init.lua

   1 tga_encoder = {}
   2
   3 local image = setmetatable({}, {
   4         __call = function(self, ...)
   5                 local t = setmetatable({}, {__index = image})
   6                 t:constructor(...)
   7                 return t
   8         end,
   9 })
  10
  11 function image:constructor(pixels)
  12         self.bytes = {}
  13         self.pixels = pixels
  14         self.width = #pixles[1]
  15         self.height = #pixels
  16
  17         self:encode()
  18 end
  19
  20 function image:write(size, value)
  21         -- TGA uses little endian encoding
  22         local l = #self.bytes
  23         for i = 1, size do
  24                 local byte = value % 256
  25                 value = value - byte
  26                 value = value / 256
  27                 self.bytes[l + i] = byte
  28         end
  29 end
  30
  31 function image:encode_colormap_spec()
  32         -- first entry index
  33         self:write(2, 0)
  34         -- number of entries
  35         self:write(2, 0)
  36         -- number of bits per pixel
  37         self:write(1, 0)
  38 end
  39
  40 function image:encode_image_spec()
  41         -- X- and Y- origin
  42         self:write(2, 0)
  43         self:write(2, 0)
  44         -- width and height
  45         self:write(2, width)
  46         self:write(2, height)
  47         -- pixel depth
  48         self:write(1, 24)
  49         -- image descriptor
  50         self:write(1, 0)
  51 end
  52
  53 function image:encode_header()
  54         -- id length
  55         self:write(1, 0) -- no image id info
  56         -- color map type
  57         self:write(1, 0) -- no color map
  58         -- image type
  59         self:write(1, 2) -- uncompressed true-color image
  60         -- color map specification
  61         self:encode_colormap_spec()
  62         -- image specification
  63         self:encode_image_spec()
  64 end
  65
  66 function image:encode_data()
  67         for _, row in ipairs(self.pixels) do
  68                 for _, pixel in ipairs(row) do
  69                         self:write(1, row[3])
  70                         self:write(1, row[2])
  71                         self:write(1, row[1])
  72                 end
  73         end
  74 end
  75
  76 function image:encode()
  77         -- encode header
  78         self:encode_header()
  79         -- no color map and image id data
  80         -- encode data
  81         self:encode_data()
  82         -- no extension area or file footer
  83 end
  84
  85 function image:save(filename)
  86         self.data = self.data or string.char(unpack(self.bytes))
  87         local f = assert(io.open(filename))
  88         f:write(data)
  89         f:close()
  90 end
  91
  92 tga_encoder.image = image