MovieClip loop query.

Astirian · August 2017

Hi guys,

I'm trying to get a path animation going for my enemies in my game. Pathfinding is good but when I try to iterate over the path points with a MovieClip, it's producing strange results. It is as if my loop isn't waiting for the animation to finish before moving on to the next i.

The other thing is the bump implementation (which I have commented out). Am I better off with just calculating every coord between path points and using world:move on those?

Here's muh hacky code:

function GameScene:moveToPlayer(pursuer)
 
	pursuer.pursuitState = "following"
 
	if pursuer.path ~= nil then
		for i = 1, table.getn(pursuer.path) do
 
			local newX = pursuer.path[i].x -1-- Secret Sauce. Shh!
			local newY = pursuer.path[i].y -1
 
			local goalX, goalY = newX * boardRectSize , newY * boardRectSize
			-- local actualX, actualY, cols, len = world:move(pursuer, goalX, goalY)
 
			local mc1 = MovieClip.new{
				{1, 100, b, {x = {pursuer:getX(), goalX, "linear"}, y = {pursuer:getY(), goalY, "linear"}}}
			}
 
			print("I want to move to "..goalX..", "..goalY..". My actuals are "..actualX..", "..actualY)
			--pursuer:setPosition(actualX , actualY)
 
--[[
			-- prints "Collision with A"
			for i=1,len do -- If more than one simultaneous collision, they are sorted out by proximity
				local col = cols[i]
				print("Collision with "..col.other.name)
			end
]]--
		end
	end
end

HubertRonald · August 2017

Hi @Astirian
Yes it's happened because you're the same local object "mc1" in your "for loop" so you get strange results 'cos refresh the same local object in each loop.

So first you can defined local variable mc1={} outside of you "for loop" and after you can put the next (I haven't had test it yet):

if next(pursuer.path) ~= nil then --verify if table isn't empty
    local mc1 = {}
    local newX, newY, goalX, goalY --it's better define local variables outside of the loop
    for i, v in pairs(pursuer.path) do
           local newX, newY = v.x -1, v.y -1
	   local goalX, goalY = newX * boardRectSize , newY * boardRectSize
 
	   mc1[#mc1+1] = MovieClip.new{
		{startTime(i), finalTime(i), b, {x = {pursuer:getX(), goalX, "linear"}, y = {pursuer:getY(), goalY, "linear"}}}
			} -- in this part I don't know how you define time in animation (*/)
 
   end
end

(* )/ But another consideration if the time is progressive in your animation, take be careful! for example, I use the next trick:

local vel = 7 --frame speed
for i=1,4 do
	print(i, i+(i-1)*(vel-1), i*vel+i-1)
		--or
	print( i, (i-1)*vel+1, i*vel+(i-1) )
        mc1[#mc1+1] = MovieClip.new{ (i-1)*vel+1,  i*vel+(i-1) --... and so on
end
--[[
print results:
1	1	7
2	8	15
3	15	23
4	22	31
]]

But finally all depends on what you really want to do

Astirian · August 2017

Ah thank you @HubertRonald, I was just thinking this morning that I was mixing my peanut butter with my spaghetti bolognese if you'll excuse the expression.

When I move my player, I move his bitmap and bump.lua body by 1 pixel in the same function on every frame. This is a combination of bump's world:move() and setPosition().

I figured if I wanted to do the same with the enemies, I would need to get a line between each valid path point (i in pursuer.path), and get every co-ordinate along that line. I could then have a nested loop inside my path points loop. Which sounds a bit hairy to be honest.

I think the thing I was missing was velocity!

(and also of course, fixing my dodgy vars)

Thanks! I will try implementing this tonight when I get home.

Astirian · August 2017

Hmm... Had a play with this again tonight, the enemies eventually make it to the destination but it is as if the loop does not wait for the MovieClip to finish.

I can see this because the getX() on the start of every loop teleports the enemy back slightly to a previous point in the path.

And also the path becomes warped as the enemy proceeds, almost as if he starts taking a shortcut because the goalX and goalY have changed mid tween...

antix · August 2017

@Astirian I have a couple of questions..
1. Do your monsters only move in four directions, ie left, right, up, down?
2. Do you want your monsters to move at the same speed when moving from point to point?

edit: nevermind I got curious and made an example 8-} 8-} 8-}

antix · August 2017

As an exercise I made a little example of an agent that follows a path. The agent only moves in one of four directions (left, right, up, or down) at any time which works pretty well. When the agent reaches the end of the path it starts at the beginning again. Hopefully this will be enough that you can get your head around it.. or mash it into your own code

I absolutely recommend http://www.gameaipro.com/ with regards to this kind of thing as well. The first book (it's FREE) contains a very good section on state based agents, which this example uses. It is totally worth a read, and the earlier section on random numbers is fascinating

Agent = Core.class(Bitmap)
 
function Agent:init(texture) -- this only needs to be called once
  self:reset()  
end
 
function Agent:reset() -- we call this to actually initialize the agent
  local x, y = 0, 0
 
  self.position = {x = x, y = y}
  self.velocity = {x = 0, y = 0}
 
  self.speed = 0.3 -- how fast this agent can move (in pixels per frame)
 
  self.state = "nothing" -- what the agent is currently doing
 
  self.direction = "right" -- which direction the agent is travelling
  self.path = {}
  self.pathPos = 1
  self.destination = {}
 
--  if BUMP:hasItem(self) then
--    BUMP:update(self, x, y) -- just update if it already exists in bump
--  else
--    BUMP:add(self, x, y, 16, 16) -- otherwise add it
--  end
end
 
function Agent:setState(state) -- set what this agent will do from now on
  self.state = state
end
 
function Agent:setPath(path) -- set the path this agent will follow
  self.path = path
  self.pathPos = 1
  self.destination = path[1]
  self:chooseDirection() -- choose movement direction
end
 
function Agent:advancePath() -- set agent to move towards next waypoint in current path
  local path = self.path
  local pathPos = self.pathPos + 1
 
  if pathPos > #path then
 
    -- at this point the agent has completed the path so you could choose 
    -- a new state or choose and generate a new path. for this example we 
    -- are just resetting the path position to the start so the agent will 
    -- walk about in a loop.
 
    pathPos = 1
  end
 
  self.destination = path[pathPos] -- set new destination
  self.pathPos = pathPos
  self:chooseDirection() -- choose movement direction
end
 
function Agent:chooseDirection() -- choose movement direction to next waypoint
  local p = self.position
  local v = self.velocity
  local d = self.destination
 
  local x, y = p.x, p.y -- current world position
  local vx, vy = 0, 0 -- initial velocities
  local dx, dy = d.x, d.y -- destination position
 
  local speed = self.speed -- how fast this agent can move
 
  if dx ~= x then -- if x is different then we will move on x axis (left/right)
 
    if dx < x then -- if destination is to left we will move left
      self.direction = "left"
      vx = -speed
    else -- otherwise we will move right
      self.direction = "right"
      vx = speed
    end
 
  else -- otherwise we will move on y axis (up/down)
 
    if dy < y then -- if destination is to above we will move up
      self.direction = "up"
      vy = -speed
    else -- otherwise we will move down
      self.direction = "down"
      vy = speed
    end
 
  end
 
  v.x, v.y = vx, vy -- set velocities
end
 
function Agent:update(dt)
  local p = self.position
  local v = self.velocity
  local d = self.destination
 
  local x, y = p.x + v.x, p.y + v.y -- move
  local dx, dy = d.x, d.y -- we check against these
 
  local state = self.state
  if state == "patrol" then
    local advance = false
 
    local path = self.path
    local dir = self.direction
    if dir == "left" then
      if x <= dx then
        x = dx
        advance = true
      end
    elseif dir == "right" then
      if x >= dx then
        x = dx
        advance = true
      end
    elseif dir == "up" then
      if y <= dy then
        y = dy
        advance = true
      end
    else -- must be down then
      if y >= dy then
        y = dy
        advance = true
      end
    end
 
    p.x, p.y = x, y -- update positions
    self:setPosition(x, y)
--    BUMP:update(self, x, y) -- agents only need to be updated.. not moved
 
    if advance then -- advance path if required
      self:advancePath()
    end
 
  elseif state == "" then
    -- some other state
  else
    -- no state
  end
 
  -- process stuff here that happens regardless of state, things like
  -- checking if the agent can see the player, animating the agent, etc
 
end

Astirian · August 2017

Thanks again @antix! At this stage you're like some sort of awesome Code Santa/Mentor. I will get to work.

I need to stop trying to do everything in the scene and start making proper classes for things, I'm being a bit too procedural I think.

Lots of homework to do, that book you mentioned looks fantastic! I'll definitely give it a read. On a side note I recently picked up Level Up by Scott Rogers, once I've got the basics down and a few more light games out the door I'm planning to start coming up with my own gameplay concepts.

antix · August 2017

@Astirian, you're welcome.

You should definitely be creating small reusable classes. Having lots of classes makes it a lot easier to prototype possible new games. I mashed together a basic platformer in a day and a half recently and that would not have been possible if I didn't have all those little classes just waiting to be combined into something new.

The Game AI Pro book is pretty big (there are like three books now) but you only need to read sections as required or when you feel like reading something technical

I might grab that other book by Scott Rogers if the price ever drops ~:>

Astirian · August 2017

Ooooh, so close now. It's mostly there, the critters are just stopping after the second path point for some reason. Closing in on it though!

Edit: Sorted it, I was calling setPath() on every update, d'oh!

HubertRonald · August 2017

Nice sample @antix

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