vector.lua

vector = {}
vector.__index = vector

function vector.new(x,y)
    local v = {x = x or 0, y = y or 0}
    setmetatable(v, vector)
    return v
end

function vector:unpack()
    return self.x, self.y
end

function vector.__add(a,b)
    return vector.new(a.x+b.x, a.y+b.y)
end

function vector.__sub(a,b)
    return vector.new(a.x-b.x, a.y-b.y)
end

function vector.__mul(a,b)
    if type(a) == "number" then 
        return vector.new(a*b.x, a*b.y)
    elseif type(b) == "number" then
        return vector.new(b*a.x, b*a.y)
    else
        return a.x*b.x + a.y*b.y
    end
end

function vector.__div(a,b)
    if type(b) ~= "number" then
        error("cannot divide vector by vector.") end
    return vector.new(a.x / b, a.y / b)
end

function vector.len2(a)
    return a*a
end

function vector.len(a)
    return math.sqrt(a*a)
end

function vector.normalize_inplace(a)
    local l =  vector.len(a)
    a.x = a.x / l
    a.y = a.y / l
    return a
end

function vector.normalized(a)
    return a / vector.len(a)
end

function vector.dist(a, b)
    return vector.len(b-a)
end

function vector.clone(a)
    return vector.new(a.x, a.y)
end