Dynamic in-game object creation and manipulation

[Tomi]

No, not so weird, SilverWarior, after all you are right: if I would like help from an English-speaking programmer community, the best is when I write my codes totally in English in order to better understand.
Therefore today I have made a small program, which is focusing the "bullet appearing" problem:

unit Unit1;


{$mode objfpc}{$H+}


interface


uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, ExtCtrls;


type


  { TForm1 }


  TForm1 = class(TForm)
    Timer1: TTimer;
    procedure FormClose(Sender: TObject; var CloseAction: TCloseAction);
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;


type TGameObject=class(TObject)
  private
  public
    xplace,yplace,celx,cely,movedir: integer;
    itsimage: TBitmap;
    canshoot: boolean;
    shoottimer: byte;
    constructor create(xplacehere,yplacehere: longint; imagehere: Tbitmap);
end;


var
  Form1: TForm1;
  backgroundimg,bulletimg,spaceshipimg: TBitMap;
  spaceship: TGameObject;
  bullet: array [0..100] of TGameObject;
  numofbullets: integer;


implementation


{$R *.lfm}


constructor TGameObject.create(xplacehere,yplacehere: integer; imagehere: Tbitmap);
begin
        xplace:=xplacehere;
        yplace:=yplacehere;
        itsimage:=imagehere;
end;


{ TForm1 }


procedure TForm1.FormCreate(Sender: TObject);
var initialmovedir: shortint;
begin
  backgroundimg := TBitmap.Create;
  backgroundimg.LoadFromFile('kepek/urhatter.bmp');
  bulletimg:=TBitMap.Create;
  bulletimg.LoadFromFile('kepek/ell_lov.bmp');
  bulletimg.transparent:=true;
  spaceshipimg:=TBitMap.Create;
  spaceshipimg.LoadFromFile('kepek/ell1.bmp');
  spaceshipimg.transparent:=true;
  randomize;
  if round(random(2))=1 then initialmovedir:=-2 else initialmovedir:=2;
  spaceship:=TGameObject.create(Form1.ClientWidth div 2,spaceshipimg.height,spaceshipimg);
  spaceship.movedir:=initialmovedir;
  spaceship.shoottimer:=100;
  spaceship.canshoot:=false;
  numofbullets:=0;
end;


procedure TForm1.FormClose(Sender: TObject; var CloseAction: TCloseAction);
begin
  backgroundimg.free;
  bulletimg.free;
  spaceshipimg.free;
end;


procedure TForm1.Timer1Timer(Sender: TObject);
var i,j: integer;
begin
  Form1.Canvas.StretchDraw(Rect(0, 0, ClientWidth, ClientHeight), backgroundimg);
  if spaceship.shoottimer>0 then dec(spaceship.shoottimer) else spaceship.canshoot:=true;
  if (spaceship.xplace+spaceship.movedir>=ClientWidth-spaceshipimg.width) or (spaceship.xplace+spaceship.movedir<=1) then
  begin
       if spaceship.yplace+spaceshipimg.height<ClientHeight then
          spaceship.yplace:=spaceship.yplace+spaceshipimg.height
       else
           spaceship.yplace:=spaceshipimg.height;
       spaceship.movedir:=-spaceship.movedir;
  end
  else
  begin
       spaceship.xplace:=spaceship.xplace+spaceship.movedir;
  end;
  Form1.Canvas.Draw(spaceship.xplace,spaceship.yplace,spaceshipimg);
  if (round(random(50))=1) and (spaceship.canshoot=true) then
  begin
       bullet[numofbullets]:=TGameObject.create(spaceship.xplace,spaceship.yplace,bulletimg); {!!!WRONG!!!}
       inc(numofbullets);
       spaceship.canshoot:=false;
       spaceship.shoottimer:=100;
  end;


  if numofbullets>0 then
  begin
       i:=0;
       while i<numofbullets-1 do
       begin
            if bullet[i]<>nil then
            begin
                if bullet[i].yplace>ClientHeight then
                begin
                    freeandnil(bullet[i]);
                    if i=numofbullets-1 then
                            dec(numofbullets)
                    else
                    begin
                            for j:=i+1 to numofbullets-1 do
                                bullet[j-1]:=bullet[j];
                            dec(numofbullets);
                            dec(i);
                    end;
                end
                else
                begin
                    bullet[i].yplace:=bullet[i].yplace+4;
                    Form1.Canvas.Draw(bullet[i].xplace,bullet[i].yplace,bulletimg);
                end;
            end;
            inc(i);
       end;
  end;
end;


end.

Maybe somebody can help me...

[User137]

The last loop is still bothering me, it is needlessly complicated and could make errors. Like i suggested earlier, here's how it would look:

  for i:=numofbullets-1 downto 0 do
  begin
    bullet[i].yplace:=bullet[i].yplace+4;
    if bullet[i].yplace>ClientHeight then
    begin
      bullet[i].Free;
      dec(numofbullets);
      bullet[i]:=bullet[numofbullets];
    else begin
      Form1.Canvas.Draw(bullet[i].xplace, bullet[i].yplace, bulletimg);
    end;
  end;