Exemple #1
0
        /// <summary>
        /// Close off a <see cref="GraphicsPath"/> that defines a curve
        /// </summary>
        /// <param name="pane">A reference to the <see cref="GraphPane"/> object that is the parent or
        /// owner of this object.</param>
        /// <param name="curve">A <see cref="LineItem"/> representing this
        /// curve.</param>
        /// <param name="arrPoints">An array of <see cref="PointF"/> values in screen pixel
        /// coordinates representing the current curve.</param>
        /// <param name="count">The number of points contained in the "arrPoints"
        /// parameter.</param>
        /// <param name="yMin">The Y axis value location where the X axis crosses.</param>
        /// <param name="path">The <see cref="GraphicsPath"/> class that represents the curve.</param>
        public void CloseCurve( GraphPane pane, CurveItem curve, PointF[] arrPoints,
									int count, double yMin, GraphicsPath path )
        {
            // For non-stacked lines, the fill area is just the area between the curve and the X axis
            if ( pane.LineType != LineType.Stack )
            {
                // Determine the current value for the bottom of the curve (usually the Y value where
                // the X axis crosses)
                float yBase;
                Axis yAxis = curve.GetYAxis( pane );
                yBase = yAxis.Scale.Transform( yMin );

                // Add three points to the path to move from the end of the curve (as defined by
                // arrPoints) to the X axis, from there to the start of the curve at the X axis,
                // and from there back up to the beginning of the curve.
                path.AddLine( arrPoints[count - 1].X, arrPoints[count - 1].Y, arrPoints[count - 1].X, yBase );
                path.AddLine( arrPoints[count - 1].X, yBase, arrPoints[0].X, yBase );
                path.AddLine( arrPoints[0].X, yBase, arrPoints[0].X, arrPoints[0].Y );
            }
            // For stacked line types, the fill area is the area between this curve and the curve below it
            else
            {
                PointF[] arrPoints2;
                int count2;

                float tension = _isSmooth ? _smoothTension : 0f;

                // Find the next lower curve in the curveList that is also a LineItem type, and use
                // its smoothing properties for the lower side of the filled area.
                int index = pane.CurveList.IndexOf( curve );
                if ( index > 0 )
                {
                    CurveItem tmpCurve;
                    for ( int i = index - 1; i >= 0; i-- )
                    {
                        tmpCurve = pane.CurveList[i];
                        if ( tmpCurve is LineItem )
                        {
                            tension = ( (LineItem)tmpCurve ).Line.IsSmooth ? ( (LineItem)tmpCurve ).Line.SmoothTension : 0f;
                            break;
                        }
                    }
                }

                // Build another points array consisting of the low points (which are actually the points for
                // the curve below the current curve)
                BuildLowPointsArray( pane, curve, out arrPoints2, out count2 );

                // Add the new points to the GraphicsPath
                path.AddCurve( arrPoints2, 0, count2 - 2, tension );
            }
        }
Exemple #2
0
        /// <summary>
        /// Draw the this <see cref="CurveItem"/> to the specified <see cref="Graphics"/>
        /// device.  The format (stair-step or line) of the curve is
        /// defined by the <see cref="StepType"/> property.  The routine
        /// only draws the line segments; the symbols are drawn by the
        /// <see cref="Symbol.Draw"/> method.  This method
        /// is normally only called by the Draw method of the
        /// <see cref="CurveItem"/> object
        /// </summary>
        /// <param name="g">
        /// A graphic device object to be drawn into.  This is normally e.Graphics from the
        /// PaintEventArgs argument to the Paint() method.
        /// </param>
        /// <param name="scaleFactor">
        /// The scaling factor to be used for rendering objects.  This is calculated and
        /// passed down by the parent <see cref="GraphPane"/> object using the
        /// <see cref="PaneBase.CalcScaleFactor"/> method, and is used to proportionally adjust
        /// font sizes, etc. according to the actual size of the graph.
        /// </param>
        /// <param name="pane">
        /// A reference to the <see cref="GraphPane"/> object that is the parent or
        /// owner of this object.
        /// </param>
        /// <param name="curve">A <see cref="LineItem"/> representing this
        /// curve.</param>
        public void DrawCurveOriginal( Graphics g, GraphPane pane,
										  CurveItem curve, float scaleFactor )
        {
            Line source = this;
            if ( curve.IsSelected )
                source = Selection.Line;

            float tmpX, tmpY,
                    lastX = float.MaxValue,
                    lastY = float.MaxValue;
            double curX, curY, lowVal;
            PointPair curPt, lastPt = new PointPair();

            bool lastBad = true;
            IPointList points = curve.Points;
            ValueHandler valueHandler = new ValueHandler( pane, false );
            Axis yAxis = curve.GetYAxis( pane );
            Axis xAxis = curve.GetXAxis( pane );

            bool xIsLog = xAxis._scale.IsLog;
            bool yIsLog = yAxis._scale.IsLog;

            float minX = pane.Chart.Rect.Left;
            float maxX = pane.Chart.Rect.Right;
            float minY = pane.Chart.Rect.Top;
            float maxY = pane.Chart.Rect.Bottom;

            using ( Pen pen = source.GetPen( pane, scaleFactor ) )
            {
                if ( points != null && !_color.IsEmpty && this.IsVisible )
                {
                    //bool lastOut = false;
                    bool isOut;

                    // Loop over each point in the curve
                    for ( int i = 0; i < points.Count; i++ )
                    {
                        curPt = points[i];
                        if ( pane.LineType == LineType.Stack )
                        {
                            if ( !valueHandler.GetValues( curve, i, out curX, out lowVal, out curY ) )
                            {
                                curX = PointPair.Missing;
                                curY = PointPair.Missing;
                            }
                        }
                        else
                        {
                            curX = curPt.X;
                            curY = curPt.Y;
                        }

                        // Any value set to double max is invalid and should be skipped
                        // This is used for calculated values that are out of range, divide
                        //   by zero, etc.
                        // Also, any value <= zero on a log scale is invalid
                        if ( curX == PointPair.Missing ||
                                curY == PointPair.Missing ||
                                System.Double.IsNaN( curX ) ||
                                System.Double.IsNaN( curY ) ||
                                System.Double.IsInfinity( curX ) ||
                                System.Double.IsInfinity( curY ) ||
                                ( xIsLog && curX <= 0.0 ) ||
                                ( yIsLog && curY <= 0.0 ) )
                        {
                            // If the point is invalid, then make a linebreak only if IsIgnoreMissing is false
                            // LastX and LastY are always the last valid point, so this works out
                            lastBad = lastBad || !pane.IsIgnoreMissing;
                            isOut = true;
                        }
                        else
                        {
                            // Transform the current point from user scale units to
                            // screen coordinates
                            tmpX = xAxis.Scale.Transform( curve.IsOverrideOrdinal, i, curX );
                            tmpY = yAxis.Scale.Transform( curve.IsOverrideOrdinal, i, curY );
                            isOut = ( tmpX < minX && lastX < minX ) || ( tmpX > maxX && lastX > maxX ) ||
                                ( tmpY < minY && lastY < minY ) || ( tmpY > maxY && lastY > maxY );

                            if ( !lastBad )
                            {
                                try
                                {
                                    // GDI+ plots the data wrong and/or throws an exception for
                                    // outrageous coordinates, so we do a sanity check here
                                    if ( lastX > 5000000 || lastX < -5000000 ||
                                            lastY > 5000000 || lastY < -5000000 ||
                                            tmpX > 5000000 || tmpX < -5000000 ||
                                            tmpY > 5000000 || tmpY < -5000000 )
                                        InterpolatePoint( g, pane, curve, lastPt, scaleFactor, pen,
                                                        lastX, lastY, tmpX, tmpY );
                                    else if ( !isOut )
                                    {
                                        if ( !curve.IsSelected && this._gradientFill.IsGradientValueType )
                                        {
                                            using ( Pen tPen = GetPen( pane, scaleFactor, lastPt ) )
                                            {
                                                if ( this.StepType == StepType.NonStep )
                                                {
                                                    g.DrawLine( tPen, lastX, lastY, tmpX, tmpY );
                                                }
                                                else if ( this.StepType == StepType.ForwardStep )
                                                {
                                                    g.DrawLine( tPen, lastX, lastY, tmpX, lastY );
                                                    g.DrawLine( tPen, tmpX, lastY, tmpX, tmpY );
                                                }
                                                else if ( this.StepType == StepType.RearwardStep )
                                                {
                                                    g.DrawLine( tPen, lastX, lastY, lastX, tmpY );
                                                    g.DrawLine( tPen, lastX, tmpY, tmpX, tmpY );
                                                }
                                                else if ( this.StepType == StepType.ForwardSegment )
                                                {
                                                    g.DrawLine( tPen, lastX, lastY, tmpX, lastY );
                                                }
                                                else
                                                {
                                                    g.DrawLine( tPen, lastX, tmpY, tmpX, tmpY );
                                                }
                                            }
                                        }
                                        else
                                        {
                                            if ( this.StepType == StepType.NonStep )
                                            {
                                                g.DrawLine( pen, lastX, lastY, tmpX, tmpY );
                                            }
                                            else if ( this.StepType == StepType.ForwardStep )
                                            {
                                                g.DrawLine( pen, lastX, lastY, tmpX, lastY );
                                                g.DrawLine( pen, tmpX, lastY, tmpX, tmpY );
                                            }
                                            else if ( this.StepType == StepType.RearwardStep )
                                            {
                                                g.DrawLine( pen, lastX, lastY, lastX, tmpY );
                                                g.DrawLine( pen, lastX, tmpY, tmpX, tmpY );
                                            }
                                            else if ( this.StepType == StepType.ForwardSegment )
                                            {
                                                g.DrawLine( pen, lastX, lastY, tmpX, lastY );
                                            }
                                            else if ( this.StepType == StepType.RearwardSegment )
                                            {
                                                g.DrawLine( pen, lastX, tmpY, tmpX, tmpY );
                                            }
                                        }
                                    }

                                }
                                catch
                                {
                                    InterpolatePoint( g, pane, curve, lastPt, scaleFactor, pen,
                                                lastX, lastY, tmpX, tmpY );
                                }

                            }

                            lastPt = curPt;
                            lastX = tmpX;
                            lastY = tmpY;
                            lastBad = false;
                            //lastOut = isOut;
                        }
                    }
                }
            }
        }
Exemple #3
0
        /// <summary>
        /// Build an array of <see cref="PointF"/> values (pixel coordinates) that represents
        /// the current curve.  Note that this drawing routine ignores <see cref="PointPairBase.Missing"/>
        /// values, but it does not "break" the line to indicate values are missing.
        /// </summary>
        /// <param name="pane">A reference to the <see cref="GraphPane"/> object that is the parent or
        /// owner of this object.</param>
        /// <param name="curve">A <see cref="LineItem"/> representing this
        /// curve.</param>
        /// <param name="arrPoints">An array of <see cref="PointF"/> values in pixel
        /// coordinates representing the current curve.</param>
        /// <param name="count">The number of points contained in the "arrPoints"
        /// parameter.</param>
        /// <returns>true for a successful points array build, false for data problems</returns>
        public bool BuildPointsArray( GraphPane pane, CurveItem curve,
			out PointF[] arrPoints, out int count )
        {
            arrPoints = null;
            count = 0;
            IPointList points = curve.Points;

            if ( this.IsVisible && !this.Color.IsEmpty && points != null )
            {
                int index = 0;
                float curX, curY,
                            lastX = 0,
                            lastY = 0;
                double x, y, lowVal;
                ValueHandler valueHandler = new ValueHandler( pane, false );

                // Step type plots get twice as many points.  Always add three points so there is
                // room to close out the curve for area fills.
                arrPoints = new PointF[( _stepType == ZedGraph.StepType.NonStep ? 1 : 2 ) *
                                            points.Count + 1];

                // Loop over all points in the curve
                for ( int i = 0; i < points.Count; i++ )
                {
                    // make sure that the current point is valid
                    if ( !points[i].IsInvalid )
                    {
                        // Get the user scale values for the current point
                        // use the valueHandler only for stacked types
                        if ( pane.LineType == LineType.Stack )
                        {
                            valueHandler.GetValues( curve, i, out x, out lowVal, out y );
                        }
                        // otherwise, just access the values directly.  Avoiding the valueHandler for
                        // non-stacked types is an optimization to minimize overhead in case there are
                        // a large number of points.
                        else
                        {
                            x = points[i].X;
                            y = points[i].Y;
                        }

                        if ( x == PointPair.Missing || y == PointPair.Missing )
                            continue;

                        // Transform the user scale values to pixel locations
                        Axis xAxis = curve.GetXAxis( pane );
                        curX = xAxis.Scale.Transform( curve.IsOverrideOrdinal, i, x );
                        Axis yAxis = curve.GetYAxis( pane );
                        curY = yAxis.Scale.Transform( curve.IsOverrideOrdinal, i, y );

                        if ( curX < -1000000 || curY < -1000000 || curX > 1000000 || curY > 1000000 )
                            continue;

                        // Add the pixel value pair into the points array
                        // Two points are added for step type curves
                        // ignore step-type setting for smooth curves
                        if ( _isSmooth || index == 0 || this.StepType == StepType.NonStep )
                        {
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }
                        else if ( this.StepType == StepType.ForwardStep ||
                                        this.StepType == StepType.ForwardSegment )
                        {
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = lastY;
                            index++;
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }
                        else if ( this.StepType == StepType.RearwardStep ||
                                        this.StepType == StepType.RearwardSegment )
                        {
                            arrPoints[index].X = lastX;
                            arrPoints[index].Y = curY;
                            index++;
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }

                        lastX = curX;
                        lastY = curY;
                        index++;

                    }

                }

                // Make sure there is at least one valid point
                if ( index == 0 )
                    return false;

                // Add an extra point at the end, since the smoothing algorithm requires it
                arrPoints[index] = arrPoints[index - 1];
                index++;

                count = index;
                return true;
            }
            else
            {
                return false;
            }
        }
Exemple #4
0
        /// <summary>
        /// Build an array of <see cref="PointF"/> values (pixel coordinates) that represents
        /// the low values for the current curve.
        /// </summary>
        /// <remarks>Note that this drawing routine ignores <see cref="PointPairBase.Missing"/>
        /// values, but it does not "break" the line to indicate values are missing.
        /// </remarks>
        /// <param name="pane">A reference to the <see cref="GraphPane"/> object that is the parent or
        /// owner of this object.</param>
        /// <param name="curve">A <see cref="LineItem"/> representing this
        /// curve.</param>
        /// <param name="arrPoints">An array of <see cref="PointF"/> values in pixel
        /// coordinates representing the current curve.</param>
        /// <param name="count">The number of points contained in the "arrPoints"
        /// parameter.</param>
        /// <returns>true for a successful points array build, false for data problems</returns>
        public bool BuildLowPointsArray( GraphPane pane, CurveItem curve,
						out PointF[] arrPoints, out int count )
        {
            arrPoints = null;
            count = 0;
            IPointList points = curve.Points;

            if ( this.IsVisible && !this.Color.IsEmpty && points != null )
            {
                int index = 0;
                float curX, curY,
                        lastX = 0,
                        lastY = 0;
                double x, y, hiVal;
                ValueHandler valueHandler = new ValueHandler( pane, false );

                // Step type plots get twice as many points.  Always add three points so there is
                // room to close out the curve for area fills.
                arrPoints = new PointF[( _stepType == ZedGraph.StepType.NonStep ? 1 : 2 ) *
                    ( pane.LineType == LineType.Stack ? 2 : 1 ) *
                    points.Count + 1];

                // Loop backwards over all points in the curve
                // In this case an array of points was already built forward by BuildPointsArray().
                // This time we build backwards to complete a loop around the area between two curves.
                for ( int i = points.Count - 1; i >= 0; i-- )
                {
                    // Make sure the current point is valid
                    if ( !points[i].IsInvalid )
                    {
                        // Get the user scale values for the current point
                        valueHandler.GetValues( curve, i, out x, out y, out hiVal );

                        if ( x == PointPair.Missing || y == PointPair.Missing )
                            continue;

                        // Transform the user scale values to pixel locations
                        Axis xAxis = curve.GetXAxis( pane );
                        curX = xAxis.Scale.Transform( curve.IsOverrideOrdinal, i, x );
                        Axis yAxis = curve.GetYAxis( pane );
                        curY = yAxis.Scale.Transform( curve.IsOverrideOrdinal, i, y );

                        // Add the pixel value pair into the points array
                        // Two points are added for step type curves
                        // ignore step-type setting for smooth curves
                        if ( _isSmooth || index == 0 || this.StepType == StepType.NonStep )
                        {
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }
                        else if ( this.StepType == StepType.ForwardStep )
                        {
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = lastY;
                            index++;
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }
                        else if ( this.StepType == StepType.RearwardStep )
                        {
                            arrPoints[index].X = lastX;
                            arrPoints[index].Y = curY;
                            index++;
                            arrPoints[index].X = curX;
                            arrPoints[index].Y = curY;
                        }

                        lastX = curX;
                        lastY = curY;
                        index++;

                    }

                }

                // Make sure there is at least one valid point
                if ( index == 0 )
                    return false;

                // Add an extra point at the end, since the smoothing algorithm requires it
                arrPoints[index] = arrPoints[index - 1];
                index++;

                count = index;
                return true;
            }
            else
            {
                return false;
            }
        }
Exemple #5
0
        /// <summary>
        /// Render the <see cref="Line"/>'s as vertical sticks (from a <see cref="StickItem" />) to
        /// the specified <see cref="Graphics"/> device.
        /// </summary>
        /// <param name="g">
        /// A graphic device object to be drawn into.  This is normally e.Graphics from the
        /// PaintEventArgs argument to the Paint() method.
        /// </param>
        /// <param name="pane">
        /// A reference to the <see cref="ZedGraph.GraphPane"/> object that is the parent or
        /// owner of this object.
        /// </param>
        /// <param name="curve">A <see cref="CurveItem"/> representing this
        /// curve.</param>
        /// <param name="scaleFactor">
        /// The scaling factor to be used for rendering objects.  This is calculated and
        /// passed down by the parent <see cref="GraphPane"/> object using the
        /// <see cref="PaneBase.CalcScaleFactor"/> method, and is used to proportionally adjust
        /// font sizes, etc. according to the actual size of the graph.
        /// </param>
        public void DrawSticks( Graphics g, GraphPane pane, CurveItem curve, float scaleFactor )
        {
            Line source = this;
            if ( curve.IsSelected )
                source = Selection.Line;

            Axis yAxis = curve.GetYAxis( pane );
            Axis xAxis = curve.GetXAxis( pane );

            float basePix = yAxis.Scale.Transform( 0.0 );
            using ( Pen pen = source.GetPen( pane, scaleFactor ) )
            {
                for ( int i = 0; i < curve.Points.Count; i++ )
                {
                    PointPair pt = curve.Points[i];

                    if ( pt.X != PointPair.Missing &&
                            pt.Y != PointPair.Missing &&
                            !System.Double.IsNaN( pt.X ) &&
                            !System.Double.IsNaN( pt.Y ) &&
                            !System.Double.IsInfinity( pt.X ) &&
                            !System.Double.IsInfinity( pt.Y ) &&
                            ( !xAxis._scale.IsLog || pt.X > 0.0 ) &&
                            ( !yAxis._scale.IsLog || pt.Y > 0.0 ) )
                    {
                        float pixY = yAxis.Scale.Transform( curve.IsOverrideOrdinal, i, pt.Y );
                        float pixX = xAxis.Scale.Transform( curve.IsOverrideOrdinal, i, pt.X );

                        if ( pixX >= pane.Chart._rect.Left && pixX <= pane.Chart._rect.Right )
                        {
                            if ( pixY > pane.Chart._rect.Bottom )
                                pixY = pane.Chart._rect.Bottom;
                            if ( pixY < pane.Chart._rect.Top )
                                pixY = pane.Chart._rect.Top;

                            if ( !curve.IsSelected && this._gradientFill.IsGradientValueType )
                            {
                                using ( Pen tPen = GetPen( pane, scaleFactor, pt ) )
                                    g.DrawLine( tPen, pixX, pixY, pixX, basePix );
                            }
                            else
                                g.DrawLine( pen, pixX, pixY, pixX, basePix );

                        }
                    }
                }
            }
        }
Exemple #6
0
        /// <summary>
        /// Draw the this <see cref="CurveItem"/> to the specified <see cref="Graphics"/>
        /// device using the specified smoothing property (<see cref="ZedGraph.Line.SmoothTension"/>).
        /// The routine draws the line segments and the area fill (if any, see <see cref="FillType"/>;
        /// the symbols are drawn by the <see cref="Symbol.Draw"/> method.  This method
        /// is normally only called by the Draw method of the
        /// <see cref="CurveItem"/> object.  Note that the <see cref="StepType"/> property
        /// is ignored for smooth lines (e.g., when <see cref="ZedGraph.Line.IsSmooth"/> is true).
        /// </summary>
        /// <param name="g">
        /// A graphic device object to be drawn into.  This is normally e.Graphics from the
        /// PaintEventArgs argument to the Paint() method.
        /// </param>
        /// <param name="scaleFactor">
        /// The scaling factor to be used for rendering objects.  This is calculated and
        /// passed down by the parent <see cref="GraphPane"/> object using the
        /// <see cref="PaneBase.CalcScaleFactor"/> method, and is used to proportionally adjust
        /// font sizes, etc. according to the actual size of the graph.
        /// </param>
        /// <param name="pane">
        /// A reference to the <see cref="GraphPane"/> object that is the parent or
        /// owner of this object.
        /// </param>
        /// <param name="curve">A <see cref="LineItem"/> representing this
        /// curve.</param>
        public void DrawSmoothFilledCurve( Graphics g, GraphPane pane,
                                CurveItem curve, float scaleFactor )
        {
            Line source = this;
            if ( curve.IsSelected )
                source = Selection.Line;

            PointF[] arrPoints;
            int count;
            IPointList points = curve.Points;

            if ( this.IsVisible && !this.Color.IsEmpty && points != null &&
                BuildPointsArray( pane, curve, out arrPoints, out count ) &&
                count > 2 )
            {
                float tension = _isSmooth ? _smoothTension : 0f;

                // Fill the curve if needed
                if ( this.Fill.IsVisible )
                {
                    Axis yAxis = curve.GetYAxis( pane );

                    using ( GraphicsPath path = new GraphicsPath( FillMode.Winding ) )
                    {
                        path.AddCurve( arrPoints, 0, count - 2, tension );

                        double yMin = yAxis._scale._min < 0 ? 0.0 : yAxis._scale._min;
                        CloseCurve( pane, curve, arrPoints, count, yMin, path );

                        RectangleF rect = path.GetBounds();
                        using ( Brush brush = source._fill.MakeBrush( rect ) )
                        {
                            if ( pane.LineType == LineType.Stack && yAxis.Scale._min < 0 &&
                                    this.IsFirstLine( pane, curve ) )
                            {
                                float zeroPix = yAxis.Scale.Transform( 0 );
                                RectangleF tRect = pane.Chart._rect;
                                tRect.Height = zeroPix - tRect.Top;
                                if ( tRect.Height > 0 )
                                {
                                    Region reg = g.Clip;
                                    g.SetClip( tRect );
                                    g.FillPath( brush, path );
                                    g.SetClip( pane.Chart._rect );
                                }
                            }
                            else
                                g.FillPath( brush, path );
                            //brush.Dispose();
                        }

                        // restore the zero line if needed (since the fill tends to cover it up)
                        yAxis.FixZeroLine( g, pane, scaleFactor, rect.Left, rect.Right );
                    }
                }

                // If it's a smooth curve, go ahead and render the path.  Otherwise, use the
                // standard drawcurve method just in case there are missing values.
                if ( _isSmooth )
                {
                    using ( Pen pen = GetPen( pane, scaleFactor ) )
                    {
                        // Stroke the curve
                        g.DrawCurve( pen, arrPoints, 0, count - 2, tension );

                        //pen.Dispose();
                    }
                }
                else
                    DrawCurve( g, pane, curve, scaleFactor );
            }
        }
Exemple #7
0
        /// <summary>
        /// Create a URL for a <see cref="CurveItem" /> that includes the index of the
        /// point that was selected.
        /// </summary>
        /// <remarks>
        /// An "index" parameter is added to the <see cref="Url" /> property for this
        /// link to indicate which point was selected.  Further, if the 
        /// X or Y axes that correspond to this <see cref="CurveItem" /> are of
        /// <see cref="AxisType.Text" />, then an
        /// additional parameter will be added containing the text value that
        /// corresponds to the <paramref name="index" /> of the selected point.
        /// The <see cref="XAxis" /> text parameter will be labeled "xtext", and
        /// the <see cref="YAxis" /> text parameter will be labeled "ytext".
        /// </remarks>
        /// <param name="index">The zero-based index of the selected point</param>
        /// <param name="pane">The <see cref="GraphPane" /> of interest</param>
        /// <param name="curve">The <see cref="CurveItem" /> for which to
        /// make the url string.</param>
        /// <returns>A string containing the url with an index parameter added.</returns>
        public virtual string MakeCurveItemUrl( GraphPane pane, CurveItem curve, int index )
        {
            string url = _url;

            if ( url.IndexOf( '?' ) >= 0 )
                url += "&index=" + index.ToString();
            else
                url += "?index=" + index.ToString();

            Axis xAxis = curve.GetXAxis( pane );
            if (	xAxis.Type == AxisType.Text && index >= 0 &&
                    xAxis.Scale.TextLabels != null &&
                    index <= xAxis.Scale.TextLabels.Length )
                url += "&xtext=" + xAxis.Scale.TextLabels[index];

            Axis yAxis = curve.GetYAxis( pane );
            if (	yAxis != null && yAxis.Type == AxisType.Text && index >= 0 &&
                    yAxis.Scale.TextLabels != null &&
                    index <= yAxis.Scale.TextLabels.Length )
                url += "&ytext=" + yAxis.Scale.TextLabels[index];

            return url;
        }