Fastcast projectile prediction?

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#1

Hey, so I’ve been using fastcast a lot for my opensource gun system. And i really need a way to predict where will a projectile land without actually firing it. I’ve tried looking through fastcast code but couldn’t figure much out, im terrible at math. Maybe someone has done it before?

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#2

I don’t know fastcast too well as I usually make my own projectile class so I’m not sure what the exact code to do this would look like. However it just comes down to simulating like 5 seconds worth of the projectile in a single moment.
For example: have a for loop complete several iterations of the projectile physics step.

#3

This handy Wikipedia article gives you a formula for calculating the range of a projectile given velocity, angle, and vertical height:

Once you find the distance, just offset it relative to the LookVector of the projectile’s velocity.

#4

I’ve considered this a few times but i was always eager to find a method that doesn’t involve finding an angle. I thought that if fastcast only requires the origin part then I can probably get the same result without an angle

#5

What’s stopping you from just calculating the angle

--ToOrientation returns 3 values but we only need the X axis rotation (the gun elevation)
--The X axis happens to be the first value
local xRot: number = CFrame.lookAt(Vector3.zero, gun.CFrame.LookVector):ToOrientation()

Otherwise, the only other way is to actually simulate the projectile step by step to see where it would land via a loop and raycasting, which at this point you’ve basically made your own fastcast module.

#6

Fastcast is mostly using projectile motion, so if you use the same equations it should follow the same path:

--g gravity, v velocity, t time, p initial position
local function projectileMotionEquation(g, v, initialPosition, t)
--See Ego Mooses tutorial on integrating projectile motion equation
	return 0.5 * g * t ^ 2 + v * t + initialPosition
end

local function raycastAlongQuadraticPath(g, v, initialPosition, endTime, raycastParams)
	local segments = 10*math.round(endTime*3) -- based on default beam adjust if needed
	local timeGapIncrements = endTime/segments

	local currentTime = 0
	for i=1, segments do
		local point1 = projectileMotionEquation(g,v,initialPosition,currentTime)
		local point2 = projectileMotionEquation(g,v,initialPosition,currentTime+timeGapIncrements)
		local direction = point2-point1
		local rayResult = workspace:Raycast(point1,direction,raycastParams)
		if rayResult then
			return rayResult
		end
		currentTime += timeGapIncrements
	end
end
#7

I havent tries this yet, but I hope it helps
Just make another function that predicts the position and set that as the target position
You can use the direction variable for the raycast info

local distance = (originPosition - targetPosition)
local travelTime = distance / studsPerSecond
local offset = -(velocity * travelTime)
local direction = targetPosition + offset