TweenModel

--By xXxMoNkEyMaNxXx
--localize variables
local tick=tick

local pi=math.pi
local tau=2*pi
local atan2=math.atan2
local cos=math.cos
local sin=math.sin
local tan=math.tan
local exp=math.exp
local log=math.log
local acos=math.acos
local sqrt=math.sqrt
local max=math.max

--CFrame a model
local function MulCFrame(obj,cf)
    if obj:IsA'BasePart' then
        obj.CFrame=cf*obj.CFrame
    end
    for _,child in next,obj:GetChildren() do
        MulCFrame(child,cf)
    end
end
local function SetModelCFrame(model,CFrame)
    MulCFrame(model,CFrame*model:GetModelCFrame():inverse())
end

--Quaternion spherical-linear interpolation stuff
local function Qinv(q)--Inverse. (q^-1)
    local w,x,y,z=q[1],q[2],q[3],q[4]
    local m=w*w+x*x+y*y+z*z
    if m>0 then
        return {w/m,-x/m,-y/m,-z/m}
    else
        return {0,0,0,0}
    end
end

local function Qmul(q1,q2)
    local w1,x1,y1,z1,w2,x2,y2,z2=q1[1],q1[2],q1[3],q1[4],q2[1],q2[2],q2[3],q2[4]
    return {w1*w2-x1*x2-y1*y2-z1*z2,w1*x2+x1*w2+y1*z2-z1*y2,w1*y2-x1*z2+y1*w2+z1*x2,w1*z2+x1*y2-y1*x2+z1*w2}
end

local function Qpow(q,exponent,choice)
    choice=choice or 0
    local w,x,y,z=q[1],q[2],q[3],q[4]
    local vv=x*x+y*y+z*z
    if vv>0 then
        --Convert to polar form and exponentiate (all in one go)
        local v=sqrt(vv)
        local m=(w*w+vv)^(0.5*exponent)
        local theta=exponent*(atan2(v,w)+tau*choice)--swag
        local s=m*sin(theta)/v
        return {m*cos(theta),x*s,y*s,z*s}
    else--This is a regular number.  srs.  lol.
        if w<0 then--Quaternions, umad? u dun fool me nub
            local m=(-w)^exponent
            local s=m*sin(pi*exponent)*sqrt(3)/3
            return {m*cos(pi*exponent),s,s,s}
        else
            return {w^exponent,0,0,0}
        end
    end
end

local function QuaternionFromCFrame(cf)
    local mx,my,mz,m00,m01,m02,m10,m11,m12,m20,m21,m22=cf:components()
    local trace=m00+m11+m22
    if trace>0 then
        local s=sqrt(1+trace)
        local recip=0.5/s
        return s*0.5,(m21-m12)*recip,(m02-m20)*recip,(m10-m01)*recip
    else
        local big=max(m00,m11,m22)
        if big==m00 then
            local s=sqrt(1+m00-m11-m22)
            local recip=0.5/s
            return (m21-m12)*recip,0.5*s,(m10+m01)*recip,(m02+m20)*recip
        elseif big==m11 then
            local s=sqrt(1-m00+m11-m22)
            local recip=0.5/s
            return (m02-m20)*recip,(m10+m01)*recip,0.5*s,(m21+m12)*recip
        elseif big==m22 then
            local s=sqrt(1-m00-m11+m22)
            local recip=0.5/s
            return (m10-m01)*recip,(m02+m20)*recip,(m21+m12)*recip,0.5*s
        end
    end
end

--Linear interpolation from where <model> currently is to <targetCFrame> in <period> seconds
local function TweenModel(model,targetCFrame,period)
    period=period or 1
    local c0=model:GetModelCFrame()
    local q0={QuaternionFromCFrame(c0)}
    local q1={QuaternionFromCFrame(targetCFrame)}
    if q0[1]*q1[1]+q0[2]*q1[2]+q0[3]*q1[3]+q0[4]*q1[4]<0 then
        q1={-q1[1],-q1[2],-q1[3],-q1[4]}
    end
    local dq=Qmul(Qinv(q0),q1)
    local t0=tick()
    repeat
        wait()
        local t=(tick()-t0)/period
        if t>1 then
            break
        end
        local qt=Qmul(q0,Qpow(dq,t))
        local pt=c0.p:lerp(targetCFrame.p,t)
        SetModelCFrame(model,CFrame.new(pt.x,pt.y,pt.z,qt[2],qt[3],qt[4],qt[1]))
    until t>=1
    SetModelCFrame(model,targetCFrame)
end

--use it like this:
TweenModel(workspace.Model,CFrame.new(25*(2*math.random()-1),25*math.random(),25*(2*math.random()-1),2*math.random()-1,2*math.random()-1,2*math.random()-1,2*math.random()-1),4)--4 is how many seconds it should take