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TMS VCL Chart
Add custom X-axis values via an event

To override the standard X-axis values drawn by TAdvChartView an event OnXAxisDrawValue event is available for each serie. To add an event handler for OnXAxisDrawValue, declare a procedure and assign it to the serie.OnXAxisDrawValue event like in the code snippet below: 
AdvChartView.Panes[0].Series[0].OnXAxisDrawValue := XAxisDrawValue;

procedure TForm.XAxisDrawValue(Sender: TObject; Serie: TChartSerie;
  Canvas: TCanvas; ARect: TRect; ValueIndex, XMarker: integer; Top: Boolean;
  var defaultdraw: Boolean);
begin
  //Insert Code here
end;
In this event, the Serie parameter returns the Serie for which the X-axis value needs to be drawn. Further, the Canvas and rectangle within this canvas where can be drawn is returned. ValueIndex returns the index of the value along the X-axis. Top indicates whether the X-axis is on top or below the chart. Finally, by setting the DefaultDraw parameter to false, the chart itself will no longer draw the X-axis value.
The technique illustrated with following sample. Some points were added in a serie and for each odd value on the X-Axis we want to display a Car brand in the X-axis: 
procedure TForm.XAxisDrawValue(Sender: TObject; Serie: TChartSerie;
  Canvas: TCanvas; ARect: TRect; ValueIndex, XMarker: integer; Top: Boolean;
  var defaultdraw: Boolean);
  
const
  lst: array[0..4] of String = ('Audi', 'BMW', 'Mercedes', 'Bugatti', 'Porsche');
var
  s: String;
  th, tw: integer;
begin
  if Odd(ValueIndex) then
  begin
    Canvas.Font.Size := 12;
    s := lst[Random(Length(lst))];
    th := Canvas.TextHeight(s);
    tw := Canvas.TextWidth(s);
    Canvas.TextOut(Xmarker - (tw div 2), ARect.Top + th, s);
  end;
end;