Функция построения графика

private
   FPoints: array [0..144] of TPoint;
 
 {...}
 
 procedure TForm1.CalculateGraph;
 var
   xRangePixels, yRangePixels: Integer;
   origin: TPoint;
   radian, interval: Double;
   i: Integer;
 begin
   { 
    We calculate the sinus curve in the interval -2Pi..+2Pi, 
    with a resolution of 4Pi/144, as a series of points that 
    will be connected by a polyline. The graph is scaled to fit into 
    the paintbox. The origin of the coordinate system is the center 
    of the paintbox. The default windows coordinate system is inverted, 
    the Y axis points downward! 
  }
   xRangePixels := (paintbox1.Width - 2) div 4; { pixels in Pi }
   yRangePixels := (paintbox1.Height - 2) div 2; { pixels in 1 }
   origin       := Point(paintbox1.Width div 2, paintbox1.Height div 2);
   radian       := -2.0 * Pi;
   interval     := 4.0 * Pi / 144.0;
   for i := 0 to High(FPoints) do
    begin
     FPoints[i].X := origin.x + Round(radian * xRangePixels / Pi);
     FPoints[i].Y := origin.y - Round(sin(radian) * yRangePixels);
     radian       := radian + interval;
   end;
 end;
 
 procedure TForm1.PaintBox1Paint(Sender: TObject);
 var
   origin: TPoint;
   xRangePixels, yRangePixels: Integer;
 begin
   with PaintBox1.Canvas do
    begin
     { Fill background in white }
     Brush.Color := clBtnFace;
     Brush.Style := bsSolid;
     Fillrect(paintbox1.BoundsRect);
 
     { Paint a coordinate cross }
     origin    := Point(paintbox1.Width div 2, paintbox1.Height div 2);
     Pen.Color := clBlack;
     Pen.Style := psSolid;
     Pen.Width := 1;
     MoveTo(1, origin.Y);
     LineTo(paintbox1.Width - 1, origin.y);
     MoveTo(origin.x, 1);
     LineTo(origin.x, paintbox1.Height - 1);
 
     { Paint some tickmarks and label the axis }
     Font.Name    := 'Symbol';
     Font.Size    := 8;
     Font.Color   := clBlack;
     xRangePixels := (paintbox1.Width - 2) div 4; { pixels in Pi }
     yRangePixels := (paintbox1.Height - 2) div 2; { pixels in 1 }
 
     { X axis }
     MoveTo(origin.x - 2 * xRangePixels, origin.y - 4);
     LineTo(origin.x - 2 * xRangePixels, origin.y + 4);
     TextOut(origin.x - 2 * xRangePixels + 2, origin.y + 2, '-2p');
     MoveTo(origin.x - xRangePixels, origin.y - 4);
     LineTo(origin.x - xRangePixels, origin.y + 4);
     TextOut(origin.x - xRangePixels + 2, origin.y + 2, '-p');
     MoveTo(origin.x + xRangePixels, origin.y - 4);
     LineTo(origin.x + xRangePixels, origin.y + 4);
     TextOut(origin.x + xRangePixels - 2 - TextWidth('p'), origin.y + 2, 'p');
     MoveTo(origin.x + 2 * xRangePixels, origin.y - 4);
     LineTo(origin.x + 2 * xRangePixels, origin.y + 4);
     TextOut(origin.x + 2 * xRangePixels - 2 - TextWidth('2p'), origin.y + 2, '2p');
 
 
     { Y axis }
     MoveTo(origin.x - 4, origin.y - yRangePixels);
     LineTo(origin.x + 4, origin.y - yRangePixels);
     TextOut(origin.x + 4, origin.y - yRangePixels, '1.0');
     MoveTo(origin.x - 4, origin.y - yRangePixels div 2);
     LineTo(origin.x + 4, origin.y - yRangePixels div 2);
     TextOut(origin.x + 4, origin.y - (yRangePixels + TextHeight('1')) div 2, '0.5');
     MoveTo(origin.x - 2, origin.y + yRangePixels div 2);
     LineTo(origin.x + 2, origin.y + yRangePixels div 2);
     TextOut(origin.x + 3, origin.y + (yRangePixels - TextHeight('1')) div 2, '-0.5');
     MoveTo(origin.x - 2, origin.y + yRangePixels);
     LineTo(origin.x + 2, origin.y + yRangePixels);
     TextOut(origin.x + 3, origin.y + yRangePixels - TextHeight('1'), '-1.0');
 
     {Paint the graph }
     Pen.Color := clBlue;
     Polyline(FPoints);
   end;
 end;
 
 procedure TForm1.FormResize(Sender: TObject);
 begin
   CalculateGraph;
 end;
 
 procedure TForm1.FormCreate(Sender: TObject);
 begin
   CalculateGraph;
 end;

Взято с сайта: https://www.swissdelphicenter.ch