tokyo-wangan-racing/tools/diag_centrefix.luau

--[[
	diag_centrefix.luau -- test whether centreFix is applied in the wrong order.

	The build does:
	    shell:PivotTo(body.CFrame * heightCF * CFrame.Angles(0,yaw,0) * centreFix)

	centreFix is a translation derived from the shell's CURRENT (unrotated)
	AABB centre. Placing it to the RIGHT of CFrame.Angles means it is expressed
	in the ROTATED frame, so a 180-degree yaw negates its X and Z. For the three
	shells with yaw ~= 0 this is harmless. For hatch_junk and hyper_x (yaw 180)
	it moves the shell by -2 * centreLocal instead of cancelling the offset.

	This measures the resulting AABB-centre error for BOTH orderings, per shell.
	The numbers can come out either way -- if the current ordering is fine, both
	errors are ~0 and the hypothesis is dead.
]]

local RS = game:GetService("ReplicatedStorage")
local SSS = game:GetService("ServerScriptService")

local out = {}
local function log(s)
	table.insert(out, s)
end

local TARGETS = { "rx7_fc", "silv_s15", "gtr_r34", "hatch_junk", "hyper_x" }
local shells = {}
for _, root in ipairs({ RS, SSS, game:GetService("ServerStorage"), workspace }) do
	for _, d in ipairs(root:GetDescendants()) do
		if d:IsA("Model") and d:FindFirstChild("Wheels") and not shells[d.Name] then
			for _, t in ipairs(TARGETS) do
				if d.Name == t then
					shells[d.Name] = d
				end
			end
		end
	end
end

-- Replicate trueAABB: min/max corner over all BaseParts, world space.
local function trueAABB(model)
	local lo, hi
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("BasePart") then
			local p = d.Position
			lo = lo and Vector3.new(math.min(lo.X, p.X), math.min(lo.Y, p.Y), math.min(lo.Z, p.Z)) or p
			hi = hi and Vector3.new(math.max(hi.X, p.X), math.max(hi.Y, p.Y), math.max(hi.Z, p.Z)) or p
		end
	end
	return lo, hi
end

log(string.format("%-11s %-10s %-22s %-14s %s", "shell", "yaw", "centreLocal(x,z)", "CURRENT err", "FIXED err"))
log(string.rep("-", 82))

for _, name in ipairs(TARGETS) do
	local shell = shells[name]
	if not shell then
		log(string.format("%-11s NOT FOUND", name))
		continue
	end

	-- yaw the solver would compute
	local pivotInv = shell:GetPivot():Inverse()
	local wf = shell:FindFirstChild("Wheels")
	local fSum, fN, rSum, rN = Vector3.zero, 0, Vector3.zero, 0
	for _, w in ipairs(wf:GetChildren()) do
		local sum, n = Vector3.zero, 0
		if w:IsA("BasePart") then
			sum, n = w.Position, 1
		end
		for _, d in ipairs(w:GetDescendants()) do
			if d:IsA("BasePart") then
				sum, n = sum + d.Position, n + 1
			end
		end
		if n > 0 then
			local lp = pivotInv * (sum / n)
			local h = w.Name:sub(1, 1):upper()
			if h == "F" then
				fSum, fN = fSum + lp, fN + 1
			elseif h == "R" then
				rSum, rN = rSum + lp, rN + 1
			end
		end
	end
	local yaw = 0
	if fN > 0 and rN > 0 then
		local nose = (fSum / fN) - (rSum / rN)
		if math.abs(nose.X) + math.abs(nose.Z) > 0.05 then
			yaw = -math.atan2(nose.X, -nose.Z)
		end
	end

	local lo2, hi2 = trueAABB(shell)
	local centreLocal = shell:GetPivot():Inverse() * ((lo2 + hi2) / 2)
	local centreFix = CFrame.new(-centreLocal.X, 0, -centreLocal.Z)

	-- Simulate both orderings against an identity body at the origin.
	local body = CFrame.new()
	local rot = CFrame.Angles(0, yaw, 0)

	-- Where does the shell's AABB centre land, relative to the body axis?
	-- Model the centre as a point at centreLocal in the shell's pivot frame.
	local centrePoint = CFrame.new(centreLocal.X, 0, centreLocal.Z)

	local currentCF = body * rot * centreFix
	local fixedCF = body * centreFix * rot -- translation applied BEFORE rotation

	local curCentre = (currentCF * centrePoint).Position
	local fixCentre = (fixedCF * centrePoint).Position

	local curErr = math.sqrt(curCentre.X ^ 2 + curCentre.Z ^ 2)
	local fixErr = math.sqrt(fixCentre.X ^ 2 + fixCentre.Z ^ 2)

	log(
		string.format(
			"%-11s %-10s (%+.2f,%+.2f)%-8s %-14s %s",
			name,
			string.format("%+.0f deg", math.deg(yaw)),
			centreLocal.X,
			centreLocal.Z,
			"",
			string.format("%.3f", curErr),
			string.format("%.3f", fixErr)
		)
	)
end

log("")
log("err = how far the shell's AABB centre sits from the chassis axis (studs).")
log("A large CURRENT err on the 180-degree shells with a near-zero FIXED err")
log("confirms the ordering bug. If both columns match, the hypothesis is WRONG")
log("and the offset is not the cause of the reversal.")

return table.concat(out, "\n")