Shooting enemies

[veethree]

So i've been working on a game based on my rough and unfinished Space game. The idea is almost the same, Except this one will have enemies, shooting and all that stuff. My problem is with the enemies. Right now i can spawn the enemies (press y ingame) but they don't do anything, I wanted to make sure i can de-spawn them before i start writing some sort of AI for them, And that's where the problem is. If i spawn 2 enemies, then shoot (space ingame) the first one i spawned, The game crashes. If i however shoot the 2nd one first, then the first one, It's all good..So yeah..that's where you guys come in..any help is appreciated.

Here's the code that deletes the enemies so you don't have to look for it:

Code: Select all

	for i=1, #enemies do
		for c=1, #bullets do
			if checkcollision(bullets[c].x, bullets[c].y, 10, enemies[i].x, enemies[i].y, 50) then
				table.remove(enemies, i)
			end
		end
	end

That's in enemy.lua


The code is pretty messed up right now, Plus a bunch of bugs..Any suggestion regarding that are welcome too..

also, Don't worry about the ship being referred to as "car" in the code..the idea started as a car game. lol

[tentus]

Well, to start with, I could not recommend altering a table that you are looping through. If you insist on doing so, at the very least you need to loop backwards. A better solution would probably to loop through the enemies and then bullets, and when they collide, add that enemy to a "to be deleted" list. Then go through a new loop and delete the marked enemies.

[Ellohir]

Yeah, insert them in a table so you can show some nice explosions before removing them

[veethree]

Well, to start with, I could not recommend altering a table that you are looping through. If you insist on doing so, at the very least you need to loop backwards. A better solution would probably to loop through the enemies and then bullets, and when they collide, add that enemy to a "to be deleted" list. Then go through a new loop and delete the marked enemies.

Wouldn't i have to alter the table which i'm looping through anyway? I mean with that i still have to remove the entry in the enemies table, i'd just do it with a different loop, Isn't that basically the same?

I did manage to get it to work though, Haven't fully tested it but it seems to work allright so far. I just added a boolean to the enemies called "isdead", and in the collision loop if a collision is detected it sets the isdead variable for the said enemy to true, And a different loop is running through the table checking for isdead's set to true and if it finds one it removes it.

Code: Select all

	-- Enemy - bullet collisions
	for i=1, #enemies do
		for c=1, #bullets do
			if checkcollision(bullets[c].x, bullets[c].y, 10, enemies[i].x, enemies[i].y, 50) then
				enemies[i].isdead = true
			end
		end
	end
	
	-- enemy removal
	for i=1, #enemies do
		if enemies[i].isdead == true then
			table.remove(enemies, i)
			break
		end
	end

[waraiotoko]

If you spawn many enemies and kill them rapidly your game crashes (cannot index enemy table), since you edit the table you're looping through.

[tentus]

You still need to loop backwards through the removal process if you want to do it that way.

Code: Select all

-- enemy removal
   for i=#enemies, 1, -1 do
      if enemies[i].isdead == true then
         table.remove(enemies, i)
         break
      end
   end

I would recommend making a list (a local variable) like so:

Code: Select all

local isdead = {}
-- Enemy - bullet collisions
for i=1, #enemies do
	for c=1, #bullets do
		if checkcollision(bullets[c].x, bullets[c].y, 10, enemies[i].x, enemies[i].y, 50) then
			isdead[#isdead + 1] = i
		end
	end
end

And then you can use the list to remove enemies.

[coffee]

Yeah, insert them in a table so you can show some nice explosions before removing them

or don't remove them if you want them to be show them dead on the floor or can be risen again as zombies

[waraiotoko]

Yeah, insert them in a table so you can show some nice explosions before removing them

or don't remove them if you want them to be show them dead on the floor or can be risen again as zombies

I never delete enemies, you could potentially resurrect them even after re-starting the game and re-loading your save.

Also, the ghosts from MGS3 come to mind.