Simple 2D layer for games.

layer.lua

#!/usr/bin/luajit

local ffi = require 'ffi'

local layer_mt = {}

function layer_mt:top_left(x, y)
    self._x1, self._y1 = x - 1, y - 1
end

function layer_mt:index(x, y)
    x, y = x + self._x1, y + self._y1
    if x < 1 or y < 1 or x > self._width or y > self._height then
        return 0
    else
        return 1 + (x - 1) + (y - 1) * self._width
    end
end

function layer_mt:get(x, y)
    return self._cells[self:index(x, y)]
end

function layer_mt:set(x, y, v)
    x, y = x + self._x1, y + self._y1
    if x < 1 or y < 1 or x > self._width or y > self._height then
        return
    end

    self._cells[1 + (x - 1) + (y - 1) * self._width] = v
end

function layer_mt:get_width()
    return self._width
end

function layer_mt:get_height()
    return self._height
end

function layer_mt:fill(v)
    for i = 0, self._width * self._height do
        self._cells[i] = v
    end
end

function layer_mt:set_default(v)
    self._cells[0] = v
end

local function layer(ctype, width, height)
    local self = {}
    self._ctype = ctype
    self._width = width
    self._height = height
    self._x1, self._y1 = 0, 0
    self._cells = ffi.new(ctype .. '[?]', 1 + width * height)

    setmetatable(self, {__index = layer_mt})

    return self
end

return layer