Clear lines drawn with TCanvas

Question

I am using TCanvas to draw a blue line whenever the left mouse button is clicked, and a red line whenever the right mouse button is clicked. Currently whenever I click another line is drawn on the chart. What I want to do is to clear the old line, and then draw a new line.

Below is some sample code.

The code for the onClick event

procedure TForm2.Chart1ChartClick(Sender: TJvChart; Button: TMouseButton;
   Shift: TShiftState; X, Y, ChartValueIndex, ChartPenIndex: Integer;
   var ShowHint, HintFirstLineBold: Boolean; HintStrs: TStrings);

begin


   if Button = mbLeft then
   begin

     canvas.pen.color := clblue;
     PlotHorizontal(X, Y);


   end
     else if Button = mbRight then
     begin

        Canvas.Pen.color := clred;
        PlotHorizontal(X, Y);

     end

end;

The PlotHorizontal procedure

procedure TForm2.PlotHorizontal(X, Y : integer);

begin
   with canvas do
   begin
   // draw the horizontal line
      MoveTo(X, Y);
   // without the 4 the line doesn't seem to reach the end of the graph
      LineTo(X, Chart1.Options.XStartOffset -4);
      MoveTo(X, Y);
      LineTo(X, Chart1.Options.XStartOffset +
       + Chart1.Options.Yend);
   end;
end;

Answer 1

I was able to get it working, by saving the old X, and Y values for where the lines were draw. Then when the mouse was clicked again, I refreshed the chart, and redrew the line again.