Asset

1. Overview

This is a general abstraction for handling assets in Gestlings.

An asset is a data structure that can be represented as a Lua table, that can be loaded/saved to disk.

The marshaling process is as follows: a lua table is converted to msgpack, then encoded in base64.

2. Tangled File

Called asset.lua.

Asset = {}

<<asset>>
return Asset

3. New: create a new instance of Asset

In order to read/write assets, the asset library must be instantiated. This is done to allow the base64 and msgpack components to be passed in as optional arguments in the configuration.

function Asset:new(o)
    o = o or {}
    o.msgpack = o.msgpack or msgpack
    o.base64 = o.base64 or base64
    setmetatable(o, self)
    self.__index = self
    return o
end

4. Instantiate

The instantiate function is a helper function that shaves off a few steps and turns this process into a one-liner.

Asset is instantiated by first loading this module, laoding the base64/msgpack components, then creating a single instance with the new method.

function Asset.instantiate()
    return Asset:new {
        msgpack=dofile("util/MessagePack.lua"),
        base64=dofile("util/base64.lua")
    }
end

5. Save: Save an asset to a file

function Asset:encode(data)
    local data_packed = self.msgpack.pack(data)
    local data_b64 = self.base64.encode(data_packed)
    return data_b64
end
function Asset:save(data, filename)
    -- local data_packed = self.msgpack.pack(data)
    -- local data_b64 = self.base64.encode(data_packed)
    local data_b64 = self.encode(self, data)

    local fp = io.open(filename, "wb")
    for p=1,#data_b64, 40 do
        fp:write(string.sub(data_b64, p, p + 39) .. "\n")
    end
    fp:close()
end

6. Load: Load an asset from a file

function Asset:decode(data_packed_b64)
    local data_packed = self.base64.decode(data_packed_b64)
    local data = self.msgpack.unpack(data_packed)
    return data
end
function Asset:load(filename)
    local fp = io.open(filename, "rb")
    assert(fp ~= nil, "Could not read file: " .. filename)
    local data_packed_b64 = fp:read("*all")
    fp:close()
    -- local data_packed = self.base64.decode(data_packed_b64)
    -- local data = self.msgpack.unpack(data_packed)
    data = self.decode(self, data_packed_b64)
    return data
end