Finding the closest position

[BruceTheGoose]

Code: Select all

allies = {}
enemies = {}

for _,v in ipairs(allies) do
      if v.target == 0 then
        for i = 1, #enemies do
          v.currentBest = getMagnitude(v.x,enemies[i].x + enemy:getWidth()/2,v.y,enemies[i].y + enemy:getHeight()/2)
          if getMagnitude(v.x,enemies[i].x + enemy:getWidth()/2,v.y,enemies[i].y + enemy:getHeight()/2) >= v.currentBest then
            v.target = enemies[i]
            v.angle = math.atan2((enemies[i].y-v.y),(enemies[i].x - v.x))
          end
        end
      end
end

So I'm having trouble finding the appropriate way to find the nearest position of all the enemies and setting the target to the closest enemy.
The above code works but it does not look for the closest enemy. Instead, the allies go to the newest enemy spawned. If you can help me I would really appreciate it.

[kikito]

Funny, I was re-reading this blogpost in which I wrote code to do the very thing that you ask. See if this helps you:

http://kiki.to/blog/2012/03/16/small-fu ... -universe/

[BruceTheGoose]

Coincidence? Thank you so much I'll look into it

[BruceTheGoose]

If you use lots of functions like this one, your code tends to become unmanageable, especially if you return to it after not touching it for several months. It’s a code that you understand while you are writing, and certainly the machine understands it, but it doesn’t have “signposts” for future visitors. They have to “explore” it to know it.

I'm gonna rewrite all my code now

[BruceTheGoose]

So I re-wrote my bullets and I'm getting a stupid error. I suspect the reason for the error is that I haven't created a new bullet and I'm calling its update function. Here is the code.

Code: Select all

Bullet = {}

function Bullet:New(x,y,x1,y1,rot,type,damage,speed)
  
  local startX = x
  local startY = y
  
  local angle = math.atan2((y1+troop:getHeight()/2-startY),(x1+troop:getWidth()/2-startX))
  
  self.x = x
  self.y = y
  
  self.rot = rot
  self.type = type
  self.damage = damage
  self.speed = speed
  self.y1 = y1
  self.x1 = x1
  self.dx = self.speed * math.cos(angle)
  self.dy = self.speed * math.sin(angle)
  self.timer = 0
  
end

function Bullet:update(dt)
 -- self:collide()
  self.x = self.x + (self.dx * dt)
  self.y = self.y + (self.dy * dt)
  self.timer = self.timer + dt
  if self.timer >= 2 then
    --self:remove()
  end
end

function Bullet:draw()
  if self.type == "elixir" then
    love.graphics.draw(elx,self.x,self.y,self.rot,1,1,elx:getWidth()/2,elx:getHeight()/2)
  end
end

function Bullet:collide()
end

function Bullet:remove()
  self = nil
end

The error is: bullet.lua:28: attempt to perform arithmetic on field 'dx' (a nil value)

Also how would I remove a bullet? Would

Code: Select all

self = nil

work?

[Robin]

Please upload a .love. I suspect you're calling Bullet:update(dt) somewhere and that'll never work.

Also, Bullet:New is... not what you want it to do.

So instead:

Code: Select all

Bullet.__index = Bullet

function Bullet.New(x,y,x1,y1,rot,type,damage,speed)
  
  local startX = x
  local startY = y
  
  local angle = math.atan2((y1+troop:getHeight()/2-startY),(x1+troop:getWidth()/2-startX))
  
  local self = {} -- kind of misleading name, but I'm too lazy to change all the other variables
  self.x = x
  self.y = y
  
  self.rot = rot
  self.type = type
  self.damage = damage
  self.speed = speed
  self.y1 = y1
  self.x1 = x1
  self.dx = self.speed * math.cos(angle)
  self.dy = self.speed * math.sin(angle)
  self.timer = 0
  return setmetatable(self, Bullet)
end

Something like that.

Recommended reading: Chapter 13 of PIL.

Also how would I remove a bullet? Would

Code: Select all

self = nil

work?

No. You need to keep a list of bullets and remove them from that list.

[BruceTheGoose]

Here

[Robin]

Okay, so you do a lot of things like:

Code: Select all

for _,v in ipairs(Bullet) do Bullet.update(dt)end

That doesn't work! That function needs a "self" argument. Either do:

Code: Select all

for _,v in ipairs(Bullet) do Bullet.update(v, dt)end

or:

Code: Select all

for _,v in ipairs(Bullet) do v:update(dt)end

(This is possible because of the __index and setmetatable I suggested.)

The same goes for Tower and Troop. So what's left to do?

When creating new objects, do something like this:

Code: Select all

Tower[#Tower + 1] = Tower.new(...)

Insert this at the end of love.update:

Code: Select all

for i = #Bullet, 1, -1 do if Bullet[i].remove then table.remove(Bullet, i) end end

Then you can do for remove:

Code: Select all

function Bullet.remove(self)
  self.remove = true
end

[BruceTheGoose]

Thank you so much!