Spawn # of objects based on another object moving

Questions
1

I want to have a plane move on screen and drop off “minions” as it moves. I have it working, but it never stops. I can’t delete the object when it hits the end of screen nor have it stop after dropping a certain # of minions. I have this script attached to the plane as it flys from left to right.

go.property(“acceleration”, 200)
go.property(“max_speed”, 400)
go.property(“right_left”, 1)

local spawn_timer = nil
local i = 1
local numMinions = 3

function init(self)
– movement input
self.input = vmath.vector3()

-- the current direction of movement
self.direction = vmath.vector3()

-- the current speed (pixels/second)
self.speed = 0

--spawn minions  
if i<numMinions then
	spawn_timer = timer.delay(.25, true, spawnMinion)
	i=i+1
end

end

function update(self, dt)
self.input.x = self.right_left
self.direction = self.input
– increase speed
self.speed = self.speed + self.acceleration * dt
– cap speed
self.speed = math.min(self.speed, self.max_speed)

-- move the game object
local p = go.get_position()
p = p + self.direction * self.speed * dt
go.set_position(p)

-- reset input
self.input = vmath.vector3()

end

function spawnMinion(self)
local p = go.get_position()
local pos = vmath.vector3(p.x, p.y, 0)
local minion_id = factory.create("#minionfactory", pos, nil, nil, .4)
end

function final(self)
– Cancel the timer when the script is deleted
timer.cancel(spawn_timer)
go.delete()
end

2 
...
local function spawnMinion()
  local p = go.get_position()
  local pos = vmath.vector3(p.x, p.y, 0)
  local minion_id = factory.create("#minionfactory", pos, nil, nil, .4)
end

-- this factory now manages the spawns and the timer
local function spawnFactory()
  if i < numMinions then
    spawnMinion()
    i = i + 1
  else
    timer.cancel(spawn_timer)
  end
end

function init(self)
  self.input = vmath.vector3()
  self.direction = vmath.vector3()
  self.speed = 0
 
  -- start the spawn factory
  spawn_timer = timer.delay(0.25, true, spawnFactory)
end

function update(self, dt)
  self.input.x = self.right_left
  self.direction = self.input
  self.speed = self.speed + self.acceleration * dt
  self.speed = math.min(self.speed, self.max_speed)

  local p = go.get_position()
  p = p + self.direction * self.speed * dt
  go.set_position(p)

  -- Get the current window width as defined in your game.project
  local window_width = tonumber(sys.get_config("display.width"))
  -- Check if the objects x position is greater than the screen width
  if go.get_position().x > window_width then
    go.delete()
    timer.cancel(spawn_timer)
  end
   
  self.input = vmath.vector3()
end

code not tested, hope it works
anyway, just ask if something is not clear enough

2 Likes
3

Thank you. I ended up putting two trigger box colliders on the sides of the screen. I’m not sure what is better…calculating the position or using a trigger collider. Both work though.

But I did have a major issue (that I couldn’t see). I was spawning all objects at ones (like 3 minions) then the pause and it would spawn 3 more…since they were on top of each other I couldn’t tell. I’m trying your spawnfactory suggestion to see if that fixes it. Thank you.

4

Finally figured it out. The timer runs like a co-routine. So once you go to it…it keeps running. So you have to stop the timer to stop the spawning. Maybe the documentation said that but I must have missed it. If not the documentation should make it clear that the timer runs until it is stopped.

5

Seems pretty clear in the docs to me? The 2nd argument determines if it auto-repeats or is a one-time thing.

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image889×411 23.6 KB

3 Likes
6

It was the timer issue I had that was messing up my thinking (as you replied on the other topic). Now that I have the self. variables fixed I’m good to go. Thank you.

1 Like