plot a function?

Author :Perter Below

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;