How to make good dodging AI

[Gunroar:Cannon()]

This is the main boid code I use

Code: Select all

--[[
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local require = old_require or require

if (...) then
  local _PATH = (...):match('%w+%.')
  require  ('toybox.libs.steering.src.core.math')
  local Vec = require ('toybox.libs.steering.src.core.vector')
  
  local Zero = Vec()
  
  local min, random, cos, sin, tau = math.min, math.random, math.cos, math.sin, math.tau
  local l2Abs, rSign = math.localToAbsoluteReference, math.randomSign
  
  local function getTarget(target)
    if target.x then
      return target
    elseif target.pos then
      return target.pos
    elseif target.agent then
      return target.agent.pos or error("Agent incomplete!")
    end
    error("Invalid target")
  end
  
  local function _getHunter(hunter)
    if hunter.pos then
      return hunter
    elseif hunter.x then
      return {pos=hunter, vx=hunter.vx, vy = hunter.vy}
    elseif hunter.agent then
      return hunner.agent
    end
    error("Invalid hunter")
  end
  
  local function getHunter(h)
    h = _getHunter(h)
    h.vel = h.vel or Vec(h.vx or 0, h.vy or 0)
    return h
  end
    
  
  local SteeringBehaviour = {}

  function SteeringBehaviour.seek(agent,targetPos)
    local targetPos = getTarget(targetPos)
    
    local requiredVel = (targetPos - agent.pos):normalize() * agent.maxVel
    return requiredVel - agent.vel
  end

  function SteeringBehaviour.flee(agent,targetPos, panicDistance)
    local targetPos = getTarget(targetPos)
    if panicDistance then
      if agent.pos:distSqTo(targetPos) < panicDistance * panicDistance then
        local requiredVel = (agent.pos - targetPos):normalize() * agent.maxVel
        return requiredVel - agent.vel     
      end
    end
    return Zero
  end
  
  local DecelerationType = {slow = 3, normal = 2, fast = 1}  
  function SteeringBehaviour.arrive(agent, targetPos, typeDec)
local targetPos = getTarget(targetPos)
    local vTarget = targetPos - agent.pos
    local distToTarget = vTarget:mag()
    if distToTarget > 0 then
      typeDec = typeDec or 'normal'
      local vel = distToTarget/DecelerationType[typeDec]
      vel = min(vel, agent.maxVel:mag())
      local requiredVel = vTarget * (vel/distToTarget)
      return requiredVel - agent.vel
    end
    return Zero
  end
  
  function SteeringBehaviour.pursuit(agent, runaway)
    runaway = getHunter(runaway)
    local vRunaway = runaway.pos - agent.pos
    local relativeHeading = agent.velHeading:dot(runaway.velHeading or Vec(0,0))
    if vRunaway:dot(agent.velHeading) > 0 and relativeHeading < -0.95 then
      return SteeringBehaviour.seek(agent,runaway.pos)
    end
    local predictTime = vRunaway:mag()/(agent.maxVel:mag()+runaway.vel:mag())
    return SteeringBehaviour.seek(agent,runaway.pos + runaway.vel * predictTime)
  end
  
  function SteeringBehaviour.evade(agent,hunter)
    hunter = getHunter(hunter)
    local vHunter = hunter.pos - agent.pos
    local predictTime = vHunter:mag()/(agent.maxVel:mag() + hunter.vel:mag())    
    return SteeringBehaviour.flee(agent, hunter.pos + hunter.vel * predictTime,100)
  end
  
  function SteeringBehaviour.wander(agent, radius, distance, jitter)
    jitter = jitter or 10
    radius = radius or 100
    distance = distance or 100
    local jitterThisFrame = jitter * agent.dt
    local theta = random() * tau
    local targetPos = Vec(radius * cos(theta), radius * sin(theta))
    targetPos = targetPos + Vec((random()*rSign() * jitterThisFrame),
                                (random()*rSign() * jitterThisFrame))    
    targetPos:normalize()
    targetPos = targetPos * radius
    local targetAtDist = targetPos + Vec(distance,0)
       
    local newTargetPos = l2Abs(targetAtDist, agent.velHeading, agent.velPerp, agent.pos)
    --[[
    print('agentVelH', agent.velHeading)
    print('agentVelPerp', agent.velPerp)
    print('agentpos', agent.pos)
    print('newTargetPos', newTargetPos)
    --io.read()
    --]]
    return newTargetPos - agent.pos
    
  
  end
  
  return SteeringBehaviour
end  

It works okay for simple AI that follows the player with seek and pursuit, but when it tries to dodge bullets, using evade, it works poorly by kind of going in one direction.

Any ideas to improve it?

[darkfrei]

This is the main boid code I use

It works okay for simple AI that follows the player with seek and pursuit, but when it tries to dodge bullets, using evade, it works poorly by kind of going in one direction.

Any ideas to improve it?

Can you please provide a small working example as .love file?

[Gunroar:Cannon()]

I don't really think the love file would help. Has to much unnecessary code to be readable by someone else. The void library is available on github I think.

What I'm hoping for is if anyone can see any problem with the evade code.

If you really want a love file I'll put it but my code's really messy.

[darkfrei]

Looks like typo:
elseif hunter.agent then
return hunner.agent

[pgimeno]

Can you please provide a small working example as .love file?

I don't really think the love file would help. Has to much unnecessary code to be readable by someone else. The void library is available on github I think.

What I'm hoping for is if anyone can see any problem with the evade code.

If you really want a love file I'll put it but my code's really messy.

Where did you get that a "small working example" means to post your whole project?

[Gunroar:Cannon()]

Looks like typo:
elseif hunter.agent then
return hunner.agent

Heheh. I doubt though. "Check if there's still an agent and return one if there is, but if there isn't then throw an error".

Where did you get that a "small working example" means to post your whole project?

Okay, fair enough. But, unfortunately for me, these days my coding is dependant on the toybox/LGML lib I use and I kind of don't have enough will to do a raw example from scratch (which is why I posted on general, just looking for ideas).

And also to me, the project is kind of "small" (but no the code base is not) .
I might still post my other messed up example, but basically I 'm asking whether the steering behaviour lib works well.
The lib

[Ross]

Well if I wanted to dodge a bullet, I would try to move perpendicular to the bullet's velocity vector.

[pgimeno]

Well if I wanted to dodge a bullet, I would try to move perpendicular to the bullet's velocity vector.

Curiously enough, that is not always optimal, but I have no idea how to calculate the optimal angle.

The program below shows that all other things things being equal, moving slightly backwards (a=-100) instead of perpendicular (a=-90) buys the second one just enough time to move a bit more out of the way and avoid the bullet.

Code: Select all

local bullet1 = {x = 300, y = 300, w = 10, h = 10, a = math.rad(180), sp = 20}
local bullet2 = {x = 700, y = 300, w = 10, h = 10, a = math.rad(180), sp = 20}

local dodger1 = {x = 100, y = 260, w = 80, h = 80, a = math.rad(-90), sp = 6.6}
local dodger2 = {x = 500, y = 260, w = 80, h = 80, a = math.rad(-100), sp = 6.6}

local hit1 = false
local hit2 = false

local function collide(ax1, ay1, ax2, ay2, bx1, by1, bx2, by2)
  return math.max(ax1, bx1) < math.min(ax2, bx2)
     and math.max(ay1, by1) < math.min(ay2, by2)
end

local function objectUpdate(self, dt)
  self.x = self.x + math.cos(self.a) * self.sp * dt
  self.y = self.y + math.sin(self.a) * self.sp * dt
end

function love.update(dt)
  objectUpdate(bullet1, dt)
  objectUpdate(bullet2, dt)
  objectUpdate(dodger1, dt)
  objectUpdate(dodger2, dt)
  if collide(bullet1.x, bullet1.y, bullet1.x + bullet1.w, bullet1.y + bullet1.h,
             dodger1.x, dodger1.y, dodger1.x + dodger1.w, dodger1.y + dodger1.h)
  then
    hit1 = true
  end

  if collide(bullet2.x, bullet2.y, bullet2.x + bullet2.w, bullet2.y + bullet2.h,
             dodger2.x, dodger2.y, dodger2.x + dodger2.w, dodger2.y + dodger2.h)
  then
    hit2 = true
  end
end

local function objectDraw(self)
  love.graphics.rectangle("fill", self.x, self.y, self.w, self.h)
end

function love.draw()
  if hit1 then
    love.graphics.setColor(1, 0, 0)
  else
    love.graphics.setColor(1, 1, 1)
  end
  objectDraw(bullet1)
  objectDraw(dodger1)

  if hit2 then
    love.graphics.setColor(1, 0, 0)
  else
    love.graphics.setColor(1, 1, 1)
  end
  objectDraw(bullet2)
  objectDraw(dodger2)
end

[knorke]

I think it is hard to answer the question without knowing more details.
For example what kind of movement physics are there?
Is it "instant" like Pacman or is there inertia?
How many bullets are there?
Is it possible to use tactics that makes it harder for the enemy to line up a good shot in the first place?

[Gunroar:Cannon()]

I guess it's instant. If I add inertia I'll just try and tweak the code. My main problem is that the library doesn't work for fleeing as I thought it should when I use it.