vector_ffi.lua

local ffi = require "ffi"

ffi.cdef [[
  typedef struct {
    float x;
    float y;
  } vector;
]]

local storage_size = 8096
local storage = ffi.new("vector[?]", storage_size)
local storage_pointer = 0

function vector(x, y)
    local v = storage[storage_pointer]
    storage_pointer = storage_pointer + 1

    v.x = x or 0
    v.y = y or 0

    return v
end

function reset_vector_storage()
    storage_pointer = 0
end

local vector_meta = {
    __add = function(v1, v2)
        return vector(v1.x + v2.x, v1.y + v2.y)
    end,
    __sub = function(v1, v2)
        return vector(v1.x - v2.x, v1.y - v2.y)
    end,
    __mul = function(v1, v2)
        if ffi.istype("vector", v1) then
            if ffi.istype("vector", v2) then
                return vector(v1.x * v2.x, v1.y * v2.y)
            else
                return vector(v1.x * v2, v1.y * v2)
            end
        else -- v1 is number
            if ffi.istype("vector", v2) then
                return vector(v1 * v2.x, v1 * v2.y)
            end
        end

        return vector(v1.x * v2.x, v1.y * v2.y)
    end,
    __div = function(v1, v2)
        if ffi.istype("vector", v1) then
            if ffi.istype("vector", v2) then
                return vector(v1.x / v2.x, v1.y / v2.y)
            else
                return vector(v1.x / v2, v1.y / v2)
            end
        else -- v1 is number
            if ffi.istype("vector", v2) then
                return vector(v1 / v2.x, v1 / v2.y)
            end
        end

        return vector(v1.x / v2.x, v1.y / v2.y)
    end,
    __unm = function(v)
        return vector(-v.x, -v.y)
    end,
    __tostring = function(v)
        return "(" .. tonumber(v.x) .. "," .. tonumber(v.y) .. ")"
    end,
    __index = {
        persist = function(v)
            return ffi.new("vector", v.x, v.y)
        end,
        set = function(target, source)
            target.x = source.x
            target.y = source.y
        end,
        length = function(v)
            return math.sqrt(v.x * v.x + v.y * v.y)
        end,
        unpack = function(v)
            return v.x, v.y
        end
    }
}

ffi.metatype("vector", vector_meta)