Simplify and refactor code, improve performance

diff --git a/init.lua b/init.lua
index 45b9e85a238701cbf5f5f4cc5cb42826fcbdba28..96afda5e131ca4eb9a9f6adda339fef1f3182524 100644 (file)
--- a/init.lua
+++ b/init.lua
@@ -1,7 +1,5 @@
 tga_encoder = {}
 
-local LUA_ARGS_LIMIT = 1000
-
 local image = setmetatable({}, {
        __call = function(self, ...)
                local t = setmetatable({}, {__index = self})
@@ -11,8 +9,7 @@ local image = setmetatable({}, {
 })
 
 function image:constructor(pixels)
-       self.bytes = {}
-       self.chunks = {self.bytes}
+       self.data = ""
        self.pixels = pixels
        self.width = #pixels[1]
        self.height = #pixels
@@ -20,87 +17,59 @@ function image:constructor(pixels)
        self:encode()
 end
 
-function image:insert(byte)
-       table.insert(self.bytes, byte)
-       if #self.bytes == LUA_ARGS_LIMIT then
-               self.bytes = {}
-               table.insert(self.chunks, self.bytes)
-       end
-end
-
-function image:littleendian(size, value)
-       for i = 1, size do
-               local byte = value % 256
-               value = value - byte
-               value = value / 256
-               self:insert(byte)
-       end
-end
-
 function image:encode_colormap_spec()
-       -- first entry index
-       self:littleendian(2, 0)
-       -- number of entries
-       self:littleendian(2, 0)
-       -- number of bits per pixel
-       self:insert(0)
+       self.data = self.data
+               .. string.char(0, 0) -- first entry index
+               .. string.char(0, 0) -- number of entries
+               .. string.char(0) -- bits per pixel
 end
 
 function image:encode_image_spec()
-       -- X- and Y- origin
-       self:littleendian(2, 0)
-       self:littleendian(2, 0)
-       -- width and height
-       self:littleendian(2, self.width)
-       self:littleendian(2, self.height)
-       -- pixel depth
-       self:insert(24)
-       -- image descriptor
-       self:insert(0)
+       self.data = self.data
+               .. string.char(0, 0) -- X-origin
+               .. string.char(0, 0) -- Y-origin
+               .. string.char(self.width  % 256, math.floor(self.width  / 256)) -- width
+               .. string.char(self.height % 256, math.floor(self.height / 256)) -- height
+               .. string.char(24) -- pixel depth (RGB = 3 bytes = 24 bits)
+               .. string.char(0) -- image descriptor
 end
 
 function image:encode_header()
-       -- id length
-       self:insert(0) -- no image id info
-       -- color map type
-       self:insert(0) -- no color map
-       -- image type
-       self:insert(2) -- uncompressed true-color image
-       -- color map specification
-       self:encode_colormap_spec()
-       -- image specification
-       self:encode_image_spec()
+       self.data = self.data
+               .. string.char(0) -- image id
+               .. string.char(0) -- color map type
+               .. string.char(2) -- image type (uncompressed true-color image = 2)
+       self:encode_colormap_spec() -- color map specification
+       self:encode_image_spec() -- image specification
 end
 
 function image:encode_data()
        for _, row in ipairs(self.pixels) do
                for _, pixel in ipairs(row) do
-                       self:insert(pixel[3])
-                       self:insert(pixel[2])
-                       self:insert(pixel[1])
+                       self.data = self.data
+                               .. string.char(pixel[3], pixel[2], pixel[1])
                end
        end
 end
 
-function image:encode()
-       -- encode header
-       self:encode_header()
-       -- no color map and image id data
-       -- encode data
-       self:encode_data()
-       -- no extension area
+function image:encode_footer()
+       self.data = self.data
+               .. string.char(0, 0, 0, 0) -- extension area offset
+               .. string.char(0, 0, 0, 0) -- developer area offset
+               .. "TRUEVISION-XFILE"
+               .. "."
+               .. string.char(0)
 end
 
-function image:get_data()
-       local data = ""
-       for _, bytes in ipairs(self.chunks) do
-               data = data .. string.char(unpack(bytes))
-       end
-       return data .. string.char(0, 0, 0, 0) .. string.char(0, 0, 0, 0) .. "TRUEVISION-XFILE." .. string.char(0)
+function image:encode()
+       self:encode_header() -- header
+       -- no color map and image id data
+       self:encode_data() -- encode data
+       -- no extension or developer area
+       self:encode_footer() -- footer
 end
 
 function image:save(filename)
-       self.data = self.data or self:get_data()
        local f = assert(io.open(filename, "w"))
        f:write(self.data)
        f:close()