Dynamic in-game object creation and manipulation

[Tomi]

please post your code for how you setup the array of bullets

I'm using fixed length arrays:

bullets: array [0..100] of TBullet;

Then in a Timer event I create, move and destroy the bullets:

if (plshoot=true) and (plcanshoot=true) then
  begin
         abullet:=TBullet.create(Player.Left,Player.Top,bulletpic);
         bullets[numofbullets]:=abullet;
         inc(numofbullets);
  end;


  if numofbullets>=1 then
  begin
       for i:=0 to numofbullets-1 do
       begin
        if bullets[i]<>nil then
        begin
            bullets[i].yplace:=bullets[i].yplace-4;
            if bullets[i].yplace<10 then
            begin
                 freeandnil(bullets[i]);
                 if i=numofbullets-1 then
                    dec(numofbullets)
                 else
                 begin
                      for j:=i+1 to numofbullets-1 do
                          bullets[j-1]:=bullets[j];
                      dec(numofbullets);
                 end;
            end;
        end;
       end;
  end;

(I have already corrected the first variable of the loops from 1 to 0, as you wrote.)
When I press the fire button, the bullets are only flash at the top of the player. :-/

[SilverWarior]

Is your numofbullets global variable or is it declared inside Timers OnEvent method.
If it is declared in an OnTimer event method that means that it is cleared after ending of each Timer cycle and then recreated in another cycle with default value which is 0.

[Tomi]

The numofbullets is a global variable; only the i and j variables are declared in the timer.

[Tomi]

Hello and happy new year, everybody!


At last, my first game with Lazarus is done: a small space shooter, with some enemies, one boss and power-ups.
It's name is "Space Defender" and you can download from here:
http://www.programozzunk.ucoz.hu/laz...k/spacedef.zip
Unfortunately it has some bugs:
- the appearance of bullets of enemies sometimes happens in wrong place,
- the sprites of the spacehips are flashing,
- sometimes the game throw you out, when the player is rebirth at the boss and you press buttons.
In spite of all this, I hope that you will enjoy this game, but if you will find the solutions for these bugs, please tell me.

[User137]

Does the order really matter for bullets and possibly glowing particles and the like? I find it redundant to, say if index 10 is removed from list of 100 bullets you would move all remaining 90 or so of them 1 backwards... It is simpler to move the last index in place of the removed one. 1 operation vs 90 operations. In order for this to work, you need to use a "downto" in the for loop, going from the last item to 0.

for b:=bullets-1 downto 0 do
  with bullet[b] do begin
    Move;
    dec(AliveTime);
    if AliveTime < 0 then begin
      dec(bullets);
      //bullet[b].Free; // Free it here if you must. Not needed if using records
      bullet[b]:=bullet[bullets]; // Replace current bullet with last one.
    end;
  end;

New bullets will then always be added to the end.

[Tomi]

Hello User137!


My main problem the appearance of enemy's bullets, which happening at wrong place. Its may has to do with moving and deleting of the bullets?
I do it as follows:

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

Maybe it is wrong?

[Tomi]

Maybe I find what is wrong in my code: I have to put the drawings in the Timer event, not in Formpaint. Ehhh... I need more experience with Lazarus.