New to lua, need help with tables (and now collisions)

[fylth]

Hey all, i've been trying to make a simple game with Love, and have ran into a small problem. I'm entirely new to lua, however the alternatives to Love were Gamemaker (not a whole lot of control) or VB (not really suitable). I've managed to make a simple games so far (well, I say game, it's a ship that flies), however I have no idea how to make the gun shoot without deleting previous bullets. I'm guessing to use an array/table, but i'm having trouble getting it to work. After trying for several days i've decided to ask for help.

*edit* Also this would be useful for creating waves of enemy, instead of one at a time (not that i've implemented this yet)

[nevon]

I haven't actually read through your code, but I'll give you an idea of how you can do it.

A bullet is a table containing the bullet's X and Y coordinates. You could have a bunch of other stuff in there, of course, like the vector it's travelling along or whatever, but nevermind that for now.

You would then have another table containing all active bullets. Let's call this table "projectiles".

Then you could do something like the following:

Code: Select all

function love.load()
    projectiles = {}
    bulletspeed = 50
end

function love.update(dt)
    local removetable = {}

    for i,v in ipairs(projectiles) do
        --update the bullets to move them
        v.x = v.x + bulletspeed*dt

        --Check if it's out of bounds
        if v.x > 800 then --if the screen is 800px wide        
            table.insert(removetable, i)
        end
    end

    for i,v in ipairs(removetable) do
        --If the bullet is in the removetable, remove it from the projectiles table
        table.remove(projectiles, v-i+1) --The offset is so that it doesn't go out of sync with the projectiles table
    end
end

function love.keypressed(key, unicode)
    if key == " " then
        --if the user presses space, create a bullet
        table.insert(projectiles, {x=50, y=300}) --example values
    end
end

It's very possible that I screwed something up in the above code, but hopefully it'll give you an idea.

[Thursdaybloom]

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Thanks Nevon

I'll post my reply anyway for you fylth

You're only defining a single bullet.

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bullet = {
	image = love.graphics.newImage("bullet.png"),
	x = 0,
	y = 0
	}

When you press space to shoot the bullet you're editing the values for this single bullet so every press of space resets these parameters.

Code: Select all

if love.keyboard.isDown(" ") then
		shoot = true
		local randnum = math.random(-8, 8)
		bullet.x = player.x + (28 + randnum)
		bullet.y = player.y 
	end
	
	bullet.y = bullet.y - 3

You can see above that pressing space resets bullet.y to player.y. You're taking a single image file and changing its location. You need to instead be creating a new bullet entry each time you press space. You can keep the bullet table you have and just create new entries in it, for example bullet[1].y and bullet[2].y

[fylth]

Ah, thankyou very much, the comments in your code really helped me understand what was going on

I'll have a go at implementing this now, thanks again

[fylth]

Ok, I think I have most of the code working, as in I don't get any crashes, however the image of the bullet isn't being created. Here's the updated code (probably needs some cleaning up now, that comes after functionality)

[TechnoCat]

You are just nearly there.
First, you had:

Code: Select all

function love.keypressed(key,unicode)
    if keypressed == " " then

You probably meant

Code: Select all

function love.keypressed(key,unicode)
    if key == " " then

Second, you need to draw the bullets in love.draw() now.
put this somewhere in love.draw()

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  for i,v in ipairs(projectiles) do
    love.graphics.draw(v.image, v.x,v.y)
  end

[fylth]

Awesome, worked a treat Now I just need some enemy spawns and a score system and we have a game! Best get to work hadn't I

[TechnoCat]

Awesome, worked a treat Now I just need some enemy spawns and a score system and we have a game! Best get to work hadn't I

Don't forget collision detection.

[fylth]

Well I finally got some time away from doing assignment work to work on this some more, and I almost immediately hit another roadblock: Collisions.

Now to me this seems like it should be simple, check if two sprites are in the same location, if so delete both sprites (I plan on making it reduce health eventually so that I can have incrementally hard waves, but I would rather get this working at all to start with)

I've tried two different methods of using this, one quite complicated and one less so (which I saw in an example in another thread so thought was worth a try). Any idea what I need to change?

Code: Select all

	for i,v in ipairs(enemy) do
		enemyx = v.x
		enemyy = v.y
		for i,v in ipairs(projectiles) do
			bulletx = v.x
			bullety = v.y
--			if bulletx > (enemyy - 32) and bullety < (enemyy) and bulletx > (enemyx + 32) and bullety < (enemyx) then
--				table.remove(enemy, i) 
--				table.remove(projectile, i)
			
			if bulletx == enemyx and bullety == enemyy then
				table.remove(enemy, i) 
				table.remove(projectile, i)
			end
		end
	end

(I've got the first method I tried commented out still)

Thanks for any help!

[Ryne]

Doing coordinate collisions could be a problem depending on the type of game, unless it's a side-scroller without the ability to jump. Since your sprites could be 32x32 and only have a single pixel collision point, technically the images could be touching but not collide. I was thinking of a way to create a pixel barrier around the sprite the same way but I don't think it would be very efficient. I'm not great with collisions myself but I think I've seen something about using "bounding boxes", I'm not certain if that was about collisions or not, though it seemed to be. Good luck!