Алгоритм Брезенхэма построения линии в Lazarus (Pascal)

unit Unit1;
 
{$mode objfpc}{$H+}
 
interface
 
uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, ExtCtrls,
  StdCtrls;
 
type
 
  { TForm1 }
 
  TForm1 = class(TForm)
    Button1: TButton;
    PaintBox1: TPaintBox;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.lfm}
 
{ TForm1 }
 
procedure DrawLine(x0,y0,x1,y1:integer;col:TColor);
var
  dx,dy,sx,sy,d,d1,d2,x,y,i:integer;
begin
 
  if (x1>x0) then dx:=x1-x0 else dx:=x0-x1;
  if (y1>y0) then dy:=y1-y0 else dy:=y0-y1;
 
  if (x1>=x0) then sx:=1 else sx:=-1;
  if (y1>=y0) then sy:=1 else sy:=-1;
 
  if (dy<dx) then
  begin
       d:=(dy<<1)-dx;
       d1:=dy<<1;
       d2:=(dy-dx)<<1;
       Form1.PaintBox1.Canvas.Pixels[x0,y0]:=col;
       x:=x0+sx;
       y:=y0;
       for i:=1 to dx do
       begin
         if (d>0)  then
         begin
         d:=d+d2; y:=y+sy;
         end else d:=d+d1;
         Form1.PaintBox1.Canvas.Pixels[x,y]:=col;
         x:=x+sx;
        end;
   end
   else
   begin
     d:=(dx<<1)-dy;
     d1:=dx<<1;
     d2:=(dx-dy)<< 1;
     Form1.PaintBox1.Canvas.Pixels[x0,y0]:=col;
     x:=x0;
     y:=y0+sy;
     for i:=1 to dy do
       begin
 
         if (d>0) then
         begin
             d:=d+d2;
             x:=x+sx;
         end
         else d:=d+d1;
         Form1.PaintBox1.Canvas.Pixels[x,y]:=col;
         y:=y+sy;
       end;
 
   end;
 
end;
 
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  DrawLine(0,0,300,200,clBlack);
end;
 
end.