How can I draw filled polygons in RChart? I need to draw polygons in the coordinate system of the chart which can be zoomed an panned.

Answer:

Primarily, RChart does not offer any polygons as drawing elements. However, you can use the event OnDataRendered to draw any number and complexity of polygons in an RChart. Following is a simple code snippet (the full program for Delphi 6 can be downloaded from here):

    const
      maxP = 10;
      RealPG : array[1..MaxP, 1..2] of double = ((3,3), (4,3), (5,5), (6,2), (5,1),
                                                 (4,-2), (-2,-4), (-2,-1), (-1,2), (0,1));
    ..
    ..
    ..

    (******************************************************************************)
    procedure TForm1.RChart1DataRendered(Sender: TObject; var Canvas: TCanvas;
      Top, Left: Integer);
    (******************************************************************************)

    var
      Polygon : array[1..MaxP] of TPoint;
      i       : integer;
      x,y     : integer;

    begin
    for i:=1 to MaxP do
      begin
      RChart1.R2M(RealPG[i,1],RealPG[i,2], x, y);
      Polygon[i].x := x-Left;
      Polygon[i].y := y-Top;
      end;
    Canvas.Brush.Color := clYellow;
    Canvas.Pen.Color := clBlack;
    canvas.Polygon (Polygon);
    end;