vector.lua

local ffi = require "ffi"

ffi.cdef [[
  void* malloc(size_t size);

  typedef struct {
    float x;
    float y;
  } vector;
]]

local storage_size = 1024 * 1024
local storage = ffi.new("vector[?]", storage_size)
local storage_pointer = 0

function vector(x, y)
    if storage_pointer >= storage_size then
        storage_pointer = storage_pointer + 1
        return ffi.new("vector", x or 0, y or 0)
    end

    local v = storage[storage_pointer]
    storage_pointer = storage_pointer + 1

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

    return v
end

function get_storage_watermark()
    return storage_pointer
end

function reset_vector_storage()
    if storage_pointer >= storage_size then
        print("WARNING: Storage size of", storage_size, "issued", storage_pointer - storage_size + 1, "extra elements")
    end

    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 type(v1) == "number" then -- v2 is a vector
            return vector(v1 * v2.x, v1 * v2.y)
        elseif type(v2) == "number" then -- v1 is a vector
            return vector(v1.x * v2, v1.y * v2)
        end

        return vector(v1.x * v2.x, v1.y * v2.y)
    end,
    __div = function(v1, v2)
        if type(v1) == "number" then -- v2 is a vector
            return vector(v1 / v2.x, v1 / v2.y)
        elseif type(v2) == "number" then -- v1 is a vector
            return vector(v1.x / v2, v1.y / v2)
        end

        return vector(v1.x / v2.x, v1.y / v2.y)
    end,
    __eq = function(v1, v2)
        if v2 == nil then return false end

        return v1.x == v2.x and v1.y == v2.y
    end,
    __unm = function(v)
        return vector(-v.x, -v.y)
    end,
    __tostring = function(v)
        return string.format("(%.2f, %.2f)", v.x, v.y)
    end,
    __index = {
        persist = function(v)
            return ffi.new("vector", v.x, v.y)
        end,
        set = function(target, source, second_value)
            if second_value ~= nil then
                target.x = source
                target.y = second_value
            else
                target.x = source.x
                target.y = source.y
            end
        end,
        length = function(v)
            return math.sqrt(v.x * v.x + v.y * v.y)
        end,
        normalize = function(v)
            return v / v:length()
        end,
        dot = function(a, b)
            return a.x * b.x + a.y * b.y
        end,
        unpack = function(v)
            return v.x, v.y
        end
    }
}

ffi.metatype("vector", vector_meta)