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Rich-text area for JavaFX
There is a newer version: 0.11.3
package org.fxmisc.richtext;

import static org.fxmisc.richtext.model.TwoDimensional.Bias.*;

import java.util.ArrayList;
import java.util.List;

import javafx.geometry.Point2D;
import javafx.geometry.Rectangle2D;
import javafx.scene.control.IndexRange;
import org.fxmisc.richtext.model.TwoLevelNavigator;

import javafx.scene.shape.PathElement;
import javafx.scene.text.HitInfo;
import javafx.scene.text.TextFlow;
import javafx.scene.shape.LineTo;
import javafx.scene.shape.MoveTo;

/**
 * Adds additional API to {@link TextFlow}.
 */
class TextFlowExt extends TextFlow {
    
    private TextFlowLayout layout;
    
    private TextFlowLayout textLayout()
    {
        if ( layout == null ) {
            layout = new TextFlowLayout( this, getManagedChildren() );
        }
        return layout;
    }

    int getLineCount() {
        return textLayout().getLineCount();
    }

    int getLineStartPosition(int charIdx) {
        TwoLevelNavigator navigator = textLayout().getTwoLevelNavigator();
        int currentLineIndex = navigator.offsetToPosition(charIdx, Forward).getMajor();
        return navigator.position(currentLineIndex, 0).toOffset();
    }

    int getLineEndPosition(int charIdx) {
        TwoLevelNavigator navigator = textLayout().getTwoLevelNavigator();
        int currentLineIndex = navigator.offsetToPosition(charIdx, Forward).getMajor();
        int minor = (currentLineIndex == getLineCount() - 1) ? 0 : -1;
        return navigator.position(currentLineIndex + 1, minor).toOffset();
    }

    int getLineOfCharacter(int charIdx) {
        TwoLevelNavigator navigator = textLayout().getTwoLevelNavigator();
        return navigator.offsetToPosition(charIdx, Forward).getMajor();
    }

    PathElement[] getCaretShape(int charIdx, boolean isLeading) {
        return caretShape(charIdx, isLeading);
    }

    PathElement[] getRangeShape(IndexRange range) {
        return getRangeShape(range.getStart(), range.getEnd());
    }

    PathElement[] getRangeShape(int from, int to) {
        return rangeShape(from, to);
    }

    PathElement[] getUnderlineShape(IndexRange range) {
        return getUnderlineShape(range.getStart(), range.getEnd());
    }

    /**
     * @param from The index of the first character.
     * @param to The index of the last character.
     * @return An array with the PathElement objects which define an
     *         underline from the first to the last character.
     */
    PathElement[] getUnderlineShape(int from, int to) {
        // get a Path for the text underline
        List result = new ArrayList<>();
        
        PathElement[] shape = rangeShape( from, to );
        // The shape is a closed Path for one or more rectangles AROUND the selected text. 
        // shape: [MoveTo origin, LineTo top R, LineTo bottom R, LineTo bottom L, LineTo origin, *]

        // Extract the bottom left and right coordinates for each rectangle to get the underline path.
        for ( int ele = 2; ele < shape.length; ele += 5 )
        {
            LineTo bl = (LineTo) shape[ele+1];
            LineTo br = (LineTo) shape[ele];
            double y = br.getY() - 2.5;
            
            result.add( new MoveTo( bl.getX(), y ) );
            result.add( new LineTo( br.getX(), y ) );
        }

        return result.toArray(new PathElement[0]);
    }

    CharacterHit hitLine(double x, int lineIndex) {
        return hit(x, textLayout().getLineCenter( lineIndex ));
    }

    CharacterHit hit(double x, double y) {
        TextFlowSpan span = textLayout().getLineSpan( (float) y );
        Rectangle2D lineBounds = span.getBounds();
        
        HitInfo hit = hitTest(new Point2D(x, y));
        int charIdx = hit.getCharIndex();
        boolean leading = hit.isLeading();

        if ( ! leading ) {
            // If this is a wrapped paragraph and hit character is at end of hit line, make sure that the
            // "character hit" stays at the end of the hit line (and not at the beginning of the next line).
            leading = (getLineCount() > 1 && charIdx + 1 >= span.getStart() + span.getLength());
        }

        if(x < lineBounds.getMinX() || x > lineBounds.getMaxX()) {
            if(leading) {
                return CharacterHit.insertionAt(charIdx);
            } else {
                return CharacterHit.insertionAt(charIdx + 1);
            }
        } else {
            if(leading) {
                return CharacterHit.leadingHalfOf(charIdx);
            } else {
                return CharacterHit.trailingHalfOf(charIdx);
            }
        }
    }

}