const QString text = block.text();

            QList<QTextLayout::FormatRange> overrides;

            foreach (QString pattern, mappings.keys()) {
                QRegExp expression(pattern);
                int i = text.indexOf(expression);
                while (i >= 0) {
                    QTextLayout::FormatRange range;
                    range.start = i;
                    range.length = expression.matchedLength();
                    range.format = mappings[pattern];
                    overrides << range;

                    i = text.indexOf(expression, i + expression.matchedLength());
                }
            }

            layout->setAdditionalFormats(overrides);
            const_cast<QTextDocument *>(block.document())->markContentsDirty(
                block.position(), block.length());
        }