I want to label horizontal bar charts like the following example (ignore the numbers, they should be the value of the bar datapoint)



i.e. if the labels will fit within the bar, I want them to be white and positioned at the end of the bar.
If the label won't fit, I want it to be black and positioned after the end of the bar.
What do you suggest as the simplest way to achieve this?

Thanks
Kevin

Hi Kevin,

There is no way to conditionally color the data labels in the control and the automatic data label layout will just push the labels within the chart bounds so in this case it's probably best to use custom painting. The following code shows how to achieve this result:

  [Serializable]
  class NPaintCallback : INPaintCallback
  {
   void INPaintCallback.OnAfterPaint(NPanel panel, NPanelPaintEventArgs eventArgs)
   {
    NChart chart = (NChart)panel;
    NBarSeries bar = (NBarSeries)chart.Series[0];

    NScale2DToViewTransformation scale2View = new NScale2DToViewTransformation(chart, (int)StandardAxis.PrimaryX, (int)StandardAxis.PrimaryY);

    NTextStyle textStyle = new NTextStyle();
    textStyle.StringFormatStyle.HorzAlign = Nevron.HorzAlign.Center;

    NTextStyle textStyleBelow = new NTextStyle();
    textStyleBelow.FillStyle = new NColorFillStyle(Color.White);

    NPointF zeroPoint = new NPointF();
    scale2View.Transform(new NVector2DD(0, (double)bar.Values[0]), ref zeroPoint);

    for (int i = 0; i < bar.Values.Count; i++)
    {
     NPointF originPoint = new NPointF();

     double barValue = (double)bar.Values[i];
     scale2View.Transform(new NVector2DD(i, barValue), ref originPoint);

     string text = barValue.ToString();

     NSizeF textSize = eventArgs.Graphics.MeasureText(text, textStyle);

     int offset = 10;
     NPointF leftPoint = originPoint;
     leftPoint.X -= offset + textSize.Width;

     if (leftPoint.X > zeroPoint.X)
     {
      textStyle.FillStyle = new NColorFillStyle(Color.White);
      eventArgs.Graphics.PaintText("100", textStyle, new NPointF(originPoint.X - offset - textSize.Width / 2.0f, originPoint.Y));
     }
     else
     {
      textStyle.FillStyle = new NColorFillStyle(Color.Black);
      eventArgs.Graphics.PaintText("100", textStyle, new NPointF(originPoint.X + offset + textSize.Width / 2.0f, originPoint.Y));
     }
    }
   }
   void INPaintCallback.OnBeforePaint(NPanel panel, NPanelPaintEventArgs eventArgs)
   {
   }
  }

  private void Form1_Load(object sender, EventArgs e)
  {
   NChart chart = nChartControl1.Charts[0];
   chart.SetPredefinedChartStyle(PredefinedChartStyle.HorizontalLeft);

   NBarSeries bar = new NBarSeries();
   bar.DataLabelStyle.Visible = false;

   chart.PaintCallback = new NPaintCallback();

   bar.Values.Add(0);
   bar.Values.Add(20);
   bar.Values.Add(30);

   chart.Series.Add(bar);
  }

Hope this helps - let us know if you meet any problems.

Best Regards,
Nevron Support Team

Thanks. I now have this working - it gets quite complex coping with various permutation of chart layout and stacked bars etc.!

I have one remaining feature that I'm having trouble with. I want to display the label at the outside end of a horizontal bar, but only if it will fit in the chart area. I tried using the following code to transform the axis ranges:

              NAxis renderedAxis = chart.Axis(StandardAxis.PrimaryX);
                double minimumXAxis = renderedAxis.SeriesRange.GetBeginValue();

                // This does not read the displayed range on the axis
                renderedAxis = chart.Axis(StandardAxis.PrimaryY);
                double minimumPrimaryYAxis = renderedAxis.ViewRange.GetBeginValue();
                double maximumPrimaryYAxis = renderedAxis.ViewRange.GetEndValue();

                NPointF chartPoint = new NPointF();
                scale2ViewLeft.Transform(new NVector2DD(minimumXAxis, minimumPrimaryYAxis), ref chartPoint);
                float xPixelAtMinimumXValue = chartPoint.X;

                chartPoint = new NPointF();
                scale2ViewLeft.Transform(new NVector2DD(minimumXAxis, maximumPrimaryYAxis), ref chartPoint);
                float xPixelAtMaximumXValue = chartPoint.X;

I find that ViewRange always returns the SeriesRange. For example. my data ranges from 0 to 160, but the chart is drawn with a scale of 0 -200. There seems to be no range that returns 0 - 200. Am I missing something?

A much simpler alternative is
  this.MinimumXPixelForYAxis = 0; 
this.MaximumXPixelForYAxis = chart.ParentPanel.Bounds.Width;

which works, but I don't think it's robust. I'd prefer to get the NChart size but I can't see how to convert the NLength bounds to pixels.

What do you suggest?

Thanks

Kevin

Hi Kevin,
You need to use the ruler range - this is the final range after the view/content range has been extended by tick inflate or other range inflate:
NChart chart = nChartControl1.Charts[0];
NRange1DD rulerRange = chart.Axis(StandardAxis.PrimaryY).Scale.RulerRange;

You can also check out the chart ContentArea and PlotArea properties:
NChart chart = nChartControl1.Charts[0];
chart.ContentArea; // holds the chart area with axes
chart.PlotArea; // holds just the back chart wall area

Hope this helps - let us know if you meet any problems or have any questions.

Best Regards,
Nevron Support Team

Thanks once again. Obvious when you know how!