What's the most effective way to script a following pathfinding AI?

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#1

I’m pretty new to the pathfinding service, but I have a general grasp of how it works. I have a (somewhat) working AI that follows you which utilizes the service, walking around obstacles to get to the target. However, the movement is very buggy once you start to move.

I’m using for loops to sift through waypoints and have the NPC move to that point. When the target moves, the path is recomputed and the new waypoints are reset (and in this process, the waypoint loop breaks to prevent previous waypoints affecting it).

Alongside this, I am using while loops to change the target or recompute the path if need be.

I know this isn’t very effective, which is what brings me here today. How should I go about scripting a pathfinding AI that follows you?

Example of how my pathfinding script works:
https://gyazo.com/199cd2cab69025a723b16c3043e91b4f

Code (yes, some of the variables aren’t used, I’ve had to redo some of the code a bit and forgot to remove them):

--// SERVICES \\--
local PathfindingService = game:GetService('PathfindingService')
local RunService = game:GetService('RunService')

--// CONSTANTS \\--
local HumanoidCharacter = script.Parent
local Humanoid = HumanoidCharacter:FindFirstChildOfClass('Humanoid')

local MaxRange = 200

local RecomputeFrequency = 1
local Recomputing = false
local AutoRecompute = true
local LastPath = 0
local PathCoordinates = {}

local CurrentNodeIndex = 1

local Path = PathfindingService:CreatePath()

local FrequencyTarget
local TargetHumanoid
local LastTargetPosition

local ResettingPath = false
local IsMoving = false

local Waypoints = {}

local NPC = {}

function NPC:ComputePath()
	if not Recomputing then
		Recomputing = true
		Path:ComputeAsync(HumanoidCharacter.HumanoidRootPart.Position, TargetHumanoid.HumanoidRootPart.Position)
		Waypoints = Path:GetWaypoints()
		Recomputing = false
		ResettingPath = false
	end
end

function NPC:FollowPath()
	IsMoving = true
	local Distance
	for _, Waypoint in pairs(Waypoints) do
		if not ResettingPath then
			Humanoid:MoveTo(Waypoint.Position)
			repeat
				Distance = (Waypoint.Position - HumanoidCharacter.HumanoidRootPart.Position).Magnitude
				wait()
			until Distance <= 5
		else
			IsMoving = false
			break
		end
	end
end

function NPC:FindNewTarget()
	for _, Character in pairs(workspace:GetChildren()) do
		if Character:IsA('Model') and game:GetService('Players'):GetPlayerFromCharacter(Character) then
			if TargetHumanoid then
				if (Character.HumanoidRootPart.CFrame.p - HumanoidCharacter.HumanoidRootPart.CFrame.p).Magnitude <= MaxRange then
					if (Character.HumanoidRootPart.CFrame.p - HumanoidCharacter.HumanoidRootPart.CFrame.p).Magnitude <= (TargetHumanoid.HumanoidRootPart.CFrame.p - HumanoidCharacter.HumanoidRootPart.CFrame.p).Magnitude then
						TargetHumanoid = Character
						LastTargetPosition = TargetHumanoid.HumanoidRootPart.Position
					end
				end
			else
				if (Character.HumanoidRootPart.CFrame.p - HumanoidCharacter.HumanoidRootPart.CFrame.p).Magnitude <= MaxRange then
					TargetHumanoid = Character
					LastTargetPosition = TargetHumanoid.HumanoidRootPart.Position
				end
			end
		end
	end
end

while RunService.Heartbeat:Wait() do
	if TargetHumanoid and (TargetHumanoid.HumanoidRootPart.CFrame.p - HumanoidCharacter.HumanoidRootPart.CFrame.p).Magnitude > MaxRange then
		TargetHumanoid = nil
		LastTargetPosition = nil
		FrequencyTarget = nil
	end
	if not TargetHumanoid or FrequencyTarget ~= TargetHumanoid then
		NPC:FindNewTarget()
	end
	if TargetHumanoid and LastTargetPosition ~= TargetHumanoid.HumanoidRootPart.Position then
		ResettingPath = true
		NPC:ComputePath()
		NPC:FollowPath()
	end
	if not IsMoving and TargetHumanoid then
		ResettingPath = true
		NPC:ComputePath()
		NPC:FollowPath()
	end
	if TargetHumanoid then
		LastTargetPosition = TargetHumanoid.HumanoidRootPart.Position
		FrequencyTarget = TargetHumanoid
	end
end
11 Likes
Pathfinding AI can't catch player
#2

Depends on your needs. If I recall correctly, computation of paths is relatively expensive so you’ll want to look into a divide between raw movement towards a certain vector and pathfinding when the target is either obscured or the agent is blocked by an obstacle.

It would be helpful if you provided your current pathfinding implementation so that the code can either be built off of for a suggested fix or a refactor.

1 Like
#4

There is a commonly used pathfinding algorithm (not sure if the roblox pathfinding service uses it) it’s called the A* alogrithm and it’s rather simple, it’s really just calculating values and determining the fastest way to achieve the ending point.

image
Here is an example that was made by someone that I know, it uses the A* algorithm.

And here is a nice series that explains it really well.

All though I’d say that this algorithm works best for flat surfaces, but maybe I’m wrong.

3 Likes
#5

Yeah, I probably should’ve posted my code earlier. Edited it now.

#6

I’ll definitely look into this, thanks!

1 Like
#7

Are you asking:

  1. How best to find a path (PathfindingService vs others such as A*)?
    Whichever you choose, it will either find a path to a target position at the time it is called, or it won’t. Your implementation already seems to successfully find a path each time it tries to do so.

or

  1. How best to manage the pathfinding as the NPC follows its path to a moving target, where one possible case is that the target is not moving at a given moment?
    The Pathfinding article on developer.robolox.com does not address this very common use case, so so deciding when and how to call Pathfinding code is left up to the developer.

These are two different questions! The answer to 1) does not provide the answer to 2).

No need for For loops:

Note that the Pathfinding article on developer.robolox.com shows how to avoid For loops by using a table of waypoints and incrementing a variable named currentWaypointIndex each time the humanoid.MoveToFinished occurs, then setting humanoid:MoveTo(waypoints[currentWaypointIndex].Position) to start walking to the next waypoint. This should happen whenever the Humanoid reaches a waypoint on the path.

local function onWaypointReached(reached)
    if reached and currentWaypointIndex < #waypoints then
        currentWaypointIndex = currentWaypointIndex + 1
        humanoid:MoveTo(waypoints[currentWaypointIndex].Position)
    end
end
  
-- Connect 'MoveToFinished' event to the 'onWaypointReached' function
 humanoid.MoveToFinished:Connect(onWaypointReached)

Regardless of using PathfindingService or A* or any other method to calculate the path, you can store a table of waypoints from a path that has been successfully calculated, and use this same approach to moving from one waypoint to another.

As for moving targets, one option is GetPropertyChangedSignal("Position") on a target part.

 local targetPart = Instance.new("Part")  -- or character.HumanoidRootPart or ...
 local function onTargetPositionChanged()
      print("targetPart.Position is now " .. targetPart.Position)
      -- Now calculate a new path and start following it.
 end
 targetPart:GetPropertyChangedSignal("Position"):Connect(onTargetPositionChanged)
21 Likes
#8

I’ll try this method out later, thank you!

#9

I probably should’ve checked the rest of the article beforehand… thanks a bunch!