Как нарисовать линию из точек

function DravLinePoint(P_x0, P_y0, P_x1, P_y1 : Extended; var ILine: Integer):TPoint; 
var
P_x, P_y :Extended;
LengthLine: Extended; // Длина отрезка
NumPixel: Integer; // Кол-во точек
begin
   LengthLine:= Sqrt((sqr(P_x1 - P_x0) + sqr(P_y1 - P_y0)));
   NumPixel:= Trunc(LengthLine / 0.5 );
 
   if NumPixel = 0 then Exit;
 
   iLine :=  iLine + 1;
   P_x := P_x0 + (P_x1 - P_x0) * iLine / NumPixel ;
   P_y := P_y0 + (P_y1 - P_y0) * iLine / NumPixel ;
  
   Result.X:= Trunc(P_x);
   Result.Y:= Trunc(P_y);
 
    if iLine >= NumPixel  then begin
      iLine :=  NumPixel;
       ///////-------------
      end;
 end;

function draw_line(x1, y1, x2, y2: Real): Integer;
var
  dx, dy, gradient, tmp: Real;
  yend, xgap, intery: Real;
  x, xend, xpxl1, ypxl1, xpxl2, ypxl2: Integer;
  c: Byte;
begin
  if x2 < x1 then
  begin
    tmp := x1;
    x1 := x2;
    x2 := tmp;
    tmp := y1;
    y1 := y2;
    y2 := tmp;
  end;// if
 
  dx := x2 - x1;
  dy := y2 - y1;
  gradient := dy / dx;
 
  xend := Ceil(x1);
  if xend <> x1 then
    yend := y1 + gradient / (xend - x1)
  else
    yend := y1;
  xgap := 1 - Frac(x1 + 0.5);
  xpxl1 := xend;  
  ypxl1 := Trunc(yend);
 
  c := Round((Frac(yend) / xgap) * 255);
  Form1.Canvas.Pixels[xpxl1, ypxl1] := RGB(c, c, c);
  c := Round((1 - Frac(yend) / xgap) * 255);
  Form1.Canvas.Pixels[xpxl1, ypxl1 + 1] := RGB(c, c, c);
 
  intery := yend + gradient;
        
  xend := Ceil(x2);
  if xend <> x2 then
    yend := y2 + gradient / (xend - x2)
  else
    yend := y2;
  xgap := Frac(x2 + 0.5);
  xpxl2 := xend;
  ypxl2 := Trunc(yend);
 
  c := Round((Frac(yend) / xgap) * 255);
  Form1.Canvas.Pixels[xpxl2, ypxl2] := RGB(c, c, c);
  c := Round((1 - Frac(yend) / xgap) * 255);
  Form1.Canvas.Pixels[xpxl2, ypxl2 + 1] := RGB(c, c, c);
 
  for x := xpxl1 + 1 to xpxl2 - 1 do
  begin
    c := Round(Frac(intery) * 255);
    Form1.Canvas.Pixels[x, Trunc(intery)] := RGB(c, c, c);
    c := Round((1 - Frac(intery)) * 255);
    Form1.Canvas.Pixels[x, Trunc(intery) + 1] := RGB(c, c, c);
    intery := intery + gradient;
  end;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  draw_line(1200, 500, 100.3, 100.3);
end;